Gene H. Albrecht

Tail-length evolution in Fascicularis-group macaques (Cercopithecidae : Macaca)

In the four species of macaques that constitute the fascicularis-group, relative tail length generally decreases with increasing latitude, in accord with Allens Rule. Although this generalization applies to Macaca mulatta in the northern part of its range—north of ca. 26°N, it does not apply south of ca. 26°N, where the tail is anomalously short in Macaca mulatta. This suggests that the anomalously short-tailed population of Macaca mulatta did not originate within its present latitudinal range, but instead dispersed there from farther north. The anomalously short-tailed population apparently replaced a now-extinct longer-tailed population, from which founders of insular Macaca cyclopis previously had been derived. Southward dispersal of the anomalously short-tailed population of Macaca mulatta, and correlated extinction of the longer-tailed population that it apparently replaced, may have been induced by a major glacial advance.

Latitudinal, taxonomic, sexual, and insular determinants of size variation in pigtail macaques, Macaca nemestrina

Regression analysis demonstrates that body and skull size are correlated with latitude in Sundaic (Macaca nemestrina nemestrina)and Indochinese (M. n. leonina)pigtail macaques. These two contiguously distributed subspecies are unusual in that they exhibit opposite latitudinal gradients of increasing size— M. n. nemestrinabecomes larger in a southerly direction,while M. n. leoninabecomes larger in a northerly direction in accordance with the usual pattern of ecogeographic variation seen in other sympatric macaques and mammals (Bergmann ’s rule). The difference in clinal size gradients is one more of a series of characters which delineate these two macaques as natural biological populations. However, since the size gradients converge on a narrow zone along the Thai-Malay Peninsula, the use of size as a character to evaluate genetic and morphological intergradation is equivocal when population variation is considered. The third subspecies, the Mentawi Island pigtail (M. n. pagensis),is an endemic,insular isolate differentiated from the Sundaic pigtail from similar latitudes in terms of its small size. Thus, latitude, insularity, and taxonomic differentiation all affect size variation in the pigtail macaques;also,although the data are not definitive, there is the suggestion that the degree of sexual dimorphism may be an additional covariate of latitude and/or body size.

Geographic Variation in Primates

Knowledge of geographic variation is fundamental to recognizing the kinds and numbers of both living and extinct primate species. This review focuses on geographic variation in the craniodental anatomy of living primates. We limit our attention to multivariate studies that used craniometric and/or odonto-metric data to investigate differences among demes, subspecies, and closely related species. Our intent is to document the nature of geographic variation in the skulls and teeth of living primates and, then, to discuss the problems and prospects of dealing with such variation among fossils. We begin with some general background observations about geographic variation and speciation in primates.