Meeting Abstract
14.1 Tuesday, Jan. 4 Patterns of DHT variation in waterfowl and their relationship with social environment and genital morphology BRENNAN, Patricia*; GEREG, Ian; GOODMAN, Michelle; STEWART, Rosemary; PRUM, Richard; Yale University/UMASS Amherst; LRWC, Litchfield, CT; LRWC, Litchfield, CT; Indiana State University; Yale University patricia.brennan@yale.edu
Waterfowl are an interesting model system to study endocrine regulation of reproductive traits. They have a diversity of mating and social systems where the timing of development of male secondary sexual traits is often separate from the time of seasonal growth of the testis and genitalia. Genitalia are well developed in some waterfowl and they play a key role in sexual conflict and yet the hormonal mechanisms behind genital seasonality and growth in waterfowl are unknown. We measured DHT plasma levels in Ruddy ducks, a highly promiscuous species, and in Lesser Scaup a less promiscuous species over a period of 9 months. In both species there is a seasonal pattern of DHT. Lesser Scaup reach their maximum values in the spring between mid-April and mid-May and then decline quickly, similar to penis growth. In Ruddy ducks peak levels are achieved one month later and also correlate with genital changes. To determine the role of male competition on genital morphology, we kept males in one of two treatment groups: a high competition group (7M:5F, 2 replicates) or a no competition breeding pair (1M:1F, 8 replicates). DHT levels of males kept in high competition groups were significantly higher than males in the pairs in both species (LS: 953-1948 pg/mL vs. 408-992 pg/mL; RD: 220-3770 vs. 220-1220 pg/mL). Lesser Scaup males in competition groups grew significantly longer penises suggesting that absolute DHT levels may correlate with penis length in this species. Male Ruddy ducks that maintained their penis longer for a longer period of time in the competition groups had the highest levels of DHT among males, again suggesting that DHT is playing an important role in seasonal and plastic changes in genital morphology.
