Multi-locus sequence analysis indicates potential cryptic speciation in the chigger mite Neoschoengastia gallinarum (Hatori, 1920) parasitizing birds in Asia

Abstract

Abstract Background Chigger mites (Acari, Trombiculidae) cause trombiculiasis in terrestrial vertebrates worldwide and some species are also disease vectors. Neoschoengastia gallinarum is widely distributed in Asia, preferentially parasitising birds, and heavy infestations have clinical impacts on domestic fowl. In common with other trombiculid mites, the genetic diversity and potential variation in host preferences or pathology induced by N. gallinarum across its geographic range are poorly understood. Methods Neoschoengastia gallinarum larvae were collected from four species of galliform birds (encompassing free-ranging domestic, free wild, or captive wild) across four locations in Peninsular Malaysia, and from domestic chickens only from one location in Thailand. The population genetic structure of N. gallinarum was inferred from concatenated mitochondrial-encoded cytochrome c oxidase subunit I (COI), and nuclear-encoded internal transcribed spacer 2 (ITS2) and 18S ribosomal DNA gene sequences, including a comparison with previously published data from southeastern China. The Assemble Species by Automatic Partitioning (ASAP) and Automatic Barcode Gap Discovery (ABGD) methods were applied to assess evidence for cryptic divergence, and statistical parsimony (TCS) networks were used to determine relationships between haplotypes. Results Multi-locus sequence analysis revealed two monophyletic clades composed of specimens from Peninsular Malaysia or Thailand, while data from China formed a subgroup that was partially nested in the Thailand clade. Both the ABGD and ASAP methods divided the specimens into three operational taxonomic units: (1) all Peninsular Malaysia sequences, (2) Thailand sequences + China minor clade, and (3) China major clade. Correspondingly, the minimum spanning network displayed a high genetic distance between the Peninsular Malaysia and Thailand populations, and a total of 16 haplotypes were identified. Analysis of molecular variance revealed striking genetic divergence among the two populations (96.41%), which was further supported by the absence of gene flow (Nm = 0.01). The level of gene flow appeared to be higher within the Peninsular Malaysia population as indicated by a lower genetic distance (FST). Conclusions In conclusion, despite the two countries sharing a land border, the Peninsular Malaysia and Thailand populations of N. gallinarum appear to be genetically segregated and may represent distinct cryptic species.