Extreme habitats are characterized by the presence of extreme physiochemical stressors that require – of any organism tolerating them– costly adaptations that are absent in closely related species. Some organisms are able to cope with extreme environmental conditions and thrive in places that are hostile for most others, giving rise to unique ecological communities and proving life’s capacity to adapt to far from average conditions through natural selection.

Extreme conditions can occur nested within “normal” habitats on small spatial scales (e.g., hypoxic areas of lakes and swamps, highly acidic soils, or rocky outcrops without water holding potential within grasslands).Such localized extreme habitats and their inhabitants are especially valuable for evolutionary ecology research because they allow for a powerful comparative approach for testing the effects of physiochemical stressors on ecological and evolutionary processes. The presence of extreme physiochemical stressors can affect the ecology of individuals as well as the evolutionary trajectory of populations in two ways: directly by interfering with the maintenance of homeostasis in individuals and indirectly by altering other aspects of the abiotic and biotic environment. Hence, extreme and non-extreme habitats do not only differ in the presence or absence of a physiochemical stressor, but are connected by a complex environmental gradient usually involving multiple abiotic environmental factors as well as major differences in the biotic communities. I use a livebearing fish, the Atlantic molly (Poecilia mexicana),which is wide-spread throughout Central America but has also colonized multiple toxic (hydrogen sulfide-containing) springs, as a model system to study ecological and evolutionary consequences of living under extreme conditions.

My current core research project investigates local adaptation and ecological speciation in Atlantic mollies inhabiting sulfidic habitats. Using molecular genetic, morphological, and behavioral methods, I am currently investigating (i) how the fish cope with physio-chemical stressors, (ii) whether living under extreme conditions leads to adaptive trait divergence,(iii) whether divergent traits evolved independently along similar environmental gradients, and (iv) whether local adaptation leads to reproductive isolation from conspecifics residing in normal habitats.

Poecilia sulphuraria from the Baños del Azufre.	Poecilia cf. mexicana from a sulfidic spring in the Rio Puyacatengo drainage.
Sulfidic habitats are characterized by extreme hypoxia, dense bacterial growth, and reduced metazoan species diversity.	Adaptations of poeciliids to sulfidic habitats include differences in morphology, physiology, and behavior. Note the lip appendages in this P. sulphuraria.