TOWARD AN ALTERNATE THEORY
So far our attention has been focused on the wing and its derivation. Having found leads that are difficult to develop it is time to shift our observations to the other part of the flight mechanism, the flight motor, or the muscular system that moves the wi
ngs, described briefly earlier. The investigation of the more obvious "lobe" connection has kept our attention away from this topic, and it is possible some helpful clues may be met with here.
As mentioned earlier the mechanism of flight has not one but three muscular systems, the direct, the indirect and the accessory flight muscles. The direct and accessory musculature is evidently tied to flying in a straightforward manner, but the indirect m
ode is a step removed and perhaps it is worth considering especially that reason.
The indirect flight mechanism
Two sets of muscles are employed in moving the wings up and down. The dorso-ventrals, connecting the tergum and sternum vertically compresses the thorax. The dorso-longitudinals, running from the anterior to the posterior phragmata, exert a longitudinal co
mpression. Each of these two actions alternately deforms the thorax in the vertical and the horizontal direction respectively, as if it were an elastic box. Because the wing is attached to the box as a lever, it performs and up and down motion. ILL The acti
on is termed indirect because the muscles do not directly affect the wings, instead the wings move as a result of translating the thoracic deformation. The actual process is actually somewhat more complicated, but the essentials are covered by the above des
There is, however, an interesting structure connected with indirect flight mechanism discovered while studying wing movement in flies. It was discovered that here, before its action reaches the wings the thoracic deformation is first routed through an extra
mechanism. Its description is best presented diagrammatically. The alternating forces on the thorax affect a small system composed of elastic materials and sclerites. This system locks the movement in one position until opposing muscular force causes it to
lock into the other position. ILL 16 This system is called a click mechanism since with muscular drive provided, it will buckle, or click from one stable state into another. (Boettiger, E. G. & Furshpan, E., The mechanics of flight movement in Diptera. Bio
l. Bull. mar. biol. lab., Woods Hole 102, 1952) First thought to be a characteristic only of advanced fliers, such as the Diptera, click mechanisms have been shown to exit also in Orthoptera, Coleoptera and possibly, in Odonata. (Chapman, The Insects, 19
We can quote J.W.S. Pringle (Chapter 7 Locomotion, p. 435 ...): "Partly because of ...<[>the] elastic cuticle at the hinges and partly because of the general elasticity of the solid cuticle and muscle, movement of the wings is influenced by elastic for
ces. Sometimes, as in the mesothorax of Schistocerca, the wings assume a fully down position when the main flight muscles are relaxed; sometimes, as in Sphingidae and Anisoptera (Odonata), the stable position is horizontal."
Another way of defining the indirect flight mechanism is as a bistable vibrator, where the mechanical parts alternately switch from one stable position to the other. In the case of the fly
Sarcophaga, where this mechanism was first discovered, the system also possesses an intermediate unstable position. The muscles merely move the mechanism from the first stable to unstable position, from which it quickly reaches the second bistable p
osition. This means that the muscles need to exert themselves less because the energy is partly contributed by the elastic, energy-storing properties of the cuticle through the click mechanism. The mechanism itself is directly attached to the wing base, and
so the three positions produce the up, level and down positions of the wing. The speed of vibration is clearly demonstrated by the wing beat of the fly. ILL 17
We are meeting here with a mechanical vibrator, entirely analogous to an electronic oscillator or multivibrator. A basic description of this mechanism, in fact, states: "<[>the existence of these elastic forces in the wing suspension, considered together wi
th the fact that the wings have appreciable inertia, shows that the system must behave as a resonant mechanical oscillator." (J. W. S. Pringle, .Locomotion: flight, p. 437.)
The system with the click mechanism has been the classical model of indirect flight since its discovery, but more recently its presence has been questioned (Miyan, Jaleel A., and Ewing, Arthur W., Is the 'click' mechanism of Dipteran flight an artefact of
CCl4 anaesthesia?, J. exp. Biol. 116 (1985). The researchers offer a modified design, called the "locking mechanism". In another study (Ennos, A. R., A comparative study of the flight mechanism of Diptera, J exp. Biol. 127,
(1987), p. 235), present yet another modification. The final words on the precise nature of hinge mechanism is possibly not yet available, but even so, in our suggested existence for a pre-flight thoracic vibrator the exact definition of a click mechanism,
or bistable mechanism, in highly specialized insects such as Diptera, is not significant.
Finding a key
There are two systems at work here, the wings and flight motor, each dependent on the other to effect flight. Neither one alone can produce flight. What could each achieve without the other?
Based on the Paranotal Theory we can conclude the following statements:
1. Lobes without motor return us to an earlier stage, where the paranotal lobe is without any apparent use.
2. Motor without lobes or wings is just a vibrating mechanism unable to exert action
on aerodynamic agents necessary of flying.
Still, if we recognize the flight motor in the thorax as a vibrating mechanism, as it had been described by researchers, then we can say that a vibrator does perform an obvious function: it vibrates -- without any connection to other structures. this is cer
tainly possible, as indicated by two facts referred to earlier under insect sonification: "The wings movements of most insects produce a humming or buzzing sound, but in some insects the thorax is also involved in the production of sound; a bumble bee held
by the wings will still buzz." (Borror, Introduction to the Study of Insects, Holt, 1976, p. 66). The water beetle
Alicius sulcatus also produces a sound in pre-flight warm-up.
This is an important observation. A vibrating mechanism, without any relation to another object can produce sound.
Let us note that the accepted theory places the development of the wing before that of the flight mechanism. But we can change this around to a theoretical situation where the existence of the flight motor predates the appearance of the wing, allowing us to
make the following propositions:
1. The flight motor without wings is a vibrator
2. Lobes or wings added to a vibrator will also vibrate
And with that we have found a key to an alternate origin of flight.
This realization opens a new direction for inquiry. If the thoracic vibrator without wings is a sound producing structure then its possible presence in pre-flight insects needs no justification. It would be part of the assemblage of insectan sonifying equip
ment and would have an adaptive function long before the emergence of flight. Accepting such a proposal requires us only to look back and once more note how fundamental sound is in insect behavior. Making sound is a relatively simple engineering objective,
especially when compared to flying, therefore we can assume with relative confidence that sonifying was well established and diversified by the time proto-wings would appear for the first time.
Deriving the wing is comparatively easy at this point. Whether it is the paranotal lobe, or some other integumental structure, no matter what size or shape, whether it is applicable to gliding or flight or not, if attached to the vibrating organ will funct
ion by altering the acoustical characteristics. The eventual hinging of the paranotal lobe, as hypothesized by the paranotal theory becomes a small problem: the vibrating membrane or sclerites themselves are the hinge.
Thus we can clarify the ontogeny of the proto-wing. An adventitious variation in density or dimension such thickening, sclerotization, folding, or evagination at a pleural location, either itself vibrating or connected with vibrating surfaces, would tend t
o alter the frequency or other acoustic component of the sound and so enter a course of selection, eventually evolving into lobe or wing. This structural development would have had adaptive significance from its earliest appearance and therefore would have
survived and developed. What brings this about is partly the fact that the acoustic character of a relatively thin vibrating membrane or plate can be influenced by relatively small structures.
But the transformation of a relatively small, near-invisible structural addition that possessed acoustic effect would lead to an additional developments. The proto-lobe, or other proto-wing structure associated with a vibrating membrane would in itself ten
d to increase in surface area and optimize in structural and elastic characteristics to increase the amplitude of the sound. Thus it would enter the range of visibility. And since it possessed a kinetic component it would not only be visible but would attra
ct attention by virtue of its motion. It is impossible to know the vibration rates of our hypothetical thoracic sonifier, but it could have had a variable rate in which case the motion of the lobe would at times be slow enough to create maximal visual impre
ssion. Even if the rate would not be variable, the onset and the end of the vibration period, or pulse, would offer a contrast between the moving and stationary phases of the visual object. In addition, it should be noted that we are dealing now with a comb
ined audio and visual function and the two would strongly tend to reinforce each other's effects. At any rate, the original sonifier would at this point enter a relationship and a combinative selective process wherein the two components at times might reinf
orce, at other times might compete with each other.
To flight
It is impossible to speculate on the actual position and orientation of this hypothetical proto-wing or paranotal lobe. It may have been lateral and more or less perpendicular to the ground or it may have been postero-lateral, bent backwards as wings are to
day in all flying orders except Odonata and Ephemeroptera. Whether the lobes could be folded, like modern wings, is an uncertain point, but had the pre-flight lobes been large enough they most likely would tend to be employed in nuptial display, performing
a set of movements that may have included flexing.
