Sperm depletion and a test of the phenotype-linked fertility hypothesis in Gray Treefrogs (Hyla versicolor)

The phenotype-linked fertility hypothesis (PLFH) predicts that ejaculate characteristics correlate with male phenotype, and that females may select for exaggerated phenotypes to guarantee high fertilization success. Female Gray Treefrogs (Hyla versicolor LeConte, 1825) prefer males with long-duration calls and (or) calls produced at a fast rate. I tested the prediction that call duration or call rate were indicators of sperm number or viability. To assess whether female H. versicolor might benefit by identifying males with low sperm numbers, I examined the effect of mating history on sperm number and looked for evidence of sperm depletion. My study found no support for the PLFH in relation to call quality, as neither sperm number nor viability was related to call duration. I found that sperm stores are severely reduced after a single mating, and that sperm stores of males calling late in the season are often more similar to those of depleted males than unmated males. Thus, calling males may attempt to attract females without the sperm numbers necessary to fertilize the entire clutch. However, selection for females to identify males with high fertilization success may be low when all other factors that affect reproductive success (e.g., genetic benefits) are considered.