Correlations between mechanisms of acoustic vibrating membranes
(tymbals) and of flight
/ and Origin of tymbal
1. Both are some kind of vibrating mechanism, or multivibrator.
2. Both produce acoustical vibrations. Being vibrating mechanisms,
by definition, both produce sound. The wing may be viewed as an advanced
acoustic generator that not only creates sound but visual signals,
as well.
3. Both have acoustic functions. The acoustic function of tymbals
needs no proof, but with insects, the known use of wing beat vibrations
is principally with mate location by mosquitoes, not a very large
variety of insects. However, as far as we know, there may be many
more examples of communicative uses of wing vibrations that are not
as obvious as mate finding.
4. The mechanism of both employs a click action of some sort. The
wings, whether direct or indirectly driven, employ some click mechanism.
The original Dipteran click mechanism was also found to some degree
of similarity in other orders, such as Odonata LOOK UP!!, but
even if the true nature of design this mechanism is still to be described,
the fact is that the wing is by no means a freely hinged object. An
important component is elasticity, which represent an antagonistic
force for the muscles. The elasticty of the wing hinge enables the
musculatrue to save energy because after muscles have moved the wing
to one extreme position, there is no need to pull the wing back to
the initial position because the elastic energy stored at the out
movement one way will be released and converted to the movement back.
Tymbals perform precisely this action, in the simplest form. The basis
of a click mechanism, in fact, may be exhibited by the serial buckling
of the distinct ribbed sections of some tymbal membranes, especially
the multitymbal types, found in Arctidae??
5. Keep or merge with no. 4? -- Both employ high-elasticity materials,
a basic component of the multivibrator structure, and of click mechanisms.
"The capacity tostore elastic energy and subsequently to release it
at high rates is an esential ferature of the flight mechanism of most
insects." (Chapman, The Insects, p. 218)
6. Both have myogenic muscluar action.
7. Models -- another point to make: folding the wing, all plicated,
corrugated fanlike, folded back and also corrugated, with the additiojal
problems of developing flight mucsluature and control -- these are
complex things. It is easier to devlope them from precursors that
already develop to near perfection. For this reason the tymbal membrane
model, with its corugated, ribbed surface and its scelirtes and corrugtion
and bending in and out, alrready designed developed for the relatively
simple task of vibrating air, is an acceptable theoretical model of
ancestry for the flight mechanism, since the winfgs are corrugated,
have scelrites, that is pteralia, related tho this corrugation, and
it moves up and down in order to vibrate the air. Only, in the context
of the wing nad its musculature, the design of the vibrator surface,
(the wing), while vibrating the air also causes pressure inequaliies
in the air, which action creates lift.
But for the specialized design of the vibrating surface, the models
of tymbal and wing motion are basically identical.
Possible origins of the cicadan tymbal mechanism
There have been at least two ideas presented to explain the origin
of cicadan, and more generally Homopteran (Hemipteran? acc. to Pringle!),
tymbals. One derivation is from physical proximity in copulatory contacts
abd movements among insects where small cuticle-poduced clicks would
be perceveible. The other explanation, assuming the presence of wings,
would attribute the development of the tymbal to strigillation between
the first abdominal segment and some frictional surface on the wing.
(Leston and Pringle, Acoustical Behavior of Hemiptera, in Busnel,
To these we may add two other ideas:
1. One possible source for the cicadan tymbal, suggested by its anatomy,
might be respiratory movements involving muscles and the integument.
Active muscle-driven respiration in insects implies the some kind
of distension and contrction of the integument, through which air
is moved through the trachea. Since the tymbal is a part of the integument,
put into motion by muscle, it is anatomically derivable from respiration.
The communicative function may begin as a visual signal, and thorugh
increasing intesnity can produce sound. Of course, respiratiry movement
is relatively smooth, or sinusoidal, whereas the tymbal movement has
a click action, or square-wave-like motion. This elastic, click mechanism
is derivable from the elastic nature of the integument, and would
be further supported by the advantage of decreased need for muscular
2. Another possible source of cicadan ymbals is suggested by its anatomic
environment.
The cicadan tymbal is in direct proximity of the tympanum, the organ
of hearing. Fig. 000. The tympanum consists of the tympanal membrane
stretched out on a rigid frame, sensory receptors attached to the
membrane and muscles that vary the tension of the membrane. Thus,
the tympanum has all the parts to make a tymbal. Anatomically, then,
tymbals can be derived from tympana. Why not the other way around?
Because perception of sound is most likely more elementary and ancestral
than producing it. There is little sense in a species producing sounds
for intraspecific purposes if the reception is not there, but it is
still sensible to develop hearing organs for defense. Therefore, it
is plausible that tympana arose first. Incidentally, the tympanal
muscle is thought to have a protective function in releasing the tension
while the adjacent tymbal is operating at high volumes. However, it
is reasonable to think that the muscles might also serve otherwise,
perhaps to tune the resonance to for compensate variations in atmospheric
At any rate, the development of a passive receiving organ is structurally
simpler than an active one producing sound. The hearing organ
lthough it is true, an insect can produce defnsive sounds, interspecific
tools, with no need for intraspecific reception.
<[>Add to: Source of soud comunvation: maybe defensive
sound making is a good source!]