Augstenová Barbora, Johnson Pokorná Martina, Altmanová Marie, Frynta Daniel, Rovatsos Michail, Kratochvíl Lukáš
Department of Ecology, Faculty of Science, Charles University, Prague, 128 44, Czech Republic.
Institute of Animal Physiology and Genetics, The Czech Academy of Sciences, Liběchov, 277 21, Czech Republic.
Evolution. 2018 Jul 4. doi: 10.1111/evo.13543.
Snakes are historically important in the formulation of several central concepts on the evolution of sex chromosomes. For over 50 years, it was believed that all snakes shared the same ZZ/ZW sex chromosomes, which are homomorphic and poorly differentiated in "basal" snakes such as pythons and boas, while heteromorphic and well differentiated in "advanced" (caenophidian) snakes. Recent molecular studies revealed that differentiated sex chromosomes are indeed shared among all families of caenophidian snakes, but that boas and pythons evolved likely independently male heterogamety (XX/XY sex chromosomes). The historical report of heteromorphic ZZ/ZW sex chromosomes in a boid snake was previously regarded as ambiguous. In the current study, we document heteromorphic ZZ/ZW sex chromosomes in a boid snake. A comparative approach suggests that these heteromorphic sex chromosomes evolved very recently and that they are poorly differentiated at the sequence level. Interestingly, two snake lineages with confirmed male heterogamety possess homomorphic sex chromosomes, but heteromorphic sex chromosomes are present in both snake lineages with female heterogamety. We point out that this phenomenon is more common across squamates. The presence of female heterogamety in non-caenophidian snakes indicates that the evolution of sex chromosomes in this lineage is much more complex than previously thought, making snakes an even better model system for the evolution of sex chromosomes.
在性染色体进化的几个核心概念的形成过程中，蛇在历史上具有重要意义。五十多年来，人们一直认为所有蛇都共享相同的ZZ/ZW性染色体，在蟒和蚺等“基础”蛇类中，这些性染色体是同形的且分化程度低，而在“高级”（新蛇亚目）蛇类中则是异形的且分化良好。最近的分子研究表明，分化的性染色体确实在所有新蛇亚目蛇类家族中都存在，但蟒和蚺可能独立进化出了雄性异配性别（XX/XY性染色体）。先前在一种蚺科蛇中关于异形ZZ/ZW性染色体的历史报告被认为是不明确的。在当前的研究中，我们记录了一种蚺科蛇中的异形ZZ/ZW性染色体。一种比较方法表明，这些异形性染色体是最近才进化出来的，并且在序列水平上分化程度低。有趣的是，两个已确认具有雄性异配性别的蛇类谱系拥有同形性染色体，但具有雌性异配性别的两个蛇类谱系都存在异形性染色体。我们指出，这种现象在有鳞目动物中更为常见。非新蛇亚目蛇类中存在雌性异配性别表明，该谱系中性染色体的进化比先前认为的要复杂得多，这使得蛇成为研究性染色体进化的一个更好的模型系统。
