Sex-specific local life-history adaptation in surface- and cave-dwelling Atlantic mollies (Poecilia mexicana).

Rüdiger Riesch,Ingo Schlupp,David N Reznick,Martin Plath

doi:10.1038/srep22968

Abstract

Cavefishes have long been used as model organisms showcasing adaptive diversification, but does adaptation to caves also facilitate the evolution of reproductive isolation from surface ancestors? We raised offspring of wild-caught surface- and cave-dwelling ecotypes of the neotropical fish Poecilia mexicana to sexual maturity in a 12-month common garden experiment. Fish were raised under one of two food regimes (high vs. low), and this was crossed with differences in lighting conditions (permanent darkness vs. 12:12 h light:dark cycle) in a 2 × 2 factorial design, allowing us to elucidate potential patterns of local adaptation in life histories. Our results reveal a pattern of sex-specific local life-history adaptation: Surface molly females had the highest fitness in the treatment best resembling their habitat of origin (high food and a light:dark cycle), and suffered from almost complete reproductive failure in darkness, while cave molly females were not similarly affected in any treatment. Males of both ecotypes, on the other hand, showed only weak evidence for local adaptation. Nonetheless, local life-history adaptation in females likely contributes to ecological diversification in this system and other cave animals, further supporting the role of local adaptation due to strong divergent selection as a major force in ecological speciation.

Highlights

Cavefishes have long been used as model organisms showcasing adaptive diversification, but does adaptation to caves facilitate the evolution of reproductive isolation from surface ancestors? We raised offspring of wild-caught surface- and cave-dwelling ecotypes of the neotropical fish Poecilia mexicana to sexual maturity in a 12-month common garden experiment
Traits that are beneficial in the native habitat might turn out to be maladaptive in a foreign habitat, a phenomenon known as local adaptation[1,2,3]
We did not find consistent differences in body fat or interbrood intervals between both ecotypes, which could indicate that the presence of H2S in CdA is the main driver for the low body fat characteristic for wild-caught cave mollies[29,30]

Summary

Introduction

Cavefishes have long been used as model organisms showcasing adaptive diversification, but does adaptation to caves facilitate the evolution of reproductive isolation from surface ancestors? We raised offspring of wild-caught surface- and cave-dwelling ecotypes of the neotropical fish Poecilia mexicana to sexual maturity in a 12-month common garden experiment. Our results reveal a pattern of sex-specific local life-history adaptation: Surface molly females had the highest fitness in the treatment best resembling their habitat of origin (high food and a light:dark cycle), and suffered from almost complete reproductive failure in darkness, while cave molly females were not affected in any treatment. Males of both ecotypes, on the other hand, showed only weak evidence for local adaptation. This system is an example in which cave fishes co-occur with their closely related surface-dwelling relatives within the same river system[14,15], providing an excellent opportunity to investigate how adaptation to a cave environment affects life histories and, indirectly, reproductive isolation between surface and cave populations

Methods

Results

Conclusion