Dufresnes Christophe, Litvinchuk Spartak N, Rozenblut-Kościsty Beata, Rodrigues Nicolas, Perrin Nicolas, Crochet Pierre-André, Jeffries Daniel L
LASER College of Biology and the Environment Nanjing Forestry University Nanjing People's Republic of China.
Department of Animal and Plant Sciences University of Sheffield Sheffield United Kingdom.
Evol Lett. 2020 Aug 19;4(5):444-456. doi: 10.1002/evl3.191. eCollection 2020 Oct.
The growing interest in the lability of sex determination in non-model vertebrates such as amphibians and fishes has revealed high rates of sex chromosome turnovers among closely related species of the same clade. Can such lineages hybridize and admix with different sex-determining systems, or could the changes have precipitated their speciation? We addressed these questions in incipient species of toads (Bufonidae), where we identified a heterogametic transition and characterized their hybrid zone with genome-wide markers (RADseq). Adult and sibship data confirmed that the common toad is female heterogametic (ZW), while its sister species the spined toad is male heterogametic (XY). Analysis of a fine scale transect across their parapatric ranges in southeastern France unveiled a narrow tension zone (∼10 km), with asymmetric mitochondrial and nuclear admixture over hundreds of kilometers southward and northward, respectively. The geographic extent of introgression is consistent with an expansion of across 's former ranges in Mediterranean France, as also suggested by species distribution models. However, widespread cyto-nuclear discordances ( backrosses carrying mtDNA) run against predictions from the dominance effects of Haldane's rule, perhaps because Y and W heterogametologs are not degenerated. Common and spined toads can thus successfully cross-breed despite fundamental differences in their sex determination mechanisms, but remain partially separated by reproductive barriers. Whether and how the interactions of their XY and ZW genes contribute to these barriers shall provide novel insights on the debated role of labile sex chromosomes in speciation.
对两栖动物和鱼类等非模式脊椎动物性别决定不稳定性的兴趣日益浓厚，这揭示了同一进化枝密切相关物种中性染色体周转率很高。这样的谱系能否与不同的性别决定系统杂交并混合，或者这些变化是否促成了它们的物种形成？我们在蟾蜍（蟾蜍科）的初始物种中解决了这些问题，在那里我们确定了一种异配性转变，并用全基因组标记（RADseq）对它们的杂交带进行了特征描述。成年个体和同胞关系数据证实，普通蟾蜍是雌性异配（ZW），而其姊妹物种棘蟾蜍是雄性异配（XY）。对法国东南部它们的邻域分布范围内的一个精细尺度样带进行分析，发现了一个狭窄的张力带（约10公里），线粒体和核混合分别在向南和向北数百公里范围内不对称。基因渗入的地理范围与在地中海法国普通蟾蜍以前分布范围内的扩张一致，物种分布模型也表明了这一点。然而，广泛存在的细胞核与细胞质不一致性（携带普通蟾蜍线粒体DNA的回交个体）与霍尔丹法则的显性效应预测相悖，可能是因为Y和W异源配子同源物没有退化。因此，尽管普通蟾蜍和棘蟾蜍在性别决定机制上存在根本差异，但它们仍能成功杂交，但仍因生殖障碍而部分隔离。它们的XY和ZW基因的相互作用是否以及如何导致这些障碍，将为关于不稳定的性染色体在物种形成中所起作用的争论提供新的见解。
