スリランカのトクモンキーにおけるアレンの法則の検証：尾長変化は環境適応か、種分化過程か

抄録

Allen's rule first published in 1877 predicts ecogeographical anatomical variation in appendage proportions as a function of body temperature regulation. Since then this phenomenon has been tested in a variety of animal species. In macaques, relative tail length (RTL) is one of the most frequently measured appendages to test Allen's rule. To date, these studies have relied mostly on randomly collected museum specimens or the invasive and time consuming capturing of free-ranging individuals. To augment sample size, and lessen these logistical limitations, we designed and validated a novel non-invasive technique using digitalized photographs processed on LibreCAD, an open source 2D-CAD application. This was used to generate pixelated measurements to calculate a RTL equivalent, the Tail to Trunk Index (TTI) = tail (tail base to anterior tip) pixel count / trunk (neck to tail base) pixel count X 100). The TTI of 259 adult free-ranging toque macaques (Macaca sinica) from 36 locations between 7 and 2087 m above sea level (m. a. s. l.) were used in the analysis. Samples were collected from all three putative subspecies (M. s. sinica, aurifrons and opisthomelas), at locations representing all altitudinal climatic zones where they are naturally distributed. These data were used to test Allen's rule, predicting that RTL decreases with increasing altitude. Our results strongly supported this prediction. There was also a statistically significant, negative correlation between elevation and annual average temperature. The best predictor for the TTI index was elevation. This non-invasive method provides a means for quick morphometric assessment of relative body proportions, applicable for use even on unhabituated free-ranging animals, widening the range of materials available for research studying morphological characteristics and their evolution in primates.