Department of Ecology and Evolution, University of Lausanne, Switzerland.
Department of Genomes and Genetics, Institut Pasteur, Paris, France.
Genome Biol Evol. 2019 Oct 1;11(10):2954-2962. doi: 10.1093/gbe/evz219.
Sex determination has evolved in a variety of ways and can depend on environmental and genetic signals. A widespread form of genetic sex determination is haplodiploidy, where unfertilized, haploid eggs develop into males and fertilized diploid eggs into females. One of the molecular mechanisms underlying haplodiploidy in Hymenoptera, the large insect order comprising ants, bees, and wasps, is complementary sex determination (CSD). In species with CSD, heterozygosity at one or several loci induces female development. Here, we identify the genomic regions putatively underlying multilocus CSD in the parasitoid wasp Lysiphlebus fabarum using restriction-site associated DNA sequencing. By analyzing segregation patterns at polymorphic sites among 331 diploid males and females, we identify up to four CSD candidate regions, all on different chromosomes. None of the candidate regions feature evidence for homology with the csd gene from the honey bee, the only species in which CSD has been characterized, suggesting that CSD in L. fabarum is regulated via a novel molecular mechanism. Moreover, no homology is shared between the candidate loci, in contrast to the idea that multilocus CSD should emerge from duplications of an ancestral single-locus system. Taken together, our results suggest that the molecular mechanisms underlying CSD in Hymenoptera are not conserved between species, raising the question as to whether CSD may have evolved multiple times independently in the group.
性别决定的方式多种多样，可以取决于环境和遗传信号。一种广泛存在的遗传性别决定形式是单倍二倍性，即未受精的单倍体卵子发育为雄性，而受精的二倍体卵子发育为雌性。膜翅目昆虫（包括蚂蚁、蜜蜂和黄蜂在内的大型昆虫目）中单倍二倍性的分子机制之一是互补性别决定（CSD）。在具有 CSD 的物种中，一个或几个位点的杂合性会诱导雌性发育。在这里，我们使用限制位点相关 DNA 测序来确定寄生蜂丽蝇蛹集金小蜂中多基因座 CSD 的潜在基因组区域。通过分析 331 个二倍体雄性和雌性个体中多态性位点的分离模式，我们确定了多达四个 CSD 候选区域，这些区域都位于不同的染色体上。候选区域均未表现出与已被描述的蜜蜂中 csd 基因同源的证据，这表明丽蝇蛹集金小蜂中的 CSD 是通过一种新的分子机制来调控的。此外，候选基因座之间没有同源性，这与多基因座 CSD 应该是从祖先单基因座系统的重复进化而来的观点相反。总之，我们的研究结果表明，膜翅目昆虫中的 CSD 分子机制在物种之间并不保守，这引发了一个问题，即 CSD 是否可能在该类群中独立地多次进化。
