Data for: Social environment and masculinization level interact to explain male testosterone levels in a social rodent

<p><span>In vertebrates, male testosterone levels vary across the year and are generally higher during the mating period relative to the offspring-rearing period. However, male testosterone levels may also be influenced by male morphotype (males with different levels of masculinization), and by the social environment experienced within a conspecific group. In social species, it has been proposed that high levels of testosterone could be incompatible with the development of an amicable social environment. Thus, in these species, it is predicted that males have relatively low levels of testosterone. Our goal was to examine the potential association between male serum testosterone levels, male morphotype, and the social environment in the caviomorph rodent <em>Octodon</em> <em>degus</em> under natural conditions. We quantified serum testosterone levels of male degus during the periods of mating and offspring rearing, and the size and composition of social groups, including masculinization levels of male and female group members from 2009 to 2019. Our results revealed that male testosterone levels covary with the period, male morphotype, and female and male social group environments, but not with offspring social environment (total number of offspring in the social group). Additionally, male degus exhibit low levels of testosterone that are indistinguishable from female levels during mating and offspring rearing. Similar to other highly social mammals, male amicable behavior could be the best male mating strategy, implying a downregulation of males' testosterone levels.</span></p>