Monterey Bay Aquarium Research Institute, Moss Landing, CA, USA.
BMC Biol. 2009 Nov 10;7:74. doi: 10.1186/1741-7007-7-74.
Bone-eating Osedax worms have proved to be surprisingly diverse and widespread. Including the initial description of this genus in 2004, five species that live at depths between 25 and 3,000 m in the eastern and western Pacific and in the north Atlantic have been named to date. Here, we provide molecular and morphological evidence for 12 additional evolutionary lineages from Monterey Bay, California. To assess their phylogenetic relationships and possible status as new undescribed species, we examined DNA sequences from two mitochondrial (COI and 16S rRNA) and three nuclear genes (H3, 18S and 28S rRNA).
Phylogenetic analyses identified 17 distinct evolutionary lineages. Levels of sequence divergence among the undescribed lineages were similar to those found among the named species. The 17 lineages clustered into five well-supported clades that also differed for a number of key morphological traits. Attempts to determine the evolutionary age of Osedax depended on prior assumptions about nucleotide substitution rates. According to one scenario involving a molecular clock calibrated for shallow marine invertebrates, Osedax split from its siboglinid relatives about 45 million years ago when archeocete cetaceans first appeared and then diversified during the late Oligocene and early Miocene when toothed and baleen whales appeared. Alternatively, the use of a slower clock calibrated for deep-sea annelids suggested that Osedax split from its siboglinid relatives during the Cretaceous and began to diversify during the Early Paleocene, at least 20 million years before the origin of large marine mammals.
To help resolve uncertainties about the evolutionary age of Osedax, we suggest that the fossilized bones from Cretaceous marine reptiles and late Oligocene cetaceans be examined for possible trace fossils left by Osedax roots. Regardless of the outcome, the present molecular evidence for strong phylogenetic concordance across five separate genes suggests that the undescribed Osedax lineages comprise evolutionarily significant units that have been separate from one another for many millions of years. These data coupled with ongoing morphological analyses provide a solid foundation for their future descriptions as new species.
食骨蠕虫 Osedax 被证明具有惊人的多样性和广泛分布。自 2004 年首次描述该属以来，已命名了五种生活在东太平洋、西太平洋和北大西洋的 25 至 3000 米深处的物种。在这里，我们提供了加利福尼亚州蒙特雷湾的 12 个额外进化谱系的分子和形态证据。为了评估它们的系统发育关系和可能作为新未描述物种的地位，我们检查了来自两个线粒体（COI 和 16S rRNA）和三个核基因（H3、18S 和 28S rRNA）的 DNA 序列。
系统发育分析确定了 17 个独特的进化谱系。未描述谱系之间的序列差异水平与已命名物种之间的差异相似。这 17 个谱系聚类为五个支持良好的分支，这些分支在许多关键形态特征上也存在差异。确定食骨蠕虫的进化年龄取决于核苷酸替代率的先前假设。根据涉及浅海无脊椎动物分子钟校准的一种方案，食骨蠕虫与 siboglinid 亲属在古鲸类首次出现时大约 4500 万年前分裂，然后在晚渐新世和早中新世期间多样化，当时有齿和须鲸出现。或者，使用针对深海环节动物校准的较慢时钟表明，食骨蠕虫与 siboglinid 亲属在白垩纪分裂，并在早古新世开始多样化，至少在大型海洋哺乳动物出现前 2000 万年。
为了帮助解决食骨蠕虫进化年龄的不确定性，我们建议检查白垩纪海洋爬行动物和晚渐新世鲸类的化石骨骼，以寻找可能由食骨蠕虫根系留下的痕迹化石。无论结果如何，目前针对五个独立基因的强烈系统发育一致性的分子证据表明，未描述的食骨蠕虫谱系构成了具有进化意义的单位，彼此分离已有数百万年之久。这些数据加上正在进行的形态分析为它们未来被描述为新物种提供了坚实的基础。
