Barata C, Baird D, Soares A
Departamento de Biologia, Universidade de Aveiro, Campus de Santiago, 3810-193, Aveiro, Portugal.
Institute of Aquaculture, University of Stirling, FK9 4LA, Stirling, UK.
Oecologia. 2001 Oct;129(2):220-227. doi: 10.1007/s004420100712. Epub 2001 Oct 1.
Life history responses of four Daphnia magna clones at two food levels were studied to assess the importance of maturation instar on the plasticity of fitness responses under simulated mortality regimes. Females of the clones studied could vary offspring size with consequent effects on their maturation time. Significant genetic variability in life history and fitness responses, measured as the intrinsic rate of population increase, within and across food levels was observed, but most of this variation could be attributed to maturation instar differences among clones within and across environments. In the laboratory, without extrinsic mortality, females maturing earlier always had higher fitness than those maturing later, indicating a clear fitness cost of delaying maturity. Nevertheless using a model, we showed that the observed maturation instar effects on life history responses can lead to differences in fitness under different size-selective predation regimes, such that females with delayed maturity have higher fitness under invertebrate predation while females maturing earlier have higher fitness under fish predation regimes. These results suggest that intraclonal variation in offspring size and hence in the number of maturation instars can be an adaptation to living in habitats subject to temporal fluctuations in fish and invertebrate predation pressure.
研究了四个大型溞克隆在两种食物水平下的生活史响应，以评估成熟龄期对模拟死亡模式下适合度响应可塑性的重要性。所研究克隆的雌性能够改变后代大小，从而对其成熟时间产生影响。观察到在食物水平内和食物水平间，以种群内在增长率衡量的生活史和适合度响应存在显著的遗传变异性，但这种变异大多可归因于不同环境中克隆间成熟龄期的差异。在实验室中，没有外在死亡率时，早熟的雌性总是比晚熟的雌性具有更高的适合度，这表明延迟成熟存在明显的适合度代价。然而，我们通过一个模型表明，观察到的成熟龄期对生活史响应的影响会导致在不同大小选择性捕食模式下适合度的差异，即成熟延迟的雌性在无脊椎动物捕食下具有更高的适合度，而早熟的雌性在鱼类捕食模式下具有更高的适合度。这些结果表明，后代大小进而成熟龄期数量的克隆内变异可能是对生活在鱼类和无脊椎动物捕食压力随时间波动的栖息地的一种适应。
