Activity and structural complexity as possible mediators of a tadpole malformity

Background/Question/Methods The increased frequency of malformities among amphibian populations is a serious threat to their conservation. While commonly examined among amphibian adults, the characterization and study of malformities is often overlooked among the larvae. In the summer of 2006, I conducted a controlled experiment that examined the effects of three factors on wood frog (Rana sylvatica) tadpole predators—one caged predator (larvae of the diving water beetle: or one empty cage, 2) competitors—0 additional or 14 additional R. sylvatica tadpoles, and 3) artificial vegetation—0, 28 or 84 strands of green polypropylene rope. Tadpoles were kept outside in 0.5 m diameter tubs covered with fiberglass window screening. Results/Conclusions I observed that 8.8% of the tadpoles developed a lateral curvature of the tail muscle, also known as scoliosis. An analysis of variance showed that the treatments significantly affected the frequency of scoliosis; caged predators and high densities of rope strands decreased the frequency of the malformity while the high competition treatments increased the frequency. Previous research has established that tadpoles decrease activity rates in predator environments and increase activity in highly competitive environments. Indeed, my results showed a positive correlation between the mean tadpole activity of an experimental tub and the frequency of scoliosis. While the cause of tadpole scoliosis remains uncertain, most studies documenting this malformity link its occurrence with enhanced ultraviolet-B radiation (UVBR). High tadpole activity rates might increase the time spent in sunny areas, and, thus increase exposure to UVBR. A decrease in malformity rates in the high artificial vegetation treatments may be due to shading provided by the artificial vegetation. This study provides evidence that various environmental factors can influence the frequency of tadpole malformations. Future studies should integrate environmental complexity when examining the effects of harmful agents on amphibian populations.