Toxic Hydrogen Sulfide and Dark Caves: Phenotypic and Genetic Divergence Across Two Abiotic Environmental Gradients in Poecilia mexicana

• Published in: Evolution Vol. 62; no. 10; pp. 2643 - 2659
• Main Authors: Tobler, Michael, DeWitt, Thomas J, Schlupp, Ingo, García de León, Francisco J, Herrmann, Roger, Feulner, Philine G. D, Tiedemann, Ralph, Plath, Martin
• Format: Journal Article
• Language: English
• Published: Malden, USA Blackwell Publishing Inc 01.10.2008; Blackwell Publishing, Inc; Oxford University Press
• Subjects: Abiotic environmental conditions; Adaptation, Biological; Animal morphology; Animal populations; Animals; Biological Evolution; Biological variation; cave evolution; Caves; Cytochromes b - genetics; Divergent evolution; divergent natural selection; Ecological genetics; ecological speciation; Environment; Environmental Exposure; Evolution; Evolutionary biology; Evolutionary genetics; extremophile; Female; Fish; Freshwater; Gene Flow; Genetic Markers; Genetic variation; Genotype & phenotype; Geography; Gills - anatomy & histology; Hydrogen sulfide; Hydrogen Sulfide - toxicity; local adaptation; Male; Microsatellite Repeats; Original s; Phenotype; Poecilia - anatomy & histology; Poecilia - genetics; Poecilia - physiology; Poecilia mexicana; Poeciliidae; Population genetics; reproductive isolation; Selection, Genetic; Toxicity; Wildlife habitats
• ISSN: 0014-3820; 1558-5646
• DOI: 10.1111/j.1558-5646.2008.00466.x

Divergent natural selection drives evolutionary diversification. It creates phenotypic diversity by favoring developmental plasticity within populations or genetic differentiation and local adaptation among populations. We investigated phenotypic and genetic divergence in the livebearing fish Poecilia mexicana along two abiotic environmental gradients. These fish typically inhabit nonsulfidic surface rivers, but also colonized sulfidic and cave habitats. We assessed phenotypic variation among a factorial combination of habitat types using geometric and traditional morphometrics, and genetic divergence using quantitative and molecular genetic analyses. Fish in caves (sulfidic or not) exhibited reduced eyes and slender bodies. Fish from sulfidic habitats (surface or cave) exhibited larger heads and longer gill filaments. Common-garden rearing suggested that these morphological differences are partly heritable. Population genetic analyses using microsatellites as well as cytochrome b gene sequences indicate high population differentiation over small spatial scale and very low rates of gene flow, especially among different habitat types. This suggests that divergent environmental conditions constitute barriers to gene flow. Strong molecular divergence over short distances as well as phenotypic and quantitative genetic divergence across habitats in directions classic to fish ecomorphology suggest that divergent selection is structuring phenotypic variation in this system.