We also do not know what angle the proto-wings formed with the body. If the angle of orientation was towards the posterior, or in other ways not perpendicular to the pleuron, then little alteration might be needed, and if they were perpendicular to the
pleuron, moving up and down, like modern wings, then a simple vertical rotation of the proto-wings attended by some asymmetry in alternating up-and-down forces, or between the sizes of the lobes, or caused by some other aerodynamic factor, in combinatio
n with appropriate vibration rate, appropriate ratio of body weight to lobe surface, and the influence of air movement would one day automatically produce FLIGHT.
Here we can briefly summarize our conclusions so far. (To go into greater detail we will have to find supportive material which will provide factual bases for our hypothesis.
1. Some pre-flight insects employed sound communication.
2. One of the sonifying mechanisms was a thoracic buzzer or vibrator which had de- veloped from the elastic properties and the existing musculature of the thorax.
3. The proto-wing, an integumental structure appearing in association with the vibrating area
(perhaps a membrane) functioned as a modifier of the sound. This structure could be, or
could develop into a lobe and then a wing
4. This structure, the proto-wing, also took on visual functions and increased in size.
5. The sonic and visual functions tended to select the proto-wing into a flat and strong
expansion.
6. Since the mechanism of movement was already present and acting on the proto-wings, all the requisite parts to flight were present and so an automatic, adventitious occurrence of
lift and flight gained significant likelihood.
SUPPORTING FACTS
Survival of original organ and function.
The most generally supportive fact is the obvious present-day functioning of the wings and flight mechanism as sound and visual communicators. We may be seeing the continual survival of the basic
function to which the new one of flight was grafted. Within our experience flight and wings generate sound and visual effects. These effects can be produced even if minimal characteristics of flight are removed. A very short wing, although inadequate
for flight would still buzz and would still be visible. On the other hand, we cannot say that our theoretical reversal
of the evolutionary process can tell us anything about the actual forward evolution. Nevertheless, it is an interesting proposition to think that what we normally take to be
a consequence of an action of large magnitude -- flight, would be a product of actions of smaller magnitude --sound and sight.
Analogous occurrences can be found: YEAH?? Bone vs. cartilage
Wingless thoracic buzz
The thoracic buzzing in present in the bumble bee shows that the flight musculature is capable of buzzing independently of the wings. This may be circular reasoning, and perhaps the buzzing ability of the fl
ight muscles is merely a by-product of flight, however the likelihood that a thoracic vibrator existed prior to flight offers the simpler and more likely explanation. We had
already met with the following facts: a) Formerly bee-piping was thought to be produced by air forced through a spiracle, but now it is thought that "the sound is probably produced by vibration of the thoracic sclerites
and so may be regarded as a vibrating membrane mechanism." (Chapman, The Insects, 1st ed., p. 589); b) The beetle
Acilius sulcatus, family Dystiscidae, shows thoracic vibration in pre-flight warming without any observable movement of the wings or elytra. (source...)
These facts supports our suggestion that the thoracic pleuron is a likely sight for sound production because of its structural qualities and components, name
ly cuticle and sclerites. Pre-flight insects possessed sclerites in the pleura derived from implementing the action of base-leg, or coxal muscles.
The case of thoracic vibration can also be related to the click mechanism. We read that: "...a click action...may also be effective, when the wings are folded, for production of sound or in pre-flight warming." (Pringle, Locomotion: flight, p. 436, in Rain
The vibrator nature of the wing mechanism
A quote we have already seen expresses the potential sound producing properties of the wing-mover system in the thorax is expressed by the statement: "The existence of these elastic forces in the wing suspensi
on, considered together with the fact that the wings have appreciable inertia, show that
the system must behave as a resonant mechanical oscillator." (Pringle, Locomotion: Flight, p. 437). This situation indicates, it seems, both a rather obvious fact -- that insect flight produces a buzz or hum, and a more subtle point: th
at the mechanism of flight is essentially a fully constructed vibrator which can, as a by product, generate flight.
Ancient symmetrical wing venation
Pterygotes have wings with asymmetrical venation, favoring a placement of main vein trunks at the anterior margin of the wings for aerodynamic purposes. However, one of the early winged insects, the Paleozoic cockroaches show wings with symmetrical vein dis
tribution. One author, Sharov thinks this venation is a regression caused by the development of concealment-oriented behavior. He also stresses the close resemblance between veins on theses wings and veins in leaves found in association. This would indicate
a tendency toward mimicry. (Sharov, p. 114)
However, we might ponder whether with the limited abilities of sight in contemporary predators such mimicry would have developed at that time. The concealment behavior might also be doubted on the same basis. Nevertheless, the symmetrical venation of these
wings definitely indicates a primitivity in flight, and can easily be explained as being retentive features of the sonic and visual source of wings.
More on this later.
High plants
But still, the same synchrony can also be interpreted in favor of our postulations. High vegetation would greatly decrease visibility for insects and therefore mating or other interests of insects with evolving sonic-visual proto-wings would tend to gain f
rom proto-wing vibrating or flapping, or maybe fluttering in order to be seen. Or maybe coming of high plants could have been a strong triggering force in selecting from mere flutterers or vertical risers, because to fly up to a plant the insect also neede
d a minimum of flight control to land its feet on the chosen part of a plant, which may be have been at an angle. Such condition would support the alternate theory.
The arrival of high plants might also have an effect indirectly related to size. It may be that the smaller the vibrating insect, the more use would be gained from the ability to flutter up in addition to sonifying. However, considering that insects sonifyi
ng today stay stationary, such idea may make little sense.
Cicada tymbals
The nature of the sonifying tymbal mechanism of cicadas (Cicadidae) in more than one way fundamentally supports and augments our general argument. To begin with, the anatomic source of the wings, paratergal lobes and tymbal membranes is the same. All three
are integumental structures, specialized developments of the insect cuticle. The basic tymbal mechanism
ILL (Haskell!) consists of a membrane framed by a slerotized rim with a muscle attached to the membrane at its center. There may be associated resonant air chambers and additional smaller muscles attached to the membrane near the rim.
Since the membrane is taut and is outwardly convex, if the muscle pulls it in and then relaxes, the membrane will spring back to its normal position. As we know, the sound of cicadas is powerful and this fact attests to the highly efficient acoustic mechani
cs inherent in the insect cuticle. The resonating material is strong, thin. Elasticity enables it to store muscle produced energy that can be quickly released. Here we can see that the material requirements of the tymbal are the same as that of the wing. We
also notice that the elastic quality essential in the tymbal mechanism is also essential in the click mechanism. There is therefore, an remarkable agreement -- perhaps homology or even identity?
The tymbal is a monostable vibrator with only one stable position. The click mechanism has two stable positions. Considering the number of sclerites in the click articulation we can easily note that by combining two tymbal mechanisms, thereby adding to the
number of components, a bistable vibrator could be fashioned. ILL It can be demonstrated that alterations to the structure of the membrane can effectively even make several tymbals out of one:
"In Abricta and Magicidae /(cicadas?) the strongly-developed ribs of the tymbal buckle separately during the 'in' movement, so that each muscle contraction produces 7-0 pulses." (IMMS vol1, p. 184)
Indeed, the fact that in the cicada's sound mechanism the sound producing tymbals and the sound sensing tympana are practically adjacent may reflect that both work on the basis of the acoustic properties of cuticular membrane, not only suggesting a shared
ontogeny, but also that insectan construction almost treats the vibrating membranes as modules that can be wired in different ways.
It has been stated that the tymbal mechanism in Homoptera has evolved "more than once in evolution." (Leston and Pringle, in Busnel, p. 392). Such a view supports the idea that vibrating membranes constitute a structure that has a good chance of development
at different times and therefore could have formed the basis of the flight mechanism in the pre-flight era.
The tymbal and wing as tergal extensions
Both extant wing and its hypothetical ancestor, the paranotum, are viewed as extensions of the thoracic terga. But the cicadan tymbals are also regarded as sharing this anatomical feature: they are organs "located in the 1st abdominal segment, the lateral
part of the tergum of which is modified to form the striated tymbal (Leston and Pringle, in Busnel, p. 393.
The cicadan tymbal is an extension of the tergum, but it is a more a pleural then a tergal membrane. In the case of stink bugs, family Pentatomidae, however, in a number of not closely related genera have a tymbal organ involving the fusion of the first two
abdominal terga. Apodemes of these fused plates on each side of the insect are pulled by large, flat sheets of muscle attached to the third thoracic phragma. The cuticle on the "lateral areas of the fused 1st and 2nd abdominal terga...shows a varying degre
e of differentiation from that of the remainder of these two terga and from that of terga III to VII: it is often striate and there is no doubt that when pulled by..."the muscle"... it deforms sufficiently to produce sounds and falls whithin the definition
of a tymbal...". (Leston and Pringle, in Busnell, p. 404. ILL, (<;>ibid.)
