Social investment in geese

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 O 2 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).

To live in social groups is such a common situation for humans, that most are not aware how much they invest physiologically and energetically into their social contexts. Actually, higher vertebrates share a number of brain structures and physiological mechanisms used in the social domain. Based on this and on convergent selection pressures, mammals and birds developed astonishing parallel patterns of social organization. Nearly two decades of research at the Konrad Lorenz Forschungsstelle have put Greylag geese (Anser anser) on the social complexity map. These birds maintain long-term bonds and valuable relationships between pair partners and with their offspring and they support each other socially in a complex way. Via fully implanted heart rate transmitters and non-invasive analysis of corticosterone metabolites from faeces, we now linked individual and seasonal energetics to social complexity. This is possible, because heart rate and also, glucocorticoid modulation are fair approximations of oxygen consumption. By quantifying individual physiological and energetic investment into the social domain (i.e. individual stress management), we gained insight into the functionality of social organization of geese. We found that males invested particularly into their female partners, whereas the latter invested into offspring. Family members showed to be important social supporters of each other, which particularly decreased social costs in females and offspring and seems to be the base for good female fertility and reproductive success. Moreover, we found that degree of behavioural and temporal synchronization between pair partners scaled positively with the reproductive success of a pair and that this temporal patterning increases with pairbond duration. Based on our results we propose that individual social efficiency (i.e. reaching ones goals with minimum physiological and energetic investment) is an important issue in shaping social systems and that individual social competence is the behavioural side of social efficiency. The insights provided by an energetic-physiological approach to social complexity provides a base for the better understanding of vertebrate sociality in general and for the relationships of humans with their companion animals in particular.