Multi-Locus Sequence Analysis Indicates Potential Cryptic Speciation in the Chigger Mite Neoschoengastia gallinarum (Hatori, 1920) Parasitising Birds in Asia.

Simple Summary: The chigger mite Neoschoengastia gallinarum (Hatori, 1920) is a parasite that feeds on the skin tissue of birds across multiple countries in Southeast and East Asia. In domestic chickens, heavy infestations with this mite can lead to skin irritation and damage to the carcass, reducing economic value. In this study, we collected N. gallinarum samples from wild birds of conservation concern and domestic chickens in Peninsular Malaysia and Thailand. Sequence analyses of three genes from the mites were compared across four Malaysian populations, one Thai population, and previously published sequences from southeastern China. A variety of methods were applied to classify these sequences and determine the extent of interbreeding between populations. These methods agreed in identifying three clusters of sequences by country of origin, although there was partial overlap between Thailand and China. The populations from Malaysia and Thailand appear to be reproductively isolated from one another and may represent distinct species with almost identical morphological features, except for leg length. Further studies are required to determine if these genetic dissimilarities are accompanied by distinct ecological, behavioural, or pathological differences in N. gallinarum in different regions of Asia. 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 are poorly understood. This study aimed to unravel the geographical variation and population structure of N. gallinarum collected from galliform birds in Peninsular Malaysia and Thailand by inference 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. Our multi-locus sequence analysis revealed three monophyletic clades comprising (A) specimens from Peninsular Malaysia, (B) the samples from Thailand together with a minority of Chinese sequences, and (C) the majority of sequences from China. Similarly, most species delimitation approaches divided the specimens into three operational taxonomic units. Analysis of molecular variance revealed 96.41% genetic divergence between Malaysian and Thai populations, further supported by the absence of gene flow (Nm = 0.01). In conclusion, despite the two countries sharing a land border, populations of N. gallinarum from Peninsular Malaysia and Thailand appear to be genetically segregated and may represent distinct cryptic species. [ABSTRACT FROM AUTHOR]