Meeting Abstract
Males are expected to alter resource allocation strategies to maximize fertilization success under sperm competition. In the yellow dung fly, Scathophaga stercoraria, larger males typically compete for gravid females on dung in cow pastures (low sperm competition risk), while smaller males primarily mate with non-gravid females at off-pasture feeding sites (high sperm competition risk). Theoretical models predict that when large males mate off pasture they should reduce ejaculate expenditure since such matings present lower potential for reproductive pay-off than a typical dung mating, whereas small males unable to compete on dung should increase investment at feeding sites due to the greater risk of sperm competition. Here, we quantified ejaculate investment and fertilization success of small and large field- caught males in both mating environments to test patterns of resource allocation. In non-manipulated field matings, we find that small and large males differentially invest in ejaculate expenditure between mating environments in a manner consistent with theoretical expectations. However, when mating environment was manipulated, no ejaculate tailoring occurred, suggesting that males are not adjusting expenditure based on environment per se, but rather investment reflects different physiological states of large and small males at feeding sites. These findings, combined with paternity data, will provide insight into the pay-off of this long-overlooked aspect of the yellow dung fly mating system.
