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Avian eggs contain substantial amounts of maternal hormones and so provide an excellent model to study hormone-mediated maternal effects. We review this new and rapidly evolving field, taking an ecological and evolutionary approach and focusing on effects and function of maternal androgens in offspring development. Manipulation of yolk levels of androgens(More)
Avian eggs contain substantial amounts of maternal androgens, and several studies have indicated that these are beneficial for the chick. Nevertheless, there is a large and systematic variation in maternal hormone concentrations both within and between clutches. If maternal androgens also involve costs, this might explain why not all mothers put high levels(More)
We tested the hypothesis that mother birds counterbalance the negative effects of hatching asynchrony for later-hatched chicks by increasing the yolk androgen concentrations in consecutive eggs of their clutch. In doing so, they may adaptively tune each offspring's competitive ability and, thus, growth and survival. However, evidence in support of this(More)
Recent studies of animal personality have focused on its proximate causation and its ecological and evolutionary significance, but have mostly ignored questions about its development, although an understanding of the latter is highly relevant to these other questions. One possible reason for this neglect is confusion about many of the concepts and terms(More)
The work presented here aims at understanding the nature, epigenesis and function of personality types (here called behavioral profiles) in birds, focusing on a wild bird species, the great tit (Parus major). Lines bidirectionally selected for exploration show a wide array of social and non-social behavioral differences, and also some differences in(More)
Over the past decade, birds have proven to be excellent models to study hormone-mediated maternal effects in an evolutionary framework. Almost all these studies focus on the function of maternal steroid hormones for offspring development, but lack of knowledge about the underlying mechanisms hampers further progress. We discuss several hypotheses concerning(More)
The judgement of healthy subject rating the emotional expressions of a set of schematic drawn faces is validated (study 1) to examine the relationship between mood (depressed/elated) and judgement of emotional expressions of these faces (study 2). Study 1: 30 healthy subjects judged 12 faces with respect to the emotions they express (fear, happiness, anger,(More)
Developmental processes can have major impacts on the correlations in behaviour across contexts (contextual generality) and across time (temporal consistency) that are the hallmarks of animal personality. Personality can and does change: at any given age or life stage it is contingent upon a wide range of experiential factors that occurred earlier in life,(More)
We experimentally examined the effect of testosterone on the antibody response to a single immunization with sheep red blood cells in young black-headed gulls. This species performs a number of testosterone-mediated elaborate postural displays in social interactions and breeds in dense colonies in which there is a high likelihood of infectious diseases. In(More)
Avian eggs contain a variety of steroid hormones, which have been attributed as a tool for maternal phenotypic engineering. The majority of studies focuses on androgens, but also significant amounts of progesterone as well as other steroid hormones have been measured. The question if corticosterone is also present in eggs of chickens is currently under(More)