Relative Toxicity of Malathion to Trematode-Infected and Noninfected Rana palustris Tadpoles

Arch Environ Contam Toxicol (2009) 56:123128 DOI 10.1007/s00244-008-9167-9

Relative Toxicity of Malathion to Trematode-Infected and Noninfected Rana palustris Tadpoles

Sarah A. Budischak Lisa K. Belden William A. Hopkins

Received: 27 November 2007 / Accepted: 11 March 2008 / Published online: 10 April 2008 Springer Science+Business Media, LLC 2008

Abstract Amphibian populations around the world are facingthreatsthatincludediseaseandpollution.Althoughthe effect of environmental contaminants on susceptibility to infection has been demonstrated for several amphibian species, to our knowledge, the opposite interaction, infection status affecting contaminant susceptibility, has not been studied.Weconductedstandard48-htoxicityteststocompare susceptibility to malathion, a widely used organophosphate insecticide, of uninfected pickerel frog (Rana palustris) tadpoles and tadpoles infected with two levels (10 or 30 cercariae)ofthetrematodeEchinostomatrivolvis.Trematode encystment rates were high ([90%) in both trematode treatment groups. LC50 values ranged from 16.5 to 17.4 mg/L, within the range reported for other amphibian species. However, we found no differences in susceptibility to malathion among parasite treatments. Although we detected no effect of parasites on pesticide susceptibility in this system, it is important to investigate this question using other pesticides, parasites, and amphibian hosts before dismissing this potentially threatening interaction.

Introduction

Amphibian populations are declining around the world (Stuart et al. 2004; Wake 1991), and both disease (Berger

et al. 1998; Daszak et al. 1999, 2003; Kiesecker et al. 2004) and environmental contaminants (Berger 1989; Bishop et al. 1999; Davidson 2004) have been implicated in some of the declines. Not only are contaminants and disease individually important, but they might act in combination to have a larger cumulative impact on amphibian populations (Beasley et al. 2003; Kiesecker 2002). Environmental contaminants have been correlated with decreases in immune function (Christin et al. 2003, 2004; Gilbertson et al. 2003; Kiesecker 2002) and increases in prevalence of parasite infection (Christin et al. 2003; Lewis et al. 2003). Furthermore, pesticides might indirectly increase susceptibility to parasite infection by decreasing activity patterns (Bridges and Semlitsch 2000) because tadpoles can avoid free-swimming parasites by moving away or swimming in erratic patterns (Koprivnikar et al. 2006; Thiemann and Wassersug 2000).

Although the inuence of pollution on disease susceptibility has been studied in amphibians, the reverse scenario has, to our knowledge, never been tested. However, the inuence of parasite load on susceptibility to contaminants has been studied in other taxa. For...