Intraspecific and interspecific competition for mates: Rana temporaria males are effective satyrs of Rana dalmatina females

Abstract

Reproductive interference can seriously affect the reproductive success of involved individuals and may lead to local exclusion of the competitively inferior species. The components of male competitiveness in direct bodily fights for females have been studied rarely in a heterospecific context. In explosively breeding anuran amphibians, males are often coercive and indiscriminate, which frequently leads to interactions among heterospecific males. We experimentally assessed the competitiveness of male Rana dalmatina (RD) and R. temporaria (RT), two species with overlapping breeding both in time and space. The mating speed of the RD males decreased over the course of the breeding season, whereas RT males retained their swiftness. In addition, the RD males were rarely able to replace the RT males from amplexus with RD females, while takeovers frequently occurred among the RD males. Further, larger RD males were more successful in maintaining amplexus and in achieving takeovers when facing smaller conspecifics. Our results suggest that male body size is important for intraspecific competition among the RD males, but the RT males outcompete the RD males of all sizes, perhaps due to their larger body size. Hence, RT males are likely to be effective satyrs of RD females, because they may lower the reproductive success of the latter. Such interspecific differences in the competitiveness of males may represent an important mechanism that contributes to the arousal of asymmetric reproductive interference between species.

Significance statement

Reproductive interference—interactions between species during mating with negative consequences on the fitness of involved individuals—is widespread in nature. Even though differences in the competitiveness of males of interfering species may have severe consequences, competitiveness of males has rarely been studied in an interspecific scenario in vertebrates. Males of anuran amphibians are often indiscriminate and coercive and engage in bodily fights for the possession of both conspecific and heterospecific females, which may often compromise the reproductive success of involved males and females. Here, we demonstrate that interspecific differences among ranid males can be large in the swiftness of pair formation, in the ability to defend the mating position and to perform takeovers. These differences are likely to lower the reproductive performance of the competitively inferior species, potentially leading to its local extinction.