Data from: Geographic variation in sex-chromosome differentiation in the common frog (Rana temporaria)

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 harboring 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 among 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.

与鸟类和哺乳类形成鲜明对照，变温脊椎动物（ectothermic vertebrates）的性别决定系统往往具有高度动态性，部分甚至呈现多因子调控特征。学界已在普通蛙（Rana temporaria）中记录到环境与遗传双重调控效应。一个定位于最大染色体对、携带有候选性别决定基因Dmrt1的遗传连锁群，在欧洲多个种群中均与性别相关联，但这种关联在种群内部及种群间均存在显著差异。本研究显示，在横跨瑞典1500公里的样带中，不同种群的该连锁群性别关联模式存在显著分化。在北部寒带种群中，雌雄个体间的遗传分化最为显著（群体分化指数FST=0.152）；该种群存在雄性特异性等位基因，且雄性个体呈现杂合子过剩现象（雄性近交系数FIS=-0.418，雌性FIS=+0.025），这表明其为雄异配性别系统且不存在X-Y重组。与之形成对照的最南部种群（温带落叶林气候）中，雌雄个体的等位基因频率完全一致（雌雄间FST=0.007），提示该种群存在不受限制的X-Y重组。其余种群则表现出中等程度的性别分化，雄性个体可分为两类：一类与雌性个体聚类为同一组，另一类则携带雄性特异性Y单倍型。这种多态性可能源于三种情形：种群间X-Y重组模式的差异、替代性性染色体对的共选择，或是混合性别决定系统——在该系统中，雄性发育的调控因素因种群或家系不同，可分别由遗传因子或环境因子决定。本研究提出了可用于验证上述备选模型的研究方案，以厘清气候与系统地理学（phylogeography）因子对纬度梯度趋势的影响，并阐明该多态性与1930年代在普通蛙中记录的‘性别宗’之间的关联。