The hormonal control and endocrine effects of contaminants of avian secondary sex characteristics

The purpose of this study was to examine the effects of endocrine disrupting contaminants on the secondary sex characteristics of a passerine species. Features of avian species, such as plumage or integument color, are known to be important during times of sexual selection. For some species, the pigmentation and/or scheduled appearance of these features is to some degree under hormonal control, therefore it is necessary to understand how endocrine disrupting contaminants might alter these features.;For the initial experimental study conducted in fall 2001, captive American goldfinches (Carduelis tristis) were treated with testosterone and tamoxifen (an anti-estrogen) to investigate the hormonal control over a variety of morphological and physiological parameters. Testosterone treatment raised testosterone concentrations of male birds and maintained carotenoid color in the bill while tamoxifen treatment elevated body mass at the end of the study. Testosterone treated birds also had elevated hematocrit and lower molt scores from that of the control birds, but these trends were not significant. There was also a difference noted in mean reflectance of female plumage color, with the control group having a higher reflectance than that of either the two treatment groups. Since the results of that study demonstrated that testosterone affects or controls certain goldfinch features, particularly bill color, two contaminants with antiandrogenic properties, vinclozolin and linuron, were administered to captive birds during spring 2002. A known antiandrogen, flutamide, was also administered during this time as a reference chemical. The resulting effects suggested a capability for both contaminants to cause hormonal disruption. Both vinclozolin and linuron negatively affected carotenoid bill color progression and male plasma testosterone concentrations (effects ranged from slight to significant depending on dose level) and there were differences among mean reflectance of male bill color and spectral shape of female bill color with the vinclozolin group have the lowest scores. Linuron additionally delayed molt progression, lowered hematocrit, and increased the body mass of male and female birds. Flutamide treatment decreased testosterone concentrations initially, however other parameters did not appear to be affected by this treatment. Considering the multitude of effects from linuron exposure, this contaminant was chosen for further investigation during spring 2003. Similar to the previous study, linuron delayed molt progression and decreased hematocrit. Linuron also increased body mass but only at the beginning of the treatment period. For female birds, thyroxine concentrations were reduced by linuron exposure. However, contrary to the results of the previous study, there were no effects on testosterone concentrations of male birds or rate of bill color change, although treatment groups tended to have a slower progression rate of carotenoid bill color. There was also a difference noted among groups in spectral shape of female ventral plumage, but this did not appear to be due to treatment effects. Differences in results between the 2002 and 2003 studies may be due to treatment dose or timing of treatment onset as the 2003 study was started later in the season. Although there was some indication, particularly from the 2002 study, that linuron negatively impacted androgen function, there was more consistent evidence suggesting that linuron acted as a thyroid antagonist in this species.;This study demonstrated that certain contaminants can delay the goldfinches' seasonal transition into the pre-alternate plumage and breeding bill color. Since both plumage and bill color are features that have been shown to be important during mate choice, these contaminants might have an additional impact on sexual selection. In addition, linuron specifically produced effects such as higher body weight, lower hematocrit, and altered molting schedule - all effects which could potentially negatively affect the daily survival of birds. Thus, this work addresses the multiple endpoints of contaminant exposure on avian species and effects at relatively lower dose levels. (Abstract shortened by UMI.).