From water-breathing nymphs to air-breathing adults: Insects as a model system to investigate the physiological challenges associated with the transition of life from water to land

这个探索计划将采用一种新的方法，利用水生昆虫来研究从呼吸水到呼吸空气的转变过程中的生理挑战。水生昆虫支持有价值的淡水生态系统和渔业，但对水质变化高度敏感，因此了解它们的生理对于成功的环境管理至关重要。我们目前对在水和空气之间移动相关的呼吸挑战的理解来自于对水生动物，特别是脊椎动物如何适应陆地上的形态和生理功能的研究。从这个角度来看，呼吸水是祖先的状态，呼吸空气是一种衍生状态。然而，昆虫却反过来完成了这一壮举，调整了它们在陆地上呼吸空气的生理学，以适应在水中的活动。虽然所有的成虫都是呼吸空气的，但9个昆虫目的代表已经进化为发育中的两栖昆虫，在其生命周期的幼体部分作为水生若虫或拥有鳃和呼吸水的幼虫度过。这些昆虫类群为研究与水生呼吸相关的适应进化提供了一个难得的机会，并确定环境限制是否导致有鳃的昆虫汇聚到与其他水生动物类似的呼吸生理学上，或者它们陆地祖先的系统发育限制是否导致了类似于呼吸空气的动物的呼吸生理学。昆虫回到水中的生理后果尚不清楚，但有诱人的证据表明，呼吸水的若虫体内二氧化碳水平较高，通常与呼吸空气有关，这一观察结果无法用当前教科书上的教条来解释。此外，我们对使这些昆虫在变态过程中迅速从用鳃呼吸转变为使用充满空气的呼吸系统的机制和生理变化一无所知。我的研究项目旨在识别并比较呼吸水的幼虫和呼吸空气的成虫使用的呼吸和酸碱策略，并探索它们从水到陆地快速过渡过程中发生的生理变化。我将使用一系列技术，包括呼吸测量、形态测量和组织学，来揭示水生和陆地生命阶段调节其内部氧气和二氧化碳水平以及酸碱平衡所使用的不同策略。因此，这项研究计划解决了我们对昆虫生理学理解的一个根本差距，并提供了对从水到陆地过渡过程中潜在的呼吸适应进化的洞察。

This Discovery Program will take the novel approach of using aquatic insects to examine the physiological challenges associated with the transition from breathing water to breathing air. Aquatic insects support valuable freshwater ecosystems and fisheries, but are highly susceptible to changes in water quality, so understanding their physiology is of crucial importance for successful environmental management. Our current understanding of the respiratory challenges associated with moving between water and air comes from studying how aquatic animals, particularly vertebrates, have adapted their morphology and physiology to function on land. From this perspective, water-breathing is the ancestral condition and air-breathing is a derived state. The insects, however, have performed this feat in reverse, adapting their terrestrial air-breathing physiology to function in water. Although all adult insects are air-breathers, representatives of nine insect orders have evolved to be developmentally amphibious, spending the juvenile proportion of their life cycle as aquatic nymphs or larvae that possess gills and breathe water. These insect groups provide an exceptional opportunity to examine the evolution of adaptations associated with aquatic respiration, and to determine whether environmental constraints have caused gill-bearing insects to converge on a respiratory physiology comparable to other aquatic animals, or whether the phylogenetic constraints of their terrestrial ancestry have resulted in a respiratory physiology similar to air-breathing animals. The physiological consequences of the insects' return to water are not well understood, but there is tantalizing evidence that water-breathing nymphs possess elevated internal CO2 levels commonly associated with breathing air, an observation that cannot be explained by current textbook dogma. Furthermore, we know nothing of the mechanisms and physiological shifts that enable these insects, during metamorphosis, to change rapidly from breathing with gills to using an air-filled respiratory system. My research program aims to identify and compare the respiratory and acid-base strategies used by water-breathing juvenile insects with those of the air-breathing adults, and to explore the physiological changes that occur during their rapid transition from water to land. I will use a range of techniques, including respirometry, morphometry and histology, to reveal the different strategies used by the aquatic and terrestrial life stages to regulate their internal oxygen and carbon dioxide levels, and their acid-base balance. Thus, this research program addresses a fundamental gap in our understanding of insect physiology and provides insight into the evolution of respiratory adaptations underlying the transition from water to land.