Antagonistic Selection or Trait Compensation? Diverse Patterns of Predation-Induced Prey Mortality due to the Interacting Effects of Prey Phenotype and the Environment
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Differentiation among closely related prey species may result from differing adaptations to heterogeneous environments. Many studies have focused on competition for shared resources as a major factor promoting differentiation, with considerably less attention focused on interacting effects of abiotic factors and predator–prey relationships. To further investigate the effects of interacting selective factors on the outcomes of mortality and survival in aquatic prey, we conducted interrelated laboratory studies examining the effects of water colour and plant density on predator-induced mortality in four dytiscid species (Coleoptera: Dytiscidae) that varied in body size (total body length), and body colouration pattern. Body size was more strongly phylogenetically conserved than colouration pattern, and larger body size generally resulted in decreased predator-induced mortality rates. In contrast, the effectiveness of body colouration patterns in decreasing prey mortality risk depended on water colour and prey body size. In clear water, small and patterned dytiscids had mortality rates equal to medium-sized plain beetles, thereby compensating for differences in mortality risk due to body size differences. Under dark water conditions, small dytiscids experienced higher mortality rates compared to medium-sized dytiscids; however, the effectiveness of colouration patterns in medium-sized beetles decreased to the point that it became detrimental to survival, revealing antagonistic selection. We suggest that colouration patterns are not ubiquitous in prey species and cospecialization in larger size and presence of colouration patterns does not generally result in higher prey survival, because the effectiveness of the two antipredator defences may be restricted to certain phenotype × environment combinations. Our results illustrate how interactions between prey phenotype and variable environmental conditions among habitats dominated by the same predator can lead to adaptive trade-offs, which can increase the number of possible outcomes of predator mediated selection.
KeywordsAntagonistic selection Antipredator defences Body size Colour patterns Compensation
We thank Sierra Love and Catherine Gieysztor for technical support and help with sampling and the Reinhardt family for allowing us to access their property. Carly Silver, Dirk Mikolajewski, Don Yee and an anonymous reviewer provided valuable comments on an earlier version of the manuscript. Funding was provided by operating grants from Alberta Ingenuity and NSERC (Canada) to SMV and a Dean’s Doctoral Scholarship to BW. All experiments conducted for this study comply with current Canadian laws.
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