Convergent life-history shifts: toxic environments result in big babies in two clades of poeciliids |
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Authors: | Rüdiger Riesch Martin Plath Francisco J García de León Ingo Schlupp |
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Institution: | 1. Department of Zoology, Graduate Program in Ecology and Evolutionary Biology, University of Oklahoma, 730 Van Vleet Oval, Norman, OK, 73019, USA 2. Department of Ecology and Evolution, Goethe-University Frankfurt, Biologie-Campus Siesmayerstra?e, 60323, Frankfurt, Germany 3. Centro de Investigaciones Biológicas del Noroeste, S.C., Mar Bermejo No. 195, Col. Playa Palo de Santa Rita, A.P. 128, La Paz, Baja California Sur, 23090, Mexico 4. Department of Zoology, University of Oklahoma, 730 Van Vleet Oval, Norman, OK, 73019, USA
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Abstract: | The majority of studies on ecological speciation in animals have investigated the divergence caused by biotic factors like
divergent food sources or predatory regimes. Here, we examined a system where ecological speciation can clearly be ascribed
to abiotic environmental gradients of naturally occurring toxic hydrogen sulfide (H2S). In southern Mexico, two genera of livebearing fishes (Poeciliidae: Poecilia and Gambusia) thrive in various watercourses with different concentrations of H2S. Previous studies have revealed pronounced genetic differentiation between different locally adapted populations in one
species (Poecilia mexicana), pointing towards incipient speciation. In the present study, we examined female reproductive life-history traits in two
species pairs: Gambusia sexradiata (from a nonsulfidic and a sulfidic habitat) and Gambusia eurystoma (sulfide-endemic), as well as P. mexicana (nonsulfidic and sulfidic) and Poecilia sulphuraria (sulfide endemic). We found convergent divergence of life-history traits in response to sulfide; most prominently, extremophile
poeciliids exhibit drastically increased offspring size coupled with reduced fecundity. Furthermore, within each genus, this
trend increased with increasing sulfide concentrations and was most pronounced in the two endemic sulfur-adapted species.
We discuss the adaptive significance of large offspring size in toxic environments and propose that divergent life-history
evolution may promote further ecological divergence through isolation by adaptation. |
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