Reproductive ecology of treefrogs: egg size promotes reproductive effort differences between females

Reproductive patterns observed in organisms are direct outcomes of the interaction among parameters such as phylogeny, body size, and environmental characteristics. However, the action of these parameters is rarely observed in an integrated perspective in the literature. Here, we collected 109 specimens of two congeneric species of treefrogs living in the same microhabitat (bromeligenous species of genus Ololygon) to compare the reproductive patterns of the two species, evaluating the effect of different parameters on the reproductive ecology of the organisms. Our results show that morphometric measurements between females of the two species were not significantly different, indicating similar body sizes. The species exhibited different degrees of sexual dimorphism, and interspecifically, females showed significant differences in breeding traits, with the species O. perpusilla demonstrating higher reproductive effort, characterized by increased ovarian mass and increased average egg size compared to O. littorea. We observed that differences in reproductive effort were strongly associated with egg size, which drove higher reproductive investment in O. perpusilla females. We conclude that although the species share many traits commonly related to the degree of reproductive investment, other drivers, not yet completely understood, may influence the reproductive aspects of organisms, generating unexpected patterns.