I attended a presentation by Bruce Robertson on evolutionary traps. This describes a situation where a previously reliable signal used to trigger a fitness-increasing response becomes associated instead with fitness reduction when the response is made. An example Robertson gave was that of just-hatched sea turtles, which have to make their way from high on a beach to the water in order to have a chance at living to adulthood. The timing of hatching generally coincided with a phase of the moon such that hatchlings could orient to the moonlight and that would take them to the water. With the introduction of brightly lit human properties on the coast, hatchlings may instead head inland, where it is very unlikely that they will survive. Robertson expanded on this to discuss how preferences in organisms may elicit maladaptive responses to entirely novel cues, and how these situations arise in an evolutionary framework.
In the evening, researchers presented their work in a poster session. This is Diane’s favorite part of almost any scientific conference. Generally, you can directly engage the researcher concerning the work being presented. As a matter of form, there has been a paradigm shift in how one presents a poster. Back in the 1980s and 1990s, it was pretty much a given that a “poster” presentation was actually comprised of many individually printed sheets of paper that were laid out on backing board. The number of presentations that made use of a single poster-sized printout were generally pretty small. That has changed, inverting the frequencies of each type of presentation. Nowadays, poster-sized printouts comprise most presentations. At the session here at ABS, I only recall one presentation made via the method of tacking up many letter-sized pieces of printed paper. All the rest were poster-sized prints. Clearly, print shops are doing some good business in preparing these materials.
On to the content. I made my way around the pavilion, looking for posters that dealt with bioacoustics, and particularly those where signal analysis played a big role in the research. Of these, I spent more time talking with Jennifer Hamel concerning her work than with anyone else. The following is the abstract from the program:
LIL’ CLICK-ZIPPER: A NEW SONG MORPH IN THE AMBLYCORYPHA ROTUNDIFOLIA COMPLEX (KATYDIDS)
Phaneropterine katydids engage in duets as part of their pair-forming system. The calling songs of males in the genus Amblycorypha are complex, and often contain several components produced in varying temporal sequences. There are two described species in the rotundifolia complex, A. alexanderi and A. rotundifolia, that occur in western North Carolina. Both A. alexanderi and A. rotundifolia are cryptic species and do not differ morphologically, but their acoustic signals differ significantly. Because their calling songs are used in pair formation and act as species isolating mechanisms, the analysis of katydid songs offers an easy method for finding undescribed species. Analyses of male songs and duets of an Amblycorypha population at Rich Mountain, N.C., showed both male songs and duets to be significantly different from the species currently known for western North Carolina. Additionally, significant morphological differences were found between this group and a neighboring population of A. alexanderi, suggesting that this population represents an undescribed species in the rotundifolia complex.
(Source: ABS 2005 Abstract Book)
There’s a bit of a difference in terminology between that used by the katydid research community and the marine mammal community. For us (the marine mammal folks), a click is a single transient-like acoustic event, and a click train is a sequence comrpised of a number of clicks with relatively short inter-click intervals. For them (the katydid folks), a single transient-like event is a spike, and a click is a sequence comprised of some number of spikes with relatively short inter-spike intervals. And, of course, the method of production of clicks in, say, bottlenose dolphins and spikes in katydids are quite different. Dolphins produce clicks by passing air through the phonic lips, structures in the nasal passage about 2.5 cm below the blowhole. Katydids utilize a stridulation mechanism, which involves moving a scraper along a file, and in at least some, they may produce tones by exciting a resonance in a tegmen (one of the front pair of wings).
I’m hoping to be able to correspond with Hamel and obtain a sample recording of the Rich Mountain katydid. I’m interested in applying the click-picking techniques I developed for the analysis of dolphin biosonar to other bioacoustic examples, and the katydid call waveform looks like it may be amenable to the same techniques I used.
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