Phylogeny and biogeography of the mountain semi-slugs genus <i>Microparmarion</i> (Gastropoda: Ariophantidae) in northern Borneo

ABSTRACT Understanding the evolutionary history, genetic diversity and distribution patterns of terrestrial gastropods in tropical regions—especially in light of climatic fluctuations and tectonic activity—is a pivotal challenge in biogeography and evolutionary biology. This study focuses on semi-slugs of the genus Microparmarion, endemic to northern Borneo. Using mitochondrial cytochrome c oxidase subunit I (COI) and 16S ribosomal RNA (16S rRNA) gene fragment sequences, we investigated phylogenetic relationships among six Microparmarion species in the region. Our combined dataset provided a well-resolved phylogeny, confirming the monophyly of each species and clarifying previous taxonomic uncertainties. Sequence divergence analyses revealed higher divergences in COI than in 16S rRNA, both within and among populations, with substantial interspecific divergences (COI: 10–11%). Haplotype network analyses uncovered distinct population structures characterized by diverse haplotypes and limited gene flow among populations, suggesting the influence of historical isolation and restricted dispersal. Ecological niche models indicated an expanded range for Microparmarion simrothi during cooler glacial periods and a contraction of suitable habitats for M. basifixus, implying differing responses to historical climatic conditions. Our findings suggest that mountain ranges like Mount Kinabalu served as important interglacial and glacial refugia for these species, influencing their current distribution patterns and genetic diversity. This study highlights the significant roles of historical climatic events and topographical barriers in shaping the evolutionary history of Microparmarion species in northern Borneo.