Body size drives male reproductive success through nest competition and paternal care in the toad Leptobrachium boringii

Amphibians display remarkable diversity in reproductive strategies, yet life-history studies in an evolutionary context remain limited. Thus, in this study, the mechanism by which male reproductive strategies influence reproductive success in the Emei mustache toad, Leptobrachium boringii , was investigated by integrating 3 years of field behavioural observations with microsatellite analyses. We found that males enhance reproductive success through nest competition and parental care, with body mass as the most influential factor. Based on body mass, males’ nest-site competition strategies were classified into three types: nest defence, exploitative and satellite. Significant differences in body mass and reproductive success were found amongst the three strategies, with nest-defensive males producing the most offspring, followed by exploitative and satellite males. Regarding parental care, egg-guarding duration positively correlated with offspring survival; caring males had more offspring and higher offspring survival than noncaring males. Notably, egg-guarding duration was positively associated with body mass, indicating that heavier males provide longer parental care, which explains their greater reproductive success. Collectively, these results indicate that body mass is a pivotal factor shaping male reproductive strategies and reproductive outcomes in L. boringii , acting through the synergistic effects of strategy differentiation and parental care. Our findings not only advance understanding of the mechanism linking individual traits to reproductive success but also provide a scientific basis for phenotypic conservation of rare and endangered amphibians. • Nest competition and parental care affect reproduction of male L. boringii. • Larger males have higher reproductive success due to nest defence than small ones. • High male body mass leads to extended paternal care. • It boosts offspring survival and reproductive success. • Body mass is the primary determinant of reproductive success in male L. boringii.