PhD ceremony Ms. B. de Jong: Testosterone a female hormone. Testing the function and evolution of testosterone in female birds

PhD ceremony: Ms. B. de Jong, 12.45 uur, Academiegebouw, Broerstraat 5, Groningen

Dissertation: Testosterone a female hormone. Testing the function and evolution of testosterone in female birds

Promotor(s): prof. A.G.G. Groothuis, prof. J. Komdeur, prof. L. Lens

Faculty: Mathematics and Natural Sciences

Testosterone (T) plays an important role in regulating male reproduction behaviour. T-levels vary seasonally, with a peak at the beginning of the breeding season, when females are most fertile, and lower levels thereafter. Recently, it has been found that females also have a peak in T-levels, although at lower levels than in males. However, in contrast to males, the functional role of T in females is poorly understood.

To investigate whether peak testosterone levels in females are adaptive, T-levels were manipulated by Berber de Jong in free-living female blue tits (Cyanistes caeruleus). T levels were experimentally elevated in females, or T effectiveness was lowered by blocking androgen receptors with Flutamide. These two groups were compared to sham treated females (control group). In addition, adaptiveness of seasonal profile of female T-levels was investigated in free-living great tits (Parus major).

In this experiment, T-levels were elevated for a longer period than would naturally occur in females and compared to controls. In female blue tits, T-treatment accelerated nest building and increased territorial defence. Also, T-treatment lowered the number of extra pair offspring in the nest but did not affect reproductive success (clutch size, brood size, and fledgling number) and survival among the three treatments. In female great tits, prolonged elevated T-levels reduced incubation temperature and reproductive success. Combining these results, De Jong concludes that present day T-levels might be adaptive in females since T positively affected nest-building activity and aggression. But these effects do not result in ultimate benefits, such as increased reproductive success or survival, for T-females.