Department of Ecology and Evolution, Biophore, University of Lausanne, CH-1015 Lausanne, Switzerland.
Mol Ecol. 2010 May;19(9):1760-2. doi: 10.1111/j.1365-294X.2010.04608.x.
Sex determination can be purely genetic (as in mammals and birds), purely environmental (as in many reptiles), or genetic but reversible by environmental factors during a sensitive period in life, as in many fish and amphibians (Wallace et al. 1999; Baroiller et al. 2009a; Stelkens & Wedekind 2010). Such environmental sex reversal (ESR) can be induced, for example, by temperature changes or by exposure to hormone-active substances. ESR has long been recognized as a means to produce more profitable single-sex cultures in fish farms (Cnaani & Levavi-Sivan 2009), but we know very little about its prevalence in the wild. Obviously, induced feminization or masculinization may immediately distort population sex ratios, and distorted sex ratios are indeed reported from some amphibian and fish populations (Olsen et al. 2006; Alho et al. 2008; Brykov et al. 2008). However, sex ratios can also be skewed by, for example, segregation distorters or sex-specific mortality. Demonstrating ESR in the wild therefore requires the identification of sex-linked genetic markers (in the absence of heteromorphic sex chromosomes) followed by comparison of genotypes and phenotypes, or experimental crosses with individuals who seem sex reversed, followed by sexing of offspring after rearing under non-ESR conditions and at low mortality. In this issue, Alho et al. (2010) investigate the role of ESR in the common frog (Rana temporaria) and a population that has a distorted adult sex ratio. They developed new sex-linked microsatellite markers and tested wild-caught male and female adults for potential mismatches between phenotype and genotype. They found a significant proportion of phenotypic males with a female genotype. This suggests environmental masculinization, here with a prevalence of 9%. The authors then tested whether XX males naturally reproduce with XX females. They collected egg clutches and found that some had indeed a primary sex ratio of 100% daughters. Other clutches seemed to result from multi-male fertilizations of which at least one male had the female genotype. These results suggest that sex-reversed individuals affect the sex ratio in the following generation. But how relevant is ESR if its prevalence is rather low, and what are the implications of successful reproduction of sex-reversed individuals in the wild?
性别决定可以是纯粹的遗传因素（如哺乳动物和鸟类），也可以是纯粹的环境因素（如许多爬行动物），或者是遗传因素，但在生命的敏感时期可以被环境因素逆转，如许多鱼类和两栖动物（Wallace 等人，1999 年；Baroiller 等人，2009a 年；Stelkens 和 Wedekind，2010 年）。这种环境性别逆转（ESR）可以通过温度变化或暴露于激素活性物质来诱导。ESR 长期以来一直被认为是在鱼类养殖场生产更有利可图的单性文化的一种手段（Cnaani 和 Levavi-Sivan，2009 年），但我们对其在野外的流行程度知之甚少。显然，诱导的雌性化或雄性化可能会立即扭曲种群的性别比例，并且一些两栖动物和鱼类种群确实报告了扭曲的性别比例（Olsen 等人，2006 年；Alho 等人，2008 年；Brykov 等人，2008 年）。然而，性别比例也可能受到例如分离干扰因子或性别特异性死亡率的影响。因此，在野外证明 ESR 需要鉴定性连锁遗传标记（在没有异型性染色体的情况下），然后比较基因型和表型，或与似乎性反转的个体进行实验杂交，然后在非 ESR 条件下饲养后代并在低死亡率下进行性别鉴定。在本期杂志中，Alho 等人（2010 年）研究了环境性别逆转（ESR）在普通青蛙（Rana temporaria）和一个性别比例扭曲的种群中的作用。他们开发了新的性连锁微卫星标记，并测试了野外捕获的雄性和雌性成年个体，以确定表型和基因型之间是否存在潜在的不匹配。他们发现相当一部分表型雄性具有雌性基因型。这表明存在环境雄性化，其流行率为 9%。作者随后测试了 XX 雄性是否自然与 XX 雌性繁殖。他们收集了卵群，发现其中一些确实具有 100%的女儿的原始性别比例。其他卵群似乎是由至少一名雄性具有雌性基因型的多雄受精产生的。这些结果表明，性反转个体影响下一代的性别比例。但是，如果其流行率相当低，并且性反转个体在野外成功繁殖的影响是什么？
