Reproduction, embryonic development, and maternal transfer of contaminants in the amphibian Gastrophryne carolinensis

Abstract

Although many amphibian populations around the world are declining at alarming rates, the cause of most declines remains unknown. Environmental contamination is one of several factors implicated in declines and may have particularly important effects on sensitive developmental stages. Despite the severe effects of maternal transfer of contaminants on early development in other vertebrate lineages, no studies have examined the effects of maternal transfer of contaminants on reproduction or development in amphibians. We examined maternal transfer of contaminants in eastern narrow-mouth toads (Gastrophryne carolinensis) collected from a reference site and near a coal-burning power plant. Adult toads inhabiting the industrial area transferred significant quantities of selenium and strontium to their eggs, but Se concentrations were most notable (up to 100 microg/g dry mass). Compared with the reference site, hatching success was reduced by 11% in clutches from the contaminated site. In surviving larvae, the frequency of developmental abnormalities and abnormal swimming was 55-58% higher in the contaminated site relative to the reference site. Craniofacial abnormalities were nearly an order of magnitude more prevalent in hatchlings from the contaminated site. When all developmental criteria were considered collectively, offspring from the contaminated site experienced 19% lower viability. Although there was no statistical relationship between the concentration of Se or Sr transferred to eggs and any measure of offspring viability, our study demonstrates that maternal transfer may be an important route of contaminant exposure in amphibians that has been overlooked.

Figure 1

Relationship between Se (A) and Sr (B) concentrations (μg/g dry mass) in female G. carolinensis and their eggs. Females were collected from both contaminated and reference sites but bred under controlled, uncontaminated conditions. Female concentrations were determined 48 hr after oviposition. (A) y = 1.0255x − 0.0448, r² = 0.9415. (B) y = 0.2634x − 0.0237, r² = 0.4026.

Figure 2

Relationship between Se and Hg concentrations maternally transferred to eggs. The solid line represents the probability (logistic regression model) of transferring Hg to eggs at concentrations above detection limits (0.11 ng/g).

Figure 3

Total body burden (μg) of Se (A) and Sr (B) in female G. carolinensis collected from both contaminated and reference sites. Total body burden is partitioned between eggs and the postovipositional female carcass. Sr in reference eggs is not visible on the graph because these eggs only contained an average of 0.29 μg Sr. Percentages above bars signify the proportion of the total body burden that was transferred to eggs at oviposition.