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Publication
Social stimuli, testosterone, and aggression in gull chicks: Support for the challenge hypothesis
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Advisor(s)
Abstract(s)
We tested the challenge hypothesis for the hormonal regulation
of aggression in chicks of the black-headed gull,
Larus ridibundus. Chicks of this species are highly aggressive
toward conspecifics, but never to peers that hatched
from the same clutch (modal clutch size is three). Therefore,
in the first experiment small families were housed
together in large groups (challenged condition) and compared
to families kept isolated (nonchallenged condition).
As expected, in the challenged condition during the initial
stage of territory establishment basal levels of testosterone
(T) were clearly higher than those in the nonchallenged
condition. In the second experiment we tested the effect of
a short social challenge on short-term T-fluctuations. The
design was based on an earlier experiment, showing that
after temporary T-treatment chicks become very sensitive
to social challenges while having low basal T-levels. We
now show that these social challenges induce brief elevations
in plasma T-levels. These peaks are similar to those
in previously untreated chicks but untreated chicks do not
respond with aggression to a challenge. Therefore, we
conclude that the initial exposure to elevated T-levels increases
the sensitivity to brief changes in T induced by
social challenges. In this way exposure to T, that may be
detrimental for development, is minimized while birds remain
able to defend territories. This is the first report
showing that the challenge hypothesis as established for
adult birds, is also applicable for aggressive behavior in
young birds outside the sexual context. Furthermore we
suggest that a phase of priming with T is necessary to
obtain the high behavioral responsiveness to a challenge.
Description
Keywords
Testosterone Challenge hypothesis Aggression Black-headed gull Territorial behavior Chick Ontogeny Priming Sensitization Organizing effects External stimuli
Citation
Hormones and Behavior, 41, 173-182