Dragonfly nymphs are aquatic and breathe water using a rectal gill. However, it has long been known that the nymphs of many species appear to possess the ability to breathe air, either during their final instar when they leave the water prior to metamorphosis, or during periods of aquatic hypoxia. The aerial gas exchange associated with these activities has not been quantified. This study used flow-through respirometry to measure the rate of aerial CO2 release (V̇CO2) from dragonfly nymphs as a proxy for their aerial gas exchange, both across development and in response to progressive aquatic hypoxia. It examined a total of four species from two families (Libellulidae and Aeshnidae). In both families, the late-final instar nymphs developed functional mesothoracic spiracles, allowing them to breathe air by positioning their head and thorax above the water's surface. While breathing air in this position, the nymphs could also ventilate their submerged rectal gill. Thus, during bimodal gas exchange in normoxic water, it was calculated that aeshnid nymphs expelled 39% of their respiratory CO2 into the air through their spiracles, while libellulid nymphs expelled 56% into the air. Decreasing the aquatic PO2 to 2.5 kPa and then below 1 kPa increased the proportion of respiratory CO2 expelled into the air from 69% to 100%, respectively. Thus, bimodally breathing late-final nymphs can vary how they partition gas exchange between their spiracles and their gill depending on aquatic PO2. Aeshnid nymphs of all developmental stages were also found to use their rectal gill as an air-breathing organ; pre-final nymphs performing 'surface skimming' while late final nymphs aspirated air bubbles directly into their gill's branchial basket. Mass-specific rates of aerial V̇CO2 also increased as the nymphs approached metamorphosis. These findings indicate that aeshnid nymphs are capable of accessing aerial O2 across development using their rectal gill as an air breathing organ, while the aquatic nymphs of both aeshnid and libellulid dragonflies undergo a progressive shift towards using the atmosphere for respiration as they approach metamorphosis.

中文翻译：

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跨越发展的蜻蜓若虫的双峰气体交换策略。

蜻蜓若虫是水生生物，可通过直肠g呼吸水。然而，早就知道，许多物种的若虫似乎具有呼吸空气的能力，无论是在变态前离开水面的最后一生，还是在水生低氧时期。与这些活动有关的空中气体交换尚未量化。这项研究使用流通式呼吸测定法来测量蜻蜓若虫在整个发育过程中以及对进行性水生低氧的反应中向空中释放的二氧化碳的速率（V̇CO2），作为其空中气体交换的代表。它检查了来自两个科（Libellulidae和Aeshnidae）的总共四个物种。在这两个家庭中，晚期的若虫若虫都发育了功能性的中胸廓气门，将他们的头部和胸部放置在水面之上，从而呼吸空气。如果以这种姿势呼吸空气，若虫也可以为其水下直肠g通风。因此，在含氧量高的水中进行双峰气体交换时，据计算，若虫类若虫将其呼吸中的CO2的39％通过其气孔排放到空气中，而如虫类若虫则将其56％的呼吸CO2排放到空气中。将水生PO2降低至2.5 kPa，然后降至1 kPa以下，分别将排放到空气中的呼吸道CO2的比例从69％增加到100％。因此，双峰呼吸的最后若虫可以根据水生PO2改变气孔和partition之间的气体交换分配方式。还发现所有发育阶段的Aeshnid若虫都使用其直肠g作为呼吸器官。前若虫进行“表面撇除”，而最后若虫则将气泡直接吸入their的小basket中。若虫接近变态，空中V̇CO2的质量比率也增加。这些发现表明，以其g作为呼吸器官，网纹若虫能够通过发育途径获取空气中的O2，而网纹蜻蜓和带鳞蜻蜓的水生若虫在接近变态时逐渐向利用大气呼吸的方向转变。