San Francisco State University, California, United States
Invasive species pose a major threat to our world's biodiversity. One such invasive species is the American bullfrog, Rana catesbeiana. This animal is a serious widespread invader across the globe, threatening the continued existence of many endemic species. This is seen in California, where established populations continue to spread and wreak havoc on wildlife communities. This project looks at the direct effects the American bullfrog has on wildlife communities by describing their diet composition in a novel area of study. Stomach contents of Rana catesbeiana specimens captured from 6 different sites near the Yuba River between Tahoe and Plumas National Forests (Sierra Nevada mountains) were examined. Stomach contents were weighed, measured, and identified in order to compile a list of numbers and types of prey species consumed. This project also examines the indirect effects Rana catesbeiana has on native amphibian communities by investigating its role as a reservoir species of the fungal pathogen Batrachochytrium dendrobatidis (Bd). qPCR analysis was done on swabs collected from 9 different sites; 3 bullfrog-only water bodies, 3 native amphibian only water bodies, and 3 water bodies where both overlap (6 bullfrog sites being where specimens were collected for stomach analysis). This comparison allowed us to assess differences in the number of Bd positive reads from site to site and between species, and will give insight to pathogen load differences between bullfrogs and native amphibians.A total of 179 bullfrogs have been dissected so far, with only 10 (5.6%) stomachs being found empty. Only 7 (3.9%) stomachs were found to contain vertebrate prey, with the rest (90.5%) being invertebrate prey only. Vertebrate prey consisted of the invasive signal crayfish (family Astacidae), True Minnows (family Leuciscidae), an unidentified bird spp., and an unidentified amphibian spp. Invertebrate prey consisted primarily of Coleoptera in the families Carabidae (Ground beetles) and Hydrophilidae (Water Scavenger beetles), along with Isopoda belonging to the family Armadillidiidae (Pill bugs). Gerridae (Water Striders) species from the order Hemiptera were also found in numerous quantities. In addition, 149 swabs have been collected so far (85 bullfrog, 64 native amphibians). 92 of these swabs tested positive for Bd, with 61 of them coming from bullfrogs and 31 from native amphibians. In conclusion, Rana catesbeiana populations in this study voraciously consume prey items, both native and introduced, while also harboring a high frequency of Batrachochytrium dendrobatidis, thereby affecting wildlife communities directly and indirectly.
