How sexual conflict and reproduction drive the sex dependent evolution of life history traits

Abstract

Sexual conflict is inevitable in all sexually reproducing species as males and females are selected to maximise their own fitness often at the expense of their mate. This conflict can intensify the already costly nature of reproduction for female mammals. To examine the effects of territory turnover of a dominant male to pregnant females and their resulting offspring, we exposed females to a novel male in late pregnancy. These females spent less time nursing their pups, who subsequently had a low weaning weight and suffered oxidative costs at adulthood. We believe the change in behaviour is a result of the females strategically altering their investment in relation to their perceived chances of offspring’s survival. To partition the costs of male presence and mating from those of reproduction we housed females with males of differing gonadal status and allowed half access to a refuge. We found no costs of male mating, presence or insemination, suggesting the costs associated with these behaviours may be subtler than currently predicted. However, females housed with castrated males exhibited more refuging behaviour and higher stress levels. To examine the cause of this response, we again housed females with males of differing gonadal status and supplemented each cage with the scent of an unfamiliar dominant, subordinate or castrated male. While we replicated the effect of castrated males on female stress levels, we found that this can be ameliorated after exposure to the scent of an intact male, either dominant or subordinate. This shows that the signal(s) eliciting this response in females can be transferred in soiled bedding, but that it is not due to subordination. Lastly, we investigated genetic sexual conflict to attempt to provide further evidence for Haig’s kinship theory of genomic imprinting. We used Igf2 knockout mice to explore whether paternally expressed genes in offspring reduce maternal reproductive success. We mated females to male Igf2 KO homozygotes and found that females did show reduced metabolic costs. This shows foetal/placental Igf2 upregulates maternal metabolism, imposing energetic demands on the mother in the manner predicted by Haig’s kinship hypothesis.