Subterranean Fishes of the World

3276

2017

AIM 2017

Divergent selection is usually associated with contrasting morphologies in the speciation process. Here we investigate the patterns of body shape variation among sympatric Astyanax (Characidae) morphotypes from three lake systems (Lake Catemaco, Mexico and Lakes Managua and Nicaragua, Nicaragua). Previous phylogenetic studies have shown that each lake correspond to an independent lineage in the Astyanax evolutionary history, being the most southern populations the oldest ones (Nicaraguan Lakes), while the Lake Catemaco population correspond to the most recent lineage. Using geometric morphometric analysis, we developed a MANCOVA model to evaluate the effect in body shape of: adaptive divergence (morphotypes), size (centroid), habitat (lake system factor), variation of size between morphotypes (interaction morphotype*centroid) and variation of body shape of morphotypes between lakes (interaction morphotype*lake). Lake system was the most important factor explaining the morphological variation (showing a strong effect of habitat on body shape) followed by morphotype. Both morphotypes from Catemaco Lake showed the body mass concentrated at the anterior part compared to body mass equally distributed on body in Nicaraguan specimens. Related to adaptive divergence by trophic morphology, Bramocharax morphotype from the three lakes showed a component of parallel evolution of body shape (longer head-snout and a slender body), which is consistent with the theoretical expectation for fish adapted to high sustained swimming speeds and related to an openwater environment. Also as predicted, lineage age was correlated with morphological divergence: the older Nicaraguan morphotypes (about 6.9 m.y. old) showed a higher morphological divergence. Additionally, we performed a phylogenetic reconstruction including specimens of Bramocharax morphotype from Managua Lake and Costa Rican Rivers, in order to clarify its relationships with other Bramocharax morphotype populations.

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