The 82nd Annual Meeting of the American Association of Physical Anthropologists (2013)

Are pygmy tarsiers phyletic dwarves? An allometric analysis of tarsier limb proportions


Department of Anthropology, Texas A&M University

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Phyletic dwarfism is a density-dependent adaptive process where lineages experience size reduction in response to resource limitations. Dwarfed lineages may exhibit allometric patterns that are opposite from interspecific trends. This study examines whether morphometrics can clarify if the highland pygmy tarsier (Tarsius pumilus) is truly a phyletic dwarf. I conducted an allometric analysis of pygmy tarsier limb proportions based on standard external measurements of live tarsiers (n=61). Linear characters were standardized by log transformation or scaling the variable by the cube root of body mass. To test the hypothesis that pygmy tarsiers have distinct body proportions from other species, I used canonical discriminant analysis on scaled linear characters to generate functions that predict group membership according to "pygmy" status, species, and geographic location. Pygmy tarsiers were significantly different from other (non-pygmy) tarsier species. A stepwise variable-selection procedure selected hindlimb, upper leg, and hindfoot lengths as good candidates for discrimination, where 100% classified correctly. Further, linear regression of log-transformed mass and forelimb lengths revealed that while non-pygmy species exhibit a negative slope, pygmy tarsiers exhibit a positive slope. Canonical functions additionally discriminate between species, as well as geographic regions. These results suggest that a) tarsier species can be accurately distinguished based on limb proportions, regardless of body weights and b) pygmy tarsier limb proportions cannot be explained solely by an allometric decrease in size. Therefore, pygmy tarsier body proportions may indicate that the species has undergone an evolutionary size reduction, possibly in relation to decreased resource availability at higher altitudes.

This study was funded by the National Science Foundation Doctoral Dissertation Improvement Grant, Primate Conservation, Inc., Conservation International Primate Action Fund, American Society of Primatologists Conservation Small Grant, Explorers Club Exploration Fund, and the Texas A&M University Department of Anthropology.

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