Ravosa M J
Department of Cell and Molecular Biology, Northwestern University Medical School, Chicago, IL 60611-3008, USA.
Am J Primatol. 1998;45(3):225-43. doi: 10.1002/(SICI)1098-2345(1998)45:3<225::AID-AJP1>3.0.CO;2-Y.
A series of 20 craniodental measurements was obtained for two sister taxa: Nycticebus coucang (common slow loris) and N. pygmaeus (pygmy slow loris). Multivariate analysis of variance was performed with adult data to describe patterns of subspecific and specific variation in this genus. The geometric mean of adult cranial dimensions was compared to field data on latitudinal coordinates for available specimens to investigate if size variation in Nycticebus is clinal in nature. Ontogenetic series for larger-bodied N. coucang and smaller-bodied N. pygmaeus were compared to test the hypothesis that species and subspecific variation in skull form results from the differential extension of common patterns of relative growth. A MANOVA provides independent support of Groves's [pp. 44-53 in Proceedings of the Third International Congress on Primatology, Vol. 1 (Basel: S. Karger), in 1971)] classification of Nycticebus into two species, with four subspecies in the common slow loris and one form of the pygmy slow loris. Within N. coucang, cranial proportions for all four subspecies are ontogenetically scaled, and size differentiation is mainly clinal (Bergmann's Rule). N. c. bengalensis represents the most northerly disposed and the largest form. N. c. javanicus represents the next-largest form and is located in a southerly direction the next-farthest away from the equator. N. c. coucang and N. c. menagensis are both equatorial; however, the latter subspecies is the smallest. A genetic basis for some of the taxonomic variation between N. c. coucang and N. c. menagensis is supported by such nonclinal variation in body size. Variation in the presence/absence of I2 is not size-related but rather tracks geographic proximity and isolating factors which predate the most recent inundation of the Sunda Shelf. Although they inhabit a nonequatorial environment, pygmy slow lorises are the smallest of all Nycticebus. As N. pygmaeus is sympatric with N. c. bengalensis, the largest slow loris, it appears that the evolution of its smaller body size represents a case of character displacement. Unlike N. coucang, skull size becomes significantly smaller in more northern N. pygmaeus. This may also reflect character displacement between sympatric sister taxa underlain by a cline-dependent ecological factor which is marked in more northerly latitudes. On the other hand, the negative correlation between body size and latitude in N. pygmaeus could be due to the influence of nonprimate fauna, such as predators, which themselves evince a similar clinal pattern. Analyses of relative growth indicate that skull proportions in the two species of Nycticebus are ontogenetically scaled in two-thirds of the cases. All but one of the seven comparisons (interorbital breadth) which do not indicate ontogenetic scaling represent part of the masticatory complex. This likely reflects a reorganization of N. pygmaeus maxillomandibular proportions linked to smaller size and changes in diet.
对两种姐妹分类群进行了一系列20项颅齿测量：懒猴（普通懒猴）和侏蜂猴（倭蜂猴）。使用成年个体数据进行多变量方差分析，以描述该属种下和种间变异模式。将成年颅骨尺寸的几何平均值与现有标本的纬度坐标实地数据进行比较，以研究懒猴属的体型变异在本质上是否呈渐变群模式。对体型较大的懒猴和体型较小的倭蜂猴的个体发育序列进行比较，以检验以下假设：头骨形态的种间和种下变异是由相对生长的共同模式差异扩展导致的。多变量方差分析为格罗夫斯（1971年，第三届国际灵长类动物学大会论文集，第1卷，巴塞尔：S. 卡尔格出版社，第44 - 53页）将懒猴分为两个物种的分类提供了独立支持，普通懒猴有四个亚种，倭蜂猴有一个类型。在懒猴中，所有四个亚种的颅骨比例在个体发育过程中呈比例缩放，体型分化主要呈渐变群模式（伯格曼法则）。孟加拉懒猴是分布最靠北且体型最大的类型。爪哇懒猴是第二大体型类型，位于离赤道第二远的南方。懒猴指名亚种和门氏懒猴都分布在赤道地区；然而，后者是最小的亚种。懒猴指名亚种和门氏懒猴之间某些分类变异的遗传基础得到了这种体型非渐变群变异的支持。I2存在与否的变异与体型无关，而是与地理接近程度和隔离因素相关，这些因素早于巽他陆架最近一次被淹没。尽管倭蜂猴栖息在非赤道环境中，但它是所有懒猴中体型最小的。由于倭蜂猴与体型最大的懒猴——孟加拉懒猴同域分布，其较小体型的进化似乎是一个特征取代的例子。与懒猴不同，在更靠北的倭蜂猴中，头骨尺寸显著变小。这也可能反映了同域分布的姐妹分类群之间的特征取代，其背后是一个在更靠北纬度更为明显的依赖渐变群的生态因素。另一方面，倭蜂猴体型与纬度之间的负相关可能是由于非灵长类动物群（如捕食者）的影响，这些捕食者本身也呈现出类似的渐变群模式。相对生长分析表明，在三分之二的情况下，两种懒猴的头骨比例在个体发育过程中呈比例缩放。七项未显示个体发育比例缩放的比较（眶间宽度）中，除一项外，其余均为咀嚼复合体的一部分。这可能反映了倭蜂猴上颌下颌比例与较小体型和饮食变化相关的重组。
