Meeting Abstract

P1.21  Wednesday, Jan. 4  Combined effects of social stress and an agricultural pesticide on tadpole growth and development OSTER, J.M.*; WELCH, A.M.; College of Charleston, SC; College of Charleston, SC

Human impacts on the environment pose a threat to natural populations. Environmental contaminants such as pesticides can negatively affect growth, development, reproductive success and survival in a wide range of species. Stress from contaminants may produce even more severe outcomes when coupled with normal biotic stressors. Intraspecific competition is a widespread source of biotic stress, particularly when resources are limited. We predicted that the stress of being an inferior competitor would increase an individual’s vulnerability to environmental toxins. We tested this idea by exposing size-structured groups of southern toad (Anaxyrus terrestris) tadpoles to a common insecticide (carbaryl) or a no-pesticide control. We found that size-advantaged tadpoles generally metamorphosed earlier. However, tadpoles that were initially smaller ultimately grew to larger sizes at metamorphosis. Once the larger competitors metamorphosed, the smaller individuals were apparently released from competition and grew rapidly. Food limitation intensified competition, leading to a greater delay in metamorphosis for small individuals. The pesticide inhibited growth for all size classes. However, the outcome of competition was affected by pesticide exposure. Under food-limited conditions, the competitive suppression of smaller individuals was less pronounced when tadpoles were exposed to the pesticide, suggesting that the larger individuals were less effective competitors in the presence of carbaryl. Understanding how stressors interact allows us to better assess the risks faced by amphibian populations in human-impacted environments, and simple laboratory studies may underestimate the effects of contaminant exposure under realistic ecological conditions.