Chromosomal rearrangements are thought to be an important driving force underlying lineage diversification, but their link to speciation continues to be debated. Antarctic teleost fish of the family Nototheniidae (Notothenioidei) diversified in a changing environmental context, which led to ecological, morphological, and genetic differentiation among populations. In addition, extensive chromosomal repatterning accompanied species divergence in several clades. The most striking karyotypic changes involved the recent species radiation (about 10 My) of the genus Trematomus, with chromosomal pair numbers ranging between 29 and 12. These dramatic reductions in chromosome number resulted mostly from large-scale chromosome fusions. Multiple centric and/or tandem fusions have been hypothesized in at least seven of the twelve recognized Trematomus species. To reconstruct their evolutionary history, we employed comparative cytogenomics (BAC-FISH and chromosome painting) to reveal patterns of interspecific chromosomal orthologies across several notothenioid clades. We defined orthologous chromosomal segments of reference, termed Structural Units (SUs). SUs were identified in a total of 18 notothenioid species. We demonstrated for the first time that SUs were strongly conserved across every specimen examined, with chromosomal syntenies highlighting a paucity of intrachromosomal macro-rearrangements. Multiple independent fusions of these SUs were inferred in the Trematomus species, in contrast to the shared SU fusions in species of the sister lineage Notothenia. The SU segments were defined units of chromosomal rearrangement in the entire family Nototheiidae, which diverged from the other notothenioid families 20 My ago. Some of the identified chromosomal syntenies within the SUs were even conserved in their closest relatives, the family Eleginopsidae. Comparing the timing of acquisition of the fusions in the closely related genera Notothenia and Trematomus of the nototheniid species family, we conclude that they exhibit distinct chromosomal evolutionary histories, which may be relevant to different speciation scenarios.

中文翻译：

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多次独立的染色体融合伴随着南极硬骨目Trematomus（Notothenioidei：Nototheniidae）的辐射。

染色体重排被认为是谱系多样化背后的重要驱动力，但它们与物种形成的联系仍在争论中。Nototheniidae（Notothenioidei）家族的南极硬骨鱼在不断变化的环境中变得多样化，这导致了种群间的生态，形态和遗传分化。此外，广泛的染色体重排伴随物种在多个进化枝中的分化。最为显着的核型变化涉及Trematomus属的最近物种辐射（约10 My），染色体对数在29至12之间。这些染色体数的急剧减少主要是由于大规模染色体融合所致。在十二种公认的Trematomus物种中，至少有七种假设了多重中心和/或串联融合。为了重建它们的进化历史，我们采用了比较细胞基因组学（BAC-FISH和染色体涂画）来揭示跨多个类异戊二烯进化枝的种间染色体正交排列的模式。我们定义了参考的直系染色体片段，称为结构单位（SU）。在总共18种类胡萝卜素物种中鉴定出SU。我们首次证明，SUs在每个检查的标本中都是高度保守的，其染色体同构体突出了很少的染色体内宏重排。与姐妹谱系Notothenia的物种中共有的SU融合体相反，在Trumatomus物种中推断出这些SU的多个独立融合体。SU段是整个Nototheiidae家族中染色体重排的定义单位，它与其他类异戊二烯类家族不同20我以前。SU中某些已鉴定的染色体同系甚至在其最接近的亲缘种（Eleginopsidae家族）中也得到了保守。比较了在异齿亚科物种家族的紧密相关属的Notothenia和Trematomus属中融合体的获取时间，我们得出的结论是，它们表现出不同的染色体进化历史，这可能与不同的物种形成情况有关。