Male mammals respond to a risk of sperm competition conveyed by odours of conspecific males

Abstract

Sperm competition occurs when a female copulates with two or more males and the sperm of those males compete within the female's reproductive tract to fertilize her eggs. The frequent occurrence of sperm competition has forced males of many species to develop different strategies to overcome the sperm of competing males. A prevalent strategy is for males to increase their sperm investment (total number of sperm allocated by a male to a particular female) after detecting a risk of sperm competition. It has been shown that the proportion of sperm that one male contributes to the sperm pool of a female is correlated with the proportion of offspring sired by that male. Therefore, by increasing his sperm investment a male may bias a potential sperm competition in his favour. Here we show that male meadow voles, Microtus pennsylvanicus, increase their sperm investment when they mate in the presence of another male's odours. Such an increase in sperm investment does not occur by augmenting the frequency of ejaculations, but by increasing the amount of sperm in a similar number of ejaculations.

Genetic and phenotypic influences on copulatory plug survival in mice

“…Male mate choice (Dewsbury, 1982;Drickamer et al, 2003;Edward and Chapman, 2011;Ramm and Stockley, 2014) and the dynamic adjustment of ejaculate allocation (Wedell et al, 2002;Delbarco-Trillo and Ferkin, 2004) suggest that ejaculates are costly to produce and conserved when possible. Plug-forming proteins account for nearly one third of the total protein abundance of the ejaculate in mice, suggesting that this structure is a major reproductive investment for males (Lundwall et al, 1997;Lin et al, 2002;Dean et al, 2011).…”

Social cues of sperm competition influence accessory reproductive gland size in a promiscuous mammal

“…Most attention to date has focused on exploring male responses to immediate cues of sperm competition risk or intensity such as the number of competitors present at the time of mating [6][7][8]. For example, male meadow voles (Microtus pennsylvanicus) increase their sperm allocation when ejaculating under an elevated risk of sperm competition [19] and human males produce ejaculates with a higher proportion of motile sperm [20]. The seminal fluid protein content of ejaculates may also vary adaptively according to the immediate sperm competition risk [21].…”

“…Male bank voles should therefore be sensitive to cues of average sperm competition level in their local environment and tailor investment in ejaculate production accordingly. Conspecific odours convey information concerning sperm competition risk and intensity [19,29,34] and are used for individual recognition in rodents [35], including bank voles [36]. We therefore predicted that frequent exposure to social odours of rival males would stimulate increased investment in ejaculate production by male bank voles.…”

An Ontology for Comparative Cognition: A Functional Approach

“…Our male is capable of detecting these many marks, identifying the donor, and identifying the identity of the donors that deposited the most and the freshest marks (Ferkin, Dunsavage, & Johnston, 1999;Ferkin, Mech, & Paz-y-Mino, 2001;Ferkin et al, 2004a;Ferkin, Pierce, Sealand, & delBarco-Trillo, 2005). He then is able to distinguish between the different scent donors and respond accordingly to the donor are of most interest to him; this donor would likely be a sexually receptive female with whom he would attempt to copulate (delBarco-Trillo & Ferkin, 2004). Our vole's discrimination between the different scent donors would have involved perceptual learning.…”

“…If on the other hand, our vole has frequent opportunities to mate with females, he may stop his search for this female when he encounters the odor of a weasel or a male conspecific (delBarco-Trillo & Ferkin, 2004).…”