57.1 Thursday, Jan. 5 Experimental evidence for a role of prolactin in modulating avian clutch-size RYAN, C.P.*; DAWSON, A.; SHARP, P.J.; WILLIAMS, T.D. ; Simon Fraser University, Burnaby, Canada; Centre for Ecology and Hydrology, Edinburgh, U.K.; The Roslin Institute, University of Edinburgh, U.K. ; Simon Fraser University, Burnaby, Canada email@example.com
Clutch-size is one of the most important contributors to lifetime fitness in birds, and a multitude of ultimate explanations have been proposed to explain observed clutch-sizes in birds. However, surprisingly little is known about the underlying, proximate, physiological mechanisms involved in clutch-size determination. The role of prolactin in incubation behaviour is relatively well-supported. However, the predominant model for hormonal control of clutch size, which predicts an inhibitory role of prolactin on follicle development, currently has very limited empirical support, despite widespread acceptance. Using a repeated-measures design, we investigated the role of prolactin in clutch-size determination in captive-breeding female zebra finches (Taeniopygia guttata). We used the dopamine receptor agonist, bromocriptine, to manipulate prolactin levels, and recorded changes in clutch-size and other parameters of maternal investment. In a complementary experiment, we also manipulated clutch-size using an egg removal protocol, and examined effects on circulating prolactin levels. We found a significant effect of bromocriptine on clutch-size, but in the opposite direction than predicted from previous findings. The relationship between clutch-size, plasma prolactin levels, and other hormones and measures of maternal investment will be discussed.