Pantalacci Sophie, Sémon Marie, Martin Arnaud, Chevret Pascale, Laudet Vincent
Institut de Génomique Fonctionnelle de Lyon, Université de Lyon, CNRS, INRA, Ecole Normale Supérieure de Lyon, 69364 Lyon Cedex 07, France.
Evol Dev. 2009 Jul-Aug;11(4):422-33. doi: 10.1111/j.1525-142X.2009.00348.x.
Metazoans are largely made of repeated parts, and metazoan evolution is marked by changes in the number of these parts, called meristic evolution. Understanding the mechanisms associated with meristic changes is thus a critical issue to evolutionary developmental biology. Palatal rugae are sensory ridges regularly arranged on the hard palate of mammals. They develop sequentially following mesio-distal growth of the palate, and activation-inhibition mechanisms very likely control spacing and timing of this sequential addition. In this study, we characterized trends in rugae number evolution among muroid rodents, showing that most species display 8+/-1 rugae, changes by one being very frequent in the phylogeny. We then compared development of three muroid species: mouse (nine rugae), rat (eight), and golden hamster (seven). We showed that palatal growth rate, spacing, and addition rate in mouse/rat were remarkably similar (with respect to the embryo size difference), and that increase to nine rugae in mouse is achieved by postponing the end of the addition process (hypermorphosis). Such a heterochronic shift may be typical of +/-1 variations observed among muroid rodents. In contrast, decrease to seven rugae in golden hamster is attributed to early growth termination (progenesis) of the palate, which correlates with the severe shortening of gestation in this species. Our results provide an experimental support to the intuitive view that heterochronies are especially relevant to meristic evolution of traits that rely on a sequential addition process. We also interpret our results in the light of developmental constraints specifically linked to this kind of process.
后生动物主要由重复的部分组成，而后生动物的进化以这些部分数量的变化为标志，这种变化被称为数量性状进化。因此，了解与数量性状变化相关的机制是进化发育生物学的一个关键问题。腭皱襞是哺乳动物硬腭上规则排列的感觉嵴。它们随着腭的近远中向生长而依次发育，激活-抑制机制很可能控制着这种依次添加的间距和时间。在本研究中，我们描述了鼠形啮齿动物腭皱襞数量进化的趋势，表明大多数物种有8±1条腭皱襞，在系统发育中数量变化一条的情况非常常见。然后，我们比较了三种鼠形物种的发育情况：小鼠（九条腭皱襞）、大鼠（八条）和金黄仓鼠（七条）。我们发现，小鼠/大鼠的腭生长速率、间距和添加速率非常相似（考虑到胚胎大小差异），小鼠中九条腭皱襞的增加是通过推迟添加过程的结束（形态过度发育）实现的。这种异时性变化可能是鼠形啮齿动物中观察到的±1变化的典型特征。相比之下，金黄仓鼠腭皱襞减少到七条归因于腭的早期生长终止（幼态成熟），这与该物种妊娠期的严重缩短相关。我们的结果为这样一种直观观点提供了实验支持，即异时性变化与依赖于依次添加过程的性状的数量性状进化特别相关。我们还根据与这种过程特别相关的发育限制来解释我们的结果。
