Extreme environments and the origins of biodiversity: Adaptation and speciation in sulphide spring fishes

Organisms adapted to physiochemical stressors provide ideal systems to study evolutionary mechanisms that drive adaptation and speciation. This review study focuses on livebearing fishes of the Poecilia mexicana species complex (Poeciliidae), members of which have repeatedly colonized hydrogen sulphide (H 2 S)‐rich springs. H 2 S is a potent respiratory toxicant that creates extreme environmental conditions in aquatic ecosystems. There is also a...