Abigail Moore, “Does Size-Assortative Mating Improve Fertilization Success in Grey Treefrogs?”
Mentor: Gerlinde Höebel, Biological Sciences

Success of external fertilization is often optimized by the closeness of egg and sperm release. In frogs, males and females perform amplexus, mating embrace, during egg laying. We hypothesized that size-assortative mating improves fertilization success. This hypothesis makes two predictions: (1) fertilization success should be correlated with a particular within-pair size difference; and (2) size differences observed in nature should align with the optimal size ratio. To test prediction (1) we collected 20 pairs of Eastern Grey Treefrogs (Hyla versicolor), and allowed them to oviposit into separate marked containers. Fertilized embryos, at four days post-oviposition, were distinguishable from unfertilized eggs. Proportions of fertilized eggs were then calculated using photo analysis. The body length of each adult frog was measured using calipers. Size ratios for each adult pair was compared to the fertilization success of their eggs. We also collected additional mated pairs and measured their size ratios. We found that there is indeed a size ratio that optimizes fertilization success, but that about 50% of the breeding population does not mate with optimally size-matched partners.

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