Two points can be made about the Pentatomid tymbal. First, it shows segmental fusion to create rigidity (for the tymbal rim) and tergal deformation produced by a dorsal longitudinal muscle, leading to sound generation. Analogously, the indirect wing mechani
sm is also involved with segmental fusion for thoracic rigidity and with deformation involving dorsal longitudinal muscles.
Secondly, We meet here a vibrating surface which is none other than the lateral tergal edge, an exact homologue of the source of the paranota, or of wings.
No doubt this is due to the necessity for a rigid pleuron, mostly covered by sclerotized areas. This situation may show a dissimilarity, but we can note that tymbalic sound production need not require extended membranes. In the Pentatomidae (Hemiptera), or
stink bugs, tymbalic vibrating plate is rather narrow
The comparison of the tymbal and the wing mechanism is not entirely new
In a flight system where each neural impulse generates a single corresponding muscular action, is limited to insects with low wing beat. Such ordinary muscles are called neurogenic, or synchronous. The Odonata and ... are instances.
Add rate figures here:
Asynchronous (or fibrillar) muscles, found only in insects, are called myogenic; they respond to a single neural impulse by going into a period of self-sustained contraction and relaxation. Nerves are unable to steadily supply impulses above a certain rate.
Muscles can contract and relax at a much faster rate. LOOK UP RATES The high wing movement rate of insects like Diptera, or flies, for example, asynchronous muscle. The wing rate this way can be much higher than neurogenic, synchronous triggering w
ould allow.
The tymbals in some cicadas are synchronous, in others, asynchronous. This fact has been cited as a parallel to the distribution involving insects of synchronous and asynchronous sources of wing vibration: "Just as in the flight system some species have syn
chronous and some have an asynchronous rhythmic mechanism, so in cicadas some species are synchronous and some are asynchronous in the excitation of their timbal muscles." (J. W. S. Pringle, The evolution of the fibrillar muscle in insects, J. exp. Biol. 94
We do not know whether this sharing of asynchronous muscles has been separately developed from a meed for high vibration rate or if it points to a shared ancestry, but the latter presumption certainly supports our proposition, especially when added to the n
umber of other supportive analogies.
The model analogy between tymbal and wing
The schematic diagram of the tymbal mechanism shows a frame surrounding a membrane with an attached muscle. This muscle sets and maintains the vibration in motion. The auxiliary muscles attached near the rim control the tension of the membrane and therefore
control the volume and other characteristics of the vibration. The diagram of the wing bearing thorax also presents a frame, which is formed by the hard dorsum, sternum and pleuron. The unsclerotized area is the membrane where the wing is hinged. The two t
ypes of muscles in the tymbal are analogous to the direct and accessory muscles of the wing. TO BE FINISHED!! 10/20
The vibrating pterothoracic pleuron
There is process that observed in Diptera and also in Hymenoptera, (the wasp
Polistes). In studies of wing movement it was found that the pleuron moves in and out as the up and downstrokes of the wing alternate. (draw ILL <;> p. 369, Ennos: Flight mech of Diptera). (Boettiger, E. G. (1957). The machinery of insect flight. In
Recent Advances in Invertebrate Physiology (ed. B. T. Scheer), pp. 117-142. University of Oregon Publications.) Clearly, the thorax behaves as a vibrator, and the pleuron is the moving membrane. If the flight mechanism is removed, there still remai
ns a complete vibrator mechanism. Nor is this pleural vibration an effect of specialization, involving the click mechanism, for example, because the wasp Polistes has no click device.
Analogy of small muscles as modulators
The tymbal is activated by a main muscle which is responsible for the basic vibration, but the curvature and tension of the tymbal is modulated by a number of smaller muscles attached to the edges of the membrane.
"These muscles, according to Pringle's work on Cicadas, serve to increase the curvature of the tymbals and in this way increase the volume of sound..." (Haskell p. 52). We may see here an analogy with the muscles of the wing, where the direct muscle is
responsible for the main upward movement and the accessory muscles modulate this movement by bending the wing.
Distribution of tymbals
Tymbal organs are not limited to the cicadas and related families? (Homoptera), but also can be found among the Hemiptera, or true bugs, (family? Pentomidae), and among Lepidoptera, or butterflies and moths. W
e read that certain mechanisms which have been termed 'tymbal organs" "are widely distributed.?? add Noctuida (Lepidoptera) .FIX
Ancient origin of tymbals
In frictional, or strigillating, sound production of insects, the sequence of evolution is not easily perceptible because the "polymorphism and the multiplicity of localisation within the family, the absence of transitional forms between one type and anoth
er, and the impossibility of recognizing a phylogenetic connexion in these erratic appearances, entitle us to think that, at least in Crustacea, Arachnida, and as regards insects, in Coleoptera, stridulation is a late acquisition. It is a response of the sp
ecific potentialities of each group to an urge, a tendency, a 'need' experienced by the group. On the other hand the homogeneity found among Orthoptera and Homoptera leaves room for the supposition of more ancient development (or at least potentiality of de
velopment) in the evolutionary process." (Dumortier, Sound emission apparatus in Arthropoda, p. 337, in R. - G. Busnel, ed., Acoustic Behaviour of Animals, !963.) The presumed antiquity of Homopteran tymbal mechanisms therefore suggests that these structure
s would be present in the pre-flight era and could furnish the chronology for the arisal of flight from some kind of vibrating mechanism.
Tymbals on lateral surface - Analogy between abdomen and thorax
The tymbal organs of the cicada occur on the dorso-lateral surface of the first abdominal segment. This lateral placement is analogous to that of the wing articulation. In fact, tymbal membranes can be found on the dorso-lateral surfaces of the fused first
and second thoracic? terga in Pentatomidae. (What about all that bottom placement talked about??)
Tymbals on thoracic pleuron
It is helpful for our proposition to find that tymbals organs can turn up on the thoracic pleuron, the location of the wing and part of its mechanismg, as well. We read that certain structures which have been termed 'tymbal organs" "are widely distributed a
mongst the Lepidoptera. The organ situated in the thorax of certain Arctiidae and Syntomidae (Lepidoptera), is a modification of the metepisternal sclerite, which forms a membranous covering over a cavity. This membrane, the tymbal, is said to be vibrating
by rapid alterations of the shape of the cavity, probably brought about by contractions of the
dorso-ventral flight muscle The noise produced by the insect when on the wing is a crackling sound, and in certain genera, such as Setina, is said to be audible over considerable distances." (Haskell. p. 54,)
The spiracles
An basic point that seems to support the Paranotal Theory is that both the wing and paranotal lobes lie above the thoracic spiracles. This fact strengthens the supposition that the wings are extensions of the dorsum, and not of some structure located below
the line of spiracles, such as the legs. Although we are not suggesting any linear, direct connection between the wing mechanism and the cicadan tymbal, it is interesting to note that the tymbal also lies above the abdominal spiracles. This can be seen in t
he Homopterans Platypleura capitata (a cicada), Tettigarcta tomentosa (Leston and Pringle, Acustical Behavior in Hemiptera, in Busnel, Acoustic Bechaiov in Animals, 1963, pp.394-395), and
Neophilaenus campestris (Haskell, Insect Sounds, 1961, p. 53), It is implied, therefore, that a hypothetical vibrating membrane structure could have existed on the thorax above the spiracle, as well.
(Note that in an illustration of the tymbal of Cystostomata saundersii
the spiracle is not below the tymbal, but is located approximately one-third of the way up the edge of the tymbal membrane (Simmons and Young, The tymbal mechanism and song patterns of the Bladder cicada, Cystostoma saundersii, J. exp Biol (1978) 76, p.
29) However, the tymbal is significantly enlarged on this insect, and this fact could account for the tymbal's reaching below the spiracle. Still, two-thirds of the tymbal surface and most certainly, the attachment of the tymbal muscle to it are found abov
e the spiracle.)
The placement of wings above the spiracles is also a fact leveled against the gill theory of wing origins, since gills are associated with the lower half of the body. Nevertheless, ideas are not always necessarily clear-cut, and it happens that a researcher
, "looked carefully into this question and found that in Hemimetabola (Hemiptera and Orthoptera) as well as in Coleoptera and Lepidoptera, the imaginal discs of the wings invariably appear at about the level of the spiracles. He could not find the slightest
evidence for the development of wings by extension from the terga. (Wigglesworth, The evotion of insect flight, in Insect Flight, ed. Rainey, p. 260-261)
The attachment of the tymbal muscle
The tymbal muscle of Platypleura capitata is attached at the top of the membrane ILL (<;>my Museum notes, Pringle, p .3). This fact, also, is not explicitly supportive, but nevertheless is interesting in that it shows an analogy with the place of wi
ng attachment.
The line of tymbal buckling!!! I think this is nx!!
