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Climate, not Quaternary biogeography, explains skull morphology of the long-tailed macaque on the Sunda Shelf

Grunstra, Nicole D.S.; Louys, Julien; Elton, Sarah

Climate, not Quaternary biogeography, explains skull morphology of the long-tailed macaque on the Sunda Shelf Thumbnail


Nicole D.S. Grunstra

Julien Louys


Sundaland, comprising the low-lying Sunda Shelf, the major islands of Borneo, Sumatra, and Java, as well as many smaller surrounding islands, formed a contiguous landmass through much of the Pliocene and Pleistocene. Subsequent late-Pleistocene rising sea levels have often been invoked as major zoogeographic barriers to gene flow and associated phenotypic and taxonomic divergence of Sundaic mammals. However, previous examinations of mammalian biogeography have painted a complex picture, suggesting that mammalian diversification in the region cannot easily be explained by a single overarching biogeographical phenomenon. Instead, it may be that the significant climatic changes and their concomitant impacts on local environments were the more significant control. In this context, we study adult skull morphology of a widely distributed primate in insular and continental Southeast Asia, the long-tailed macaque (Macaca fascicularis), using a 3D geometric morphometric (GM) approach. We used principal component analysis and linear discriminant function analysis to analyze the associations between morphological divergence and island biogeography, taxonomy, and phylogeny. Reduced rank regressions (RRR) were employed to investigate associations with climate of the present and last interglacials and the last glacial maximum (LGM). There was very poor morphological divergence and discrimination among specimens from different biogeographical zones. There was also large overlap between M. fascicularis subspecies in skull size and shape, with M. f. fascicularis occupying the largest range of size and shape variation, consistent with its wide geographical distribution. Nonetheless, sundaic M. f. fascicularis and M. f. philippinensis, restricted to the Philippines, were successfully discriminated on size and shape, supporting the latter as a valid subspecies. There was moderate morphological differentiation associated with the deepest split in mitochondrial DNA lineages (M. f. aureus versus the rest) in skull size and shape. Contrary to biogeography, we detected strong associations between skull morphology and climate. Skull form (size and shape combined) was better explained by climate closer to present conditions and correlated most strongly with the current interglacial, even though past climatic conditions do show correlations with cranial morphology. We found no strong evidence that cranial and mandibular variation in M. fascicularis consistently tracks insularity caused by Quaternary sea level change. Instead, the morphological overlap evident in our sample indicates connections between subspecies and is consistent with the history of Sundaland as a single landmass for large portions of the Quaternary.


Grunstra, N. D., Louys, J., & Elton, S. (2023). Climate, not Quaternary biogeography, explains skull morphology of the long-tailed macaque on the Sunda Shelf. Quaternary Science Reviews, 310, Article 108121.

Journal Article Type Article
Acceptance Date May 4, 2023
Online Publication Date May 19, 2023
Publication Date Jun 15, 2023
Deposit Date Jul 6, 2023
Publicly Available Date Jul 6, 2023
Journal Quaternary Science Reviews
Print ISSN 0277-3791
Publisher Elsevier
Peer Reviewed Peer Reviewed
Volume 310
Article Number 108121


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