Amphibian intersex in suburban landscapes

Abstract

Within the last decade, reproductive abnormalities have been discovered in wild amphibian populations of multiple species and in a variety of regions in North America. Predominantly, these field studies have focused on agricultural landscapes. In this study, we worked in suburban environments based on preliminary evidence showing that amphibian populations can display surprisingly high frequencies of reproductive deformities, including intersex traits. Here, we report results from 28 suburban ponds located near onsite septic systems as well as those located in sewered neighborhoods. Caffeine, an indicator of domestic wastewater contamination, was detected in more than 70% of all ponds; prevalence of contamination was indistinguishable for ponds in sewered neighborhoods and those served by onsite septic systems. Among green frogs (Rana (=Lithobates) clamitans) collected from the same ponds, intersex was detected in each population; on average, one male in five showed evidence of intersex. This frequency was insensitive to wastewater treatment mode. Given prior findings that intersex is absent or rare in less developed landscapes, our results suggest that domestic wastewater contamination in suburban contexts may be more widespread than is generally appreciated and should be investigated as a contributor to intersex in wild amphibians. This hypothesis is consistent with abundant prior research on wild riverine and estuarine fish populations associating reproductive deformities with wastewater exposure.