SGER: Reproductive Biology of Female King Penguins

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Considerable evidence has accumulated that female birds may exert control over the sex ratio of their offspring. Under optimal conditions, more female chicks are produced; and under poor environmental conditions, more of the young are males. There are several plausible explanations for this. In some cases, young males disperse and so under stressful conditions do not compete with parents or siblings. In other instances where habitat conditions are favorable, mothers with new chicks are assisted by older female offspring, increasing reproductive success. In species that lay clutches with multiple eggs, there can be chicks of both sexes and self-assessment of parent condition may not be as crucial. However, in other species such as penguins, only one or two eggs are laid during each breeding season. In this situation, the application of the strategy of sex ratio allocation requires that females must be very capable of assessing their condition and that of their mates. This Small Grant for Exploratory Research will investigate the sex ratio of king penguin chicks relative to the condition of the parents to determine if females are controlling the gender of chicks. Sex determination will be accomplished by DNA analyses of blood samples, a new method to be tested on king penguins in this project. Quantifying parental condition will be done by several standard methods, including measures of body size, parasite load, and immunocompetence. This study will also explore the possibility that plumage coloration is an indicator of condition in penguins as it is in other bird and fish species. Plumage color is from diet-derived carotenoids and may be a useful proxy for evaluating health and fitness. Penguins are dominant predators in their environment and shifts in a population parameter as fundamental as offspring sex ratio might reflect changes in climate or in distribution and abundance of food resources. The results of this work, which will be conducted in collaboration with scientists from the French Antarctic Program, will provide a better understanding of penguin population dynamics and the complex mechanisms of environmental biofeedback.