Behavioral Ecology of cave dwelling and extremophile poeciliid fishes: Influence of darkness, hydrogen sulfide and low food availability on the behavior, reproductive life-history traits and sexual selection in mollies (Poecilia mexicna, P. sulphuraria) and mosquitofisch (Gambusia holbrooki, G. eurystoma)
Final Report Abstract
In classical models of (allopatric) speciation, adaptation to divergent environmental conditions was not a necessary prerequisite for reproductive isolation to evolve; however, an increasing body of literature provides theoretical and empirical support for the idea that ecology can play an important role during speciation processes (especially in sym- and parapatric systems). 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 gradients. Extreme habitats challenge animals with highly adverse conditions, like extreme temperatures or toxic substances such as hydrogen sulfide (H2S). The projects have examined speciation processes in extremophile poeciliid fishes from southern Mexico, with a focus on Poecilia mexicana inhabiting a sulfidic 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 have examined mechanisms by which poeciliids manage to cope with the environmental stressors, and provided evidence for adaptive divergence on various levels such as morphology, physiology, reproductive life history, trophic ecology and behavior, whereby an attempt was made to distinguish between the evolutionary effects of darkness and/or hydrogen sulfide. On a morphological level, sitespecific selective regimes lead to pronounced (heritable) divergence in traits like head size, and extremophile fish from sulfidic habitats have convergently evolved larger heads, allowing for increased total gill filament area, and thus, more efficient oxygen uptake, which may be essential under sulfidic, hypoxic conditions. Also several behaviors are derived in extremophiles, for instance, aggressive and sexual behaviors are reduced, which is likely driven by energy limitation, as most available energy must be channeled into detoxification processes. 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, suggesting a mechanism that has been termed “isolation-byadaptation”. Mechanisms leading to this small-scale genetic differentiation were also examined; these include direct selection against migrants, competitive exclusion, and mate choice for mating partners from the same, locally adapted population.
Publications
- (2007) Local adaptation and pronounced genetic differentiation in an extremophile fish, Poecilia mexicana, from a Mexican cave with toxic hydrogen sulfide. Molecular Ecology 16:967–976
Plath M, Hauswaldt JS, Moll K, Tobler M, García de León FJ, Schlupp I, Tiedemann R
- (2008) Does divergence in female mate choice affect male size distributions in two cave fish populations? Biology Letters 4:452–454
Tobler M, Schlupp I, Plath M
- (2008) Toxic hydrogen sulfide and dark caves: phenotypic and genetic divergence across two abiotic environmental gradients in Poecilia mexicana. Evolution 62:2643–2659
Tobler M, DeWitt TJ, Schlupp I, García de León FJ, Herrmann R, Feulner PGD, Tiedemann R, Plath M
- (2009) Natural and sexual selection against immigrants maintains differentiation among micro–allopatric populations. Journal of Evolutionary Biology 22:2298–2304
Tobler M, Riesch R, Tobler CM, Schulz–Mirbach T, Plath M
- (2010) An indigenous religious ritual selects for resistance to a toxicant in a fish (Poecilia mexicana, Poeciliidae). Biology Letters (online first)
Tobler M, Culumber ZW, Plath M, Winemiller KO, Rosenthal GG
- (2010) Locally adapted fish populations maintain small–scale genetic differentiation despite perturbation by a catastrophic flood event. BMC Evolutionary Biology 10:256 (electronic publication)
Plath M, Hermann B, Schröder C, Riesch R, Tobler M, García de León FJ, Schlupp I, Tiedemann R
