Coppard Simon E, Lessios H A
Smithsonian Tropical Research Institute, Box 0843-03092, Balboa, Panama.
Hamilton College, Department of Biology, 198 College Hill Road, Clinton, New York, 13323, USA.
Sci Rep. 2017 Sep 14;7(1):11520. doi: 10.1038/s41598-017-11875-w.
Vicariant events have been widely used to calibrate rates of molecular evolution, the completion of the Central American Isthmus more extensively than any other. Recent studies have claimed that rather than the generally accepted date of ~3 million years ago (Ma), the Isthmus was effectively complete by the middle Miocene, 13 Ma. We present a fossil calibrated phylogeny of the new world sand dollar genus Encope, based on one nuclear and four mitochondrial genes, calibrated with fossils at multiple nodes. Present day distributions of Encope are likely the result of multiple range contractions and extinction events. Most species are now endemic to a single region, but one widely distributed species in each ocean is composed of morphotypes previously described as separate species. The most recent separation between eastern Pacific and Caribbean extant clades occurred at 4.90 Ma, indicating that the Isthmus of Panama allowed genetic exchange until the Pliocene. The rate of evolution of mitochondrial genes in Encope has been ten times slower than in the closely related genera Mellita and Lanthonia. This large difference in rates suggests that splits between eastern Pacific and Caribbean biota, dated on the assumption of a "universal" mitochondrial DNA clock are not valid.
地理隔离事件已被广泛用于校准分子进化速率，其中中美洲地峡的形成对校准的影响比其他任何事件都更为广泛。最近的研究表明，中美洲地峡并非如普遍认为的那样在约300万年前（Ma）形成，而是在中新世中期，即13 Ma时就已基本完成。我们基于一个核基因和四个线粒体基因构建了新世界沙钱属Encope的化石校准系统发育树，并在多个节点用化石进行校准。Encope现今的分布可能是多次分布范围收缩和灭绝事件的结果。现在大多数物种是单一地区的特有物种，但每个海洋中都有一个分布广泛的物种，它由以前被描述为不同物种的形态型组成。东太平洋和加勒比海现存分支之间的最近一次分离发生在490万年前，这表明巴拿马地峡直到上新世仍允许基因交流。Encope线粒体基因的进化速率比密切相关的Mellita属和Lanthonia属慢十倍。这种速率上的巨大差异表明，基于“通用”线粒体DNA时钟假设确定的东太平洋和加勒比海生物群之间的分裂时间是无效的。
