Ryan T J, Semlitsch R D
Savannah River Ecology Laboratory, Drawer E, Aiken, SC 29802, USA.
Proc Natl Acad Sci U S A. 1998 May 12;95(10):5643-8. doi: 10.1073/pnas.95.10.5643.
Morphological features such as size and shape are the most common focus in studies of heterochronic change. Frequently, these easily observed and measured features are treated as a major target of selection, potentially ignoring traits more closely related to fitness. We question the primacy of morphological data in studies of heterochrony, and instead suggest that principal sources of fitness, such as life history characteristics, are not only the chief targets of selection, but changes in them may necessitate changes in other (subordinate) elements of the organism. We use an experimental approach to investigate the timing of metamorphosis and maturation in a facultatively paedomorphic salamander, Ambystoma talpoideum. We determine that individuals possessing the well-known paedomorphic phenotype are peramorphic with regard to maturation, through the process of predisplacement (an earlier onset of maturation). Combining the well studied ecology of dimorphic A. talpoideum populations with theories of heterochronic mechanisms and life history evolution, we conclude that age at maturation is the principal target of selection and that morphological changes are secondary effects. Increased attention to the intimate connection between life history evolution and heterochrony is the most promising route to a better understanding of both.
诸如大小和形状等形态特征是异时变化研究中最常见的关注点。通常，这些易于观察和测量的特征被视为选择的主要目标，这可能会忽略与适应性更密切相关的性状。我们质疑形态学数据在异时性研究中的首要地位，相反，我们认为适应性的主要来源，如生活史特征，不仅是选择的主要目标，而且它们的变化可能需要生物体其他（次要）元素发生变化。我们采用实验方法来研究兼性幼态持续蝾螈（美洲钝口螈）的变态和成熟时间。我们确定，具有著名幼态持续表型的个体在成熟方面是超形态型的，这是通过提前移位（成熟提前开始）的过程实现的。将对二态性美洲钝口螈种群的深入研究生态学与异时机制和生活史进化理论相结合，我们得出结论：成熟年龄是选择的主要目标，而形态变化是次要影响。更多地关注生活史进化与异时性之间的紧密联系是更好理解这两者的最有前途的途径。
