Male reproductive tactics in house mice: Consistent individual differences, intrinsic factors and density effects

Alternative reproductive tactics (ARTs) describe non-reversible or flexible alternative strategies that secure fertilization. For example, some male defend territories with females while others attempt sneaky matings. Often, ARTs are considered to be status-dependent and are explained by differences in mass or competitive ability. However, most studies on ARTs only approximate their fitness effect, ignore males that never reproduced and consider status (e.g. weight) as the sole mediator of ARTs. We used 244 male mice, Mus musculus domesticus, from semi-natural populations, to describe ARTs in Mus Musculus for the first time. We followed males throughout their life and categorized them as territorials or roamers over multiple monthly intervals, after validating our method of assigning tactics with detailed spatial data. We explored if tactic choice is repeatable, whether multiple social and/or intrinsic factors predict tactic choice and transitions between tactics, and tested for fitness and physiological differences between ARTs. Tactic choice was repeatable, but males switched flexibly between tactics. Tactic choice was associated with mass, age, the operational sex ratio and population size. Territorials had a higher probability of reproduction, but a lower gonadosomatic index. Our results reveal a personality component of ARTs, confirm equal mean fitness among tactics and suggest tactic choice as a multifaceted decision under various selective pressures.