Toxic hydrogen sulphide shapes brain anatomy: a comparative study of sulphide-adapted ecotypes in the Poecilia mexicana complex
T. Schulz-Mirbach, C. Eifert, R. Riesch, M. S. Farnworth, C. Zimmer, D. Bierbach, S. Klaus, M. Tobler, B. Streit, J. R. Indy, L. Arias-Rodriguez and M. Plath
Version of Record online: 22 JUN 2016 | DOI: 10.1111/jzo.12366
The teleost brain is an energetically costly organ. This raises the questions of how brain anatomy is shaped by divergent ecological factors in contrasting (extreme/resource-limited vs. benign) environments, and how shared (‘convergent’) anatomical changes of the teleost brain are reflected in species that transitioned several times along a replicated, natural toxicity gradient. We therefore compared ecotypes in the P. mexicana species complex that have independently evolved increased tolerance to hydrogen sulphide (H2S) in three river drainages in southern Mexico. We found shared and unique patterns of brain size variation; habitat type, and to a lesser degree drainage system of origin and sexual dimorphism, affected the size of the brain, the brain regions and eye diameter. Turbidity and toxicity in sulphidic habitats may explain patterns of brain size divergence. Nonetheless, some unique patterns of brain differentiation suggest as yet unidentified differences in selection regimes between different sulphidic springs.