Rodrigues Nicolas, Vuille Yvan, Loman Jon, Perrin Nicolas
Department of Ecology and Evolution, University of Lausanne, Lausanne 1015, Switzerland
Department of Ecology and Evolution, University of Lausanne, Lausanne 1015, Switzerland.
Proc Biol Sci. 2015 May 7;282(1806):20142726. doi: 10.1098/rspb.2014.2726.
Sex-chromosome differentiation was recently shown to vary among common frog populations in Fennoscandia, suggesting a trend of increased differentiation with latitude. By rearing families from two contrasted populations (respectively, from northern and southern Sweden), we show this disparity to stem from differences in sex-determination mechanisms rather than in XY-recombination patterns. Offspring from the northern population display equal sex ratios at metamorphosis, with phenotypic sexes that correlate strongly with paternal LG2 haplotypes (the sex chromosome); accordingly, Y haplotypes are markedly differentiated, with male-specific alleles and depressed diversity testifying to their smaller effective population size. In the southern population, by contrast, a majority of juveniles present ovaries at metamorphosis; only later in development do sex ratios return to equilibrium. Even at these later stages, phenotypic sexes correlate only mildly with paternal LG2 haplotypes; accordingly, there are no recognizable Y haplotypes. These distinct patterns of gonadal development fit the concept of 'sex races' proposed in the 1930s, with our two populations assigned to the 'differentiated' and 'semi-differentiated' races, respectively. Our results support the suggestion that 'sex races' differ in the genetic versus epigenetic components of sex determination. Analysing populations from the 'undifferentiated race' with high-density genetic maps should help to further test this hypothesis.
最近研究表明，在斯堪的纳维亚半岛的普通青蛙种群中，性染色体分化存在差异，这表明存在随着纬度增加而分化加剧的趋势。通过饲养来自两个对比种群（分别来自瑞典北部和南部）的家系，我们发现这种差异源于性别决定机制的不同，而非XY重组模式的差异。来自北方种群的后代在变态时呈现出相等的性别比例，其表型性别与父本LG2单倍型（性染色体）密切相关；相应地，Y单倍型明显分化，具有雄性特异性等位基因且多样性降低，这证明其有效种群规模较小。相比之下，在南方种群中，大多数幼体在变态时具有卵巢；直到发育后期性别比例才恢复平衡。即使在这些后期阶段，表型性别与父本LG2单倍型的相关性也较弱；因此，没有可识别的Y单倍型。这些性腺发育的不同模式符合20世纪30年代提出的“性族”概念，我们的两个种群分别被归为“分化”和“半分化”性族。我们的结果支持了“性族”在性别决定的遗传与表观遗传成分方面存在差异的观点。利用高密度遗传图谱分析来自“未分化性族”的种群，应有助于进一步验证这一假设。
