Intersex Frogs Concentrated in Suburban and Urban Landscapes

Abstract

The occurrence of intersex characteristics in amphibians has been linked to pesticide exposure in the laboratory and proximity to agricultural activity within natural populations. But, overall, the ecology of amphibian intersex is poorly known and, specifically, its occurrence in many landscape types and regions is unstudied. We offer the first analysis of the frequency of amphibian intersex across a range of land covers representing the major landscape types within a region. We used remotely sensed information to characterize land cover surrounding 4774 potential sampling locations within the Connecticut River Valley. From among these, we selected 24 ponds to collect postmetamorphic green frogs (Rana clamitans) from four land cover types: undeveloped, agricultural, suburban, and urban. Collected males were preserved and, then, prepared gonadal tissue samples were screened for the presence of testicular oocytes. A total of 233 animals was examined. Thirteen percent of all male green frogs had gonads containing testicular oocytes. Sexual abnormalities were not randomly distributed among sites or landscape types. Suburban landscapes had the highest frequency of abnormalities (21%), and both suburban and urban land covers were positively associated with the presence of abnormalities within a population. There was no evidence of a positive association with agricultural land cover. Examination of amphibian intersex across a range of contexts reveals that developed landscapes may be hotspots for abnormal sexual development. This new finding suggests that other mechanisms, not previously considered, could contribute to intersex in natural amphibian populations.