Among cooperative breeding animals, within group differences in behaviour are often striking, however, the physiological mechanisms underlying these differences remain poorly understood. Glucocorticoids (GC), a class of hormones produced in response to stressors, may play an essential role in this by linking external stimuli with phenotypic expression of behaviour.

In many cooperative species, individuals show striking variation in contributions to cooperative activities. In our population of habituated meerkats (Suricata suricatta) in South Africa, GC levels were found to be positively associated with pup provisioning rates, but negatively with the decision to babysit, suggesting that GC may not underlie helping behaviour per se, but particular behaviours associated with certain types of helping behaviour. For instance, elevated GC levels may increase foraging effort and levels of alertness and hence facilitate pup provisioning.

Another feature of many cooperative animals is the variation in reproduction among group members, subordinate individuals often reproducing at markedly lower rates than dominants. In our meerkats, aggression from dominants towards subordinates leads to temporal evictions from the group. These evictions are accompanied by increased GC levels as well as increased abortion rates and reduced conception rates, suggestion a role for GC underlying the distribution of reproduction within groups.

Traditionally, individual differences in GC levels were thought to be rank related, subordinates having higher levels than dominants. However, evidence accumulates that in many species, including meerkats, subordinates do not have higher GC levels than dominants. It is therefore hypothesised that not social status per se, but social challenges and the degree of social support associated with social status underlie variation in GC levels.

  <>For my PhD, I will examine how social stimuli, including within group conflict, between group conflict and positive social interactions, affect levels of stress hormones and whether this depends on dominance status and life history stage. Secondly, using experimental manipulation of GC levels, I will examine how stress hormones affect reproductive and cooperative behaviour.

Previous Research
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During my MSc with Jan Komdeur and Michael Magrath at Groningen University, the Netherlands, I studied the relation between colony size and breeding success in the fairy martin (Petrochelidon ariel), the relation between oxidative stress levels and social status in the cooperatively breeding Seychelles warbler (Acrocephalus sechellensis) and breeding tactics in blue tits (Cyanistes caeruleus). In addition, I worked as an assistant with the Max Planck Institute on sexual signalling in the purple-crowned fairy-wren (Malurus coronatus), with the Netherlands Institute of Ecology on breeding tactics in great tits (Parus major) and with Basel University on communication in nightingales (Luscinia megarhynchos).