Male mating success is related to body condition and stress-induced leukocyte response in an anuran with scramble competition

Abstract

Competition among males can be a decisive factor for successful mating in anuran explosive breeders with a male-biased population sex ratio. The Yungas Red-belly Toad (Melanophryniscus rubriventris (Vellard, 1947)) is an explosive breeder where males exhibit a classic scramble competition. We studied the body size, body condition, and stress-induced leukocyte response of M. rubriventris males under natural scenarios of scramble competition. We hand-captured adult males (categorised as single, in pairs, or in mating balls) and determined their body mass and length, body condition, and their leukocyte profile. We found that males in pairs had significantly higher body mass than single males and those in mating balls. We found the highest percentage of individuals with better body condition within the paired males who showed significantly higher body condition index value than singles or those in mating balls. Amplectant males (those collected in pairs or in mating balls) had a significantly lower proportion of lymphocytes and higher neutrophil–lymphocyte ratios than singles. Amplectant males showed significantly higher proportions of neutrophils or eosinophils than singles. Our results suggest that M. rubriventris males with better body condition can be more successful in acquiring mates, although scramble competition among males can trigger a stress response.