Abstract

Understanding the costs and benefits of plural breeding, a reproductive strategy in which direct reproduction is shared by females in multi-female groups, requires that we examine the impact of males on females. The aim of this study was to examine potential additional fitness costs associated with male social organization to plurally breeding females in the caviomorph rodent, Octodon degus. Using a 10-year dataset, we used linear mixed model approaches to determine if male social organization was related to body mass, access to food resources, abundance of fleas, and glucocorticoid levels of females during offspring care. The body mass of adult females during lactation was negatively associated with the number of adult males per group and was marginally lower in groups with multiple males than in groups without males. Close examination of these trends suggests that the most biologically relevant difference is between groups with multiple males and groups without males. Male social organization did not impact female access to food, ectoparasitic flea loads, and FCM levels. Abundance of food and ectoparasite levels covaried with year of study and across females, while FCM levels varied across social groups examined. Altogether, these results suggest that the presence of male degus in multi-female groups has a small but negative effect on the condition of females. The lack of statistically significant relationships with other variables and untested conditions of the social environment and individual condition suggest that how males impact females is complex and condition-dependent. © 2025 Wiley-VCH GmbH. Published by John Wiley & Sons Ltd.