Sex ratio variation determines the ecological impacts of mosquitofish populations

Authors: David C Fryxell, Heather A Arnett, Travis M. Apgar, Kyla M. Roessler, Michael T. Kinnison, Eric P. Palkovacs

Year: 2014 (xlvi)

Abstract

The western mosquitofish, Gambusia affinis, is a common desert aquatic invader which has strong impacts on native communities and ecosystems. Populations of the sexually dimorphic western mosquitofish vary drastically in sex ratio across space and time. Here we tested whether the ecological impacts of G. affinis populations depend on the sex ratio using experimental pond ecosystems. Populations of twelve mature mosquitofish were introduced to thirty 1,136 liter experimental ponds in replicated sex ratio treatments of 0, 25, 50, 75, and 100 percent male fish. Six ponds served as fishless control treatments. Community ecological and ecosystem responses were then measured weekly for a month. After two weeks a positive trend in zooplankton counts and a negative trend in pelagic chlorophyll A concentration emerged with increasing proportion of males. Interestingly, this cascading effect of sex ratio affected pond temperature and pH as well. Nonlinear patterns in some response variables at some timepoints suggest sex ratio effects are not due solely to biomass differences between the sexes. Attempts to reduce mosquitofish population size that modify sex ratio due to sex-biased capture rates are likely to modify the ecological impacts of the species.

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