Diverse reproductive barriers in hybridising crickets suggests extensive variation in the evolution and maintenance of isolation
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Reproductive barriers reduce gene flow between populations and maintain species identities. A diversity of barriers exist, acting before, during and after mating. To understand speciation and coexistence, these barriers need to be quantified and their potential interactions revealed. We use the hybridising field crickets Gryllus bimaculatus and G. campestris as a model to understand the full compliment and relative strength of reproductive barriers. We find that males of both species prefer conspecific females, but the effect is probably too weak to represent a barrier. In contrast, prezygotic barriers caused by females being more attracted to conspecific male song and preferentially mounting and mating with conspecifics are strong and asymmetric. Postzygotic barriers vary in direction; reductions in fecundity and egg viability create selection against hybridisation, but hybrids live longer than pure-bred individuals. Hybrid females show a strong preference for G. bimaculatus songs, which together with a complete lack of hybridisation by G. campestris females, suggests that asymmetric gene flow is likely. For comparison, we review reproductive barriers that have been identified between other Gryllids and conclude that multiple barriers are common. Different species pairs are separated by qualitatively different combinations of barriers, suggesting that reproductive isolation and even the process of speciation itself may vary widely even within closely related groups.
KeywordsGryllus bimaculatus Gryllus campestris Gryllidae Reinforcement Sexual selection Mate choice Speciation
We would like to thank Gina Conte, Seth Rudman and Rolando Rodríguez-Muñoz for valuable advice and Rolando for cricket collecting. Four anonymous Peerage of Science reviewers gave very constructive advice for which we are very thankful. T. V. was supported by a Rubicon grant from the Netherlands Organization for Scientific Research and the NSERC-CREATE Training Program in Biodiversity Research from Canada. F.T. was supported by the European Social Fund. T. T. was supported by grants from the Natural Environment Research Council.
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