Agricultural effects on amphibian parasitism: importance of general habitat perturbations and parasite life cycles.

Agricultural activity can alter host-parasite interactions through associated contaminants and habitat perturbations. It is critical to determine whether agricultural effects are widespread or limited to specific types of agriculture. We examined influences of soybean agriculture on trematode parasitism of larval amphibians (grey tree frogs; Hyla versicolor) to assess the potential effects of a commonly applied pesticide (glyphosate) and landscape factors relative to previous field studies focusing on the herbicide atrazine. Overall, trematode parasite infection did not differ between soybean-adjacent and nonagricultural ponds (87.7% and 72.6% mean infection, respectively). However, host-generalist echinostome species were more common in tadpoles from soybean-associated ponds (86.3% mean infection versus 36.2% in nonagricultural ponds) as well as sites with large or short average distances to forest cover and roads, respectively. In contrast, the occurrence of a host-specialist (Alaria sp.) group was greater in nonagricultural ponds (50.3% mean infection versus 9.8% in soybean-associated ponds) and increased with shorter distances to the closest forest patch and smaller average forest distance. Because glyphosate was not detected at any site and landscape influences were parasite-specific, we suggest that agriculture may have broad effects on wildlife diseases through habitat alterations that affect pathogen transmission via host habitat suitability. Notably, nonagricultural ponds had a lower mean distance to the nearest forest patch and lower mean forest distance compared with soybean-adjacent ponds. As a result, we emphasize the need for wider investigations of habitat perturbations generally associated with agriculture for host-pathogen interactions, and consequently, wildlife conservation and management strategies.