Antipredator responses of the morphs of an amphibian species match their differential predation pressures

Abstract

Abstract: Escape efficiency typically relies on locomotor performance, which depends on morphology. Moreover, flight initiation distance (FID, the distance from an approaching predator at which a prey starts flight) is behaviourally adjusted to minimize the costs of escape. When conspecifics with distinct heritable traits are subjected to differential predator pressure, specialized antipredator strategies may evolve. Phenotypic variants associated to sex and other polymorphisms may be susceptible of suffering predator attacks to different extents. Herein, we used striped and mottled morphs of the polymorphic frog Discoglossus galganoi to test for differences between morphs and sex in predation pressure and concomitant antipredator responses. Firstly, we used plasticine models to assess predation pressure (by a natural set of local predators ranging from snakes to birds and mammals) on both striped and mottled morphs. Then, we tested for differences on morphology, locomotor performance, FID, and their interactions between morphs and sexes. Striped models were more often attacked, which suggests that striped frogs are under stronger predation pressure. Morphology was similar between morphs, and so was locomotor performance. However, FID was greater in striped than in mottled individuals. Contrastingly, sexes did not differ in FID, but males had longer limbs and greater locomotor performance than females, which is common in other taxa. Nonetheless, both sexes displayed similar FID. Finally, FID was greater in larger individuals, but unrelated to locomotor performance. These results support the hypothesis that different antipredator strategies are tuned to divergent predation risk suffered by sexes and morphs. Significance statement: Even within a species, individuals with different characteristics may undergo dissimilar selective pressures. If these traits are heritable, concomitantly divergent responses to such pressures may evolve. One of the most evident sources of intraspecific variation is sex. However, each morph in polymorphic species may also suffer divergent pressures. Among selective pressures, predation is of outstanding relevance due to its devastating effects on prey’s fitness. Herein, using plasticine models of the stripped and the mottled morph of Discoglossus galganoi frogs, we confirm that predator pressure varies between morphs (strong evidence already suggests that male anurans are under greater predation pressure than females). The antipredator responses of actual males and females of both morphs are accordingly adjusted: locomotor performance is greater in males, whereas striped individuals, which are under stronger predation pressure, start fleeing an approaching sham predator at greater distances.