Meeting Abstract
The fitness consequences of group living have been difficult to study in cooperatively breeding species, where it remains challenging to disentangle the benefits of living in a social group from those of alloparental care behavior. Both group living and alloparental care may increase the ability of organisms to cope with harsh environments, though the former remains poorly studied. We use a long-term dataset collected in cooperatively breeding superb starlings (Lamprotornis superbus) to determine the fitness consequences of group living, as social groups are significantly larger than, and uncorrelated to, the number of alloparents present in each group. We examined (i) whether social group size increased adult survival, (ii) whether group size served to buffer against harsh environmental conditions, and (iii) whether survival benefits of social group size were mediated by physiological traits (i.e. glucocorticoid hormones, oxidative stress, and immune function). Survival models showed that group size was positively correlated to adult survival, though differently between the sexes: female survival increased with group size similarly across all environmental conditions, whereas male survival increased with group size in periods of average or above average pre-breeding rainfall (though there was no benefit to living in the largest group under harsh conditions for males). We also found that physiological state did vary according to social group size, though individuals in the smallest and largest social groups paid the greatest physiological cost. Our results suggest that while individuals in the largest social groups gain the largest fitness benefits, they simultaneously experience the greatest physiological costs. Harsh environmental conditions may increase social conflict, particularly in males, leading to reduced benefits of group living under harsh dry years.
