Asymmetry, testis and sperm size in yellow dung flies

1. Fluctuating asymmetry (FA), small random deviations from perfect bilateral symmetry, is a widely used measure of developmental stability, and has been linked to fitness measures including male primary reproductive traits such as sperm quality. However, there have been relatively few investigations of potential associations between these male traits and FA, and hence the current balance of evidence is equivocal. 2. There is also evidence that levels of FA vary across populations with, for example, organisms inhabiting marginal populations often displaying increased FA. Moreover, environmental variation may select for different levels of developmental buffering across populations that are only revealed in 'common garden' experiments. 3. Investigations of potential associations between male leg FA and testis and sperm size in Yellow Dung Flies are reported here. In addition, levels of FA in a mainland and two island populations were compared when flies were reared under common conditions. 4. No associations were found between any measure of FA and sperm size (or variation) or testis size. Additionally, no evidence was found that FA varied across the three populations when flies were reared under identical controlled conditions.