A morphological gradient revisited: cave mollies vary not only in eye size

  • Maxwell E. Fontanier
  • Michael Tobler


In the Mexican Cueva del Azufre, cave-dwelling Atlantic mollies (Poecilia mexicana, Poeciliidae) have been reported to exhibit a pronounced gradient in eye size from front cave chambers towards rear cave chambers. Here, we re-examined this morphological gradient using a geometric morphometric analysis of body shape to test for variation along the gradient in traits other than eye size. Our results indicate that fish within the cave also vary in head size. Whereas differences in eye size appear to be related to differences in the amount of light received among cave chambers, variance in head size coincides with differences in hydrogen sulfide concentrations. Consequently, the morphocline within the Cueva del Azufre is more complex than previously assumed and raises interesting new questions on the mechanisms maintaining these morphological variations on such a small spatial scale.


Cave biology Environmental gradient Hydrogen sulfide Local adaptation Morphocline Poeciliidae 



We thank Manfred Schartl for the stimulating discussion. Martin Plath and Aldemaro Romero kindly commented on an earlier version of the manuscript. Financial support came from the Swiss National Science Foundation (to M.T.). The Mexican government (DGOPA/16986/191205/8101, DGOPA/02232/230706/1079, and DGOPA/06192/240608/1562) as well as the Municipio de Tacotalpa (SM/581/2008) kindly issued research permits.


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Copyright information

© Springer Science+Business Media B.V. 2009

Authors and Affiliations

  1. 1.Department of Biology and Department of Wildlife and Fisheries SciencesTexas A&M UniversityCollege StationTXUSA

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