Date of Award

1-1-1990

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

Abstract

I examined the endocrinological regulation of social behavior in two sympatric species of sandpipers exhibiting very different social systems. Semipalmated Sandpipers (Calidris pusilla) are monogamous and territorial, while Red-necked Phalaropes (Phalaropus lobatus) are facultatively polyandrous and non-territorial. Both parents incubate equally in the Semipalmated Sandpiper, while only male phalaropes care for eggs and young. By comparing circulating hormone levels (prolactin, testosterone, progesterone, and estradiol) between species and sexes throughout the breeding season, differences in hormonal profiles were related to behavior.Blood samples were collected in the summers of 1985 to 1987 from individuals of both species breeding in a 3 km$\sp2$ area at La Perouse Bay, 40 km east of Churchill, Manitoba.High prolactin levels were correlated with persistent incubation behavior. There was no difference in prolactin levels between the equal incubating sexes of the Semipalmated Sandpiper. Prolactin levels in this species increased significantly at the onset of incubation. Incubating male Red-necked Phalaropes had higher levels of prolactin than did nonincubating females and males.Changes in prolactin levels, however, did not explain the early brood desertion of female Semipalmated Sandpipers.Gonadal steroid levels (testosterone, progesterone, and estradiol) were not sex-reversed in the sex-role reversed species. Therefore, circulating testosterone levels cannot explain why female phalaropes are more aggressive than males. There was little difference in patterns of testosterone levels between territorial male Semipalmated Sandpipers and non-territorial male Red-necked Phalaropes.Capture and sampling techniques in this study affected behavior and survival very little in either species. Examination of the effect of handling and sampling stress on hormone levels of experimental birds indicated that effects were variable, but significant changes in hormone levels found during the breeding season in nonexperimental birds should be valid.In summary, circulating levels of hormones were directly related to behavior in some instances (e.g., prolactin), while in other cases they were not (e.g., steroids). I suggest that plasma levels of hormones are more likely to reflect behavioral variations, particularly sex differences, when the hormones involved do not serve an over-riding physiological function, as do gonadal steroids.

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