Abundant variation in microsatellites of the parasitic nematode Trichostrongylus tenuis and linkage to a tandem repeat

An understanding of how genes move between and within populations of parasitic nematodes is important in combating the evolution and spread of anthelmintic resistance. Much has been learned by studying mitochondrial DNA markers, but autosomal markers such as microsatellites have been applied to only a few nematode species, despite their many advantages for studying gene flow in eukaryotes. Here, we describe the isolation of 307 microsatellites from Trichostrongylus tenuis, an intestinal nematode of red grouse. High levels of variation were revealed at sixteen microsatellite loci (including three sex-lined loci) in 111 male T. tenuis nematodes collected from four hosts at a single grouse estate in Scotland (average He = 0.708; mean number of alleles = 12.2). A population genetic analysis detected no deviation from panmixia either between (FST = 0.00) or within hosts (FIS = 0.015). We discuss the feasibility of developing microsatellites in parasitic nematodes and the problem of null alleles. We also describe a novel 146-bp repeat element, TteREP1, which is linked to two-thirds of the microsatellites sequenced and is associated with marker development failure. The sequence of TteREP1 is related to the TcREP-class of repeats found in several other trichostrongyloid species including Trichostrongylus colubriformis and Haemonchus contortus.