Alloparents in the Mongolian gerbil: impact on long-term reproductive performance of breeders and opportunities for independent reproduction

Abstract

The presence of alloparents in cooperatively breeding groups may enhance the reproductive performance of the breeding pair but tests of this hypothesis in mammalian cooperative breeders have typically examined short periods in the reproductive life span of breeders. The present experiment was designed to evaluate the long-term effects of the presence of alloparents on reproductive performance under laboratory conditions in Mongolian gerbils (Mertones unguiculalus), and to evaluate the possibility that alloparents may attempt independent reproduction during their tenure as alloparents. Pairs were established with either 0 or 4 alloparents and breeding performance was monitored over a 13.5-month period. The presence of alloparents did not enhance reproductive rates in breeding pairs, and neither enhanced nor delayed developmental rates in offspring. Variation in litter size, offspring survival, pup growth, and interbirth interval did not vary significantly as a function of the breeding females' reproductive tenure. Seven of 49 female alloparents of breeding age in family groups produced offspring. Alloparent breeding was associated with long interbirth intervals in the breeding adult female. Neonatal survival in litters born to alloparents was higher in litters that were temporally synchronized with litters produced by the older breeding female than in asynchronously produced litters. Under the conditions in this experiment, then, few indirect benefits accrue to helpers as a consequence of their alloparental effort, and immediate (the opportunity for independent reproductive attempts) and delayed (parental skills acquisition) direct benefits may account for helping behavior in this species.