Meeting Abstract
Butachlor, an anti-androgenic endocrine disruptor, is the most common herbicide used in rice agriculture throughout the Philippines and Southeast Asia. The recommended application rate of 4.8 mg/l is toxic to amphibians inhabiting rice ecosystems. However, several species are able to persist and even flourish in these modified habitats. To determine if two dominant amphibians in the Philippines exhibit developmental responses to butachlor exposure that influence interspecific competition, the following hypotheses were tested: 1) Differences in the developmental response of invasive Rhinella marina and native Fejervarya vittigera tadpoles to a low dose of butachlor render R. marina less susceptible 2) Due to compromised development, butachlor intensifies interspecific competition incurring an advantage to the less susceptible R. marina. A laboratory experiment was conducted at the International Rice Research Institute (IRRI), and F. vittigera and R. marina tadpoles were exposed both independently and in combination (competition) to an environmentally relevant concentration of butachlor (0.2 mg/L). Three initial results emerged. 1) When tadpoles were not in competition, butachlor exposure did not affect survivorship or activity. 2) In competition, butachlor treated water significantly lowered survival of R. marina tadpoles. No difference was observed in percent survival for F. vittigera across treatments. 3) F. vittigera were significantly less active than R. marina in competition. Preliminary outcomes indicated an interaction between susceptibility to butachlor and interspecific competition in two dominant rice paddy amphibians. However, the direction of this interaction was contrary to our hypotheses, suggesting that invasive R. marina is more sensitive to butachlor in a competitive environment than endemic F. vittigera.
