Social performance and physiology are closely linked in all social vertebrates. Individual investment into the social domain is an important component of total "stress" load (the energetic requirements of homeostasis: "allostatic load": McEwen and Wingfield 2003). According to our pilot estimates based on heart rate and time budget data in greylag geese, up to 15% of the total energy may be spent in social interactions, although these only consume approx. 5% of the time budget. Individuals will vary in social behavioural and related physiological efficiency because of sex, social status and personality. Ultimately, this will affect reproductive success. We plan to
investigate individual investment into the social domain with heart rate (FH)-transmitter-implanted, free-living and hence, socially fully intact greylag geese. In addition, glucocorticoid modulation (BR) by different challenges will be measured non-invasively. FH is probably the most integrative parameter for "physiological investment" into a certain domain. Because FH is correlated with oxygen consumption, it may also be considered a good estimate of energy expenditure. We plan to observe, and experimentally challenge, 25 long-term (18 months) FH-transmitter implanted geese of different social categories (both sexes, pair bond, including family, juvenile and singletons) and, in addition, non-implanted individuals. Geese are already implanted at the planned start of this proposed project, in January 2006. Simultaneous FH and behavioural recordings, including time budgets, in combination with BR will allow to estimate individual energy expenditure for behaviour in general and for social contexts in particular.
Internal data storage of 2 min means of FH and body temperature will be read out after explantation and related to social and seasonal parameters over 18 months. Thereby, we will be able to answer the question, whether, and to what degree, social investment varies with season. In addition, geese will be experimentally challenged by dense feeding situations, model predators, immobilisation, etc., also to categorize their individual behavioural phenotype (coping style). Thereby, we will be able to compare FH and BR modulation between individuals and to estimate within-population variability. BR will be monitored non-invasively, via faeces by EIA, in control situations as well as after challenges. Results shall be integrated into a general model of physiological investment to contribute to the explanation of vertebrate sociality. FH-based equivalents of O2 consumption with special emphasis on the
individual investment into the social domain will be calculated over the year and serve as the common currency linking individual physiology and social behaviour. We predict, that individual efficiency in the social domain will vary with sex, social connectedness and personality. Such an energy-based model will finally allow us to
appreciate 1) social physiology as a major factor, besides brain mechanisms, for the striking parallelism in social patterns, between mammals and birds and 2), vice versa, will provide a deeper understanding for the selection pressures acting upon social physiology (i.e. the mechanisms of allostasis).
