An experimental study on the causes of sex-biased mortality in the black-headed gull – the possible role of testosterone

Black-headed Gull (Larus ridibundus) Science Article 2


During early development male offspring in avian species often suffer from enhanced mortality compared to female offspring. This has been attributed to different nutritional requirements, as sex-biased mortality has been reported particularly in sexually size-dimorphic species. However, other traits of the male phenotype, such as the embryonic hormone profile, have been suggested to contribute to this male disadvantage. In particular the negative effects of sex steroids on immune function may be causally involved. We investigated the role of testosterone in the expression of male phenotype disadvantage through an experimental reduction of the availability of testosterone receptors by in-ovo injection of an anti-androgen (Flutamide

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