New North American paratenic hosts of Anguillicola crassus and molecularly-inferred source of invasion.
Brown bullhead (Ameiurus nebulosus), pumpkinseed (Lepomis gibbosus) and bluegill (Lepomis macrochirus) collected from the Paskamansett River, Massachusetts, were infected with larval Anguillicola crassus. These are new records of paratenic hosts of A. crassus in North America, although infected brown bullhead and pumpkinseed have been found in Europe. Prevalence was 64-100% and mean abundance 5.50-9.32. Morphological identification of L3 was confirmed by molecular sequence analysis of mitochondrial cytochrome c oxidase subunit I (COI, barcode) and the nuclear large subunit nLSU (28S) ribosomal RNA genes. Analysis of COI sequences from larval and adult worms from the Paskamansett River and nLSU (sequences from those L3 and adults from the Mira River, Cape Breton, Nova Scotia) showed that the COI gene better discriminated among species of Anguillicola than did the nLSU gene. At least 9% difference in sequence similarity was found between A. crassus and other species with COI, whereas there was overlap in the nLSU sequence similarity between A. crassus and other Anguillicola species. Comparative sequence analysis suggests that North American A. crassus originated from Japan, whereas European A. crassus originated from Taiwan, in agreement with previous studies. Two single nucleotide polymorphism (SNP) markers, SNP390 and SNP91 in COI and nLSU, respectively, are informative for differentiating between North American and European sources. Analyses with both genes also supports the monophyly of the Anguillicolidae.