Sexual differences in adult body size [sexual size dimorphism (SSD)] and color (sexual dichromatism) are widespread, and both male- and female-biased dimorphisms are observed even among closely related species. A growing body of evidence indicates testosterone can regulate growth, thus the development of SSD, and sexual dichromatism. However, the mechanism(s) underlying these effects are conjectural, including possible conversions of testosterone to estradiol (E) or 5α-dihydrotestosterone (DHT). In the present study, we hypothesized that the effects of testosterone are physiological responses mediated by androgen receptors, and we tested two specific predictions: (1) that DHT would mimic the effects of testosterone by inhibiting growth and enhancing coloration, and (2) that removal of endogenous testosterone via surgical castration would stimulate growth. We also hypothesized that females share downstream regulatory networks with males and predicted that females and males would respond similarly to DHT. We conducted experiments on eastern fence lizards (), a female-larger species with striking sexual dichromatism. We implanted Silastic tubules containing 150 µg DHT into intact females and intact and castrated males. We measured linear growth rates and quantified color for ventral and dorsal surfaces. We found that DHT decreased growth rate and enhanced male-typical coloration in both males and females. We also found that, given adequate time, castration alone is sufficient to stimulate growth rate in males. The results presented here suggest that: (1) the effects of testosterone on growth and coloration are mediated by androgen receptors without requiring aromatization of testosterone into E, and (2) females possess the androgen-receptor-mediated regulatory networks required for initiating male-typical inhibition of growth and enhanced coloration in response to androgens.
Protection of shorebirds along coasts where they congregate during migration is an important conservation goal, yet little is known about the reasons that attract people to beaches. Data on perceptions can be used to develop and implement educational and conservation programs, enhancing both visitor experiences and shorebird survival. Urbanization is encroaching on many beaches and estuaries that are necessary stopover sites for migrant birds. This study examines perceptions of visitors at 9 Delaware Bay beaches during the critical northward shorebird migration using interviews (N = 279). We examine the hypothesis that visitors come to Delaware Bay beaches mainly to see the shorebirds (including Red Knots, Calidris canutus rufa) and the crabs whose eggs sustain the shorebirds. Only 60 % of visitors were there primarily to see the shorebirds and crabs, the rest were there for the scenery, tranquility, fishing, or other recreation activities, despite access restrictions. Even when asked what makes the beach attractive, from 17 % (people interested in birds) to 62 % (people interested in crabs) listed tranquility and scenery. Older people rated the importance of research and protection of shorebirds (and crabs) higher than younger people. Over 40 % did not want to see any changes to beaches, while 28 % wanted to see improvements, and 24 % wanted to see more restoration and conservation. Nearly 60% said these beaches would be less attractive if there were more people. These perceptions can aid managers, conservationists and communities improve beaches for both migratory shorebirds and human use.
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