Abstract
Sexual reproduction in animals requires close interactions with the opposite sex. These interactions may generate costs of reproduction, because mates can induce detrimental physiological or physical effects on one another, due to their interest in maximising their own fitness. To understand how a male’s presence influences aspects of female physiology implicated in reproductive costs in mice, independent of offspring production, we paired females with vasectomised, castrated or intact males, or other females. Being paired with a male, irrespective of his gonadal status, increased female weight. This effect was transient in females paired with castrated males but more persistent in those with vasectomised males. Those paired with males also showed an increase in corticosterone, suggesting an increased stress response. However, this was dependent on the gonadal status of the male housing partner, since those housed with vasectomised males had lower corticosterone than those with castrated males. Altered energy metabolism was only detectable in pregnant females, and oxidative stress was not consistently affected by a female’s housing partner. These results suggest that a male’s presence alters female weight, and stresses associated with reproduction could be induced by simply the presence of a male, but reduced by mating and/or being solicited to mate.
Highlights
Sexual reproduction in animals, by its nature, requires interactions with members of the opposite sex; at the very least, close proximity interactions for the mixing of gametes, but often sustained close contact during mating, post-copulatory guarding, and any subsequent joint parental care
Interactions and which are generated by offspring production are often complicated by the fact that interactions with males lead to fertilisation, and costs of male presence are usually tied to the costs of paternal care
Female weight changed over the experiment in a manner that was dependent on housing partner
Summary
By its nature, requires interactions with members of the opposite sex; at the very least, close proximity interactions for the mixing of gametes, but often sustained close contact during mating, post-copulatory guarding, and any subsequent joint parental care. Glucocorticoids can help adapt metabolism to the requirements of reproductive allocation, with levels increasing during pregnancy in mice[13,14], but their production in some contexts can be harmful, and has been highlighted as a potential physiological cost of male harassment and sexual cohesion[15]. Such effects have been noted in pregnant and lactating chacma baboons (Papio hamadryas ursinus) when immigrant males take over a natal area[16]. Oxidative stress has been suggested as a potentially important cost of reproduction[18,19], which might be linked to increased glucocorticoids[20] or metabolism[17], and could be generated by allocation during pregnancy and lactation (but see [18] for a critical discussion), or conceivably from interactions with males
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