Male-male aggressive interactions in the emerald glass frog (Espadarana prosoblepon)

Determining the factors influencing the outcome of male-male aggressive interactions increases our understanding of their likelihood of achieving reproductive success. Male-male aggressive behavior in the emerald glass frog (Espadarana prosoblepon) and its underlying causes were studied at Las Cruces Biological Station, Costa Rica, during July 2011. Male E. prosoblepon have a structure called a humeral hook, which is a bony spine projecting from the humerus, which may act as a weapon during male-male combat. In this study, we (1) surveyed male abundance nightly for approximately 3 weeks, (2) quantified variation in male body size and humeral hook size, and (3) assessed fighting behavior of males placed in an experimental arena. We investigated how size of the humeral hook and male body size influenced the outcome of aggressive interactions. Male abundance varied nightly, as did the likelihood that males placed together would fight. Aggressive interactions ranged from calling to extended wrestling bouts. Male abundance and fighting may be correlated with daily weather patterns. Male body size and the size of the humeral spine varied considerably between individuals; however, additional data are needed to understand the relationship between these traits and fighting ability. This research is pertinent for understanding the influence of male traits on the reproductive success of E. prosoblepon and its overall natural history.