Estimating the Dynamics of Sexual Selection in Changing Environments
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Measuring sexual selection in changing environments is challenging, as the targets and mechanisms of selection can vary with the environment. Here, we present the results of an unusually comprehensive study of the influence of human-disturbed habitat structure on sexual selection in the threespine stickleback Gasterosteus aculeatus. We included all episodes of sexual selection, used molecular parentage assignments, and applied several metrics of sexual selection. The results show that the influence of altered habitat structure on sexual selection dynamics is more complex than previously thought, with the influence varying among selection episodes and male groups. Increased habitat structure relaxed the opportunity for sexual selection across episodes, but incorrect conclusions were reached if the analysis was restricted to resource-holding males or based on mating success. A novel finding, revealed by the parentage analysis, is a reduction in sneak fertilization in disturbed environments. This relaxed the opportunity for sexual selection as sneaking had increased the skew in mating success in less structured habitats, because of nesting males with a high mating success sneaking the most. Thus, the influence of environmental change on an alternative reproductive behavior amplified alterations in sexual selection. This emphasizes the need to consider more hidden processes than previously done when investigating how human disturbances modify sexual selection.
KeywordsHabitat change Male–male competition Mate choice Multiple cues Selection indices Alternative reproductive behavior
We thank Tiina Salesto and Miia Mannerla for assistance, Steven Shuster for advice on the calculation of opportunity for sexual selection metrics, Hannu Mäkinen for advice on the microsatellite primers, and Tvärminne Zoological Station for providing working facilities. The experimental procedures were approved by the Animal Care Committee of the University of Helsinki (86-06) and by the National Animal Experiment Board in Finland (STH421A). The work was funded by the Academy of Finland and the University of Helsinki to UC.
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