PARENT SESSION
PT2 - Endocrine Disruption
Tuesday, 19 November 2002
8:00 AM to 6:30 PM
Exhibit Hall
(P565) Chick oviduct estrogen bioassay predicts adult reproductive performance of songbirds.
Millam, James*,1, Craig-Veit, Christina1, 1 University of California, Davis, CA, USA
ABSTRACT- We have shown that seven days` oral exposure to estradiol benzoate masculinizes female zebra finch (Taeniopygia guttata) song control nuclei in the brain such that as adults they can sing, whereas normally only males sing (Quaglino et al., Horm Behav 41: 236-241, 2002). We have also reported that this treatment produces sex-specific reproductive impairments in both sexes: males show decreased fertility and females lay eggs that are more likely to break (Millam et al., Horm Behav 40: 542-549, 2001). Doses of estradiol benzoate that produce these impairments also induce growth in the zebra finch chick oviduct bioassay, as does methoxychlor (Millam et al., Environ Toxicol Chem, in press). Based on methoxychlor`s ability to induce oviduct growth, we asked whether post-hatch oral exposure to methoxychlor impairs adult reproductive performance, similarly to estradiol benzoate. Zebra finch chicks were orally dosed from days of age 5 through 11 with either canola oil (vehicle control) or 1000 nmol/g body weight methoxychlor dissolved in canola oil. As adults (>120 days of age), male and female finches were housed communally and provided with nest boxes to encourage breeding (n= 10 pairs per treatment). Methoxychlor significantly reduced number of eggs candled fertile (p<0.01), percentage of eggs cracked/broken and missing (p<0.002) and number of hatched chicks (p<0.03), as compared to canola-treated controls. Latency to the onset of egg laying, number of eggs per clutch and percentage of dead embryos did not differ. This degree and type of reproductive impairment is similar to that induced by a hundred-fold lower dose of estradiol benzoate. This suggests that oral exposure of wild songbird chicks to methoxychlor and other xenobiotic estrogens may induce oviduct growth that could be used to predict impairment in adult reproduction.
Key words: endocrine disruption, sexual differentiation, birds, methoxychlor