The auditory thresholds of the AN2 interneuron and the behavioural thresholds of the anti-bat flight-steering responses that this cell evokes are less sensitive in female Pacific field crickets that live where bats have never existed (Moorea) compared with individuals subjected to intense levels of bat predation (Australia). In contrast, the sensitivity of the auditory interneuron, ON1 which participates in the processing of both social signals and bat calls, and the thresholds for flight orientation to a model of the calling song of male crickets show few differences between the two populations. Genetic analyses confirm that the two populations are significantly distinct, and we conclude that the absence of bats has caused partial regression in the nervous control of a defensive behaviour in this insect. This study represents the first examination of natural evolutionary regression in the neural basis of a behaviour along a selection gradient within a single species.
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Acknowledgements For assistance while in the field, we thank Neil Davies and the staff of the Richard B. Gump South Pacific Research Station (Moorea, Polynésie française), Gerald McCormack (Cook Islands Natural Heritage Project, Rarotonga, Cook Islands), and Chris R. Pavey (Department of Natural Resources, Environment and the Arts, Australia). We thank David Fang of the UC Riverside Genomics Center for assistance with the microsatellite analysis and Cheryl Hayashi for laboratory space. We also thank Michelle Venance, Steve Fynk, Millie Engel, Shannon Venance, and Maura Purdon for their field proficiency at cricket collecting. This work was supported by the Natural Sciences and Engineering Research Council of Canada Discovery Grants to J.H.F and G.S.P., a Journal of Experimental Biology Traveling Fellowship to H. M. t. H., a National Science Foundation Grant Doctoral Dissertation Improvement Grant to R.M.T. and M.Z., and a University of California Pacific Rim Mini-Grant to R. M.T. Studies were carried out in accordance with permits issued by the Délégation à la Recherche (Polynésie française), the Cook Islands Foundation for National Research (Cook Islands), and the Department of the Environment and Heritage and Northern Territory Parks and Wildlife (Australia).
- Genetic isolation
- Island biology
- Sensory ecology