Social factors and parasite load in greylag geese

Social contexts are among the most potent stressors, affecting individual behaviour, physiology and the immune system. Because of their immediate metabolic costs and their delayed contingencies with the immune system, social challenges are directly fitness-relevant. Not all members of a population are equally affected, because individuals differ in their responses to stressors according their social embedding, personality, status, sex, age, etc.. We previously estimated individual investment into the social domain via heart rate (HR) and immunoreactive glucocorticoid metabolites (CORT) in free-living greylag geese. Now we propose to extend this successful line of social complexity research in birds, towards potential constraints particularly immune parameters and parasites. The contingencies of (social) stress with the immune system, parasites are in principle, reasonably well known, but this is the first attempt to investigate the interactions of these factors via a systemic approach. To achieve this we suggest an observational part and three experiments. We plan to monitor individual parasite burden, immunocompetence (differential blood count, phytohaemagglutinin skin test) and social behaviour of focal individuals, at regular intervals. In addition to the 20 previously implanted geese, from which extensive behavioural, HR and CORT data has been collected in the past three years, we will include individuals which are affected by major social challenges (e.g. loss of partner, challenged by a rival) as well as unchallenged `control` individuals. We expect challenged individuals to show higher CORT excretion than securely embedded, unchallenged individuals (minutes to hours from the challenge), decreased immune parameters (within a few days) and increased parasite burden (within one to two weeks). With our experiments we intend to manipulate both, parasite burden and socially induced stress level of individuals. In the first experiment we will treat individuals of six different social groups (proactive and reactive paired males, proactive and reactive paired females as well as proactive and reactive unpaired males) against parasites, as a measure to standardize `baseline` infection levels of the focal individuals. Thereafter, the rate of parasite re-infection will be monitored in the different groups. We expect unpaired as well as reactive individuals to be re-infected to a higher degree than paired and proactive individuals. In a second, social challenge experiment, we plan to isolate individuals (hand-raised juveniles as well as adult geese) for 2 days. During this isolation period and after the individuals re-joined the flock, their CORT excretion, parasite burden and that of their social allies will be followed. We expect that CORT of the isolated individual and its partner will increase shortly after separation, which may be followed by a response in parasite load a few days later, depending on personality and pair bond quality parameters. In a third experiment, we plan to elevate glucocorticoid levels via an ACTH challenge in yet another group of geese and monitor immune parameters and parasite burden thereafter. In all of the three experiments we plan to employ General Linear Models (GLM; or GLMM , if appropriate) to analyse the influence of different factors (sex, age social status, personality) on different parameters (HR, CORT, parasite burden, immune parameters). With the proposed project we aim at gaining an integrated view onto the contingencies between social embedding, stress coping and parasites in a socially complex bird, the greylag goose. We plan to take advantage of the unique possibility of studying free- living animals in an intact social environment, of which detailed behavioural as well as physiological data have been collected over years.

In humans and other mammals clear contingencies were found between social relationships, stress load, immune system function and health. Although Birds and mammals are 220 Million years phylogenetically separate, preliminary evidence indicated that these principles of social psychosomatics are rather similar in the two vertebrate phyla. These relationships between social embedding and health were at the focus of FWF-Project P21489-B17 Social factors and parasite load in Greylag geese. The research was conducted at the Konrad Lorenz Research station by a team consisting of Kurt Kotrschal, Post Docs Sonja Ludwig, Claudia Wascher, Isabella Scheiber und Didone Frigerio and a number of masters and practicum students, mainly from Austria and Germany. In a total of nine sub-studies we either manipulated experimentally the social context or glucocorticoid stress hormone levels to investigate the connections to the immune system (blood parameters) and parasite load (from faeces, which were also used to analyse corticosterone metabolites by EIA). In addition, we conducted a few add-on pilot studies on the relationship between social behaviour and parasite load in Bald ibis and in Carrion crows. In the core studies in Greylag geese, among other things, we experimentally increased glucocorticoid levels, removed pair partners for a few days or observed social behaviour in a majority of flock individuals from which we also collected faeces for the analysis of stress hormone metabolites and parasites. As expected, we found clear contingencies between social behaviour and the modulation of stress hormones. By and large, we also found the expected relationships between stress hormones, immune system and parasite excretion. We therefore could show a psychosomatic connection also in birds. The results of this project will be publishes in a number of peer-reviewed papers and were featured in a few books and handbook articles. Sonja Ludwig and Claudia Wascher left the project for scientific positions in Scotland and Spain, for Didone Frigerio, this project was a scientific re-start after her period of maternal leave.