Department of Evolution, Ecology, and Organismal Biology, University of California, Riverside, CA, USA.
J Anat. 2021 Mar;238(3):720-742. doi: 10.1111/joa.13341. Epub 2020 Oct 21.
Selection experiments can elucidate the varying course of adaptive changes across generations. We examined the appendicular skeleton of house mice from four replicate High Runner (HR) lines bred for physical activity on wheels and four non-selected Control (C) lines. HR mice reached apparent selection limits between generations 17 and 27, running ~3-fold more than C. Studies at generations 11, 16, and 21 found that HR mice had evolved thicker hindlimb bones, heavier feet, and larger articular surface areas of the knee and hip joint. Based on biomechanical theory, any or all of these evolved differences may be beneficial for endurance running. Here, we studied mice from generation 68, plus a limited sample from generation 58, to test whether the skeleton continued to evolve after selection limits were reached. Contrary to our expectations, we found few differences between HR and C mice for these later generations, and some of the differences in bone dimensions identified in earlier generations were no longer statistically significant. We hypothesize that the loss of apparently coadapted lower-level traits reflects (1) deterioration related to a gradual increase in inbreeding and/or (2) additional adaptive changes that replace the functional benefits of some skeletal changes.
选择实验可以阐明适应变化在各世代的不同进程。我们检查了来自四个重复的高奔跑（HR）线和四个非选择的对照（C）线的家鼠附肢骨骼。HR 老鼠在第 17 到 27 代之间达到了明显的选择极限，比 C 老鼠多跑了约 3 倍。在第 11、16 和 21 代的研究中发现，HR 老鼠的后肢骨骼更厚，脚部更重，膝关节和髋关节的关节表面区域更大。根据生物力学理论，这些进化差异中的任何一个或全部都可能有利于耐力跑步。在这里，我们研究了第 68 代的老鼠，加上第 58 代的有限样本，以测试在达到选择极限后骨骼是否继续进化。与我们的预期相反，我们发现这些后期世代的 HR 和 C 老鼠之间几乎没有差异，而且在前几代中确定的一些骨骼尺寸差异不再具有统计学意义。我们假设，明显的共适应低层次特征的丧失反映了（1）与近亲繁殖逐渐增加相关的退化，和/或（2）替代一些骨骼变化功能优势的额外适应性变化。
