Graduate Program in Evolutionary Anthropology, Duke University, Durham, North Carolina, USA.
Department of Basic Medical Sciences, University of Arizona College of Medicine Phoenix, Phoenix, Arizona, USA.
Am J Primatol. 2021 Jun;83(6):e23259. doi: 10.1002/ajp.23259. Epub 2021 Apr 1.
The ability to safely ascend and descend is critical to the success of arboreal animals. Nonprimate mammals typically descend supports headfirst aided by their claws, but primates must rely on grasping, and use a variety of behaviors to move down within an arboreal environment, including headfirst and tailfirst descending. This study assesses hypothesized body mass limits on vertical headfirst descent and identifies approximate support orientations and diameters at which headfirst descent is ceased in a sample of nine strepsirrhines species ranging in mass from 0.06 to 4.5 kg. Species under 1 kg, arboreal quadrupeds Cheirogaleus medius and Microcebus murinus, and slow climber Nycticebus pygmaeus, always descended supports headfirst regardless of orientation and diameter as long as a grasp could be established. Arboreal quadrupedal species above 1 kg, Daubetonia madagascariensis, Eulemur coronatus, Eulemur mongoz, Lemur catta, and Varecia variegata differed in the orientation at which they ceased using headfirst descent and the types of alternative descending behaviors they employed. Lemur catta, a highly terrestrial species, started to employ tailfirst descents at 45° and completely stopped using headfirst descent on steeper and thicker supports. Other arboreal quadrupeds, D. madagascariensis, E. coronatus, E. mongoz, and V. variegata, began using tailfirst descent at 60°. The vertical clinging and leaping species Propithecus coquereli rarely engaged in above branch quadrupedalism, and individuals were observed using tailfirst descents on supports as shallow as 15°. This study shows the ways in which mass and anatomy may constrain use of headfirst descent through arboreal environments, and the alternate strategies strepsirrhine primates employ to descend.
安全地上上下下的能力对树栖动物的成功至关重要。非灵长类哺乳动物通常会借助爪子，头朝下地从支撑物上下来，但灵长类动物必须依靠抓握，并且使用各种行为在树栖环境中移动，包括头朝下和尾朝下。本研究评估了假设的体重限制对垂直头朝下下降的影响，并确定了在一个体重范围从 0.06 到 4.5 公斤的九种懒猴物种样本中，头朝下停止的近似支撑方向和直径。体重低于 1 公斤的物种，树栖四足动物 Cheirogaleus medius 和 Microcebus murinus，以及缓慢攀爬的 Nycticebus pygmaeus，只要能够建立抓握，总是头朝下支撑物。体重超过 1 公斤的树栖四足动物，Daubetonia madagascariensis、Eulemur coronatus、Eulemur mongoz、Lemur catta 和 Varecia variegata，在停止使用头朝下下降的方向和它们使用的替代下降行为类型上有所不同。高度陆地物种 Lemur catta 开始使用尾朝下下降的角度为 45°，并且在更陡峭和更厚的支撑物上完全停止使用头朝下下降。其他树栖四足动物，D. madagascariensis、E. coronatus、E. mongoz 和 V. variegata，开始在 60°时使用尾朝下下降。垂直悬挂和跳跃物种 Propithecus coquereli 很少进行树枝上的四足行走，观察到个体在支撑物上使用尾朝下下降，支撑物的深度只有 15°。本研究表明了体重和解剖结构如何通过树栖环境限制头朝下下降的使用，以及懒猴类灵长类动物采用的替代下降策略。