A third point of interest is that the line of buckling of the tymbal in at least
Platypleura capitata lies at roughly at 45*. While wings developing from paranotal lobes would first hinge on a horizontal axis, in extant flight wings do not hinge in a horizontal plane. The general ---
Dorsoventral muscles and thoracic deformation
Aside from the above case of Lepidoptera, tymbals activated by dorsoventral muscle shave also been reported in the Pentatomidae (Heteroptera). Here the vibrating system is built on the episternum, a thoracic location connected to wing articulation, where <[>
a sclerite has developed into a vibrating membrane]?, the action of which is caused by indirect
dorso-ventral muscles, the main agents of flight. We see, then, an existing structure that is very close to the model proposed by us for the origin of wings and its mechanism. The fact that the dorsoventral muscles are capable of producing tymba
lic vibration emphasizes that such action and structure could have occurred in our hypothetical pre-flight thoracic vibrator.
In cicada, as well, dorso-longitudinal muscles may take part in the activation of the tymbal. "Another muscle considered to have a possible role in sound production (Pringle, 1954) is the dorsal muscle. This flat muscle extends longitudinally between the a
nterior and posterior margins of the 1st abdominal segment, passing across the dorsal rim of the tymbal."
ILL (Simmons and Young, 1978 p. 31) Since the muscle does not connect to the tymbal, its action would affect the tymbal by deformation of the first abdominal segment.
Thoracic tymbal activated by thoracic deformation
To illustrate the existence of a tymbal driven by thoracic deformation we can once more the Lepidoptera mentioned above. The tymbal cavity of the Arctiidae and Syntomidae mentioned above has described as being deformed by the dorsoventral muscles.
Tymbal action by direct wing muscle
There is at least one known instance where a direct flight muscle operates a tymbal. Concerning the tymbal organs in some Arctiidae (Lepidoptera) we read that not only is the location of this tymbal on the side of the meta- thorax, but that its "main effec
tor muscle is the coxo-basalar muscle". (Chapman/ Sound production, p. 694.)This fact illustrates another analogy between the flight mechanism and the proposed ancestral thoracic vibrator.
Possible origins of ancestral lobe/wing as part of tymbalic structure
Tymbal membranes are often covered by a sclerotized plate. Such an extension over a resonating cavity may suggest yet another variation for the origin of the proto-wing: instead of being the vibrating part, it may have developed as an accessory structure to
the tymbal. We have mentioned the idea that lobes may have originally appeared as minute structures modifying or amplifying the sound. It might be asked that if cicadas can produce intense sound with the unadorned membranes, what need would be there for am
plifying it. An answer may lie in the fact we can find tymbal organs that produce sounds of extremely low amplitude. In many Auchenorrhynchan families (Delphacidae, Cixiidae, Cercopidae, Membracidae, Cicellidae) the "sounds produced by these insects are alw
ays of low intensity and not always audible to the unaided ear..." (IMMS p. 184). Cicadas are medium to large insects, 25 mm to 50 mm \, but smaller insects would have smaller tymbal organs with lower intensity sound, and would arguably benefit from increa
sed sound volume.
Synchrony of tymbals
The studies on cicadas show that in the typical case the two tymbals, on opposite sides of the body, work synchronously. This characteristic is in perfect accordance with the synchronicity of the wings on each side. Although in some cicadas (Magicida and Fi
dicina) the opposite tymbals are not in phase -- a fact that may or may not be significant in our discussion -- such independence is advantageous in communication since it doubles vibration rate, and it may be advantageous in flight because independent cont
rol of the opposite wings refines flight control.
The range of tymbalic vibration rate encompasses wing beat rates
SPECIFY WHICH CICADA __THIS NEED S MORE DETAILS ON VIBRATION RATES
It is noteworthy that the cicadan tymbal vibrates naturally at 4500 Hz, a rate rather over the rate of insectan wing beat in general. The high end of wing beat frequency is somewhat over 1000 Hz, presenting no problem in matching the sound producing vibrati
on rates to those of wing beats. Carpocoris (Pentatomidae) has a wing beat rate of 150-200 Hz, somewhere in the middle of the entire the range of wing frequencies ranging from 8-12 Hz to over 1000 Hz. The extension by wings is known to reduce the ba
sic vibration rate of the click mechanism because of its own inertia and air resistance.
<[>Look up: Odonata beat rate and size?]
The fact that the frequency range of tymbalic oscillation is considerably higher than frequency of oscillation needed in wing movement clearly enables the tymbalic vibration system to provide an efficient source of flight movement without additional develo
pment. The only possible requirement for the vibratory mechanism may be the acquisition of sufficient power. With the availability of the thorax, the structure of which would already possess more tightly integrated segments, and a more sclerotized pleuron t
o give leg movement a more stable base, such additional power may have been accessible to a thoracic vibrator.
Power of tymbals
The activation of the tymbals in cicadas show the availability of considerable power. Both the calling song, used in mating call, and the so-called protest song, issued by an insect being handled, can be intense.
"The most noticeable feature of these songs is that they are extraordinarily loud. A group of males calling in a nearby tree can render conversation impossible, and it is actually painful to hold a protesting insect close to one's ear. Measurements of the s
ound pressure level at 20 cm from the singing insect were obtained..." and in "both species, the protest song consistently registers about 110 dB SPELL, which is indeed a very loud sound for an insect to produce."
"In Cyclochila] australasiae, the calling song is sometimes louder than the protest song...The subdued calling song may be quieter than the protest song, registering about 108 dB SPL, but a vigorously calling male may register 115 dB SPL or
more. These values do not represent momentary peaks of sound intensity: males of
C. australasiae are capable of maintaining their loud song for many minutes on end. (Young, 1990, p. 48.)
Clearly, the power necessary for flight is no less potentially available in a vibrating membrane mechanism than is the range of beat frequencies.
Similarities between tymbal ribs and wing pteralia
It is not implausible that some kind of timbal mechanism was in fact the ancestor of flight because there are curious analogues, or perhaps even homologues, that the two share.
First, there is the matter of corrugation. Tymbal membranes have been found to possess corrugated areas. But then one of the basic structural qualities the wing membrane is its corrugated surface. This quality is normally called "fluting", and is adjacent v
eins are alternately on the top of a ridge or in the bottom of a groove. This parallel may only indicate that to strengthen a membrane, or a plate, nature uses corrugation, but it also suggests yet another analogy between the two systems under discussion.
Secondly, there is the row of sclerites on tymbal membranes similar to the row of sclerites, or pteralia, on the wing base, connected with both the venation, that is the architecture, and the muscular control of the wing. In existing insects the pteralia, o
r axillary plates, which are small sclerites on the wing membrane at its base, have interlocked and sometimes fused into complex mechanical arrangements to function in flexing, bending and folding the wings. But in the earliest fossil wings the pteralia exh
ibit a primitive state: they are never fused and are more or less similarly sized and shaped, and aligned along the wing base.
ILL <<Boudreaux Such an arrangement is analogous not only in appearance, but in function as well, to the sclerites found on multitymbal membranes. In both cases the sclerites are lined up in a row, and in both cases they alter the fundamental movem
ent of the membrane to which they are attached. On the wing the pteralia either provide attachment to muscles performing up vertical wing movement or enable to break the plane of the membrane in order to flex it or fold it. In the timbal case the line of sc
lerites similarly cause the membrane to break its plane in a series of discrete bucklings. The similarity fails only in that the microtymbal sclerites are vertically arrayed, as opposed to the arrangement of the pteralia in a horizontal row.
The tymbal membranes of cicadas exhibit a number of sclerotized ribs which cover the membrane in a parallel array, long ribs interspersed with short ones.
ILL <;>Simmons & Young The number of ribs varies with the species. Cystosoma saundersii, the Australian bladder cicada, possesses seven long ribs and seven short ribs.
Cyclochila australasiae shows four long and four short ones,
Abricta and Magicida each have about ten ribs. The arrangement and even the magnitude of the numbers of ribs present an interesting parallel to lay-out of wing base pteralia in a hypothetical archetypal venation of the wing, as represented
by the forewings of the fossil Boltopruvosita nigra (Palaeodictyoptera), Namurian, Upper Carboniferous. ILL <;>Boudreaux p. 183.) The pteralia number five, matching the number of ribs in the cicada
Platypleura capitata, which has three long and two short ribs. The number of basic veins on the archetypal wings is seven, although the last one, the anal veins vary in number -- something that seems to fall into the range of cicadan ribs. T
he number of veins, related, of course, is related to the number of pteralia, because the veins are extensions of the pteralia. Unlike in the case of the microtymbal sclerites mentioned above, the tymbalic ribs are alined in a horizontal row, exactly as the
base sclerites of the wings.
Another curious, though most likely, adventitious, parallel can be seen between existing tymbals and the above mentioned forewings of
Boltopruvosita nigra. It is the fact that cicada tymbal ribs diminish in size from posterior to anterior, while the sizes of pteralia in
Boltopruvosita serially diminish as well, though in the opposite direction.
