Department of Ecology and Evolution, University of Lausanne, CH 1015, Lausanne, Switzerland.
Mol Ecol. 2014 Jul;23(14):3409-18. doi: 10.1111/mec.12829. Epub 2014 Jun 28.
In sharp contrast with birds and mammals, sex-determination systems in ectothermic vertebrates are often highly dynamic and sometimes multifactorial. Both environmental and genetic effects have been documented in common frogs (Rana temporaria). One genetic linkage group, mapping to the largest pair of chromosomes and harbouring the candidate sex-determining gene Dmrt1, associates with sex in several populations throughout Europe, but association varies both within and among populations. Here, we show that sex association at this linkage group differs among populations along a 1500-km transect across Sweden. Genetic differentiation between sexes is strongest (FST = 0.152) in a northern-boreal population, where male-specific alleles and heterozygote excesses (FIS = -0.418 in males, +0.025 in females) testify to a male-heterogametic system and lack of X-Y recombination. In the southernmost population (nemoral climate), in contrast, sexes share the same alleles at the same frequencies (FST = 0.007 between sexes), suggesting unrestricted recombination. Other populations show intermediate levels of sex differentiation, with males falling in two categories: some cluster with females, while others display male-specific Y haplotypes. This polymorphism may result from differences between populations in the patterns of X-Y recombination, co-option of an alternative sex-chromosome pair, or a mixed sex-determination system where maleness is controlled either by genes or by environment depending on populations or families. We propose approaches to test among these alternative models, to disentangle the effects of climate and phylogeography on the latitudinal trend, and to sort out how this polymorphism relates to the 'sexual races' described in common frogs in the 1930s.
与鸟类和哺乳动物形成鲜明对比的是，变温脊椎动物的性别决定系统通常具有高度的动态性，有时是多因素的。环境和遗传效应都在普通青蛙（Rana temporaria）中得到了证实。一个遗传连锁群，映射到最大的一对染色体上，并包含候选性别决定基因 Dmrt1，与欧洲多个种群的性别相关，但这种关联在种群内和种群间都存在差异。在这里，我们表明，在跨越瑞典的 1500 公里长的切片上，这个连锁群的性别关联在不同种群之间存在差异。性别的遗传分化最强（FST 为 0.152）在北部北方种群中，雄性特异性等位基因和杂合子过剩（FIS 为-0.418 在雄性中，+0.025 在雌性中）证明了雄性异配性系统和缺乏 X-Y 重组。相比之下，在最南端的种群（森林气候）中，两性共享相同的等位基因，频率相同（两性之间的 FST 为 0.007），这表明没有限制重组。其他种群表现出中间水平的性别分化，雄性分为两类：一些与雌性聚类，而另一些则表现出雄性特异性 Y 单倍型。这种多态性可能是由于不同种群在 X-Y 重组模式、替代性染色体对的共选择或混合性别决定系统中的差异所致，在这种系统中，雄性是由基因或环境控制的，这取决于种群或家族。我们提出了一些方法来测试这些替代模型，以厘清气候和系统地理学对纬度趋势的影响，并理清这种多态性与 20 世纪 30 年代在普通青蛙中描述的“性种族”之间的关系。
