U.S. Department of Agriculture: Agricultural Research Service, Lincoln, Nebraska


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U.S. Government Works


Infection, Genetics and Evolution 12 (2012) 530–538


The genetic diversity within and among parasite populations provides clues to their evolutionary history. Here, we sought to determine whether mitochondrial and microsatellite DNA variation could be used to evaluate the extent of differentiation, gene flow and historical reproductive isolation among the freeze resistant parasites Trichinella nativa and the Trichinella T6 genotype infecting wolverines (Gulo gulo) in Nunavut, Canada. To this end, we genotyped Trichinella isolates derived from the diaphragms of 39 wol- verines from this locale to reference strains of T. nativa and the Trichinella T6 genotype. Results showed that among a subset of 13 isolates examined, individuals resembled T. nativa in their mitochondrial DNA, but resembled the Trichinella T6 genotype when assayed at expansion segment V and the internal tran- scribed spacer of the nuclear rDNA. To adjudicate among these conflicting diagnoses, we further charac- terized each isolate at several nuclear microsatellite loci and again compared these to data from reference strains. Statistical assignment established that the nuclear genomes of most Nunavut isolates corre- sponded to those of the Trichinella T6 genotype; however, two isolates corresponded to T. nativa, and one isolate exhibited equal similarity to both reference strains. Taken as a whole, the evidence suggests that these isolates derive from the T. nativa matrilineage, but that their nuclear genomes resemble indi- viduals previously designated as Trichinella T6. Assuming distinct lineages, this argues for cross-hybrid- ization among these genotypes. Although introgression has occurred, recognizable genetic distinctions persist. One possibility is that selection disfavors the survival of hybrid offspring in most instances. Alter- natively, the recent disappearance of glacial barriers might have increased contact, and therefore intro- gression. Broader geographic sampling will be required to determine the extent to which hybridization occurs beyond this particular geographic focus.