Offspring number in a livebearing fish (Poecilia mexicana, Poeciliidae): reduced fecundity and reduced plasticity in a population of cave mollies
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Life history traits within species often vary among different habitats. We measured female fecundity in mollies (Poecilia mexicana) from a H2S-rich cave and from a neighbouring surface habitat, as well as in laboratory-reared individuals of both populations raised in either light or continuous darkness. Compared to conspecifics from surface habitats, cave-dwelling P. mexicana had reduced fecundity (adjusted for size) in the field. In the laboratory, the fecundity of surface mollies was higher in light than in darkness, whereas fecundity in the cave mollies was almost unaffected by the ambient light conditions. Our results suggest a heritable component to the reduction in fecundity in female cave mollies. Moreover, the reduced plasticity in fecundity of cave mollies in response to light conditions might be an example of genetic assimilation or channelling of a life history trait in a population invading a new environment.
KeywordsCave fish Fecundity Hydrogen sulphide Life history Evolution Phenotypic plasticity
We are grateful to the people of Tapijulapa for their hospitality during our visits. L. D. Devenport, J. C. Kelly, E. C. Marsh-Matthews and L. J. Weider helped to improve previous drafts of the manuscript with their valuable comments. The Mexican Government kindly issued permits to conduct this research (Permiso de pesca de fomento numbers: 291002-613-1577, DGOPA/5864/260704/-2408 and DGOPA/16988/191205/-8101). This work represents partial fulfilment of the PhD requirements for R.R. Financial support came from the Deutsche Forschungsgemeinschaft (SCHL 344/15-1; PL 470/1-1, 2), the University of Oklahoma, the German Ichthyological Association (to M.T. and M.P) as well as the Basler Foundation for Biological Research, the Janggen-Poehn-Foundation, the Roche Research Foundation, and the Wolfermann-Nägeli-Foundation (to M.T.). For the collection of these data, the authors have adhered to the Guidelines for the Use of Animals in Research. The experiments reported here are in agreement with the respective laws in Germany.
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