Summary: Ramm & Stockley (2009)

Sperm competition theory predicts that males will respond to an increased risk of sperm competition from rivals by increasing sperm allocation and predicts that the increase in allocation will be lower when rivals are related. Furthermore, scent-based cues could provide information on the presence and identity of conspecifics and could serve as a basis for adjusting sperm allocation. Ramm & Stockley (2009) investigated whether male house mice (Mus musculus domesticus) adjust sperm allocation in response to odour-based cues of rival males present in the environment and whether they vary sperm allocation decisions according to the relatedness of rival males. In contrast to the predictions made by sperm competition theory, Ramm & Stockley (2009) found no evidence that male house mice adjust the number of sperm allocated to an ejaculate in response to odour-based cues of immediate sperm competition risk, even though male mice were sensitive to the odour cues from rival males. They suggest that the response to cues of sperm competition risk may display considerable interspecific variability.