Thursday, August 5, 2010

PS 82-139: Agricultural land-use is associated with altered gonadal function in the giant toad, Bufo marinus

Krista A. McCoy, University of South Florida


Endocrine disrupting chemicals (EDCs) are ubiquitous pollutants that do not typically induce mortality at ecologically relevant concentrations, but instead negatively affect physiological, behavioral or developmental processes that are modulated by the endocrine system.  Agricultural contaminants are known to disrupt endocrine systems of wildlife, including amphibians, and recent studies have suggested that agricultural contaminants are associated with amphibian reproductive abnormalities.  What is less well understood is whether these alterations at the physiological level scale up to influence ecologically meaningful endpoints such as reproductive success.  Recent studies focused on the giant toad, Bufo marinus, found that the number of gonadal abnormalities per individual as well as the frequency of intersex gonads are higher at agricultural sites.  Indeed, these abnormalities were associated with altered gonadal function.  Circulating sex steroid concentrations were altered and secondary sexual traits were either feminized or demasculinized in intersex toads whereas males from agricultural areas had hormone concentrations and secondary sexual traits that were intermediate between intersex toads and non-agricultural male toads.  Since steroid hormone concentrations and secondary sexual traits are known to correlate with reproductive activity and success, affected toads may have reduced reproductive success.  Here, I explore the relationship between exposure to agricultural land-use which includes the use of EDCs and another important correlate of reproductive success in the giant toad, Bufo marinus. Specifically, I investigated whether spermatogenesis was altered in toads living in agricultural areas where endocrine disrupting pesticides are used.  I also asked if reductions in spermatogenesis were associated with gonadal morphological abnormalities found in the same frogs.  Importantly, I compare toads living in agricultural areas and those living in non-pristine suburban areas; therefore effects associated with agriculture are not simply artifacts of habitat alteration.  


I found that toads in agricultural areas exhibited reduced spermatogenesis and that those reductions were not tightly linked to gonadal morphology.  All toads living in agricultural areas had reduced spermatogenesis relative to those living in non-agricultural areas regardless of whether they were morphologically “abnormal”.  Indeed, effects I document here in toads are analogous to those found in humans living in agricultural areas and in other animals exposed to EDCs.  Similarities in reproductive dysfunction among diverse taxa living in agricultural areas suggest that many vertebrate taxa living in agricultural areas around the globe are likely experiencing some level of reproductive dysfunction that may be having deleterious effects on population health.