Cooperative signaling as a potential mechanism for cohesion in a gregarious sawfly larva, <Emphasis Type="Italic">Perga affinis</Emphasis> |
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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: | During periods of travel or dispersive activities (e.g., foraging), group-living animals face the common challenge of maintaining
a cohesive unit. At the basic level, this challenge is no different for vertebrates than it is for arthropods and is solved
through communication. Gregarious larvae of the Australian sawfly, Perga affinis, communicate via vibrational signals. The most common signal, tapping, involves striking the substrate with the sclerotized
tip of the abdomen. This study investigates the role of tapping as a mechanism of cohesion, specifically in situations between
a separated larva and a group. As nomadic foragers that move daily to new feeding locations and readily coalesce with other
colonies, the possibility of separation and potential re-aggregation arises regularly. Experiments demonstrated that tapping
facilitates cohesion as groups responded to the tapping of lone larvae and did so preferentially over other larval behaviors.
Additionally, separated larvae respond to tapping by the group through increased walking activity. It is also possible that
they receive directional information from the group's vibratory signals, although visual cues may influence orientation as
well. Tapping represents a cooperative signal and, as such, I investigated the level of investment of both parties in the
communicative exchange. While individual larvae invested more in the exchange than the group, the exchange is analogous to
the Raise-the-Stakes model of cooperation in that groups gradually increased their investment according to the cumulative
time spent tapping by the lone larva. The mutual but asymmetrical benefits received through cooperation are discussed and
compared with similar situations between parents and offspring. Not all larvae in the group participated equally, suggesting
individual differences in signaling propensity or strategy. |
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Keywords: | Cooperative communication Cohesion Asymmetrical investment Larval groups Pergidae |
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