Vibrational signals in a gregarious sawfly larva (<Emphasis Type="Italic">Perga affinis</Emphasis>): group coordination or competitive signaling? |
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Authors: | Lynn E Fletcher |
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Institution: | (1) Department of Neurobiology and Behavior, Mudd Hall, Cornell University, Ithaca, NY 14853, USA |
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Abstract: | Group living confers both benefits and costs to the individuals involved. Benefits may include enhanced defense, thermoregulation,
and increased foraging efficiency while costs often involve competition for resources such as food, shelter, and mates. Communication
provides a medium of exchange among individuals engaged in either cooperative or competitive interactions. The functional
analysis of signals within groups therefore requires testing both cooperative and competitive functions, although the latter
is infrequently done. In this paper, I study the use of two vibrational signals in a gregarious, processionary Australian
sawfly larva, Perga affinis: tapping and contractions. Tapping involves striking the substrate with the sclerotized portion of the abdominal tail and
a contraction is a fast, whole-body twitch, which is both tactile and vibrational in its transmission. For tapping, I first
demonstrate that it is a form of communication, as tapping of one larva elicits tapping in another, and that it is transmitted
through substrate vibrations. I then test whether the signal is mostly cooperative or competitive in nature by examining it
in light of two hypotheses: (1) the Group Coordination hypothesis, stating that the signal functions to maintain group cohesiveness
and (2) the Competitive Signaling hypothesis, stating that tapping serves as a competitive assessment signal between larvae
while feeding. For contractions, I test only the group coordination hypothesis that they serve to coordinate and initiate
group movement. Results support the group coordination hypothesis for each signal. While feeding, lone larvae (without potential
competitors) were significantly more likely to tap than those in groups, and this trend continued in non-feeding situations.
Contractions regularly preceded periods of group movement during processions and were given with increasing frequency before
departure from preforaging clusters. The vibrational signals in this processionary species likely function cooperatively to
maintain group cohesiveness and coordinate movement. |
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Keywords: | Vibrational signals Cooperation Communication Group living Processionary larvae |
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