Data from: Evolution in extreme environments: replicated phenotypic differentiation in livebearing fish inhabiting sulfidic springs

We investigated replicated ecological speciation in the livebearing fishes
Poecilia mexicana and P. sulphuraria (Poeciliidae), which inhabit
freshwater habitats and have also colonized multiple sulfidic springs in
southern Mexico. These springs exhibit extreme hypoxia and high
concentrations of hydrogen sulfide, which is lethal to most metazoans. We
used phylogenetic analyses to test whether springs were independently
colonized, performed phenotypic assessments of body and gill morphology
variation to identify convergent patterns of trait differentiation, and
conducted an eco-toxicological experiment to detect differences in sulfide
tolerances among ecotypes. Our results indicate that sulfidic springs were
colonized by three different lineages, two within P. mexicana and one
representing P. sulphuraria. Colonization occurred earlier in P.
sulphuraria, whereas invasion of sulfidic springs in P. mexicana was more
recent, such that each population is more closely related to neighboring
populations from adjacent non-sulfidic habitats. Sulfide spring fish also
show divergence from non-sulfidic phenotypes and a phenotypic convergence
towards larger heads, larger gills, and increased tolerance to H2S.
Together with previous studies that indicated significant reproductive
isolation between fish from sulfidic and non-sulfidic habitats, this study
provides evidence for repeated ecological speciation in the independent
sulfide spring populations of P. mexicana and P. sulphuraria.