Department of Ecology and Evolution, Biophore, University of Lausanne, 1015 Lausanne, Switzerland.
Conserv Biol. 2013 Feb;27(1):229-34. doi: 10.1111/j.1523-1739.2012.01909.x. Epub 2012 Aug 14.
In some fishes, water chemistry or temperature affects sex determination or creates sex-specific selection pressures. The resulting population sex ratios are hard to predict from laboratory studies if the environmental triggers interact with other factors, whereas in field studies, singular observations of unusual sex ratios may be particularly prone to selective reporting. Long-term monitoring largely avoids these problems. We studied a population of grayling (Thymallus thymallus) in Lake Thun, Switzerland, that has been monitored since 1948. Samples of spawning fish have been caught about 3 times/week around spawning season, and water temperature at the spawning site has been continuously recorded since 1970. We used scale samples collected in different years to determine the average age of spawners (for life-stage specific analyses) and to identify the cohort born in 2003 (an extraordinarily warm year). Recent tissue samples were genotyped on microsatellite markers to test for genetic bottlenecks in the past and to estimate the genetically effective population size (N(e)). Operational sex ratios changed from approximately 65% males before 1993 to approximately 85% males from 1993 to 2011. Sex ratios correlated with the water temperatures the fish experienced in their first year of life. Sex ratios were best explained by the average temperature juvenile fish experienced during their first summer. Grayling abundance is declining, but we found no evidence of a strong genetic bottleneck that would explain the apparent lack of evolutionary response to the unequal sex ratio. Results of other studies show no evidence of endocrine disruptors in the study area. Our findings suggest temperature affects population sex ratio and thereby contributes to population decline.
在一些鱼类中，水化学或温度会影响性别决定或产生特定于性别的选择压力。如果环境触发因素与其他因素相互作用，那么从实验室研究中很难预测由此产生的种群性别比例，而在野外研究中，异常性别比例的单一观察结果可能特别容易受到选择性报告的影响。长期监测在很大程度上避免了这些问题。我们研究了瑞士图恩湖的一种灰鳟（Thymallus thymallus）种群，该种群自 1948 年以来一直受到监测。在产卵季节，大约每周捕捞 3 次产卵的鱼类样本，并且自 1970 年以来，产卵地点的水温一直在连续记录。我们使用不同年份收集的鳞片样本来确定产卵者的平均年龄（用于特定生命阶段的分析），并识别出生于 2003 年的群体（这是一个异常温暖的年份）。最近的组织样本通过微卫星标记进行了基因分型，以检测过去是否存在遗传瓶颈，并估计遗传有效种群大小（N(e)）。性别的实际比例从 1993 年之前的大约 65%雄性变为 1993 年至 2011 年的大约 85%雄性。性别比例与鱼类在生命的第一年中经历的水温相关。性别比例最好通过幼鱼在第一个夏季经历的平均温度来解释。灰鳟的数量正在减少，但我们没有发现强有力的遗传瓶颈的证据，这可以解释对不平等性别比例的明显缺乏进化反应。其他研究的结果表明，研究区域没有内分泌干扰物的证据。我们的研究结果表明，温度会影响种群性别比例，从而导致种群数量减少。
