BACKGROUND AND AIMS Hybridisation is an important evolutionary process that can have a significant impact on natural plant populations. Eucalyptus species are well-known for weak reproductive barriers and extensive hybridisation within subgenera but there is little knowledge of whether patterns of hybridisation differ among subgenera. Here, we examine eucalypts of Westerns Australia's Stirling Range to investigate how patterns of hybridisation are associated with landscape and taxon age between the two largest Eucalyptus subgenera: Eucalyptus and Symphyomyrtus. In doing so, we tested a hypothesis of OCBIL (old, climatically buffered, infertile landscape) theory that predicts reduced hybridisation on older landscapes. METHODS SNP markers were applied to confirm the hybrid status, parentage and characterise the range of hybrid classes present in five suspected hybrid combinations for subg. Eucalyptus and three combinations for subg. Symphyomyrtus. KEY RESULTS Evidence of hybridisation was found in all combinations and parental taxa were identified for most combinations. The older parental taxa assessed within Subgenus Eucalyptus, which are widespread on old landscapes, were identified as well-defined genetic entities and all hybrids were exclusively F1 hybrids. In addition, many combinations showed evidence of clonality, suggesting that the high number of hybrids recorded from some combinations is the result of long-term clonal spread following a few hybridisation events rather than frequent hybridisation. In contrast, the species in Subgenus Symphyomyrtus, which typically occur on younger landscapes and are generally more recently evolved, showed less distinction among parental taxa and where hybridisation was detected, there were high levels of introgression. CONCLUSIONS Reduced hybridisation in Subgenus Eucalyptus relative to extensive hybridisation in Subgenus Symphyomyrtus affirmed the hypothesis of reduced hybridisation on OCBILs and demonstrate that clade divergence times, landscape age and clonality are important drivers of differing patterns of speciation and hybridisation in Eucalyptus.

中文翻译：

---

景观和分类群年龄与两种桉树（桃金娘科）亚属的不同杂交模式有关

背景和目的 杂交是一个重要的进化过程，可以对天然植物种群产生重大影响。桉树物种以弱的生殖屏障和亚属内的广泛杂交而闻名，但很少有人知道亚属之间的杂交模式是否不同。在这里，我们研究了澳大利亚西部斯特灵山脉的桉树，以研究杂交模式如何与两个最大的桉树亚属：桉树和 Symphyomyrtus 之间的景观和分类群年龄相关联。为此，我们测试了 OCBIL（旧的、气候缓冲的、贫瘠的景观）理论的假设，该理论预测旧景观上的杂交减少。方法 应用 SNP 标记来确认杂交状态，亲本并描述了 subg 的五种可疑杂交组合中存在的杂交类别范围。桉树和 subg 的三种组合。香蜂草。主要结果 在所有组合中都发现了杂交的证据，并且大多数组合都确定了亲本分类群。桉树亚属中评估的较老的亲本分类群在古老的景观中广泛分布，被确定为明确的遗传实体，所有杂种都是 F1 杂种。此外，许多组合显示出克隆性的证据，这表明从某些组合中记录的大量杂交是少数杂交事件后长期克隆传播的结果，而不是频繁杂交的结果。相比之下，亚属 Symphyomyrtus 中的物种，通常发生在较年轻的景观中并且通常是最近进化的，在亲本分类群之间显示出较少的区别，并且在检测到杂交的地方，有高水平的基因渗入。结论 桉树亚属的杂交减少相对于亚属 Symphyomyrtus 的广泛杂交证实了 OCBIL 杂交减少的假设，并证明进化枝发散时间、景观年龄和克隆性是桉树物种形成和杂交不同模式的重要驱动因素。