The University of Montana, Flathead Lake Biological Station, 32125 Bio Station Lane, Polson, Montana, 59801, USA.
Department of Biological Sciences, The University of Montana, Missoula, Montana, 59812, USA.
Ecology. 2020 Oct;101(10):e03127. doi: 10.1002/ecy.3127. Epub 2020 Aug 26.
Alluvial aquifers are key components of river floodplains and biodiversity worldwide, but they contain extreme environmental conditions and have limited sources of carbon for sustaining food webs. Despite this, they support abundant populations of aquifer stoneflies that have large proportions of their biomass carbon derived from methane. Methane is typically produced in freshwater ecosystems in anoxic conditions, while stoneflies (Order: Plecoptera) are thought to require highly oxygenated water. The potential importance of methane-derived food resources raises the possibility that stonefly consumers have evolved anoxia-resistant behaviors and physiologies. Here we tested the anoxic and hypoxic responses of 2,445 stonefly individuals in three aquifer species and nine benthic species. We conducted experimental trials in which we reduced oxygen levels, documented locomotor activity, and measured survival rates. Compared to surface-dwelling benthic relatives, stoneflies from the alluvial aquifer on the Flathead River (Montana) performed better in hypoxic and anoxic conditions. Aquifer species sustained the ability to walk after 4-76 h of anoxia vs. 1 h for benthic species and survived on average three times longer than their benthic counterparts. Aquifer stoneflies also sustained aerobic respiration down to much lower levels of ambient oxygen. We show that aquifer taxa have gene sequences for hemocyanin, an oxygen transport respiratory protein, representing a possible mechanism for surviving low oxygen. This remarkable ability to perform well in low-oxygen conditions is unique within the entire order of stoneflies (Plecoptera) and uncommon in other freshwater invertebrates. These results show that aquifer stoneflies can exploit rich carbon resources available in anoxic zones, which may explain their extraordinarily high abundance in gravel-bed floodplain aquifers. These stoneflies are part of a novel food web contributing biodiversity to river floodplains.
冲积含水层是世界范围内河流泛滥平原和生物多样性的关键组成部分，但它们包含极端的环境条件，并且维持食物网的碳源有限。尽管如此，它们还是支持着丰富的含水层石蝇种群，这些石蝇的生物量碳有很大一部分来自甲烷。甲烷通常在缺氧条件下的淡水生态系统中产生，而石蝇（目：蜉蝣目）被认为需要高度含氧的水。甲烷衍生食物资源的潜在重要性提出了这样一种可能性，即石蝇消费者已经进化出了抗缺氧的行为和生理特性。在这里，我们测试了三种含水层物种和九种底栖物种的 2445 只石蝇个体对缺氧和低氧的反应。我们进行了实验试验，降低了氧气水平，记录了运动活性，并测量了存活率。与地表栖息的底栖亲缘物种相比，来自蒙大拿州弗拉特黑德河冲积含水层的石蝇在低氧和缺氧条件下表现更好。与底栖物种相比，含水层物种在缺氧条件下能够行走的时间可持续 4-76 小时，而平均存活时间是底栖物种的三倍。含水层石蝇也能维持有氧呼吸，直到环境氧气水平低得多。我们表明，含水层类群具有血蓝蛋白的基因序列，血蓝蛋白是一种氧气运输呼吸蛋白，这代表了一种在低氧环境中生存的可能机制。在整个蜉蝣目（Plecoptera）中，这种在低氧条件下表现良好的非凡能力是独一无二的，在其他淡水无脊椎动物中也很少见。这些结果表明，含水层石蝇可以利用缺氧区丰富的碳资源，这可能解释了它们在砾石床泛滥平原含水层中异常高的丰度。这些石蝇是为河流泛滥平原贡献生物多样性的新型食物网的一部分。
