Mate-guarding behaviour in anurans: intrasexual selection and the evolution of prolonged amplexus in the harlequin toad Atelopus laetissimus

Abstract

The term ‘mate guarding’ refers to the monopolization of the reproductive potential of a conspecific. Mate guarding has been recorded in invertebrates and vertebrates, but is poorly known in anuran amphibians (frogs and toads), the terrestrial vertebrates with the highest diversity of reproductive modes. Mate guarding in anurans may consist of a prolonged amplexus or copulatory clasping by the male starting well before egg laying. In this study we combined field observations and experimental studies of the Santa Marta harlequin toad, Atelopus laetissimus , to elucidate whether prolonged amplexus (more than 1 month) in A. laetissimus evolved as a mate-guarding strategy promoted by intense intrasexual selection in males engaging in amplexus displacement attempts. First, we asked how the ability of a male to successfully defend its amplexus status against interlopers is related to body condition and 13 other morphological traits. Second, we tested whether the following characteristics were associated with mating success and mate guarding in A. laetissimus : clasp force, amplexus duration and male reproductive effort. Under natural conditions, amplectant males had significantly higher body condition, were larger and had wider forearms relative to unmated males. In trials, successful mate guarding in A. laetissimus was associated positively with body condition and clasp force, yet the overall probability of successful displacement of amplectant males was low (< 0.20). Our results support the hypothesis that intrasexual selection in A. laetissimus favours mating success of males that clasp females sooner, even before females are ready for breeding . • Mate guarding in Atelopus toads consists of prolonged amplexus that can last months. • Amplexus lasts 70–135 days in A. laetissimus. • Mate-guarding evolution in A. laetissimus is related to amplexus defence by males. • Heavier and stronger male A. laetissimus defended amplexing position successfully. • On average, a male A. laetissimus generated 52 times its body weight in clasp force.