Reproductive competition and the evolution of extreme birth synchrony in a cooperative mammal

Abstract

Reproductive events in animal societies often show a high degree of temporal clustering, but the evolutionary causes of this synchronization are poorly understood. Here, we suggest that selection to avoid the negative effects of competition with other females has given rise to a remarkable degree of birth synchrony in the communal-breeding banded mongoose (Mungos mungo). Within banded mongoose groups, births are highly synchronous, with 64 per cent of females giving birth on exactly the same night. Our results indicate that this extreme synchrony arises because offspring suffer an increased risk of infanticide if their mother gives birth before other females, but suffer in competition with older littermates if their mother gives birth after them. These findings highlight the important influence that reproductive competition can have for the evolution of reproductive synchrony.

Explaining negative kin discrimination in a cooperative mammal society

“…Infanticide is known to occur in this system, but is difficult to observe directly as it typically occurs in the den. In asynchronous litters, infanticide appears to be common because early life pup mortality is strongly dependent on the pregnancy status of other females in the group (14,15). Pups that are born early in asynchronous litters almost always die in the first few days after birth, whereas pups born last almost always survive (15).…”

“…In asynchronous litters, infanticide appears to be common because early life pup mortality is strongly dependent on the pregnancy status of other females in the group (14,15). Pups that are born early in asynchronous litters almost always die in the first few days after birth, whereas pups born last almost always survive (15). Between November 1997 and October 2015, we recorded the order in which each female gave birth in an asynchronous litter (i.e., if she gave birth first, in the middle, or last) and whether any of her pups survived the first week after birth.…”

“…Following ref. 15, we used the presence or absence of "babysitters" (adults left at the den to guard newly born pups) to measure patterns of early life litter mortality. Specifically, to determine the survival of an individual female's pups, we considered only females who gave birth early relative to the rest of the breeding females and for which the failure of a specific female's litter could be detected using cessation of babysitting (i.e., we did not consider females who gave birth when babysitting of other early-birthing females' pups was still ongoing).…”

“…To test further whether negative kin discrimination depends on the capacity of recipients to resist, we examined kin discrimination in cases of infanticide of newborn pups. Between 1 and 12 females reproduce in each breeding attempt (14) and birth is highly synchronized, with pregnant females giving birth on exactly the same morning in 63% of cases (15). Experimental and observational evidence suggests that asynchronous litters are often killed by dominant females (14,15) and that in asynchronous litters the death of a litter in the first week after birth can be used as a proxy for infanticide (15,16).…”

“…Between 1 and 12 females reproduce in each breeding attempt (14) and birth is highly synchronized, with pregnant females giving birth on exactly the same morning in 63% of cases (15). Experimental and observational evidence suggests that asynchronous litters are often killed by dominant females (14,15) and that in asynchronous litters the death of a litter in the first week after birth can be used as a proxy for infanticide (15,16). In contrast to the pattern of negative kin discrimination in the eviction of adult females, there was no evidence of kin discrimination in cases of presumed infanticide (GLMM, β ± SE = −0.64 ± 2.00, χ 2 1 = 0.10, P = 0.75; Table S7).…”