France James, Babik Wiesław, Cvijanović Milena, Dudek Katarzyna, Ivanović Ana, Vučić Tijana, Wielstra Ben
Institute of Biology Leiden, Leiden University, P.O. Box 9505, Leiden, RA 2300, The Netherlands.
Naturalis Biodiversity Center, P.O. Box 9517, Leiden, RA 2300, The Netherlands.
Genome Biol Evol. 2025 Sep 2;17(9). doi: 10.1093/gbe/evaf155.
Non-recombining regions often have profound effects on genome evolution, resulting in structures such as sex chromosomes and supergenes. Amongst the strangest examples are balanced lethal systems, such as that found in newts of the genus Triturus. These systems halve reproductive output, and the evolution of such a deleterious trait is difficult to explain. For Triturus, an intriguing model proposes that the balanced lethal system evolved from an ancestral Y-chromosome. To test this hypothesis, we identify the Y-chromosome of Triturus and verify whether it, or the balanced lethal system, is homologous to the Y-chromosome of its sister genus Lissotriton, which does not possess the balanced lethal system. We identify a set of candidate Y-linked markers in Triturus ivanbureschi and validate the male specificity of the markers in all major clades of Triturus. We place the Y-linked markers on a high-density linkage map of T. ivanbureschi that we construct with 7,233 RADseq markers. We then place both the Triturus and Lissotriton Y-linked regions within previously constructed target capture linkage maps that include genes linked to the balanced lethal system. We observe that neither the Triturus balanced lethal system, nor the Triturus Y-chromosome are homologous to the Lissotriton Y-chromosome. This is the first molecular evidence of a transition between Y-chromosome systems within salamanders. However, unless additional sex chromosome turnover events are involved, our data does not support a sex chromosome origin of the balanced lethal system.
非重组区域通常对基因组进化有深远影响，导致形成性染色体和超基因等结构。最奇特的例子之一是平衡致死系统，比如在真螈属蝾螈中发现的那种。这些系统使繁殖产出减半，而这种有害性状的进化难以解释。对于真螈来说，一个有趣的模型提出平衡致死系统是从祖先Y染色体进化而来的。为了验证这一假设，我们鉴定了真螈的Y染色体，并验证它或平衡致死系统是否与不具备平衡致死系统的姐妹属滑螈的Y染色体同源。我们在伊凡布氏真螈中鉴定出一组候选Y连锁标记，并在真螈的所有主要分支中验证了这些标记的雄性特异性。我们将Y连锁标记定位到我们用7233个RADseq标记构建的伊凡布氏真螈的高密度连锁图谱上。然后，我们将真螈和滑螈的Y连锁区域都定位到先前构建的目标捕获连锁图谱中，该图谱包含与平衡致死系统相关的基因。我们观察到，真螈的平衡致死系统和真螈的Y染色体都与滑螈的Y染色体不同源。这是蝾螈中Y染色体系统之间转变的首个分子证据。然而，除非涉及额外的性染色体更替事件，我们的数据并不支持平衡致死系统起源于性染色体的观点。
