Codivergence but Limited Covariance of Wing Shape and Calling Song Structure in Field Crickets (Gryllus)
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Morphological traits are often used in performing ecological tasks or in sexual display behaviour. Variation in morphology is thus expected to be coupled to variation in idiosyncratic behaviours across ecologically or sexually diverged lineages. However, it is poorly understood whether this prediction holds and how functional constraints, shared ancestry, or selection contribute to morphology-behaviour co-evolution. Here, we test this prediction in four cricket species, which differ strikingly in their sexually selected mate calling songs, produced by engaging their specialized forewings. Using geometric morphometrics we provide the first evidence that wing shape and size varies consistently across species. We then test whether wing shape and song co-evolve and whether co-evolution is best explained by individual-level functional/genetic covariance or by population-level evolutionary covariance. Song structure and wing shape are coupled, even after accounting for phylogeny. However, there is limited covariance within species. Thus, wing morphology and sexual signalling behaviour in crickets are likely linked due to shared (ancestral) effects from neutral and selective processes. We show that morphology and behaviour can be linked across but not within species and discuss how evolutionary stasis, genetic linkage, and evolutionary covariance help explain this pattern.
KeywordsCo-evolution Functional morphology Sexual communication Geometric morphometrics
We thank D. A. Gray for providing preliminary results of the phylogenetic relationships among the species included in this study. We also thank one anonymous reviewer and Benedikt Hallgrimsson as well as three other anonymous reviewers for comments that improved earlier versions of this manuscript. The performed experiments comply with the Principles of Animal Care (1985) of the National Institute of Health and with the current laws of Germany. This study is part of the GENART project funded by the Leibniz Association (SAW-2012-MfN-3).
Compliance with Ethical Standards
Conflict of interest
The authors declare no conflict of interest.
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