Abstract
Population divergence in sexual signals may lead to speciation through prezygotic isolation. Sexual signals can change solely due to variation in the level of natural selection acting against conspicuousness. However, directional mate choice (i.e., favoring conspicuousness) across different environments may lead to gene flow between populations, thereby delaying or even preventing the evolution of reproductive barriers and speciation. In this study, we test whether natural selection through predation upon mate‐choosing females can favor corresponding changes in mate preferences. Our study system, Oophaga pumilio, is an extremely color polymorphic neotropical frog with two distinctive antipredator strategies: aposematism and crypsis. The conspicuous coloration and calling behavior of aposematic males may attract both cryptic and aposematic females, but predation may select against cryptic females choosing aposematic males. We used an experimental approach where domestic fowl were encouraged to find digitized images of cryptic frogs at different distances from aposematic partners. We found that the estimated survival time of a cryptic frog was reduced when associating with an aposematic partner. Hence, predation may act as a direct selective force on female choice, favoring evolution of color assortative mating that, in turn, may strengthen the divergence in coloration that natural selection has generated.
Highlights
Over recent decades, it has become well established that natural selection and sexual selection, rather than neutral processes, are the main drivers of population divergence and speciation (Butlin, Bridle, & Schluter, 2009; Coyne & Orr, 2004; Nosil, 2012; Price, 2008; Schluter, 2001; Schluter & Conte, 2009)
We used an experimental approach where domestic fowl predated on digitized images of cryptic frogs against a natural habitat background, to investigate the role of natural selection in shaping female mate choice preferences
The presence of an aposematic frog on the screen did not increase the risk of predation of the cryptic frog when the two frogs where shown at a further distance from each other
Summary
It has become well established that natural selection and sexual selection, rather than neutral processes, are the main drivers of population divergence and speciation (Butlin, Bridle, & Schluter, 2009; Coyne & Orr, 2004; Nosil, 2012; Price, 2008; Schluter, 2001; Schluter & Conte, 2009). We base our experimental setup on the two following general assumptions: (1) Predators prefer to attack and eat cryptic prey over prey that signals unprofitability (here aposematism) (Darst & Cummings, 2006; Ruxton, Sherratt, & Speed, 2004) and (2) highly ornamented or brightly colored males (including aposematic males) have a mating advantage because they are more easy to find by females or they may defend better territories or provide other benefits and/or they deter rivals (Andersson, 1994). Our main aim was to use this experimental approach to test whether the survival probability (measured as the time it took the predator to localize the cryptic frog) is reduced when the cryptic frog approaches an aposematic mate
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