Population mitogenome diversity and connectivity among wild populations of Great Hornbill (Buceros bicornis) in Thailand: Implications for population recovery planning

Great Hornbill ( Buceros bicornis ) likely play an important role in Southeast Asian forests, but populations are declining due to human-induced threats. Lack of data on wild population genetic diversity and connectivity hinder conservation efforts to restore evolutionary potential to populations of such species. We applied noninvasive sampling, population genetics and phylogeographic analyses to assess genetic diversity and connectivity among three Great Hornbill wild populations across three regions of Thailand (Eastern, Western and Southern) using partial mitogenome sequences (14,118 bp) from 52 wild individuals and 97 captive individuals. Haplotype and nucleotide diversity of the Southern population was highest, compared to Eastern and Western populations. Despite higher levels of poaching and fragmentation, maintenance of mitogenome diversity in the Southern population could be due to genetic exchanges with Malaysian populations, or historically large effective populations occupying Sundaic habitats. Relatively low to moderate genetic differentiation observed among the three Thai populations suggested limited fragmentation effects on historical population connectivity. This finding aligns with the absence of population-specific clades seen in our phylogenetic analyses. The Southern population had the highest number of private haplotypes and there was significant genetic structure between Southern and Western and between Southern and Eastern populations perhaps suggesting the presence of southern glacial refugia and subsequent secondary contact following population expansion and recolonization of habitats during interglacial periods in the Late Pleistocene. These findings may provide insights for developing effective strategies for Great Hornbill reintroduction, and for monitoring the impacts of human disturbance on population genetic connectivity and species persistence in fragmented landscapes.