PhD ceremony Ms. M.S. Müller: Proximate and ultimate aspects of androgen-mediated maternal effects in relation to sibling competition in birds

PhD ceremony: Ms. M.S. Müller, 9.00 uur, Academiegebouw, Broerstraat 5, Groningen

Dissertation: Proximate and ultimate aspects of androgen-mediated maternal effects in relation to sibling competition in birds

Promotor(s): prof. A.G.G. Groothuis

Faculty: Mathematics and Natural Sciences

The thesis of Martina Müller evaluates several of the evolutionary and mechanistic hypotheses about hormone-mediated maternal effects in birds. In plants and animals, mothers pass their genes on to their offspring but can also influence their offspring in non-genetic ways by modifying the environment in which they develop. For example, mothers can produce relatively larger seeds or eggs, determine the timing at which certain offspring initiate embryonic development, or transfer different quantities of maternal hormones to offspring. Hormones are signals that regulate physiology and behavior in plants and animals and play an essential role in coordinating development. Two decades ago, bird eggs were found to contain high concentrations of testosterone that vary widely within clutches, between clutches of the same mother and also between species. Since then, maternal testosterone has been shown to have diverse effects on offspring development during the pre-natal period, the post-natal period and even into adulthood, often producing chicks that are more competitive by accelerating growth, increasing begging and aggressive behavior, and enhancing survival, although with some costs of elevated metabolic rate and compromised immune function. Testosterone has been found to vary systematically among consecutive eggs within clutches in different patterns, between clutches in accordance with variation in the environment, food availability, mate quality or the mother's condition and between species in ways predicted by their life histories which generated several interesting hypotheses about the evolutionary origins of the observed patterns and about the physiological mechanisms that underlie these patterns.

Müller has addressed the hypotheses about maternal hormones via observational and experimental studies on individuals from the same species, and by investigating the origins of between-species variation in hormone-mediated maternal effects using several comparative analyses that correlate variation in maternal testosterone between species with other aspects of their biology.