Limnology Laboratory, Department of Biology, Middle East Technical University, Ankara, Turkey.
Ecotoxicology. 2012 Mar;21(2):601-14. doi: 10.1007/s10646-011-0820-0. Epub 2011 Nov 20.
Global warming is already causing salinization of freshwater ecosystems located in semi-arid regions, including Turkey. Daphnids, which are important grazers on phytoplankton and a major food source for fish and invertebrates, are sensitive to not only changes in salinity levels, but also presence of predators. In this study, the interactive effect of salinity toxicity (abiotic factor) with predation pressure mimicked by the fish-exuded kairomone (biotic factor) and the effect of salt acclimation on daphnids were investigated. Impacts of these stressors on daphnid survival, life history and molecular profile were observed. The presence of the kairomone antagonistically alters the effect of salinity, as observed from the 24- and 48-h LC(50) values and survival results. Molecular findings provided solid evidence to this antagonism at even lower salt concentrations, for which antagonism was not evident with organismal data. Fish predation counterbalances the negative effect of salinity in terms of reserve energy density. Therefore, it is important to investigate multiple stressor effects in ecotoxicological bioassays complemented with molecular techniques. The single effect of increasing salinity resulted in increased mortality, decreased fecundity, and slower somatic growth in Daphnia, despite their acclimation to salinity. This insignificance of acclimation indicates that Daphnia do not have any physiological mechanisms to buffer the adverse effects of salinity, making it a very crucial factor. Salinity-induced reduction in population growth rate of freshwater keystone species Daphnia-despite acclimation-indicates that global warming-induced salinity may cascade through the food web and lead to dramatic environmental consequences in the structure of lake ecosystems.
全球变暖已经导致包括土耳其在内的半干旱地区淡水生态系统发生盐化。水蚤是浮游植物的重要食草动物，也是鱼类和无脊椎动物的主要食物来源，它们不仅对盐度变化敏感，而且对捕食者的存在也很敏感。在这项研究中，研究了盐度毒性（非生物因素）与鱼类分泌的信息素（生物因素）模拟的捕食压力的相互作用，以及盐度驯化对水蚤的影响。观察了这些胁迫因子对水蚤存活、生活史和分子特征的影响。信息素的存在拮抗了盐度的作用，这可以从 24 小时和 48 小时的 LC(50)值和存活结果中看出。分子研究结果甚至在更低的盐浓度下也为这种拮抗作用提供了确凿的证据，而在这些盐浓度下，用生物体数据则无法观察到拮抗作用。鱼类捕食在储备能量密度方面抵消了盐度的负面影响。因此，在生态毒理学生物测定中，结合分子技术，研究多种胁迫因子的综合影响非常重要。尽管水蚤已经适应了盐度，但盐度的单一影响会导致死亡率增加、繁殖力下降和身体生长速度减慢。这种驯化的不显著表明，水蚤没有任何生理机制来缓冲盐度的不利影响，这是一个非常关键的因素。尽管水蚤已经适应了盐度，但盐度导致淡水关键物种水蚤的种群增长率降低，这表明全球变暖引起的盐度可能通过食物网级联，并导致湖泊生态系统结构发生巨大的环境后果。
