Division of Biology and The Ecological Genomics Institute, Kansas State University, Manhattan, KS 66506, USA.
J Hered. 2010 Sep-Oct;101(5):573-80. doi: 10.1093/jhered/esq044. Epub 2010 May 7.
The evolutionary importance of ontogenetic change has been noted since Darwin. However, most analyses of phenotypic evolution focus on single landmark ages. Here, we present an inheritance study that quantifies genetic variation in pigmentation across early-age (i.e., birth to 180 days) development in 2 populations of the common garter snake, Thamnophis sirtalis. The populations are phenotypically distinct and geographically isolated (Manitoba, CA and Northern California, USA). There were highly significant differences between populations for the developmental trajectory of mean pigmentation, with the Manitoba population exhibiting a mean pigmentation level that increased across ontogeny, whereas the California population exhibited mean pigmentation that was invariant across ontogeny. Subsequent quantitative genetic analyses revealed heritable variation at all ages in Manitoba but low levels of phenotypic and genetic variation in California at all ages. A quantitative genetic decomposition of the longitudinal genetic variance-covariance matrix for the age-specific pigmentation phenotypes in the Manitoba population revealed 2 primary orthogonal axes that explained most ( approximately 100%) of the pigmentation variation across ontogeny. The primary axis, explaining 93% of the genetic variation, is an axis of genetic variation whose principal value loadings change from positive to negative across development, suggesting that the most rapid evolutionary response to selection on pigmentation variation will occur in the direction characterized by a tradeoff in early-age versus late-age pigmentation phenotypes. Pigmentation is known to be ecologically important and subject to rapid evolution under selection. Our study shows that significant differences exist between these 2 populations for their capacity to respond to selection on pigmentation which is not only influenced by the population of origin but also by the developmental process. We suggest that developmental timing may be a potential explanatory mechanism for the difference between the populations.
自达尔文以来，人们就注意到个体发育变化的进化重要性。然而，大多数表型进化分析都集中在单一的标志性年龄上。在这里，我们进行了一项遗传研究，该研究量化了 2 个普通束带蛇（Thamnophis sirtalis）种群在早期（即出生至 180 天）发育过程中色素沉着的遗传变异。这些种群在表型上有明显的区别，并且在地理上是隔离的（加拿大马尼托巴省和美国加利福尼亚北部）。两个种群的平均色素沉着发育轨迹存在显著差异，马尼托巴种群的平均色素沉着水平随着个体发育而增加，而加利福尼亚种群的平均色素沉着水平则在个体发育过程中保持不变。随后的定量遗传分析显示，马尼托巴种群在所有年龄段都存在可遗传的变异，而加利福尼亚种群在所有年龄段的表型和遗传变异水平都很低。对马尼托巴种群年龄特异性色素沉着表型的纵向遗传方差-协方差矩阵进行定量遗传分解，揭示了 2 个主要的正交轴，它们解释了个体发育过程中约 100%的色素沉着变异。主要轴解释了 93%的遗传变异，是一个遗传变异轴，其主要值加载从正到负变化，这表明对色素沉着变异的选择最快速的进化反应将发生在与早期和晚期色素沉着表型权衡的方向上。色素沉着已知在生态上很重要，并在选择下迅速进化。我们的研究表明，这两个种群在对色素沉着选择的反应能力上存在显著差异，这种差异不仅受到种群起源的影响，还受到发育过程的影响。我们认为，发育时间可能是种群之间差异的一个潜在解释机制。
