Skeletal indicators of ecological specialization in pika (Mammalia, Ochotonidae)

Measurement data from-- Reese, AT, HC Lanier, and EJ Sargis. 2013 Skeletal indicators of ecological specialization in pika (Mammalia, Ochotonidae). Journal of Morphology 274: 585-602Pika species generally fall into two ecotypes, meadow-dwelling (burrowing) or talus-dwelling, a classification that distinguishes a suite of different ecological, behavioral, and life history traits. Despite these differences, little morphological variation has previously been documented to distinguish among ecotypes. The aim of this study was to test whether postcranial features related to burrowing are present in meadow-dwelling species and whether talus-dwelling species exhibit postcranial modifications related to frequent leaping between rocks. To test this, the scapula, humerus, ulna, radius, innominate, femur, tibia, and calcaneus of 15 species were studied and measured. Twenty-three measurements were taken on 199 skeletons, and 19 indices were constructed from these measurements. Indices were compared between the two ecotypes using Student's t-test. Comparisons among ecotypes, species, and subgenera were made using one-way ANOVA with the Tukey honest significant difference post hoc test. Multivariate results were generated using principal components analyses. Thirteen forelimb and hind limb indices proved significant in distinguishing the meadow-dwelling, talus-dwelling, and intermediate forms. A number of these indices are associated with burrowing or leaping in other mammals, providing some support for the hypothesis that postcranial modifications in pika are related to locomotor differences. This evidence of morphological responses to ecological specialization will be useful for reconstructing the paleobiology of extinct taxa, assessing the behavioral variability of extant species, and improving our understanding of the evolutionary history of pikas.本数据集的测量数据源自Reese AT、Lanier HC与Sargis EJ于2013年发表的《鼠兔（哺乳纲Mammalia，鼠兔科Ochotonidae）生态特化的骨骼指示特征》一文，刊载于《Journal of Morphology》第274卷，页码585-602。鼠兔物种通常可划分为两种生态型：草甸栖居型（穴居类群）与碎石坡栖居型，该分类方式可区分一系列具有显著差异的生态、行为与生活史特征。尽管存在上述表型与生态差异，此前鲜有研究记录到可有效区分两类生态型的形态学变异特征。本研究的核心目标在于验证两个假说：其一，草甸栖居型鼠兔是否具备与穴居行为相关的颅后骨骼特征；其二，碎石坡栖居型鼠兔是否呈现出与频繁跨岩跳跃相关的颅后骨骼特化改造。为此，研究人员对15个鼠兔物种的肩胛骨（scapula）、肱骨（humerus）、尺骨（ulna）、桡骨（radius）、髋骨（innominate）、股骨（femur）、胫骨（tibia）以及跟骨（calcaneus）进行了观测与测量。研究团队对199具骨骼标本开展了23项独立测量，并基于这些测量数据构建了19项形态学指数。采用学生t检验（Student's t-test）对两类生态型的形态指数进行组间比较；同时采用单因素方差分析（one-way ANOVA）结合图基诚实显著差异事后检验（Tukey honest significant difference post hoc test），开展生态型、物种以及亚属水平的多组比较。多变量分析结果通过主成分分析（principal components analysis）生成。最终有13项前肢与后肢形态指数被证实可有效区分草甸栖居型、碎石坡栖居型以及过渡型鼠兔。其中多项指数与其他哺乳动物的穴居或跳跃运动模式高度相关，这为「鼠兔的颅后骨骼特化改造与其运动方式差异直接相关」这一假说提供了有力支撑。这项关于鼠兔形态特征响应生态特化的研究证据，将有助于重建已灭绝鼠兔类群的古生物学特征、评估现存鼠兔物种的行为变异性，以及深化学界对鼠兔整体演化历史的认知。