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Hormonal correlates of siblicide in Nazca boobies: support for the Challenge Hypothesis

Summary: Hormonal correlates of siblicide in Nazca boobies:
support for the Challenge Hypothesis
Elise D. Ferreea,1
, Martin C. Wikelskib
, David J. Andersona,*
Department of Biology, Wake Forest University, Winston-Salem, NC 27109-7325, USA
Department of Ecology & Evolutionary Biology, Princeton University, Princeton, NJ 08544, USA
Received 5 April 2004; revised 21 June 2004; accepted 22 June 2004
Available online 11 September 2004
The androgen hormone testosterone (T) mediates vertebrate aggression in many contexts and according to the Challenge Hypothesis is
up-regulated during social challenges. While originally applied to challenges experienced by breeding adults, we show for the first time that T
is similarly up-regulated during deadly sibling aggression in young birds. When two nestling Nazca boobies hatch, one--usually the older
chick--virtually always kills the other chick by pushing it from the nest. We compared concentrations of T, dehydroepiandrosterone (DHEA;
a precursor of T), and corticosterone (Cort; a stress hormone) of chicks at various stages. T was elevated during fights in both chicks in two-
chick broods, but not before and after fights, and not in chicks lacking a nest mate. DHEA was elevated 1 day after hatching and declined
with age but appeared not to vary in concert with aggression. Cort did not vary across fighting and nonfighting periods. In conjunction with
an earlier study [Tarlow, E.M., Wikelski, M., Anderson, D.J., 2001. Hormonal correlates of siblicide in Gala´pagos Nazca boobies. Horm.


Source: Anderson, David J. - Department of Biology, Wake Forest University
Wikelski, Martin - Department of Ecology and Evolutionary Biology, Princeton University


Collections: Environmental Sciences and Ecology