Department of Ecology and Evolution, University of Lausanne, Switzerland.
Sex Dev. 2013;7(5):261-6. doi: 10.1159/000351089. Epub 2013 May 31.
Contrasting with the situation found in birds and mammals, sex chromosomes are generally homomorphic in poikilothermic vertebrates. This homomorphy was recently shown to result from occasional X-Y recombinations (not from turnovers) in several European species of tree frogs (Hyla arborea, H. intermedia and H. molleri). Because of recombination, however, alleles at sex-linked loci were rarely diagnostic at the population level; support for sex linkage had to rely on multilocus associations, combined with occasional sex differences in allelic frequencies. Here, we use direct evidence, obtained from anatomical and histological analyses of offspring with known pedigrees, to show that the Eastern tree frog (H. orientalis) shares the same pair of sex chromosomes, with identical patterns of male heterogamety and complete absence of X-Y recombination in males. Conservation of an ancestral pair of sex chromosomes, regularly rejuvenated via occasional X-Y recombination, seems thus a widespread pattern among Hyla species. Sibship analyses also identified discrepancies between genotypic and phenotypic sex among offspring, associated with abnormal gonadal development, suggesting a role for sexually antagonistic genes on the sex chromosomes.
与鸟类和哺乳动物的情况形成鲜明对比的是，变温脊椎动物的性染色体通常是同态的。最近的研究表明，这种同态性是由于几个欧洲树蛙物种（如欧洲林蛙、中间林蛙和莫雷氏林蛙）中的偶尔 X-Y 重组（而非倒位）所致。然而，由于重组，性连锁基因座上的等位基因在种群水平上很少具有诊断性；性连锁的支持必须依赖于多位点关联，并结合偶尔的等位基因频率的性差异。在这里，我们使用直接证据，从具有已知家谱的后代的解剖学和组织学分析中得出，表明东方树蛙（Hyla orientalis）共享相同的一对性染色体，具有相同的雄性异型性和雄性完全缺乏 X-Y 重组的模式。通过偶尔的 X-Y 重组不断更新的祖先对性染色体的保守性，似乎是 Hyla 物种中广泛存在的模式。兄弟姐妹分析还发现了后代中基因型和表型性别之间的差异，与异常性腺发育有关，这表明性染色体上存在性拮抗基因的作用。
