A distinct mitochondrial cytochrome c oxidase subunit I lineage of the poultry red mite Dermanyssus gallinae in Tunisian egg-layer flocks.

The poultry red mite, Dermanyssus gallinae is a globally significant ectoparasite affecting layer hens, with substantial economic and animal welfare impacts. Despite its importance, the genetic diversity and population structure of Dermanyssus gallinae in North Africa remain completely uncharacterized. We conducted the first molecular phylogenetic characterization of D. gallinae in Tunisia, analyzing mitochondrial cytochrome c oxidase subunit I (COI) gene sequences from 18 specimens collected across 20 commercial layer farms in four distinct regions (Tabarka, Manouba, Nabeul, and Sfax). Phylogenetic analyses, population genetic parameters, and demographic history were assessed using maximum likelihood methods, haplotype networks, and neutrality tests. Six distinct haplotypes were identified, with a single dominant haplotype (H1) present in 72.2% of samples across all regions. Critically, all Tunisian haplotypes formed a well-supported, divergent monophyletic cluster separated from European haplotypes by a minimum of 12 mutational steps, representing a previously uncharacterized mitochondrial lineage. Genetic diversity was moderate (Hd = 0.490) with low nucleotide diversity (π = 0.01188), and demographic analyses revealed signatures of recent population expansion (Tajima's D = -2.223, p < 0.01). Population structure was limited, with 87.5% of variation occurring within populations, though significant differentiation was detected between Tabarka and Sfax (FST = 0.345, p < 0.05). This study reveals a distinct Tunisian mitochondrial lineage of D. gallinae and provides evidence for recent demographic expansion driven by poultry industry intensification and human-mediated dispersal. These findings expand the known genetic diversity of this economically important parasite and underscore the need for region-specific management strategies incorporating improved biosecurity measures to limit mite transmission through contaminated equipment and supply chains.