Nielsen S V, Banks J L, Diaz R E, Trainor P A, Gamble T
Department of Biological Sciences, Marquette University, Milwaukee, WI, USA.
Department of Biological Sciences, Southeastern Louisiana University, Hammond, LA, USA.
J Evol Biol. 2018 Apr;31(4):484-490. doi: 10.1111/jeb.13242. Epub 2018 Feb 26.
Much of our current state of knowledge concerning sex chromosome evolution is based on a handful of 'exceptional' taxa with heteromorphic sex chromosomes. However, classifying the sex chromosome systems of additional species lacking easily identifiable, heteromorphic sex chromosomes is indispensable if we wish to fully understand the genesis, degeneration and turnover of vertebrate sex chromosomes. Squamate reptiles (lizards and snakes) are a potential model clade for studying sex chromosome evolution as they exhibit a suite of sex-determining modes yet most species lack heteromorphic sex chromosomes. Only three (of 203) chameleon species have identified sex chromosome systems (all with female heterogamety, ZZ/ZW). This study uses a recently developed method to identify sex-specific genetic markers from restriction site-associated DNA sequence (RADseq) data, which enables the identification of sex chromosome systems in species lacking heteromorphic sex chromosomes. We used RADseq and subsequent PCR validation to identify an XX/XY sex chromosome system in the veiled chameleon (Chamaeleo calyptratus), revealing a novel transition in sex chromosome systems within the Chamaeleonidae. The sex-specific genetic markers identified here will be essential in research focused on sex-specific, comparative, functional and developmental evolutionary questions, further promoting C. calyptratus' utility as an emerging model organism.
我们目前关于性染色体进化的许多知识状态是基于少数具有异形性染色体的“特殊”分类群。然而，如果我们想全面了解脊椎动物性染色体的起源、退化和更替，对缺乏易于识别的异形性染色体的其他物种的性染色体系统进行分类是必不可少的。有鳞目爬行动物（蜥蜴和蛇）是研究性染色体进化的潜在模型类群，因为它们表现出一系列性别决定模式，但大多数物种缺乏异形性染色体。在203种变色龙物种中，只有3种已确定了性染色体系统（均为雌性异配，ZZ/ZW）。本研究使用一种最近开发的方法，从限制性位点相关DNA序列（RADseq）数据中识别性别特异性遗传标记，这使得在缺乏异形性染色体的物种中识别性染色体系统成为可能。我们使用RADseq及后续的PCR验证，在蒙面变色龙（Chamaeleo calyptratus）中鉴定出一个XX/XY性染色体系统，揭示了避役科中性染色体系统的一个新转变。这里鉴定出的性别特异性遗传标记对于专注于性别特异性、比较、功能和发育进化问题的研究至关重要，进一步提升了蒙面变色龙作为一种新兴模式生物的实用性。
