Senckenberg Biodiversity and Climate Research Centre (BiK-F), Georg-Voigt-Strasse 14-16, Frankfurt Am Main, Germany.
Institute for Ecology, Evolution and Diversity, Goethe University, Max-Von-Laue-Strasse. 9, Frankfurt Am Main, Germany.
BMC Biol. 2023 Apr 12;21(1):79. doi: 10.1186/s12915-023-01579-1.
Baleen whales are a clade of gigantic and highly specialized marine mammals. Their genomes have been used to investigate their complex evolutionary history and to decipher the molecular mechanisms that allowed them to reach these dimensions. However, many unanswered questions remain, especially about the early radiation of rorquals and how cancer resistance interplays with their huge number of cells. The pygmy right whale is the smallest and most elusive among the baleen whales. It reaches only a fraction of the body length compared to its relatives and it is the only living member of an otherwise extinct family. This placement makes the pygmy right whale genome an interesting target to update the complex phylogenetic past of baleen whales, because it splits up an otherwise long branch that leads to the radiation of rorquals. Apart from that, genomic data of this species might help to investigate cancer resistance in large whales, since these mechanisms are not as important for the pygmy right whale as in other giant rorquals and right whales.
Here, we present a first de novo genome of the species and test its potential in phylogenomics and cancer research. To do so, we constructed a multi-species coalescent tree from fragments of a whole-genome alignment and quantified the amount of introgression in the early evolution of rorquals. Furthermore, a genome-wide comparison of selection rates between large and small-bodied baleen whales revealed a small set of conserved candidate genes with potential connections to cancer resistance.
Our results suggest that the evolution of rorquals is best described as a hard polytomy with a rapid radiation and high levels of introgression. The lack of shared positive selected genes between different large-bodied whale species supports a previously proposed convergent evolution of gigantism and hence cancer resistance in baleen whales.
须鲸是一个巨型和高度特化的海洋哺乳动物分支。它们的基因组被用于研究它们复杂的进化历史，并解析使它们达到这些体型的分子机制。然而，仍有许多悬而未决的问题，特别是关于须鲸的早期辐射以及抗癌能力如何与其大量的细胞相互作用。小露脊鲸是须鲸中最小和最难以捉摸的一种。与近亲相比，它的体长只有一小部分，而且是一个已经灭绝的家族中唯一现存的成员。这种位置使小露脊鲸的基因组成为更新须鲸复杂进化史的有趣目标，因为它分裂了一个否则很长的分支，导致须鲸的辐射。除此之外，该物种的基因组数据可能有助于研究大型鲸鱼的抗癌能力，因为这些机制对小露脊鲸来说并不像其他巨型须鲸和露脊鲸那么重要。
在这里，我们首次提出了该物种的从头基因组，并测试了其在系统发育基因组学和癌症研究中的潜力。为此，我们从全基因组比对的片段构建了一个多物种合并树，并量化了须鲸早期进化中基因渗入的程度。此外，对大、小体型须鲸之间选择率的全基因组比较揭示了一小部分具有潜在抗癌能力的保守候选基因。
我们的结果表明，须鲸的进化最好被描述为一个具有快速辐射和高水平基因渗入的硬多枝。不同大型鲸鱼物种之间没有共享的正选择基因，这支持了以前提出的须鲸中巨型和抗癌能力的趋同进化。
