Social environment and reproductive interference affect reproductive success in the frog Rana latastei

Variation in the social environment produces selection on morphological and behavioral traits. It is less clear how the social environment generates variation in demography through behavioral mechanisms. Theory suggests that one aspect of social environment, relative abundance of heterospecifics, influences the intensity of reproductive interference and its demographic effects. These effects are countered by species recognition and female preferences. We studied the effects of social environment on reproductive success in replicated, mixed breeding populations of two ranid frogs, Rana latastei and Rana dalmatina, the former being of international conservation concern. We manipulated the social environment of female R. latastei experimentally by varying the relative abundance of potential conspecific and heterospecific sexual partners. We measured amplexus frequency and recorded the reproductive success of R. latastei females. When conspecific males were relatively uncommon, (1) the absolute and relative frequencies of conspecific amplexus decreased, indicating a breakdown of sexual isolation, (2) oviposition was less frequent, and (3) the percentage of viable embryos in deposited clutches decreased. R. latastei females in an environment of low relative conspecific abundance (1:5, R. Latastei:R. dalmatina) demonstrated 6.8% the reproductive success of females in an environment exclusively with conspecifics. We present a model for the dependence of conspecific amplexus on the social environment. We discuss several mechanisms that may influence reproduction by R. latastei, and we support conservation of the species' preferred habitat to reduce opportunities for reproductive interference that occur at shared breeding sites. Copyright 2003.