Genomic and anatomical comparisons of skin support independent adaptation to life in water by cetaceans and hippos
Genomic and anatomical comparisons of skin support independent adaptation to life in water by cetaceans and hippos
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DOI：
10.1101/2020.11.15.383638
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发表时间：
2020-11
期刊：
影响因子：
9.2
通讯作者：
M. Springer;C. Guerrero-Juarez;Matthias Huelsmann;Matthew A. Collin;K. Danil;M. McGowen;J. Oh;Raul Ramos;M. Hiller;M. Plikus;J. Gatesy
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文献类型：
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作者：
M. Springer;C. Guerrero-Juarez;Matthias Huelsmann;Matthew A. Collin;K. Danil;M. McGowen;J. Oh;Raul Ramos;M. Hiller;M. Plikus;J. Gatesy
从陆地到海洋水圈强制性栖息的宏观进化转变在哺乳动物的历史上发生过两次：鲸目和海蛞蝓。在鲸类（鲸鱼、海豚、鼠海豚）的例子中，分子遗传学提供了明确的证据，证明完全水生的鲸类和半水生的河马是彼此最近的亲属。祖先的重建进一步表明，一些适应水生领域的进化是在鲸齿类（鲸类+河马科）的共同祖先。另一种假设是，这些适应性在鲸目动物和河马中独立进化。在这里，我们专注于皮肤系统，并评估这些假设整合新的组织学数据的鲸类和河马，第一个基因组规模的数据，为侏儒河马，全面的基因组筛选和分子进化分析的蛋白质编码基因，已被灭活的河马和鲸类。我们确定了10个在鲸类和河马中失活的皮肤相关基因，包括与皮脂腺、毛囊和表皮分化相关的基因。然而，这些基因都没有表现出鲸类和河马共有的失活突变。这两个分支中皮肤基因失活的平均日期作为表型变化的代表，并表明鲸目动物（~46.5 Ma）的毛发减少/脱落、皮脂腺的丧失和角化程序的变化比河马（~30.5 Ma）早约1600万年。这些结果，再加上组织学差异的外皮和以前的分析，氧同位素从干anthracotheres（“anthracotheres”），支持的假设，水生适应进化独立的河马和鲸目动物。
The macroevolutionary transition from terra firma to obligatory inhabitance of the marine hydrosphere has occurred twice in the history of Mammalia: Cetacea and Sirenia. In the case of Cetacea (whales, dolphins, porpoises), molecular phylogenies provide unambiguous evidence that fully aquatic cetaceans and semiaquatic hippopotamids (hippos) are each other’s closest living relatives. Ancestral reconstructions further suggest that some adaptations to the aquatic realm evolved in the common ancestor of Cetancodonta (Cetacea+Hippopotamidae). An alternative hypothesis is that these adaptations evolved independently in cetaceans and hippos. Here, we focus on the integumentary system and evaluate these hypotheses by integrating new histological data for cetaceans and hippos, the first genome-scale data for pygmy hippopotamus, and comprehensive genomic screens and molecular evolutionary analyses for protein-coding genes that have been inactivated in hippos and cetaceans. We identified ten skin-related genes that are inactivated in both cetaceans and hippos, including genes that are related to sebaceous glands, hair follicles, and epidermal differentiation. However, none of these genes exhibit inactivating mutations that are shared by cetaceans and hippos. Mean dates for the inactivation of skin genes in these two clades serve as proxies for phenotypic changes and suggest that hair reduction/loss, the loss of sebaceous glands, and changes to the keratinization program occurred ~16 million years earlier in cetaceans (~46.5 Ma) than in hippos (~30.5 Ma). These results, together with histological differences in the integument and prior analyses of oxygen isotopes from stem hippopotamids (“anthracotheres”), support the hypothesis that aquatic adaptations evolved independently in hippos and cetaceans.