Corticosterone levels correlate with alloparental care in a sex-dependent manner in African striped mice, Rhabdomys pumilio
Résumé
Alloparental care of non-breeders is the main characteristic of cooperatively breeding species. While many studies have contributed to the understanding of the evolutionary reasons why individuals provide care to young that are not their own offspring, the variables influencing and causing alloparental care are less understood. We tested in African striped mice (Rhabdomys pumilio) whether age, sex, testosterone and corticosterone were correlated with alloparental care of non-breeding helpers. We studied 11 family groups under controlled conditions in the laboratory, each with two juvenile and two adult helpers, one being male and one being female in each age category. We predicted male helpers to show more alloparental care than female helpers, as males are the dispersing sex and might thus have to pay for staying. We also expected adult helpers to show more alloparental care than juvenile helpers and both corticosterone and testosterone to correlate negatively with alloparental care. We found high levels of alloparental care in non-breeding striped mice, which spent a significant amount of time in the nest, huddling and licking pups. There was neither a difference between the sexes nor between age categories (although both factors were significant in interaction terms), indicating either low costs and/or high benefits of alloparental care. Mothers showed significantly more care than helpers, and fathers showed similar levels of parental care as mothers but not significantly more than helpers. Although testosterone levels differed significantly between helpers of different age and sex, with adult male helpers showing the highest levels, we did not find any relationships between testosterone and the amount of alloparental care. Corticosterone levels were negatively correlated with alloparental care, and these effects were modulated by the sex and the age of helpers. In females, less alloparental care was shown with increasing corticosterone levels, while in males, the relationship was positive. Also, younger individuals with lower corticosterone levels showed more alloparental care than older individuals with low corticosterone levels. In sum, alloparental care is well developed in male and female non-breeding helpers of striped mice, both in adult and juvenile helpers, but independently of testosterone, with corticosterone showing an age- and sex-specific relationship with alloparental care.