Ort: Hörsaal, Museum Koenig
Zeit: 17.11.2011, 17:15h
"Extremophile" fishes: adaptations to darkness and H2S-toxicity
In classical models of (allopatric) speciation, adaptation to divergent environmental conditions was not a necessary prerequisite for reproductive isolation to evolve; however, an increasing number of studies provide theoretical and empirical support for the idea that ecology can play an important role during speciation processes (especially in sym- and parapatric systems). I propose that extremophile populations of Mexican livebearing fishes (Poeciliidae; genera Poecilia and Gambusia) are particularly well suited to examine the evolution of reproductive isolation due to divergent evolution along abiotic ecological gradient. Extreme habitats challenge animals with highly adverse conditions, like extreme temperatures or toxic substances such as hydrogen sulfide (H2S). I will primarily focus on Poecilia mexicana inhabiting a sulfurous southern Mexican limestone cave (the "cave molly" from the Cueva del Azufre) as well as several sulfidic and non-sulfidic surface streams in the vicinity of the cave. Several springs inside the cave are rich in H2S, which is toxic for metazoans even in micro-molar amounts. Only recently, we described a second cave population of P. mexicana from the nearby, but non-sulfidic Cueva Luna Azufre. Hence, P. mexicana in the study area inhabit different habitats with all combinations of the two environmental stressors H2S and/or darkness in a '2x2 factorial design'. I will demonstrate mechanisms by which poeciliids manage to cope with the environmental stressors, and provide evidence for adaptive divergence on various levels such as morphology, physiology, reproductive life history, trophic ecology and especially behavior. An attempt will be made to distinguish between the evolutionary effects of darkness and/or hydrogen sulfide. Finally, population genetic and phylogenetic analyses provided evidence for pronounced genetic differentiation, and restricted gene flow between populations in divergent habitat types, even if collection sites were only few hundred meters apart. Mechanisms leading to this small-scale genetic differentiation are discussed; these include direct selection against migrants, competitive exclusion, and mate choice for mating partners from the same, locally adapted population.
