Giardini Jamie-Lee, Yan Norman D, Heyland Andreas
University of Guelph, Integrative Biology, 50 Stone Rd East, Guelph, ON, Canada N1G 2W1.
York University, Department of Biology, 4700 Keele Street, Toronto, ON, Canada M3J 1P3.
J Exp Biol. 2015 Jul;218(Pt 13):2005-14. doi: 10.1242/jeb.123513. Epub 2015 May 5.
Ambient calcium is declining in thousands of soft-water lake habitats in temperate regions as a consequence of unsustainable forestry practices, decreased atmospheric calcium deposition and acidic deposition. As their exoskeleton is heavily reinforced with calcium, freshwater crustaceans have a high specific calcium requirement relative to other aquatic organisms. Daphnia, in particular, is an ideal crustacean for investigating the consequences of calcium decline because it is an abundant and important member of freshwater zooplankton communities. Although it has been established that adult and juvenile Daphnia have different tolerances to low ambient calcium as a result of their different life stage-specific calcium requirements, the consequences of declining calcium on embryonic development have never been investigated. Here, we describe the distribution of calcium in embryonic stages of D. magna and introduce a novel and easy to use staging scheme. We tested whether calcium can be traced from mothers to their offspring. Finally, we assessed the fitness consequences of maternal provisioning in limiting calcium environments. We found that while embryos require calcium for their development and moulting, they do not equilibrate with environmental calcium levels. Instead, we were able to trace calcium from mothers to their offspring. Furthermore, our data strongly suggest that females are faced with an allocation trade-off between providing calcium to their offspring and using it for growth and moulting. Together, these data provide novel insights into the consequences of calcium decline for freshwater zooplankton.
由于不可持续的林业实践、大气钙沉降减少和酸性沉降，温带地区数千个软水湖泊栖息地的环境钙含量正在下降。由于淡水甲壳类动物的外骨骼大量含钙强化，相对于其他水生生物，它们对钙有较高的特定需求。特别是水蚤，是研究钙含量下降后果的理想甲壳类动物，因为它是淡水浮游动物群落中丰富且重要的成员。尽管已经确定成年和幼年水蚤由于其不同的特定生命阶段钙需求而对低环境钙有不同的耐受性，但钙含量下降对胚胎发育的影响从未被研究过。在这里，我们描述了大型溞胚胎阶段钙的分布，并引入了一种新颖且易于使用的分期方案。我们测试了钙是否可以从母体追溯到其后代。最后，我们评估了在钙受限环境中母体供应对适应性的影响。我们发现，虽然胚胎发育和蜕皮需要钙，但它们不会与环境钙水平达到平衡。相反，我们能够将钙从母体追溯到其后代。此外，我们的数据强烈表明，雌性在为后代提供钙与将其用于生长和蜕皮之间面临着分配权衡。这些数据共同为钙含量下降对淡水浮游动物的影响提供了新的见解。
