PARENT SESSION
Oral Session # 99: Late-Breaking Newsworthy Presentations.
Presiding: E Preisser and G Larocque
Friday, August 8. 8:30 AM to 12:00 PM, SITCC Meeting Room 205.
Environmental endocrinology and invasive cowbird species.
Hahn, Caldwell*,1, Wingfield, John2, Fox, David3, Walker, Brian2, Richie, Jill4, 1 Caldwell_Hahn@usgs.gov, Laurel, MD, USA2 University of Washington, Seattle, WA, USA3 Louisiana State University, Baton Rouge, LA, USA4 Appalachian State University, Boone, NC, USA
ABSTRACT- Environmental endocrinology provides insight into flexibility of neuroendocrine control mechanisms in the life history cycles of invasive species. We examined the level and pattern of yolk steroid deposition in eggs of a brood parasite, the Brown-headed Cowbird (Molothrus ater), which has expanded its range from the central prairies and invaded most of North America. We compared yolk steroids levels among cowbirds and three avian host species, and we considered the behavioral and physiological strategies of parasite exploitation and host defense. Since elevated levels of yolk testosterone have been reported to directly control the relative rate of nestling growth and strength of begging vigor, we hypothesized that differences between host and parasite as well as differences within clutches effect differences in nestling competition and survival. In southern New York, we collected eggs from cowbirds, American Redstart, Red-eyed Vireo, and Veery, then we conducted radioimmunassays to measure yolk testosterone level. We statistically analyzed the relative levels of yolk testosterone among all species and within clutches according to laying order. We found that (i) host eggs had higher average levels of testosterone in nests parasitized by cowbirds than did host eggs in non-parasitized nests. (ii) Similarly, when nests were parasitized more than once, the 2nd and 3rd - laid cowbird eggs contained higher levels of yolk testosterone than the 1st cowbird egg. (iii) Host species smaller than the cowbird showed significant within-clutch variation in yolk testosterone level, (iv) higher levels in 2nd-laid eggs than in 1st laid eggs, and (v) significantly higher overall level of yolk testosterone than cowbirds. (vi) Both adult weight and egg size of a species showed negative correlation with the average level of yolk testosterone. These data suggest that yolk testosterone patterns reflect both (i) responsiveness to environmental and social cues and (ii) constraints of physiological requirements.
Key words: cowbird, invasive, yolk, testosterone