The Evolution of Male Weapons Is Associated with the Type of Breeding Site in a Clade of Neotropical Frogs.

Male weaponry evolution is often linked to male-male competition for resources or access to females, a pattern observed in well-studied taxa, such as beetles and mammals. Whether factors such as breeding site type influence weaponry evolution remains an open question. We explored this question using frogs of the subfamily Leptodactylinae, where males of species that spawn in exposed sites (water bodies) fight to hold oviposition sites or dislodge rivals during amplexus. Conversely, males of species that spawn in concealed sites (ground nests and crevices) rarely engage in physical contests. We hypothesized that male weaponry evolution would be associated with reproduction in exposed sites. Using two complementary phylogenetic comparative methods, we first found that both gains and losses of weapons occurred more frequently in species spawning in exposed sites. This unexpected finding suggests that the dynamics of weaponry evolution are more intricate than anticipated. Second, we found a macroevolutionary correlation between male weapons and breeding site type: the presence of weapons is associated with exposed sites, while their absence is associated with concealed sites. We explore how additional factors, such as population density, the energetic costs of producing and maintaining weapons, and female choice, may also influence this macroevolutionary pattern. Finally, we hope our findings stimulate further investigations into weaponry evolution in other clades of external fertilizers.