Effects of siblings on reproductive maturation and infanticidal behavior in cooperatively breeding Mongolian gerbils.

Mongolian gerbils living with their natal families undergo delayed reproductive maturation while helping to rear their younger siblings, whereas those housed away from their natal families may mature earlier but often respond aggressively to unfamiliar pups. We tested whether cohabitation with pups contributes to reproductive suppression and inhibition of infanticidal behavior, using young males and females housed with (1) their parents and younger siblings (pups), (2) parents without pups, (3) mixed-sex littermate groups, or (4) mixed-sex groups of unrelated peers. Maturation in males was inhibited by cohabitation with the parents, while maturation in females was further suppressed in the presence of pups. Males in all housing conditions showed little aggression towards unfamiliar pups, whereas females were usually infanticidal unless housed with pups. Aggression toward pups was especially pronounced in females that were pregnant or undergoing ovulatory cycles. Thus, cohabitation with younger siblings may intensify reproductive suppression and inhibit infanticidal behavior in female gerbils, whereas male gerbils exhibit parentally induced reproductive suppression and low rates of infanticide even in the absence of younger siblings.