Avian transgenerational reproductive toxicity test with in ovo exposure

Ecological risk assessment of environmental pollutants requires effective laboratory assays and extrapolation of the resultant data to wild species. Because avian reproductive disorder and accumulation of persistent compounds in wild birds and their eggs have long been observed in polluted regions, we have developed an assay for investigating whether pollutants accumulated in eggs impair the reproduction of the exposed birds and the survival of the next generation using the Japanese quail. A typical estrogenic compound, diethylstilbestrol (DES), dissolved in olive oil was injected into the air-chamber of fertilized eggs on day 10 of incubation. After sexual maturation of hatched chicks, we mated pairs of male and female quails following an observation period of egg production and collected their eggs. The collected eggs were incubated and checked for the fertility and hatchability, and then the hatchlings were raised and observed in growth for 3 weeks. A dosage of 5 ng/g per egg of DES caused eggshell thinning in eggs laid by exposed females and reduction in eggshell strength. DES also induced shortening of the left oviduct and unexpected development of the right oviduct, while testis weight was reduced symmetrically. The ability of quail pairs to produce offspring was significantly diminished by exposure of females to DES independently of exposure of males, which mainly arose from production of abnormal and inviable eggs. Fertility of normal-shelled eggs and hatchability of fertilized eggs were unchanged regardless of treatments. External morphological abnormalities, which were mostly unopened toes of the foot, were frequently observed in hatchlings from exposed males independently of exposure of females. Additionally, we attempted to extrapolate the experimental results to the northern bobwhite and to predict population trends for quails in a polluted habitat using a population projection model composed of a combination of a Leslie matrix and the logistic equation. In the event of accumulation of an estrogenic compound equivalent to a dosage of 5 ng/g DES in quail eggs, the average population size was predicted to decrease by 20.2% after 1 year, to approximately half after 4 years, and to a fifth after 14 years. When observed weakening of individuals and the risk of egg breakage are taken into consideration, the decline in population was further accelerated. The proposed assay appears to be suitable not only for assessing adverse effects of chemicals on avian reproduction but for population projection of affected wild birds.