Effects of triphenyltin on growth and development of the wood frog (Lithobates sylvaticus)

Exposure to contaminants in the environment has been suggested as a contributing cause of ongoing declines in populations of amphibians reported in certain locations around the world. In the current study, responses of the wood frog (Lithobates sylvaticus) to exposure to triphenyltin (TPT), a commonly used fungicide, during the larval period were characterized. Exposure of L. sylvaticus to 0.1, 1.0, or 5.0 μg TPT/L significantly affected survival, growth, days to metamorphosis (DTM), and abundances of transcripts of genes of interest. After seven days of exposure there were no significant effects on survival, but masses and snout-ventral length (SVL) of larvae exposed to 5.0 μg TPT/L were significantly lesser than controls. Mortality of larvae after exposure to 5.0 μg TPT/L was 100% nine days after initiation of the experiment. Larvae exposed to 0.1 or 1.0 μg TPT/L were allowed to grow for 100 days or until they reached metamorphic climax, whichever occurred earlier. Mortality of wood frogs exposed to 1.0 μg TPT/L was 80%. The LC20 or LC50 after 100 days of exposure was 0.12 or 0.34 μg TPT/L, respectively. However, DTM of larvae that survived exposure to 1.0μgTPT/L was significantly less than that of controls. Abundances of transcripts of retinoid-X-receptor (rxr) and perixosomal proliferation receptor gamma (pparγ) were significantly lesser in larvae exposed to either concentration of TPT for seven days. Also, abundances of transcripts of stearoyl-CoA desaturase-1 (scd1), fatty acid synthase (fas), lipoprotein lipase (lpl), and β-hydroxybutyrate dehydrogenase (β-hb-m) were lesser in larvae exposed to 5.0 μg TPT/L, which suggested that disruption of lipid metabolism might have affected survival in this exposure group. However, in larvae that survived to metamorphic climax during exposure to TPT for as long as 100 days, abundances of transcripts of perixosomal proliferation receptor alpha (pparα), pparγ, cytochrome p4504B1 (cyp4b1), fas, and lpl were greater than in controls, suggesting that an up-regulation of processes related to metabolism of lipids might have been important for survival and development of these animals. Overall, concentrations of TPT that are found in the environment had a significant effect on the survival and development of L. sylvaticus, and this might have been due, in part, to effects on metabolism of lipids.