Alternative reproductive tactics in female striped mice: heavier females are more likely to breed solitarily than communally

International audience1. Alternative reproductive tactics (ARTs) are discrete reproductive phenotypes governed bydecision rules called strategies. ARTs are fixed for life in species with alternative strategies,while tactic expression is plastic in species with a single strategy. ARTs have been investigatedin males of many species, but few studies have tested whether the same theoretical frameworkapplies in females.2. Female striped mice (Rhabdomys pumilio) employ three ARTs: communal breeders givebirth in a nest shared with female kin and a breeding male and show allo-parental care;returners give birth away from the shared nest and later return to it; and solitary breedersgive birth away from the shared nest and do not return to the group.3. Here, studying free-living female striped mice over six breeding seasons, we tested whetherARTs arise from alternative strategies or a single strategy.4. We also asked to what extent stochastic extrinsic factors explain whether individualsbecome solitary rather than group living.5. Females switched tactics, consistent with a single strategy, so we tested whether this representeda mixed or conditional single strategy. Only the latter predicts differences betweenARTs in traits indicating competitive ability, such as body mass or age, before individualsadopt a tactic. We weighed females at conception when they were still group living to eliminatepotential confounding effects of gestation and subsequent social tactic (solitary versusgroup living) on body mass.6. Females that went on to use a solitary ART were heavier than those that became communalbreeders and returners, in support of a conditional strategy.7. Solitary breeders also arose through extrinsic factors (mortality of all adult female groupmembers). They weighed less than females that became solitary while relatives were alive, butdid not differ in body mass from communal breeders and returners.8. We conclude that ART theory applies to both sexes, with female striped mice following aconditional single strategy. Future studies should consider the possibility that phenotypes thatsuperficially resemble evolved tactics might also arise through non-adaptive extrinsic causes