Department of Geography and Anthropology, Louisiana State University, Baton Rouge, LA, 70803.
Evolution. 2020 Nov;74(11):2465-2482. doi: 10.1111/evo.14100. Epub 2020 Oct 21.
A tenet of evolutionary theory is that phenotypic variation of a trait is inversely related to the intensity of stabilizing selection pressure. Among homologous bones, such as metapodials, a rudimentary, "nonfunctional" bone is expected to be more variable in length than nonrudimentary bones. This study compares variation and association in length among metapodials using 277 adult skeletons of Canis latrans. Canis latrans has a short, "functionless" first metacarpal (mc1) and "rudimentary, vestigial" first metatarsal (mt1). Results show that among the 10 metapodials, mt1 has the highest variation in length; other metapodials do not differ significantly from one another in their variation. Correlation coefficients for length of mc1 and mt1 with their ipsilateral metapodials 2-5 are significantly lower than coefficients for all other ipsilateral pairs. The correlation coefficient between left and right mt1 is significantly the lowest among all bilateral pairs of metapodials. Results are interpreted as follows. Mt1's high variation and low association in length are the outcome of less intense stabilizing selection pressure compared with other metapodials. The nonsignificant difference for variation in length between mc1 and metapodials 2-5 may be that mc1 is functional for development of a pollical dewclaw that helps restrain small prey.
进化理论的一个原则是，特征的表型变异与稳定选择压力的强度成反比。在同源骨骼中，例如后肢骨，预期“非功能性”的原始骨在长度上比非原始骨更具变异性。本研究比较了使用 277 只 Canis latrans 成年骨骼的后肢骨长度的变异性和关联性。Canis latrans 的第一掌骨（mc1）短而“无功能”，第一跖骨（mt1）为“原始的、退化的”。结果表明，在 10 个后肢骨中，mt1 的长度变异最大；其他后肢骨在变异方面彼此之间没有显著差异。mc1 和 mt1 与其同侧后肢骨 2-5 的长度相关系数明显低于所有其他同侧对的系数。左右 mt1 之间的相关系数是所有双侧后肢骨对中最低的。结果解释如下。与其他后肢骨相比，mt1 的长度变异性高且关联性低，这是稳定选择压力较弱的结果。mc1 和后肢骨 2-5 之间的长度变异性没有显著差异，可能是因为 mc1 对发育用于控制小型猎物的拇指爪的 dewclaw 有功能。
