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COMPARISON OF INFECTION PREVALENCE AND INTENSITY BY THE TREMATODE METAGONIMOIDES OREGONENSIS BETWEEN TWO SPECIES OF DESMOGNATHAN SALAMANDER

Abstract

Concerns over amphibian declines have focused recent research on amphibian parasites and diseases. In the southern Appalachian Mountains, adults of the trematode Metagonimoides oregonensis dwell in the intestines of raccoons with aquatic snails (Elimia proxima) serving as the first intermediate host. Cercariae leave the snail host and infect the tissue of a second intermediate host, particularly the plethodontid Desmognathus quadramaculatus, where they encyst as metacercariae. However, the closely related D. folkertsi evidently does contract this parasite. We tested the hypothesis that D. marmoratus, the phylogenetic sister of D. folkertsi, is also resistant to infection. We compared infection rates in D. marmoratus and D. quadramaculatus in a stream (Beech Creek) where they are sympatric in Towns County, Georgia. We collected salamander larvae in June and in August and tested for differences in both prevalence and intensity of infection for each collection. During June, parasite prevalence was 4/15 for D. quadramaculatus and 2/12 for D. marmoratus. For the August sample, 6/10 D. quadramaculatus were infected while 13/16 D. marmoratus had metacercariae. Contingency analysis showed no significant difference in the June (χ2 = 0.4; P = 0.53) or the August (χ2 = 1.4; P = 0.23) sample. Two-way ANOVA of log-transformed metacercarial counts showed no significant difference between species in intensity (F1,42 = 0.65; P = 0.426) but showed a significant difference between samples (F1,42 = 12.38; P = 0.001); there was also a significant interaction between species and collection (F1,42 = 12.38; P = 0.001). Mean intensity in D. quadramaculatus increased from 1.5 per salamander in June to 2.0 in August, whereas mean intensity increased from 0.17 to 2.6 in D. marmoratus. Because this trematode also infects other salamander species (e.g., Eurycea wilderae), our results support the hypothesis that D. folkertsi is unique in its ability to resist infection.

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