Presumed mechanical structure in tymbals paralleling wing hinge mechanism
It has been proposed that the tymbal possesses a structure that stops, or limits, the travel of the tymbal membrane as it relaxes. "The tymbal apodeme touches the vertical bar in the resting position and at this point of contact there is a pronounced knob o
n the vertical bar and a corresponding dip in the broad part of the tymbal apodeme. The knob on the vertical bar is slightly hollowed on its anterior surface and there is a corresponding small bulge on the shaft of the tymbal apodeme, about level with the l
imit of muscle insertion. This combination of raised and hollowed surfaces produces a precise fit between the tymbal apodeme and the knob on the vertical bar in the resting position. This arrangement strongly suggests the function of a 'return stop' to prev
ent the elasticity of the tymbal from causing overshoot during the relaxation of the tymbal muscle." (Simmons and Young, 1978).
ILL based on Simmons p. 31.) Such a structures may appear analogous to sclerotized structures of the wing mechanism that limit the extreme travel of the wing. The click mechanism is certainly connected with such function.
Association between tymbal and tympanal organs
Tympanal organs of sound reception are structurally close to the sound producing tymbal. Both are basically built on the elastic nature of the cuticle. In one case this membrane vibrates due to direct muscular action, in the other it vibrates due to incomin
g air vibrations. Both membranes possess important the muscle components. The tympanal organ exhibits an accessory tensor muscle attached to the membrane to control its tension. Perhaps this counters the effects on the membrane by atmospheric humidity and t
emperature, or it helps tune the resonance of the membrane. In the case of the tympana associated with the tymbals of the cicada, the accessory muscle on the tympanum creases the membrane during tymbalic vibration, presumably to avoid injury. (Pringle: Phys
ical analysis of cicada song, J exp Biol 31, (1954).
The fact that the hearing organs, the tympanals are adjacent to the sonifying tymbals suggests a common origin, perhaps from an array of similar structures. More will be said on this later; here it may be mentioned that we might be seeing a modular design o
f membrane with associated structures. Depending on the requirements, a muscle-controlled membrane module may be designed as emitter or receiver of vibrations.
Three thoracic vibrators?
We have been talking about "tymbals" in the singular. But based on our proposed idea of flight from thoracic vibrators, there should have been two, or even three pairs of them in the assumed ancestor of Pterygota, simply because two nota bear wings today, a
nd the fossil paranota are on the pronotum. Three vibrators may seem like an artificial assumption, considering that extant insects can do with one pair, but perhpas contrasting conditions dictate this variation. The inability to fly would increase the impo
rtnace of defensive sounds, no doubt favoring increas in amplitude. This would be served by multipying the number of sound generators. Another effect of the lack of flight might have been a lesser ability to cover distance, again favoring loud stridulation.
Anatomically, the fact that there were, assumedly, two or three vibrators also implies that the pre-flight terga at this time were still discrete, not fused, and so the thorax could not perform as the framewrok for a single vibrator.
Summary of comparing cicada tymbal and flight
The above review of comparing the flight and the tymbalic systems attempts to show the strong parallels between the two, both in structure and function. And if, as reason would suggest, sound production preceded flight, then such parallelism supports the pr
oposition that flight is a derivative of some type of sonic vibration mechanism on the thorax.
The point to make with the parallel drawn is not that flight specifically originates from timbal mechanics. We can only maintain in a general sense that flight could easily have originated from some undefined vibrating mechanism. As for the timbal analogy,
the tymbal itself may be a perfected form of a simpler, less efficient precursor, and then the derivation of both flight and tymbal mechanism from a general, simple vibrating system, and development of both from a common source into specialized structures a
re merely analogous, showing close parallels. Each structure shows a set of such vibrations modifiable by controlling accessories.
In the Appendix (p. 000) there is a comparative table listing the similarities between the two systems.
Gliding or flight may not have been the original function of wings
The classical image of the insect with the original paranotal lobes is the fossil Palaeodictyoptera. The orientation of its lobes is exactly as wings on an airplane. However, certain Paleozoic nymphs, like those of the Upper Carboniferous Palaeodictyoptera,
Blattodeae and "(Protorthoptera?)" exhibit wing pads lobes that slant postero-laterally. ILL 20 This "position of wing pads...lends weight to Sharov's proposal that insect wings were at first postero-laterally directed; but they may have been flexible enou
gh at the base to allow promotion to the perpendicular position in flight." (R. J. Wooton, The fossil record and flight p. 250). If in fact the wings at first were thus positioned, this may indicate that the wings originally had been lobes that clicked or b
uzzed and waved or flashed and would not necessarily have been positioned in any way proper for flight. A lobe set perpendicularly to the body is minimally visible when facing the insect, but maximally visible when facing the insect's side, but the angle of
a backward directed fan-like proto-wing gives maximal observability for all angles.
Mechano-acoustic properties of the insect cuticle
Assigning sound production such an important role in insects, even leading to the evolution of flight, is not an exaggeration when certain physical properties of the integument is considered. "Jensen and Weis-Fogh, 1962) give some figures for the mechanical
properties of the two types of cuticle found in the locust. The solid tanned cuticle from the thorax, legs, and wings is similar in its mechanical properties, with a coefficient of elasticity of 800-1000 kg mm-2, and a tensile strength of 8-10 kg m
m-2 for an elongation 2-3%; these are comparable to the values for oak wood" (Pringle, Locomotion: Flight p. 436)
To vibrate under minimal influence, a material object needs to be of minimal density and diameter, so that membranous or frictional sound made by insects emerge quite naturally in their magnitude of dimensions. Structural details therefore need and can be s
mall and because the hard material of insectan structure is thin and elastic, it is likely that insects will broadly develop sound making. The analogy to oak only illustrates how humans, building musical instruments that require sounding boards also rely on
its acoustic properties.
The hinged articulation of the wing to the notum
Wings had to become hinged, as required in the paranotal theory. This development is not impossible, but may depend on a number of adventitious occurrences, such as some abnormal thinning out of the paranotal lobe where it leaves the notum. The notum itself
, like the rest of an insect's exoskeleton is sclerotized, that is, the cuticle there contains hardening materials. In order to become flexible the hardening minerals would merely have to be removed. Therefore, in this respect the paranotal theory is accept
able because it builds on known biological processes.
Still, the ancestral role played a thoracic vibrator would pleasantly simplify the task of hinging: the membrane itself is a source of hinging as it buckles in and out
ILL And if the paranotal expansion was not the source of the wing, but instead, it was some evagination of a vibrating membrane then the problem of hinging may never even occurred.
The convex buckling of an elastic membrane provides a hinging element: an object, attached perpendicularly to any place on a vertically oriented membrane. will pivot at the point of attachment and its distal end will describe a vertical arc. This can be ill
ustrated by holding a pencil between the bases of two fingers, and buckling the vertically held hand in and out. ILL (GT)
The empty thorax
Today the thorax of Pterygota, or flying insects, is filled with flight muscles. "The remaining organs have shrunk to 15 per cent of the space at a generous estimate, leaving at least 85 per cent of the total available space to be taken up by the flight mus
cles." (W. Nachtigall, ... p. 68) Before flight the thorax contained only the muscles moving the body segments and controlling the coxa, or the uppermost segment of the leg, so obviously the thorax possessed latent potentials. True, there are other organs,
such as the crop, inside the thorax, but these can be eliminated from our discussion because they are common to both pre-flight and flying insects. Compared with other body parts the volume of space potentially available to the thoracic mass was relatively
undeveloped before flight -- even today the thorax is generally smaller than the abdomen. Therefore the thorax had capacity for additional musculature and integumental extensions. Put another way, by self-definition today, the thorax is capable of holding b
oth the leg and the considerably enlarged wing musculature, therefore when it had only the segmental and coxal musculature, the thorax was utilizing only a part of its total potentials. The abdomen was already specializing in other functions, so the thorax,
equipped with the surface-locomotive (and perhaps the respiratory) neuro-muscular mechanism, had an appreciable likelihood to be employed in additional functions such as sonification.
There is another reason why the thorax is best-suited for sound production. The thorax is the least mobile of the three body parts, even in the pre-flight condition, not only because locomotion by legs requires an amount of pleural rigidity, but also becaus
e it is bounded at both ends, whereas the head and the abdomen are free to move in their relation to the thorax. Therefore the thorax is less practical for use in communicating through movement. The head, already taken up with receiving visual and other inf
ormation plus feeding, leaves only the abdomen and the thorax to be compared. The abdomen can perform visual signalling -- communication through moving the abdomen is practiced among insects whose abdomina are clearly visible, such as Odonata, Drosophila, L
epidoptera.
