PDF(Pubmed)
Abstract：
The Y chromosome is theorized to facilitate evolution of sexual dimorphism by accumulating sexually antagonistic loci, but empirical support is scarce. Due to the lack of recombination, Y chromosomes are prone to degenerative processes, which poses a constraint on their adaptive potential. Yet, in the seed beetle, Callosobruchus maculatus segregating Y linked variation affects male body size and thereby sexual size dimorphism (SSD). Here, we assemble C. maculatus sex chromosome sequences and identify molecular differences associated with Y-linked SSD variation. The assembled Y chromosome is largely euchromatic and contains over 400 genes, many of which are ampliconic with a mixed autosomal and X chromosome ancestry. Functional annotation suggests that the Y chromosome plays important roles in males beyond primary reproductive functions. Crucially, we find that, besides an autosomal copy of the gene target of rapamycin (TOR), males carry an additional TOR copy on the Y chromosome. TOR is a conserved regulator of growth across taxa, and our results suggest that a Y-linked TOR provides a male specific opportunity to alter body size. A comparison of Y haplotypes associated with male size difference uncovers a copy number variation for TOR, where the haplotype associated with decreased male size, and thereby increased sexual dimorphism, has two additional TOR copies. This suggests that sexual conflict over growth has been mitigated by autosome to Y translocation of TOR followed by gene duplications. Our results reveal that despite of suppressed recombination, the Y chromosome can harbor adaptive potential as a male-limited supergene.
摘要：
从理论上讲，Y染色体通过积累性拮抗基因座来促进性二态性的进化，但是经验支持很少。由于缺乏重组，Y染色体容易发生变性过程，这对他们的适应潜力构成了限制。然而，在种子甲虫Callosobruchusmaculatus分离中，Y连锁变异会影响男性的体型，从而影响性别大小的二态性（SSD）。在这里，我们组装了C.maculatus性染色体序列，并鉴定了与Y连锁SSD变异相关的分子差异。组装的Y染色体在很大程度上是常染色体的，包含超过400个基因，其中许多是具有常染色体和X染色体混合血统的扩增蛋白。功能注释表明，Y染色体在男性中起着重要的作用，而不仅仅是主要的生殖功能。至关重要的是，我们发现,除了雷帕霉素靶基因（TOR）的常染色体拷贝，男性在Y染色体上携带一个额外的TOR拷贝。TOR是一个保守的跨类群增长调节剂，我们的结果表明,与Y相关的TOR为男性提供了改变体型的特定机会.与男性大小差异相关的Y单倍型的比较揭示了TOR的拷贝数变异，单倍型与男性体型减少有关，从而增加了性二态，有两个额外的TOR副本。这表明，通过常染色体到TOR的Y易位，然后进行基因复制，可以减轻生长中的性冲突。我们的结果表明，尽管重组受到抑制，Y染色体可以作为男性限制的超基因具有适应性潜力。
