Effects of single parenthood on mothers' behavior, morphology, and endocrine function in the biparental California mouse

Motherhood is energetically costly for mammals and is associated with pronounced changes in mothers' physiology, morphology and behavior. In ~5% of mammals, fathers assist their mates with rearing offspring and can enhance offspring survival and development. Although these beneficial consequences of paternal care can be mediated by direct effects on offspring, they might also be mediated indirectly, through beneficial effects on mothers. We tested the hypothesis that fathers in the monogamous, biparental California mouse (Peromyscus californicus) reduce the burden of parental care on their mates, and therefore, that females rearing offspring with and without assistance from their mates will show differences in endocrinology, morphology and behavior, as well as in the survival and development of their pups. We found that pups' survival and development in the lab did not differ between those raised by a single mother and those reared by both mother and father. Single mothers spent more time in feeding behaviors than paired mothers. Both single and paired mothers had higher lean mass and/or lower fat mass and showed more anxiety-like behavior in open-field tests and tail-suspension tests, compared to non-breeding females. Single mothers had higher body-mass-corrected liver and heart masses, but lower ovarian and uterine masses, than paired mothers and/or non-breeding females. Mass of the gastrointestinal tract did not differ between single and paired mothers, but single mothers had heavier gastrointestinal tract compared to non-breeding females. Single motherhood also induced a flattened diel corticosterone rhythm and a blunted corticosterone response to stress, compared to non-breeding conditions. These findings suggest that the absence of a mate induces morphological and endocrine changes in mothers, which might result from increased energetic demands of pup care and could potentially help maintain normal survival and development of pups.