Steroid hormones in hair reveal sexual maturity and competition in wild house mice (Mus musculus domesticus)

Abstract

Endocrine data from wild populations provide important insight into social systems. However, obtaining samples for traditional methods involves capture and restraint of animals, and/or pain, which can influence the animal’s stress level, and thereby undesirable release of hormones. Here, we measured corticosterone, testosterone and progesterone in the hair of 482 wild-derived house mice that experienced sexual competition while living under semi-natural conditions. We tested whether sex, age, weight and indicators of sexual maturity, reproduction and social conflicts predict hormone concentrations measured in hair (sampling at endpoint). We show that body weight, sex and age significantly predict cumulative testosterone and progesterone levels, allowing the differentiation between subadults and adults in both sexes. Corticosterone was only slightly elevated in older males compared to older females and increased with the level of visible injuries or scars. Testosterone in males positively correlated with body weight, age, testes size, and sperm number. Progesterone in females significantly increased with age, body weight, and the number of embryos implanted throughout life, but not with the number of litters when controlled for age and weight. Our results highlight the biological validity of hair steroid measurements and provide important insight into reproductive competition in wild house mice.

Immune-Endocrine Links to Gregariousness in Wild House Mice

“…Hormonal correlates of non-maternal aggression in female house mice have not been extensively studied, perhaps because laboratory strains of female mice are not prone to extensive aggression. We do however, find wild female house mice to both show aggressive behaviors and to be recipients of aggression, both in semi-natural enclosures (Carlitz et al, 2019) and in the lab (Harrison et al, 2016(Harrison et al, , 2017Lopes et al, 2018; in all of these laboratory studies, several trials had to be interrupted due to excessive aggression). It is therefore possible that due to its effects in reducing aggression, high levels of progesterone facilitate life in larger social groups in house mice.…”

“…When we used hair samples to quantify long-term secretion of steroid hormones, sex differences were found, with progesterone being higher in females and testosterone higher in males, as one would expect from basic mammalian physiology. This is an indication that using hair to assess cumulative steroid levels in mice is an appropriate method (see also Carlitz et al, 2019). Circulating (serum) corticosterone levels were higher in females than in males, even though there were no differences in capture time between males and females.…”

“…The LC-MS/MS analysis followed a validated protocol for corticosterone, testosterone and progesterone (Gao et al, 2013). The biological validity of these hair steroids was recently assessed for mice from the same population (Carlitz et al, 2019).…”

“…The hair steroid measurements reflect a long-term accumulation (over months; Carlitz et al, 2019) of these hormones. Differently from the serum corticosterone levels (which reflect secretion over the last several minutes), hair corticosterone showed no significant difference between the sexes (F = 0.908, p = 0.345), a non-significant trend toward elevation in high gregariousness phenotypes (F = 3.40, p = 0.077) and no significant interaction of these terms (F = 0.466, p = 0.50).…”

Contact patterns reveal a stable dynamic community structure with fission-fusion dynamics in wild house mice

“…In fact, this is only possible if the restructuring of direct contact patterns is mainly contained within dynamic communities and thus, if communities fission into sub-groups during summer that recombine during the cold winter period. These findings allow for speculations on the effect of intrasexual reproductive competition on the structuring of groups and dynamic communities: In house mice, both males and females compete with same-sex group members over reproduction (for a summary of the evidence see Carlitz et al, 2019), and this is expected to affect group structure seasonally. In winter, house mice might form larger groups because of thermo-regulatory benefits (winter huddles) and a lower potential for competition over mating partners.…”