Agostini Gina, Rasoazanabary Emilienne, Godfrey Laurie R
Department of Anthropology, University of Massachusetts Amherst, Amherst, Massachusetts.
Am J Primatol. 2017 Sep;79(9). doi: 10.1002/ajp.22680. Epub 2017 Jun 12.
The reddish-gray mouse lemur (Microcebus griseorufus) possesses striking phenotypic and behavioral variation. This project investigates differences in autopod proportions in neighboring populations of M. griseorufus from the Special Reserve at Bezà Mahafaly in southwest Madagascar. One population resides in an environment generally preferred by M. griseorufus-a spiny forest with large-trunked trees, vertically-oriented supports, and more open ground, while the other resides in a gallery forest with abundant small, often horizontal peripheral branches in high canopy. We demonstrate significant interpopulation differences in autopod morphophology despite no evidence of divergence in mitochondrial cytochrome b. We test two hypotheses regarding ultimate causation. The first, based on the Fine Branch Arborealism Hypothesis (FBAH), holds that autopod differences are related to different locomotor practices in the two environments, and the second, based on the Narrow Niche Hypothesis (NNH), holds that the observed differences reflect a relaxation (from ancestral to descendant conditions) of selective pressure for terrestrial locomotion and/or use of large, vertical supports combined with positive selection for locomoting in peripheral branch settings. Our data conform well to FBAH expectations and show some support for the NNH. Individuals from the gallery forest possess disproportionally long posterior digits that facilitate locomotion on small, flexible canopy supports while individuals from the spiny forest possess shorter posterior digits and a longer pollex/hallux that increase functional grasping diameter for large vertical supports and facilitate efficient ground locomotion. Focal individual data confirm differences in how often individuals descend to the ground and use vertical supports. We further show that predispersal juveniles, like adults, possess autopod morphologies suited to their natal forest. We explore two proximate mechanisms that could generate these cheiridial differences. The first posits an in vivo plastic response to different locomotor behaviors, the second posits differences that manifest in early development.
红灰鼠狐猴（Microcebus griseorufus）具有显著的表型和行为变异。本项目研究了来自马达加斯加西南部贝扎马哈法利特别保护区的相邻红灰鼠狐猴种群在足部比例上的差异。一个种群栖息在红灰鼠狐猴通常偏好的环境中——一片有大树干树木、垂直支撑物且地面较为开阔的多刺森林，而另一个种群则生活在一片廊道森林中，那里树冠高处有大量细小且通常呈水平状的外围树枝。尽管线粒体细胞色素b没有分化的证据，但我们证明了两个种群在足部形态上存在显著差异。我们检验了关于最终因果关系的两个假设。第一个假设基于细枝树栖假说（FBAH），认为足部差异与两种环境中不同的运动方式有关；第二个假设基于窄生态位假说（NNH），认为观察到的差异反映了陆地运动和/或使用大型垂直支撑物的选择压力从祖先到后代条件的放松，同时对在周边树枝环境中的运动存在正选择。我们的数据与FBAH的预期非常吻合，并对NNH有一定支持。来自廊道森林的个体后趾异常长，这有利于在细小、灵活的树冠支撑物上运动，而来自多刺森林的个体后趾较短，拇指/拇趾较长，这增加了对大型垂直支撑物的功能性抓握直径，并有利于高效的地面运动。焦点个体数据证实了个体下到地面和使用垂直支撑物的频率存在差异。我们进一步表明，像成年个体一样，扩散前的幼体也具有适合其出生森林的足部形态。我们探索了两种可能导致这些手部差异的近端机制。第一种机制假定对不同运动行为的体内可塑性反应，第二种机制假定在早期发育中表现出的差异。
