Nursing one litter of Mongolian gerbils while pregnant with another: effects on daughters' mate attachment and fecundity

Previous research has revealed profound effects of prenatal interactions among littermates on the subsequent fecundity and behaviour of female Mongolian gerbils, Meriones unguiculatus. Here, we determined whether interlitter competition for maternal resources similarly affects female phenotypes. We found that, when adult, female Mongolian gerbils whose dams were both nursing while gestating them and pregnant while suckling them (twice-challenged dams) were less likely to affiliate with their mates and less fecund than their peers reared by dams neither suckling a prior litter while gestating focal daughters nor pregnant with a subsequent litter while suckling them (not-challenged dams). Daughters of twice-challenged dams had smaller, more female-biased litters than did daughters of not-challenged dams, and the difference in behaviour of daughters of twice-challenged and not-challenged gerbil dams when choosing between their respective mates and unfamiliar males was as great as that seen in nominally monogamous and polygamous species of vole observed in similar circumstances. Our results suggest that the reproductive phenotype of females can be profoundly affected by naturally occurring variation in access to maternal resources that results from conflict between successive progeny in mammalian species where dams are sometimes both pregnant and nursing and sometimes neither pregnant with nor nursing one litter while rearing another.