Breeding success in cooperative meerkats: effects of helper number and maternal state

Studies of cooperatively breeding birds and mammals generally concentrate on the effects that helpers have on the number of reproductive attempts females have per year or on the number and size of offspring that survive from hatching/weaning to independence. However, helpers may also influence breeding success before hatching or weaning. In the present study, we used an ultrasound imager to determine litter sizes close to birth, and multivariate statistics to investigate whether helpers influence female fecundity, offspring survival to weaning, and offspring size at weaning in cooperative meerkats, Suricata suricatta. We found that the number of helpers in a group was correlated with the number of litters that females delivered each year, probably because females in large groups gave birth earlier and had shorter interbirth intervals. In addition, although pup survival between birth and weaning was primarily influenced by maternal dominance status, helper number may also have a significant positive effect. By contrast, we found no evidence to suggest that helpers have a direct effect on either litter sizes at birth or pup weights at weaning, which were both significantly influenced by maternal weight at conception. However, because differences in maternal weight were associated with differences in helper number, helpers have the potential to influence maternal fecundity and offspring size within reproductive attempts indirectly. These results suggest that future studies may need to consider direct and indirect helper effects on female fecundity and investment before assessing helper effects on reproductive success in societies of cooperatively breeding vertebrates. Copyright 2003.