Effects of wetland vs. landscape variables on parasite communities ofRana pipiens: links to anthropogenic factors

Abstract

The emergence of several diseases affecting amphibian populations worldwide has prompted investigations into determinants of the occurrence and abundance of parasites in frogs. To understand the spatial scales and identify specific environmental factors that determine risks of parasitism in frogs, helminth communities in metamorphic frogs of the northern leopard frog (Rana pipiens) were examined in relation to wetland and landscape factors at local (1 km) and regional (10 km) spatial extents in an agricultural region of Minnesota (USA) using regression analyses, ordination, and variance partitioning techniques. Greater amounts of forested and woody wetland habitats, shorter distances between woody wetlands, and smaller-sized open water patches in surrounding landscapes were the most consistently positive correlates with the abundances, richness, and diversity of helminths found in the frogs. Wetland and local landscape variables were suggested as most important for larval trematode abundances, whereas local and regional landscape variables appeared most important for adult helminths. As previously reported, the sum concentration of atrazine and its metabolite desethylatrazine, was the strongest predictor of larval trematode communities. In this report, we highlight the additional influences of landscape factors. In particular, our data suggest that anthropogenic activities that have resulted in the loss of the availability and connectivity of suitable habitats in the surrounding landscapes of wetlands are associated with declines in helminth richness and abundance, but that alteration of wetland water quality through eutrophication or pesticide contamination may facilitate the transmission of certain parasite taxa when they are present at wetlands. Although additional research is needed to quantify the negative effects of parasitism on frog populations, efforts to reduce inputs of agrochemicals into wetlands to limit larval trematode infections may be warranted, given the current high rates of amphibian declines and extinction events.

Perceptions of risk in communities near parks in an African biodiversity hotspot

“…The literature strongly supports the idea that proliferation and emergence or re-emergence of infectious diseases can be driven by land-use and other environmental factors, including climate change (Labbé et al 2015), with natural habitat loss and fragmentation from agricultural expansion being one of the most important factors (Patz et al 2004). Land-use change may affect the number of vectors and parasites as well as their interactions with hosts, ultimately affecting disease severity and occurrence (Schotthoefer et al 2011), and biodiversity declines have been linked with increases in parasitism and the spread of parasitic diseases (Hatcher et al 2012).…”

Evolved pesticide tolerance influences susceptibility to parasites in amphibians

“…Further, this study provides the first evidence in a vertebrate species that evolutionary responses to pesticides influence susceptibility to parasites. Pesticide‐mediated effects on disease outcomes are commonly documented in the literature, yet the results are often variable with pesticides increasing host tolerance to parasite infection in some cases (Coors, Decaestecker, Jansen, & De Meester, 2008; Kiesecker, 2002; Rohr, Raffel, et al., 2008) but not in others (Griggs & Belden, 2008; Marcogliese et al., 2009; Schotthoefer et al., 2011). We demonstrate that the mechanism underlying the evolution of pesticide tolerance may be critical for assessing susceptibility to parasites.…”

Combined Effects of Pesticides and Trematode Infections on Hourglass Tree Frog Polypedates cruciger

“…For several reasons, there has been considerable interest in the effects of chemical contaminants on disease risk in amphibians (Rohr et al 2009a, b; Schotthoefer et al 2011; McMahon et al 2013; Rohr et al 2013). Amphibians are considered the most threatened of all vertebrate taxa and many of their declines have been associated with infectious diseases (Blaustein and Kiesecker 2002; Stuart et al 2004).…”