The thorax, less free to move, and therefore, also more stable, is a likely location for communication which is vibration-produced, rather than kinetically-produced displays. Hence a tymbal or deformation-type vibrator would tend to be located on the thora
x. Even today the membrane-generated vibrations, that is tymbal mechanisms, are either on the least mobile section of the abdomen, directly adjoining to the thorax (Homoptera and Hemiptera), or on the thorax itself (Lepidotera).
In another sense, the head and the abdomen perform the motion, while the thorax is the stable base to which the motion is related. The other parts move, while the thorax enables them to move. The legs, wings, even head and abdomen, and tymbals on or adjace
nt to the thorax -- they all move while the thorax remains unmoving. This quality made the thorax the location of the flight mechanism, and it would also have made it a prime location for a vibrator.
Additionally, we should not forget that are two pairs of wings, the front and back wings. If they indeed originate from a vibrator mechanism, then we ought to postulate the existence of a set, perhaps a pair of vibrators on each side. This would not be in o
pposition to the tendencies of segmental anatomy, which ancestrally repeated segmentally. Furthermore, it is a fact that among cicadas, within the tymbal mechanism, the membrane of the hearing organ, the tympanal membrane, is practically contiguous with th
e tymbal membrane, in a slightly posterior position. Here we see two acoustic membranes adjacent within a single segment. It is, therefore, not without foundation to hypothesize the presence of two vibrators in series on the thorax. This proximity of tymba
l and tympanum will be discussed again.
Nature would have been exceptional had it not utilized all available opportunities to construct. Because the sclerotized, hardened parts of the integument are bounded or bridged by more flexible cuticular materials, there is possibility to fold or bend the
se sclerites relative to each other. These conditions create a potential for the
reflective?? and elastic properties of these materials, combined with muscular action, to be selected for a role in visual and sound communication.
It is certain that a significant percent of the musculature is shared by flight and the coxopleural, or leg base muscles, which existed before flight, but it is also true that flight shares muscles with another older set, the dorsoventral and dorso-longitud
inal muscles of the thorax. These muscles are agents segmental and perhaps respiratory movement in the crawling ancestors of insects. Considering that much of the flight musculature is not exclusive to fli
ght and that this musculature is also not merely potentially but actually applicable to producing sound, we can present one more fact to support the possible conifer origins of flight.
As our last point in this topic, we can also ask: if today insects employ practically all areas of the body for some sort of sound production, would it have been likely, in pre-flight days, for the thorax to be left unutilized, when it already possessed amp
le musculature and an unused pleural and nota surface?
The thorax as visual field
We had earlier stressed the importance of visual communication in insects. Today the wings and the abdomen are primary sites for visual exhibit. In the pre-flight period the wings were absent therefore the bare thorax would be have been a strong candidate f
or carrying visual information. (By controlling the wings, the present pterygote thorax, in fact, plays a part in visual kinetic communication.) In present-day flying insects the thorax is relatively short, or longitudinally compressed, a design dictated by
the engineering of walking and flight, but before flight it may very well have been closer to its full primitive, primary size. (The thorax of the fossil Lemmatomorpha shows a 1:1 size relation between the thorax and the abdomen, perhaps a sign of weaker f
lying powers.)
When adding the thorax to the abdomen, a total visual area increases by a considerable percentage and such stretch of valuable advertising surface would hardly be neglected by the rules of natural design. We can possibly imagine wingless Paleozoic insects w
ith an expanse of color, spots, patches, stripes, bands, geometric or abstract patterns stretching from the thorax to the end of the abdomen.
Here we can turn to the paranotal theory of flight and ask whether the paranotal lobe could have been a visual object? Might it had distinguished various species by its size, color, transparency or reflectivity? The insect Stenodictya had wings also
and presumably could fly. It would therefore have reason to be seen from above by rivals or mates -- such display activity can be seen in modern Odonata. The dragonflies, whether perching with wings held horizontal or vertical, seem to be advertising their
presence to others. The high reflectivity of their wings most certainly is not lost on the eyes of their conspecifics. It may be objected that the horizontal orientation of the plane of the paranotal lobe would make its angle of visibility minimal for pre-
flight, ground-dwelling insects living on the same plane, but insects most often are positioned on vegetation and rocks, which may lie at any angle to the ground or to each other.
In fact the horizontal and vertical wing position can be shown to offer maximum visibility when considering all possible viewing angles..
See appendix for more on Odonata wing display.
Visual design in communicating can also be three-dimensional and moveable -- like the modern wings and elytras. There must have been a time when wings and flight was still primitive, but when its communicative ability was widely employed. An early flier, fl
uttering the wings in a certain pattern would almost certainly be also identifying itself to a mate or rival: the expressiveness of kinetic display would be rather likely to create a strong, selectable impressivity.
Potentials in functional sclerotization of thorax Maybe to Appendix?
The development of sclerites and associated muscles to transform a vibrating membrane structure into the wing and flight structure is not an implausible proposal. Similar structural developments are the basis for most insectan faculties. We read that "...th
e development of refined interrelations between muscles and sclerites has been the principal line of evolution in the arthropods." (Snodgrass, Principals of Insect Morphology, p. 53) Whereas in the Peripatus, an arthropod close to the ancestral insect stock
, or in the soft bodied modern larvae there is minimal sclerotization, at the other extreme of insect specialization the pleuron of the burrowing centipede, the chilopod Haplophilus subterraneus,
is almost totally covered by sclerites acting as body armor against the crushing pressure encountered in burrowing.
ILL 22 (S. A. Manton, The Arthropoda, p. 378)
Sound making potentials of the thorax
The thoracic and abdominal terga and sterna, or top and bottom slcerotized plates, are separated by the pleuron, or membranous cuticle.
ILL 23 Therefore the pleuron can be thought of as a membrane stretched on a frame. Being so, with minor dimensional alterations and with sufficient muscular or neural effects supplied this membrane, stretched between the hard plates is readily adapt
able to producing or sensing air vibrations. At the present the abdomen and the thorax are utilized by insects for tymbal function, but the thorax of a pre-flight insect could perhaps have claimed more potential in sound making than the abdomen because it a
lso contained the coxopleural muscles belonging to a specialized and rhythmically refined neuromuscular system, walking. With such potentials the thorax may have had a good chance developing a dominant role in sound production.
Sound making potential of the coxal muscles
The equality of coxal and direct flight muscles is an anatomical fact and their role in flight development is part of the paranotal theory. The thoracic paranota "developed the ability slightly to pronate, supinate, elevate and depress the pads by action of
the pleural leg muscles; and ultimately. in the case of the meso and metathoracic lobes, as flapping aerofoils, powered mainly by bifunctional leg muscles including those operating in the Blattodea and perhaps supplemented by others now retained only in O
donata." (Wooton, The fossil record and flight, p. 250)
Muscles of the leg base, or coxa, which move the uppermost joint of the leg are attached to the pleuron, or side of the insect, and are inserted on the leg base. ILL Because of this anatomical situation coxal muscles can effect movement of the coxa. However
, it is also possible for such muscles to effect movement on the pleuron, as well. The only difference in what moves and what remains stable is the relative stability of the parts the muscles are attached to. Therefore, if the pleuron is immobile, the coxal
muscles contracted will move the coxa, but if the coxa is rigid, then the pleuron, will move. To immobilize the leg it is only required that the insect firmly hold onto the substrate with its tarsus, or "foot". This action is natural to insects and so it i
s quite conceivable that pre-flight insects could move or vibrate the pleuron by activating coxal muscles while the leg was held rigid. Such set-up would offer a communicative device, perhaps sonic or visual through moving, pulsing or vibrating the pleuron.
A mechanism of this type is an alternate for vibration or movement arising from thoracic deformation of tymbal vibration.
Such dynamic influence on the pleuron by coxal motor muscles has definite parallels in fight. In the case of muscles shared by legs and wings, immobilization, or putting into flight position, of legs is necessary before flight can take place. Clearly, the s
ystem assigns the legs muscles exclusively to either the wings or the legs. Had there been a pre-flight pleural vibrator activated, or at least, modified by leg muscles, this mechanism would maintain a conscious existence into the flight stage. Without mak
ing the connection in our proposal, it has been stated that the "demonstration of this bifunctional role may give the clue to the evolutionary involvement of the indirect and direct muscles in flight." (Pringle, p. 442, in Rainey, ed. Insect Flight)
In our proposition, the significance of certain leg muscles doubling as direct flight muscles is that the pre-flight leg muscles could have easily performed sound making without essential changes in leg-operating position and action. The fossil records unqu
estionably documents the existence of thoracic legs prior to flight, and since legs and sonification may share this chronological trait, the cooperation of the two in sonification is not implausible.
