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.

Figure 1.

Days asynchronous (days between first and last birth per litter) in 294 litters in which more than one female bred.

Figure 2.

The influence of (a) birth synchrony on the per cent of pups lost before emergence; (b) reproductive timing on the probability that pups survived the first week; (c) birth synchrony on the per cent of emergent pups that died before 3 months.