Strategic Adjustments in Sperm Production Within and Between Two Island Populations of House Mice

Abstract

Sperm production is physiologically costly. Consequently, males are expected to be prudent in their sperm production, and tailor their expenditure according to prevailing social conditions. Differences in sperm production have been found across island populations of house mice that differ in the level of selection from sperm competition. Here, we determined the extent to which these differences represent phenotypic plasticity and/or population divergence in sperm production. We sourced individuals from two populations at the extreme levels of sperm competition, and raised them under common‐garden conditions while manipulating the social experience of developing males. Males from the high‐sperm competition population produced more sperm and better quality sperm than did males from the low‐sperm competition population. In addition, males reared under a perceived “risk” of sperm competition produced greater numbers of sperm than males reared with “no risk.” However, our analyses revealed that phenotypic plasticity in sperm production was greater for individuals from the high‐sperm competition population. Our results are thus consistent with both population divergence and phenotypic plasticity in sperm production, and suggest that population level of sperm competition might affect the degree of adaptive plasticity in sperm production in response to sperm competition risk.

Sperm competition risk generates phenotypic plasticity in ovum fertilizability

“…Previously, we found that males from our high sperm competition population produced more sperm and better quality sperm than did males from the low sperm competition population [32]. Moreover, males reared under a perceived risk of sperm competition produced more aggressive sperm compared with males reared under no risk [32].…”

“…Previously, we found that males from our high sperm competition population produced more sperm and better quality sperm than did males from the low sperm competition population [32]. Moreover, males reared under a perceived risk of sperm competition produced more aggressive sperm compared with males reared under no risk [32]. Adaptive adjustments in the ejaculate would enhance male fitness in competitive situations [24,29] but are also likely to lead to an increased risk of polyspermic fertilizations [10].…”

“…As predicted by sperm competition theory, males from the high sperm competition population produce more sperm and better quality sperm compared with males from the low sperm competition population [32]. Moreover, males from these populations were found to increase the fertilizing potential of their sperm when reared under a risk of sperm competition [32]. Here, we exposed maturing females to different sperm competition environments by creating variation in their perception of male density.…”

“…We sourced house mice from two island populations that have rates of multiply sired litters that represent a low (17% multiple paternity) and a high (71% multiple paternity) level of sperm competition [37]. As predicted by sperm competition theory, males from the high sperm competition population produce more sperm and better quality sperm compared with males from the low sperm competition population [32]. Moreover, males from these populations were found to increase the fertilizing potential of their sperm when reared under a risk of sperm competition [32].…”

Mate-guarding in a promiscuous insect: species discrimination influences context-dependent behaviour

“…Sperm production and mating both pose non-trivial costs to males (Simmons 2001) and numerous studies have illustrated the interaction between social environment and male sexual behaviour both in insects Wigby et al 2009;Bailey 2011;Billeter et al 2012;Bailey et al 2013;Han and Brooks 2013) and vertebrates (Firman et al 2013; recently reviewed by Kelly and Jennions 2011). While males may employ a variety of strategies in response to sperm competition (including, but not restricted to: changes in sperm number (Wedell et al 2002), ejaculation size (Gage 1991;Garcia-Gonzalez and Gomendio 2004); seminal protein composition (Wigby et al 2009;Perry et al 2013) and sperm morphology (Gage 1994) behavioural changes have the benefit of being ''cheaper'' and may allow for more rapid responses to fluctuations in local environment (Bretman et al 2011).…”