sex allocation - life history
Sex allocation theory is successful in predicting sex ratio variation in some taxa, but often not in birds and mammals. An important reason may be that most theoretical models do not account for the complexities of avian and mammalian life-history. To reveal the adaptive significance of sex allocation to avian life-history, I conducted an experimental study on great tits (Parus major). I investigated the effect of manipulated brood sex ratios on long-term fitness benefits. Offspring that was raised in broods with sex ratios at parity had the highest fecundity. Since offspring recruitment, parental survival and parental future fecundity were unaffected, there was stabilizing selection for producing brood sex ratios at parity. To gain insight in the underlying mechanism I focused on different aspects of the offspringï¿½s first year. Brood sex ratio did not affect fledging behaviour, but there were some effects on social behaviour in winter, which did not correlate to fitness. As adults, individuals raised as the rare sex in a brood had larger tarsi than individuals of the abundant sex. This relationship was neither present in the nestling phase nor caused by selective disappearance. This suggests a sex-specific directional effect of brood sex ratio on the late development of the offspring, which potentially links brood sex ratio to fecundity. Stabilizing selection for brood sex ratios at parity might provide an explanation why sex allocation in birds and mammals is often subtle. Higher benefits for equal brood sex ratios counteract selection for facultative sex allocation to extreme values.
Michler SPM, Nicolaus M, Van der Velde M, Radersma R, Ubels R, Both C, Komdeur J, Tinbergen JM, 2013. Local offspring density and sex ratio affect sex allocation in the great tit. Behavioral Ecology. 24 (1): 169-181.
12/2012: Printed press. Gemengd gezin doet het goed. Article in ExperimentNL. Annual publication by The Netherlands Organisation for Scientific Research (NWO) and Quest (popular science magazine, in Dutch).
11/12/2011: Radio. News item at VARA Vroege Vogels. Weekly program about nature and environment (national radio, in Dutch).
9/12/2011: Internet. Family composition determines success of great tit parents. Article on Phys.org. International science, research and technology news website.
6/12/2011: Printed press. Gezinssamenstelling bepaalt succes van koolmees-ouders. Article in Trouw. National daily newspaper (in Dutch).
3/2011: Printed press. Kiezen voor meer zonen of dochters? Article in De Levende Natuur. Professional journal for nature conservation and management in the Netherlands and Flanders (in Dutch).