Article Review: Fighting Scars B. Curupi

Fighting scars: heavier gladiator frogs bear more injuries than lighter frogs

Authors: Aline Candaten, Angélica Gabriela Possenti, Álvaro Augusto Mainardi, Marcelo Carvalho da Rocha & Alexandre V. Palaoro

Journal: Acta Ethologica

Link: https://link.springer.com/article/10.1007/s10211-019-00333-7

Animal contests are very common in nature including contests competing for mates and competing for resources.  This study focuses on contests between male gladiator frogs (Hylidae) when they try to take over each other's nests.  These fights often result in a great amount of scarring on their backs caused by the use of a spine on the fifth digit of their front limbs.  This spine is not only used in fighting, it is also used to hold and grasp the females during amplexus. This study focused on a stream within the Turvo State Park at the Rio Grande do State, Brazil.  Methods of this study included performing surveys in which water depth and temperature of areas with B. curupi eggs present were measured as well as performing surveys to determine the abundance of sites similar to these in the area.  Male frogs found near the stream were measured, weighed and photographed. Photoshop was utilized to determine the proportion of scars covering the backs of each of these males.  Results indicated that spawning areas were rare for the population of B. curupi being investigated and most spawning areas had more than one male.  Of the 32 males in the survey only 3 did not have any scars. Based on these results, authors suggest these males are fighting due to the rarity of the resources and scars happen as a result.    Results also indicated that heavier individuals (not larger) have a greater amount of injuries than lighter individuals (shown on Figure 4 below). The information in this study is valuable because it suggests that an increase in fighting and scarring is linked to limited nest availability rather than to male density.  This research also provides insight into who is getting injured most from these fights. It would be interesting if through future research we could determine whether these spines have evolved to hold the female or for the male to male combat described in this study