Diversity and Biogeography of Treeshrews

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The Challenge: Treeshrews (order Scandentia) are small-bodied mammals endemic to South and Southeast Asia. Since it was first described in 1820, the Common Treeshrew (Tupaia glis) has had a complex taxonomic history that has led to widely variable estimates of diversity, misidentification of populations, and general confusion regarding it and closely related species. One result is that T. glis has been treated as a poorly defined “wastebasket” taxon encompassing as many as 27 named forms. 

The Science: In a series of papers using a combination of cranial characters and fine-scale characters of the hand skeleton revealed by digital xrays, we have better defined T. glis as a species and shown that a number of populations previously synonymized with it belong to other species or are distinct species in their own right. This work greatly reduced the geographic range of the Common Treeshrew, restricting it to the Malay Peninsula south of the Isthmus of Kra, the purported contact zone with its sister species, the Northern Treeshrew, T. belangeri, and adjacent offshore islands. We have further shown the existence of certain biogeographical trends, such as a reverse Bergmann’s response (smaller body size at higher latitudes) and a positive island effect, with larger body sizes on islands than on the mainland, and increasing body sizes with increasing island area. Our studies provide a means of assessing species boundaries among treeshrews, and our results so far note the need for re-assessment of the conservation status of many populations previously thought to belong to T. glis.

The Future: In addition to continuing to refine the Tupaia glis species group, we are undertaking a similar study of the Tupaia splendidula species group, populations of which have been confused with T. glis in the past.