title: Evolution in extreme environments: replicated phenotypic differentiation in livebearing fish inhabiting sulfidic springs.
abstract: We investigated replicated ecological speciation in the livebearing fish 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 nonsulfidic habitats. Sulfide spring fish also show divergence from nonsulfidic phenotypes and a phenotypic convergence toward larger heads, larger gills, and increased tolerance to H(2) S. Together with previous studies that indicated significant reproductive isolation between fish from sulfidic and nonsulfidic habitats, this study provides evidence for repeated ecological speciation in the independent sulfide spring populations of P. mexicana and P. sulphuraria.
authors.affiliation: Department of Zoology, Oklahoma State University, 501 Life Sciences West, Stillwater, Oklahoma 74078, USA. michi.tobler@okstate.edu
authors.forename: Michael
authors.initials: M
authors.lastname: Tobler
authors.forename: Maura
authors.initials: M
authors.lastname: Palacios
authors.forename: Lauren J
authors.initials: LJ
authors.lastname: Chapman
authors.forename: Igor
authors.initials: I
authors.lastname: Mitrofanov
authors.forename: David
authors.initials: D
authors.lastname: Bierbach
authors.forename: Martin
authors.initials: M
authors.lastname: Plath
authors.forename: Lenin
authors.initials: L
authors.lastname: Arias-Rodriguez
authors.forename: Francisco J García
authors.initials: FJ
authors.lastname: de León
authors.forename: Mariana
authors.initials: M
authors.lastname: Mateos
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D017753:Ecosystem; D019143:Evolution, Molecular; D005399:Fishes; D045482:Hot Springs; D006862:Hydrogen Sulfide; D000860:Hypoxia / Q000503:physiopathology; D008800:Mexico; D010641:Phenotype; D010802:Phylogeny; D011036:Poecilia / Q000033:anatomy & histology / Q000145:classification / Q000235:genetics / Q000502:physiology*; D012641:Selection, Genetic
chemical_list: D006862:Hydrogen Sulfide