Flight as originally nuptial display
The idea that the original use of wings was in mating display, as suggested by some authors, LOOK UP SOURCE!!
and the present proposition mutually support each other. Communication, whether by sound or sight, is widely employed in nuptial activities, and could have offered fertile grounds for flight development from vibratory organs. It is a an existing fact th
at the functional appearance of wings often is connected with mating activity only, cf. Ephemeroptera, or mayflies, Isoptera, or termites, and among the Hymenoptera, the ants. The fact that functional wings appear on the last instar of almost all Pterygota
is a good indication that wings first could have arisen to facilitate mate finding and for the dispersal of eggs.
The nuptial display role of flight evolution, in a way, undercuts the paranotal theory because it emphasizes the communicative rather than the locomotive role of primitive wings. This notion, on the other hand, supports our alternate theory.
Membrane deformation as common factor in flight and sound production
We have already seen that the indirect muscular activation of the wings can be technically described as the deformation of the thorax, including sclerotized plates and membranes. The principal in the action of sonic transducers such as headphones, speakers,
or eardrums are identical: deformation or distortion of a membrane. Again there is a shared basic function in the wing mechanism and audio functions. As a matter of fact, under the right circumstances we could build a model of a flying insect by designing
a strong miniature vibrator with wings attached and by electronically controlling the vibrations we could make it do something that might range from lifting up to just tipping over on one side. To obtain forward flight it would be helpful to have a composi
te vibrator, or speaker, whose membrane would be divided into several adjacent areas each controlled by a different circuit. This construction would be analogous to both the wing base mechanism with its pteralia and to multitymbal membranes with its serial
ly buckling sclerites. ILL
The receptors of sound, air movement and proprioreceptor organs of insects are also based on deformation sensing. Unlike the vertebrates, where body movement is detected by deformation of muscle, it is supposed that in insects the same is mostly perceived b
y sensing the deformation of the integument. The reversible utility of deformation is shown in Diptera. The hind wing of flies, originally full flight organs activated by thoracic deformation have become small knobs, or halteres, which through their own def
ormation under air pressure sense and control flight direction. The use of deformation, therefore is readily available and developmentally convertible for insects, suggesting once more that thoracic deformation for visual or auditory purposes had a consider
able likelihood to be the source of flight. (more on this in Appendix, under Origin of timbal mechanism)
The distribution of direct and indirect flight mechanism
The alternate theory of flight permits us to think that the click mechanism of indirect flight and the corresponding high wing rate could have preceded or could have been an variant source of flight. Direct flight, with slower wing rate could have evolved f
rom a directly driven pleural membrane)?
SUMMARY OF ALTERNATE THEORY
It is not the existence of a icadan tymbal mechanism that we are proposing as the source of insect flight. We have to take a much more general approach and merely suggest that flight would have a relatively simple, straightforward -- and perhaps even predic
table -- opportunity to emerge when starting with a membranous vibrating mechanism on the thorax of an insect.
The reasons for this possibility are:
1. Sonic and visual communication was undoubtedly present in pre-flight insects because it is relatively simple to develop and because there is a broad role for it to play in adaptation and speciation. At that time, the thorax was relatively unutilized, sin
ce it was without the flight mechanism, and could therefore be the location for a sonic or visual signalling device. This device could have been merely an area of the pleuron that could be buckled or pulsated, or else there might have been a tymbal-type or
deformation-type of vibrator. The great variety of sound-producing structures in insects suggests that it is highly variable and adaptable.
Sonic communication is more effective over distances than the visual kind, so it is likely to have been present in pre-flight time, when insects, running on legs, had considerably lesser abilities to cover geographical area, than once able to fly. Also, vis
ual and sonic structures for communication can evolve far faster than purely physiological functions, as evidenced by the fact that among insects, at least, there are far more variation in outer appearance than there are in basic structures.
2. Having accepted the extent of sonic and visual communication in insects, and its likely presence in the pre-flight population, and also having examined a set of observations that support the proposition, we can say that a vibratory structure in the thora
x would supply the flight motor and only the development of the wings from some cuticular expansion would induce flight. Such a theory, by placing the flight mechanism to precede the appearance of the wing, greatly simplifies the problem of the evolution of
the wing and the flight motor.
3. This alternate theory of flight deals more with the ontogeny of the mechanism of flight,than with that of the wing, Therefore it was significant to see a number of important analogies between the flight mechanism and tymbals. These points may be summariz
ed as:
a. Existing insectan tymbals are conceptual analogues (and perhaps even anatomical homologues of the flight mechanism, excludise of the wings.
b. There are a number of tymbal types -- showing the design's capacity for development -- in fact the Pentatomid tymbal is approxiates, with the addition of paranotal extensions, a complete homology with the action thoracic deformation and the wing itself.
end of main text
1. Charts of evolution of flight (One or more)
2. TABLE OF COMPARATIVE CORRELATIONS BTW WING AND vibrating membrane mechanism
Text: The point of this information: since it is reasonable to assume that sound production, including the tymbal mechanism, is an older development the emergence of which is relatively simple to imagine, it is possible to posit that the development of fli
ght, a far more complicated design is subsequent to the appearance of resonating membrane system. Therefore it is reasonable to assume that if there exists an unusually strong analogy and conceivably even homology between the two systems, the earlier one ma
y be a basis for the development of the later one. In other words the mechanism of flight provides nothing to positively deny that it was not originally a sound producing mechanism, perhaps of the tymbalic sort.
TABLE HERE
THiS IS PBB OUT:
3. Stridulation leading to saltation
SALTATIO EX STRIDULATIONE
In the saltatory Orthoptera we see an interesting interrelation between the development of the femur for competent jumping and the use of the femur and elytra in stridulation. Here we see two functions that support each other and also share one structural e
lement.. If the femur evolved for saltation it also supported emergence of stridulation and vice versa. Therefore one or the other could have provided the nursery condition for the other. Based on this concept an argument is presented in the
Appendix proposing that in fact Orthopteran saltation evolved from femoro- or tibio-elytral stridulation, in which case flight preceded saltation in this order.
WHERE DOES THIS GO??? TO STRIDUL origin of JUMP, where it doesn't Support! Most acridoids make no sound! "Actually, the majority acridoid world fauna is formed by the Catantopinae, Pyrgomorphidae and Acridinae, which have no sound pr
oducing mechanism, or only poorly defined ones. It is worthy of notice that an expansion of the medial area of the hindwing, forming a tympanate area, occurs not infrequently in some Acridinae in which no specialized sound-producing organs are known, for ex
ample in Acrida, Amohicremna, Entryxalis and others; Acrida, however, makes a distinct flight noise.
B. Uvarov, Grasshopper and Locust, Cambridge U Press, 1966 (I THINK this is really supportive!)
SUPPORT for STRIDULATION LEADING TO JUMP: There are femoro-tegminal and tibio-tegminal mechanisms for stridulation. Of tibial types, subfamily Hemiacridinae has rubbing by "inner spines or spurs of the hind tibia." ( though direct observations on action are
lacking. Uvarov Grasshoppers and Locust p ?
QUESTIONS ABOUT THE ORIGINS OF JUMPING --
DID SALTATION arise from stridulation IN ORTHOPTER? and NURSERY
THis = pbbly out. Incorrect.
How did jumping, using legs, originate? Jumping works through a relatively gradual build- up of elastic muscular tension which is suddenly released. The muscles involved should be of maximum cross section to yield maximal force and also short so that their
release would take minimal time in returning to relaxed state. All this would need a context and time for developing. How would such requirements be filled? It seems that such development of unusual muscle triggering is possible based on a anomalous trigge
ring of muscles by the neural system, which alone is responsible for such timing and perhaps the build-up of femoral muscle mass would be a secondary development. Such evolution obviously must have taken place with the various types of jumping insects, howe
ver, with Orthoptera another origin for jumping can be postulated. This is covered below, in SALTATIO exec STRIDULATIONE.
But then this IS SUPPORT: "Several genera of African and Asian savannah grasshoppers have spines on hind TIBIA, and they rub these against the usual scrape vein of the tegmen, but they also have the usual femoro-tegminal mechanism. "They also have well deve
loped tympanate areas of the tegmina" Uvarov p. 180 . AND there is another common mechanism: tegmino-femoral! Here roles are changed, femur has a simple scraper ridge, "which rubs against a specialized intercalary vein..." <<Uvarov, but THIS is not importa
nt!
12. LEG MUSCLES partially SAME AS STRIDULATORY MUSCLES IN ACRIDOIDS. "In acridids, where stridulation is produced by movements of the femora, muscles at the pleurocoxal and coxotrochanteral joints are involved. Some of these muscles have a dual function, si
nce they also move the wings during flight. In all the grasshoppers species studied the order of activation of the muscles is the same, with fast units becoming active after slow units." (Chapman, p. 686) GT: This may be a record of evolutionary development
: the slower neural activity belongs to visual and audio action, while the fast ones, secondary to the slow ones, developed for added intensity and velocity needed for flight.
