First mitogenome phylogeny of the sun bear Helarctos malayanus reveals a deep split between Indochinese and Sundaic lineages

The sun bear Helarctos malayanus is one of the most endangered ursids, and to date classification of sun bear populations has been based almost exclusively on geographic distribution and morphology. The very few molecular studies focussing on this species were limited in geographic scope. Using archival and non-invasively collected sample material, we have added a substantial number of complete or near-complete mitochondrial genome sequences from sun bears of several range countries of the species' distribution. We here report 32 new mitogenome sequences representing sun bears from Cambodia, Thailand, Peninsular Malaysia, Sumatra, and Borneo. Reconstruction of phylogenetic relationships revealed two matrilines that diverged similar to 295 thousand years ago: one restricted to portions of mainland Indochina (China, Cambodia, Thailand; Mainland clade), and one comprising bears from Borneo, Sumatra, Peninsular Malaysia but also Thailand (Sunda clade). Generally recent coalescence times in the mitochondrial phylogeny suggest that recent or historical demographic processes have resulted in a loss of mtDNA variation. Additionally, analysis of our data in conjunction with shorter mtDNA sequences revealed that the Bornean sun bear, classified as a distinct subspecies (H. m. euryspilus), does not harbor a distinctive matriline. Further molecular studies of H. malayanus are needed, which should ideally include data from nuclear loci.

Automated summary

This study sequenced and analyzed the mitochondrial genome of sun bears, finding two distinct lineages that correspond to different populations in mainland Indochina and Borneo, Sumatra, and Peninsular Malaysia. Furthermore, it revealed that the Bornean sun bear does not have a distinct maternal lineage. Further molecular studies, including nuclear genome data, are needed.