Data from: Recombination in the eggs and sperm in a simultaneously hermaphroditic vertebrate

When there is no recombination (achiasmy) in one sex, it is in the heterogametic one. This observation is so consistent that it constitutes one of the few patterns in biology that may be regarded as a ‘rule’ and Haldane (Haldane 1922 J. Genet. 12, 101–109. (doi:10.1007/BF02983075)) proposed that it might be driven by selection against recombination in the sex chromosomes. Yet differences in recombination rates between the sexes (heterochiasmy) have also been reported in hermaphroditic species that lack sex chromosomes. In plants—the vast majority of which are hermaphroditic—selection at the haploid stage has been proposed to drive heterochiasmy. Yet few data are available for hermaphroditic animals, and barely any for hermaphroditic vertebrates. Here, we leverage reciprocal crosses between two black hamlets (Hypoplectrus nigricans, Serranidae), simultaneously hermaphroditic reef fishes from the wider Caribbean, to generate high-density egg- and sperm-specific linkage maps for each parent. We find globally higher recombination rates in the eggs, with dramatically pronounced heterochiasmy at the chromosome peripheries. We suggest that this pattern may be due to female meiotic drive, and that this process may be an important source of heterochiasmy in animals. We also identify a large non-recombining region that may play a role in speciation and local adaptation in Hypoplectrus.

当某一性别不存在重组（无交叉现象，achiasmy）时，该性别通常为异配性别（heterogametic sex）。这一观察结果具有高度一致性，堪称生物学中为数不多可被视为“法则”的规律之一；霍尔丹（Haldane, 1922, 《遗传学杂志》*J. Genet.* 12卷：101–109，DOI: 10.1007/BF02983075）据此提出，该现象可能由性染色体上的重组抑制选择所驱动。然而，研究也发现，在缺乏性染色体的雌雄同体物种中，同样存在两性间重组率的差异（异交叉现象，heterochiasmy）。在绝大多数类群为雌雄同体的植物中，学界已提出单倍体阶段的选择可能是异交叉现象的驱动因素。但针对雌雄同体动物的相关数据仍十分匮乏，针对雌雄同体脊椎动物的相关数据则几乎空白。本研究通过对两种黑色青脂鯉（Hypoplectrus nigricans，隶属于鮨科Serranidae）开展正反交实验——这类鱼类为广泛分布于加勒比海海域的同步雌雄同体礁栖鱼类——为每个亲本构建了高覆盖度的卵子特异性与精子特异性连锁图谱（linkage map）。研究发现，卵子中的整体重组水平更高，且在染色体末端区域呈现出极为显著的异交叉现象。我们推测，该模式可能由雌性减数分裂驱动（female meiotic drive）所导致，且这一过程可能是动物界异交叉现象的重要诱因之一。本研究还鉴定出一个大型的非重组区域，该区域可能在青脂鯉属（Hypoplectrus）的物种形成与局部适应过程中发挥重要作用。