POSSIBLE ORIGINS OF SOUND COMMUNICATION
With walking established in the evolution of insects, many sclerites on the body and on the legs actively articulated, rotated, rubbed against each other. All this action would take place by the integument with its sound producing potential. Therefore it i
s possible that at the insect level these actions may produce adventitious sounds. There may be tiny creaking, squeaking, scraping and rubbing noises present and since insects approach each other in proximity and experience tactile interactions, these noise
s or low level vibrations may be perceived by them through audio or tactile receptors.
Later, with pterygotes we also can speak of wing rustling when folded and tucked, but the noise production of sclerites, if it exists to a significant degree, goes back to rather early times of insect history.
The question poses itself: if noise production and perception exists at such level, and if it no doubt is ancient, could this be the primitive psycho-physical basis of species recognition by sound in insects? Once there was a code of recognition built on o
lfactory, visual, and audio perception, sound could be an effective medium for communicating at increasing distances.
POSSIBLE ORIGINS OF THORACIC SONIFYING
Here we have to find some structure that could adventitiously produce thoracic sounds. Perhaps breathing, a function today serviced by the abdomen, was once also performed by the thorax. Such temporary structural changes as occur in breathing could offer
a basis for sound production by that body part. Breathing is affected by some combination of compression and release, achieved by intersegmental musculature and so action could become the source of a sonification process leading to vibration of the thorax
by deformation.
But since the thorax early in insectan development was assigned to house the legs and their base musculature, the movement of the coxa could also originated a development towards thoracic sonifying or perhaps, visual signalling. Just to suggest a possible
event that could relate leg movement to sound production, let us look at the leg base musculature of the typical insect.
ILL The promotor and remotor muscles of the coxa (which move rotate the coxa forward and backward) connect the coxa with the pleuron. The muscles originate on the pleuron which is the stable part and they are inserted on the coxa, which is the movi
ng part. But consider the case when the insect is holding on to the substrate, let us say, a plant stem. If the tarsus, or "foot" of the insect, grasps the stem, and generally flexes the leg muscles so that the leg is anchored against moving it, then if the
se coxopleural muscles are stimulated a reversal of movement might take place: the coxa will remain stationary and the pleuron will tend to move concavely inward. Repeated flexing of these muscles will tend produce and inward-outward movement of the pleuron
WING FOLDING - AN ALTERNATE ORIGIN - VISUAL AND NUPTIAL FUNCTIONS
If we picture primitive wings either before or after flight had been achieved, employing their wings as visual signallers, describing rituals
Having developed into large surfaces through their visual display function, pre-flight wings would probably produce pulses of whirl or buzz at various rates as well as slower visual movements, mainly rotation around the body's long axis. But what if compe
tition selected for a wider range of movements and therefore developed a fore and aft flexing of wings? This is not unreasonable to expect and would permit us to make the conclusion that flexure of wings and its consequent folding may have evolved before fl
ight. Such point of view would seem to settle the question whether Orthopteran and Ephemeropteran inability to flex wings is primary or secondary.
The fact that relatively large wings in a pre-flight insect might be psychical obstructions means that folding could also have evolved for that reason, as the accepted theory states. But there is an argument that would eliminate this possibility. And this
argument is in fact one brought up in the accepted theory, namely that early wings may have had to do with nuptial flight. If so then the nuptial period belonging to the last instar, with a purely reproductive role and without a need for nourishment, would
permit large wings whether folded or not since survival and escape would be not be a high enough criterion at this stage. However, the issue is doubly clouded by the finding of an adult Ephemeroptera with functional mouth parts in the fossil record (SOURCE
...) and by the fact that living Ephemeroptera do not fold their wings.
This idea of wing folding predating flight has been stated by at least one author although still in the context of the accepted theory: S. M. Manton writes "A narrowing of the wing base and added complexity in structure could lead to the ability to fold t
he wings when not gliding....Simple flapping flight presumably came after the ability to fold the wings." (The Arthropoda, p. 428).
Looking at the illustraion of the crosss section of folded wings, it is interesting to note that the folded, plicated? wing may be the original charater of the proto-wing; derived from the striated, ribbed nature of tymbal membranes. In this case not foldin
g the wings, but stretching them tight would be the aim of development. ILL (Snodgrass?)
THE ORIGIN OF THE WING --this should be in the text!!! Before the summary of the theory!!!
<[>THIS GOES TO THEORY OF WING ORIGINS Write: how the paranotum may not have been the ancestor of the wing. IT could also have been a membranous fold growing out of the pleural surface covering the basalar, subalare, etc?, the pleural wing/leg muscle slcer
ites. ILL Maybe this was originally a band connecting the several separate sclerites which may have together with axillaries acted as membrane subvibrators, in order to unify the sound for amplification?? and then it started making a different noise
bk of the drum pulser turning into a fan pulser (see below in *** NEW) Also: The wing could also have been a paranotal lobe, but emerging as attachments, perhaps, covers, for a timbal. They may never have been hard.]
Anyway, this is the possible reason for the fact that the wing is only hinged to the notum. And so answers the question of how the proto-lobe ancestor of the wing became hinged.
12/24 after discovering Pentatomid tymbal really:
Combined with the Pentatomid tymbals on the thorax, paranotal extensions would be a most convincing theoretical ancestor of the wing. The role of the lateral edges of the nota before any extension need take place, would be as distal? parts of the rim encomp
assing the vibrating surface, or membrane. The rims could extend laterally to increase the size of the membrane and also to increase the strength of the rim. This extension would in effect be a paranotal lobe, which would already be connected with a membran
e hinge, and a row of ribs and slcerites, from which the wings base sclerites and perhaps, rudiments of wing venation may be derived.
If then the paranotal lobe for some reason (such as aberrant development) became mobile, it would generate not only a sound of buzzing, or fanning the air (rather than pulsating it in ne direction, as a mambrane). This motion, at given speeds would be visib
le and would be a tool of visual signaling. Such adaptation would lead to size increment and when conditions were correct, flight would begin perhaps with brief, buzzing performances of lift and hovering in nuptial, rivalry, or defensive context.
The paranota could also have functioned as tymbal covers. If there was a variant of the Pentatomid tymbal with a vibrating area on the pleuron, then such a cover could becomne a visual signaler if it becaome mobile.
THE GT SOURCE OF THORACIC SONIFYING: -- still to be worked out in detail!
(To meet the requirement of relying only in documented substratum (source) for a proposed sequence of events: ) The physical properties of the cuticular materials and the presence of thoracic and leg musculature only need a novel set of neurological sti
muli to appear. There is
1. Wing muscles are partly identical or derivable with leg muscles - used originally for audio or visual communications -- The legs themselves may have been the signallers; lobes may have appeared to amplify this visual leg action; this could have had a
udio side-products.
2. Indirect wing muscles are derived
3. derivation from breathing musculature
M. D. Atkins, Introduction to Insect Behavior, Macmillan, 1980 D. J. Borror, D. M. DeLong and C. A. Triplehorn, An introduction to the study of insects, 4th
edition, Holt, Rinehart and Winston, 1976
H. B. Boudreaux, Arthropod Phylogeny with Special Reference to Insects, Wiley, 1979
R. F. Chapman, The Insects, 3rd ed., Harvard U. Press, 1982
R. G. Davies, Outlines of Entomology, 7th ed., Chapman and Hall, 1988
G. M. Hughes and P. J. Mill, Locomotion: Terrestrial, in M. Rockstein, ed.,
The Physiology of Insecta, Academic Press, 1973,
P. T. Haskell, Insect Sound, Witherby, 1961
U. Lanham, The Insects, Columbia U. Press, 1964
S. A. Manton, The Arthropoda, Clarendon Press, 1977
W. Nachtigall, Insects in Flight, McGraw-Hill, 1968
D. Otte, North American Grasshoppers, Harvard U. Press, 1984
J. W. S. Pringle, Locomotion: Flight, in M. Rockstein, ed., The Physiology of Insecta, vol. 2.
O. W. Richards and R. G. Davies, Imm's General Textbook of Entomology, 10th ed., Chap man and Hall, 1977
A. G. Sharov, Basic Arthropodan Stock with Special Reference to Insects, 1st ed., Pergamon
R. E. Snodgrass, Principles of Insect Morphology, McGraw-Hill, 1935
B. Uvarov, Grasshoppers and Locusts, Cambridge U. Press, 1966
V. B. Wigglesworth, Life of Insects, World, 1964
V. B. Wigglesworth, The evolution of insect flight, in Insect Flight, edited by R. C. Rainey,
Symposium of the Royal Entomological Society of London, 1976
R. J. Wooton: The fossil record and insect flight, in Insect Flight, edited by R. C. Rainey,
Symposium of the Royal Entomological Society of London, 1976