GENERALANDCOMPARATIVEENDOCRINOLOGY 62, 137- 144(1986) Plasma Steroid Hormone Levels in Free-Living Wilson’s Phalaropes, Phalaropus tricolor ALBERT J. FIVIZZANI, MARK A. COLWELL, AND LEWIS W. ORING Department of Biology, University of North Dakota, Grand Fob, North Dakota 58202 Accepted October 26, 1985 Blood samples collected from free-living Wilson’s phalaropes during the reproductive season were analyzed for testosterone, dihydrotestosterone, estradiol-17P, and proges- terone. Levels of testosterone were seven times greater in nonincubating males than in females. During incubation males underwent a reduction in testosterone and dihydrotestos- terone to levels similar to those of females. Estradiol-17P values were higher in females than in incubating males and comparable to values reported for other avian species. Proges- terone was significantly greater in females than in incubating or nonincubating males. Max- imum levels of progesterone were detected in laying females. Progesterone levels increased in males during incubation while testosterone and dihydrotestosterone levels decreased. These results indicate that the greater intensity of competition for mates among females and exclusive male parental care characteristic of this species is not based upon a reversal of the typical avian levels of androgens and estrogens in males and females. Z 1986 Academic Press, Inc. Intense competition by females for males and performance of the primary parental role by the males are rare traits among ver- tebrates. In birds, only about 1% of all species exhibit these characteristics. The three species of phalaropes, Wilson’s (Pha- laropus tricolor), red (P. fulicauius), and red-necked (P. lobatus), show the most ex- treme examples of sex-role reversal among birds. ,In all three species females are larger and niore brightly colored than males, fe- males compete overtly for males, and males provide all incubation and brooding duties. In other species, such as the spotted sandpiper (Actitis macularia) and northern jacana (Jacana spinosa), females compete overtly for males, but the females contribute to rearing young directly through help with incubation or brooding (spotted sandpiper), or indirectly through defense of young (northern jacana) (Oring, 1982). Endocrinologists have long recognized the usefulness of studies comparing sex- role-reversed species with those in which the male competes for mates and the fe- male provides most or all parental care. The possibility that such behavioral re- versal was based upon a preponderance of androgens in females was suggested by re- ports that the testosterone content of ovaries was greater than that of the testes in Wilson’s and red-necked plialaropes (Dyrenfurth and Hiihn, 196s; HBhn and Cheng, 1967; Hahn, 1970). These early re- ports were supported by observations that testosteione proprionate injections induced fema!e nuptial plumage in both male and female Wilson’s and red-neckea phal- aropes, whereas control injetitions or ad- ministration of other hormones resulted in winter plumage (Johns, 1964). However; in vitro cultures of Wilson’s phalarope go- nadal tissue resulted in greater test&erpde production in testes than, ovaries IcFevdd and Pfeiffer, 1968). Nevertheless, ovarian testosterone production wa$ ‘greater than that of two other avian species (house sparrows, Passer domesticus and ~killdtier, Charadrius vociferus; Nicoll metall., 19~67). In addition, brood patch deirelofimeat ip male and female Wilson’s and red-nedked 137 0016-6480186 $1.50 Copyrighi 0 1986 by Academic Press. inc. Al1 rights of reproduction in any form reserved.