Abstract
Heterakis gallinarum is one of the most recurrently diagnosed nematodes within the gastrointestinal tract of galliform birds. In the present study, we investigated the genetic diversity of 96 H. gallinarum collected from free-range chickens from different localities in Tunisia. We assessed phylogeny and genetic variability using the internal transcribed spacers (ITS) of the nuclear ribosomal DNA and the mitochondria' cytochrome c oxidase subunit I gene. Haplotype and nucleotide diversities indicate that H. gallinarum is a species with extremely low genetic diversity. Based on the networks and phylogenetic trees, there was strong support for the absence of significant geographical structuring among the H. gallinarum populations in different localities in Tunisia. Mismatch distributions and neutrality tests of both genetic markers suggest that at least one expansion event occurred in the population demographic history of H. gallinarum. Our data showed a lack of population structure using the pairwise fixation index (FST) and an extensive gene flow. It indicated that the most likely major contributor to the low genetic diversity and gene flow is the movement of the parasitized birds; in other words, the frequency of the poultry trade considerably affects patterns of worm gene flow.