Parental traits, reproductive investment, and genetic relatedness shape offspring development and morphology in an explosive-breeding toad

Background Parental effects link parental phenotype and environmental variation to offspring performance and evolutionary trajectories. However, their role remains poorly resolved in species lacking post-oviposition care, where offspring development is shaped mainly by pre-hatching parental influences. We investigated how parental phenotype, reproductive investment, and parental relatedness were associated with offspring development in the Asiatic toad ( Bufo gargarizans ). Amplectant pairs were collected from the wild, and offspring were reared under standardized laboratory conditions from fertilization to metamorphosis. Parental relatedness was estimated using microsatellite markers to evaluate how parental genetic similarity was associated with offspring developmental and morphological traits. Results We detected positive assortative pairing by body mass in B. gargarizans and strong clutch effects across offspring developmental traits, indicating substantial among-family variation. After distinguishing among parental body size, body mass, and body condition, the most consistent associations involved paternal body condition, paternal investment, and parental relatedness. Paternal body condition was positively associated with offspring growth rate during the G25-G42 interval, suggesting faster mid-stage larval growth in offspring of males in better condition. Paternal reproductive investment was positively associated with post-metamorphic morphology, particularly tibiofibula length at G46. Parental relatedness was negatively associated with length-related morphology around metamorphosis, and this association varied among developmental stages. Maternal traits showed more limited and mainly stage-dependent associations with offspring traits. Conclusions Our results show that offspring development in B. gargarizans is associated with parental phenotype, reproductive investment, and parental relatedness. Paternal body condition and paternal investment were associated with offspring growth and post-metamorphic morphology, whereas parental relatedness was negatively associated with length-related morphology around metamorphosis. These findings suggest that parental effects in this species are trait-specific and stage-dependent. They also highlight the importance of integrating paternal phenotype and parental relatedness into studies of amphibian reproductive ecology, especially in species without post-oviposition care.