Data from: Artificial selection sheds light on developmental mechanisms of limb elongation

Species diversity in limb lengths and proportions is thought to have evolved adaptively in the context of locomotor and habitat specialization, but the heritable cellular processes that drove this evolution within species are poorly understood. In this study, we take a novel “micro-evo-devo” approach, using artificial selection on relative limb length to amplify phenotypic variation in a population of mice, known as Longshanks, to examine the cellular mechanisms of postnatal limb development that contribute to intraspecific limb length variation. Cross-sectional growth data indicate that differences in bone length between Longshanks and random-bred controls are not due to prolonged growth, but to accelerated growth rates. Histomorphometric and cell proliferation assays on proximal tibial growth plates show that Longshanks’ increased limb bone length is associated with an increased number of proliferative chondrocytes. In contrast, we find no differences in other growth plate cellular features known to underlie interspecific differences in limb bone size and shape, such as the rates of chondrocyte proliferation or the size and number of hypertrophic cells in the growth plate. These data suggest that small differences among individuals in the number of proliferating chondrocytes are a potentially important determinant of selectable intraspecific variation in individual limb bone lengths, independent of body size.

物种间肢长与肢体比例的多样性被认为是在运动与栖息地特化的背景下适应性演化的产物，但驱动物种内部这一演化进程的可遗传细胞机制，目前仍未得到充分解析。本研究采用了一种全新的“微进化发育学（micro-evo-devo）”研究策略：通过对小鼠相对肢长进行人工选择，以扩增名为Longshanks的小鼠种群的表型变异，进而探究调控种内肢长差异的产后肢体发育细胞机制。横断面生长数据显示，Longshanks种群与随机繁育对照组的骨骼长度差异并非源于生长周期延长，而是源于生长速率的提升。对胫骨近端生长板开展的组织形态计量学检测与细胞增殖实验结果表明，Longshanks种群肢体骨骼长度更长，与其增殖性软骨细胞数量增多存在显著关联。与之相对，研究未发现其他已知会导致物种间骨骼大小与形态差异的生长板细胞特征存在差异，例如软骨细胞增殖速率，或是生长板内肥大细胞的尺寸与数量。上述研究结果表明，个体间增殖性软骨细胞数量的细微差异，可能是决定种内个体肢长可遗传变异的关键因素，且该关联不受个体体型大小的影响。