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EFFECT OF TREMATODE METACERCARIAL INFECTION ON LOCOMOTION BY LARVAL SALAMANDERS IN NORTHEAST GEORGIA

Abstract

Because many amphibians have suffered precipitous declines in recent decades, a great deal of research has been focused on the effects of emerging fungal and viral pathogens. However, relatively little attention has been given to the effects of macroparasites including trematodes, especially trematodes that do not produce obvious morphological abnormalities in their hosts. In the southern Appalachian Mountains of the US, a trematode currently assigned to the species Metagonimoides oregonensis, commonly utilizes lungless salamanders (Caudata: Plethodontidae) as second intermediate hosts, where metacercariae encyst within the musculature. The effects of this parasite have been presumed to be neutral because heavily infected salamanders survive. However, subtle impacts can be consequential to long-term physiological performance and survival. Metacercarial infections of the musculature in fish have been reported to negatively affect swimming performance; therefore, we tested the hypothesis that infection by this trematode species affects locomotor performance in aquatic larvae of the trematode’s primary second intermediate host, the Southern Black-bellied Salamander, Desmognathus amphileucus. We compared locomotion of a series of infected larvae, whose metacercarial cysts are easily seen through the translucent ventral wall of the trunk, with uninfected larvae by placing them in 1-m troughs of water and allowing them to move freely until they stopped. Our measured variable was time spent walking. Using non-parametric (Kaplan-Meier) survival analysis, we determined that infected salamanders stopped significantly sooner than uninfected ones (χ2 = 4.715, P = 0.299). Because infected salamanders move less, the presence of this parasite may contribute to genetic divergence in these salamanders by slowing dispersal and concomitant gene flow. Our results suggest that macroparasites can potentially have significant impacts on host biology even in the absence of such obvious effects as morphological abnormalities.

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