Endocrine Disrupters and Flavonoid Signalling

Like other stifftail ducks, lake ducks are promiscuous and boisterous in their sexual activity. One explanation for the evolution of such a long penis might be selection for its competitive advantage — for instance, groups of drakes might display their everted penises to attract females. Success in sperm competition may also be a factor. The base of the lake-duck penis is covered with spines, yet the tip is soft and brush-like. Before ejaculation, drakes probably use their penises like bottle-brushes to remove sperm stored in the oviduct by the female’s previous consort. The larger the bottle-brush, the more effective it will be, clearing the way for the drake to father the ducklings. Many questions remain unanswered. How much of his penis does the drake actually insert, and does the anatomy of the female’s oviducts make them unusually difficult to inseminate? The Argentine lake duck offers a sizeable opportunity to study sexual selection and sperm competition in birds. Kevin G. McCracken*†, Robert E. Wilson*, Pamela J. McCracken†, Kevin P. Johnson‡ *Institute of Arctic Biology and Department of Biology and Wildlife, University of Alaska Fairbanks, Fairbanks, Alaska 99775, USA e-mail: [email protected] †University of Alaska Museum, Fairbanks, Alaska 99775, USA ‡Illinois Natural History Survey, Champaign, Illinois 61820, USA