Fertilization success suggests random pairing in frogs with regard to body size

Size-assortative mating is a pattern of non-random pairing among individuals that has been presumed to arise due to the enhanced reproductive success that may accrue from mating with an individual of similar size. Its proximal mechanism may be female choice for similarly sized mates and/or large-male advantage during bouts of direct male-male competition. The hallmark for the occurrence of size-assortative mating is a significant correlation between female and male body sizes in mated pairs. In this study, we investigated the mating pattern of the emerald glass frog, Espadarana prosoblepon, whose mating system is purportedly based on female choice and therefore is a suitable study system for testing hypotheses of size-assortative mating. We specifically tested whether E. prosoblepon males found in amplexus were larger than solitary males, indicating a large-male advantage in mating and whether either larger males or size-matched pairs of frogs had a higher proportion of their eggs fertilized, consistent with a benefit to size-assortative mating. We found no evidence for any of these relationships in E. prosoblepon despite a positive correlation between female size and clutch size. Males in amplexus were not larger than unmated males, and male size did not predict the proportion of fertilized eggs. Our evidence thus indicates that the mating pattern of E. prosoblepon is random with respect to body size, in conformity with a growing body of evidence that body size is likely not a significant factor influencing mating patterns in anurans. Significance statement Size-assortative mating occurs when similarly sized individuals mate together more often than expected by chance. Studies addressing this question test for a correlation between female and male sizes within mating pairs, but few studies test whether mating with similarly sized individuals provides proximate benefits. Size-assortative mating should occur in species where mate choice is possible to occur, in which individuals can discriminate and choose to mate with similarly sized individuals. In frogs, many previous studies have searched for size-assortative mating, but evidence for its occurrence or selective advantage remains scant. We used the emerald glass frog, Espadarana prosoblepon, as a study system to test the predictions of size-assortative mating. We found that both mating preference and fertilization success are random with respect to body size.

Automated summary

The mating pattern of the emerald glass frog, Espadarana prosoblepon, is random with respect to body size, and there is no evidence for a correlation between male size and fertilization success. Therefore, body size does not appear to play a significant role in influencing mating patterns in anurans.