PhD‐theses - Ethologische Gesellschaft

HEART RATE IN GREYLAG GEESE (ANSER ANSER): IMPLICATIONS FOR THE STUDY OF
SOCIAL SYSTEMS
Claudia A. F. Wascher
claudia.wascher@klf.ac.at
Research Update
PhD thesis, supervised by Prof. Dr. K. Kotrschal, Konrad Lorenz Forschungsstelle, Universität Wien
Social contexts are among the most potent stressors, affecting individual behaviour,
physiology and the immune system. Although energetically costly, short‐term elevation of
the stress response is adaptive and unavoidable in coping with challenges. In contrast
chronic activation of the stress axes may have pathological consequences. Therefore, in
terms of an individual’s fitness and well being, it is of major importance to respond to
stressors adequately. However, not all members of a population are equally affected,
individuals differ in their responses to stressors according their social embedding,
personality, status, sex, age, etc.. In the course of my PhD I investigated the individual
investment in the social domain as measured by heart rate (HR). I recorded HR of 25 greylag
geese with fully implanted sensor‐transmitter packages for 18 months. Besides physical
activity, social interactions proved to be the strongest HR modulators. In agonistic
encounters HR increased to a greater extend, when the risk of being defeated was higher
(e.g. in interactions with an opponent who wins a higher percentage of interactions). The
present results suggest that individuals modulate their HR very flexible according to the
relevance of single agonistic encounters. Even more impressive, HR was not only modulated
by active involvement in stressful events, but also by watching interactions (“bystander
effect”). Also here, the relevance of the event determines the immediate physiological
response. Greylag geese responded stronger watching social (e.g. agonistic encounters,
arriving or departing geese) than non‐social events (e.g. vehicles passing by, thunder).
Furthermore, HR response differed, depending on the individuals involved in an event.
Geese responded stronger when watching interactions, in which the pair‐partner or a family
member was involved compared to events with non‐associated individuals. A similar picture
appeared, when comparing HR responses to conspecifics vocalisations. HR was significantly
higher if the pair‐partner called, compared to non‐associated geese. One of the key
mechanisms to optimize the investment into the social domain is social support, which is
defined as the stress‐reducing effect of the presence of a familiar social partner. Here, for
the first time, effects of passive social support with respect to HR are reported in non‐human
animals. In a stressful situation, unpaired individuals showed a significantly higher HR than
paired individuals, which indicates that having a social ally, effects an individual’s physiology.
To sum up, I found social events to have pronounced effects on an individual’s physiology.
This may have serious consequences with respect to energy expenditure and probably may
even affect an animal’s health or reproductive success. Still, individuals modulated their HR
response according to the relevance of single events (e.g. risk of being defeated, social ally
involved). Also, social support has been shown to have stress reducing effects with respect
to HR. Therefore, living in social groups for greylag geese seems potentially energetically
costly, but the individual investment is optimized by flexible modulation of the physiological
stress response according to subsequent needs and requirements.
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