Female guppies shorten brood retention in response to predator cues
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Predation risk influences the duration of offspring development in many species where embryos develop from externally shed eggs. Surprisingly, such predator-mediated effects on offspring development have rarely been explored in live-bearers. In this paper, we use the guppy (Poecilia reticulata), a live-bearing freshwater fish, to test whether the duration of brood retention (the time from mating to parturition) is influenced by experimental changes in the perceived level of predation. Because the swimming performance of female guppies is impaired during late pregnancy, we predicted that females would withhold broods for shorter periods when they are exposed to cues that signal a heightened risk of predation on adults rather than on juveniles. We therefore simulated increased risk of predation on adults by using a combination of pike-shaped models (resembling natural predators that prey on adult guppies) and ‘alarm substances’ derived from the skin extracts of adult conspecific females. Our results revealed that, under simulated predation risk, female guppies produced broods significantly more quickly than their counterparts assigned to a control group where predator cues were absent. A subsequent evaluation of offspring swimming performance revealed a significant positive association between neonate swimming speeds and the duration of brood retention, suggesting that by accelerating parturition, females may produce offspring with impaired locomotor skills. These findings, in conjunction with similar results from other live-bearing species, suggest that the conditions experienced by gestating females can generate significant variation in the timing of offspring development with potentially important implications for offspring fitness.
KeywordsPhenotypic plasticity Gestation Pregnancy Predator Brood development
We thank Ferdinando Benatelli for the help with the experiments and Jennifer Kelley and two anonymous referees for comments on a previous draft of the manuscript. This work was supported by grants from the Italian Research Ministry (AP) and the Australian Research Council (JPE). The research conformed to the relevant Italian laws governing the care of animals in research (D.L. 116/27-01-92, C.M.S. 8/22-04-94) and was authorized by the Istituto Superiore di Sanità (National Health Institute).
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