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Spiracular fluttering decouples oxygen uptake and water loss: a stochastic PDE model of respiratory water loss in insects
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In hypoxia, air-breathing fish obtain O2from the air but continue to excrete CO2into the water. Consequently, it is believed that some O2obtained by air-breathing is lost at the gills in hypoxic water.Pangasionodon hypophthalmusis an air-breathing catfish with very large gills from the Mekong River basin where it is cultured in hypoxic ponds. To understand howP. hypophthalmuscan maintain high growth in hypoxia with the presumed O2loss, we quantified respiratory gas exchange in air and water. In severe hypoxia (PO2: ≈ 1.5 mmHg), it lost a mere 4.9% of its aerial O2uptake, while maintaining aquatic CO2excretion at 91% of the total. Further, even small elevations in water PO2rapidly reduced this minor loss. Charting the cardiovascular bauplan across the branchial basket showed four ventral aortas leaving the bulbus arteriosus, with the first and second gill arches draining into the dorsal aorta while the third and fourth gill arches drain into the coeliacomesenteric artery supplying the gut and the highly trabeculated respiratory swim-bladder. Substantial flow changes across these two arterial systems from normoxic to hypoxic water were not found. We conclude that the proposed branchial oxygen loss in air-breathing fish is likely only a minor inefficiency.more » « less
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Synopsis The air–water interface of the planet’s water bodies, such as ponds, lakes, and streams, presents an uncertain ecological niche with predatory threats from above and below. As Microvelia americana move across the water surface in small ponds, they face potential injury from attacks by birds, fish, and underwater invertebrates. Thus, our study investigates the effects of losing individual or pairs of tarsi on M. americana’s ability to walk on water. Removal of both hind tarsi causes M. americana to rock their bodies (yaw) while running across the water surface at $$\pm 19^{\circ }$$, compared to $$\pm 7^{\circ }$$ in nonablated specimens. This increase in yaw, resulting from the removal of hind tarsi, indicates that M. americana use their hind legs as “rudders” to regulate yaw, originating from the contralateral middle legs’ strokes on the water’s surface through an alternating tripod gait. Ablation of the ipsilateral middle and hind tarsi disrupts directionality, making M. americana turn in the direction of their intact limbs. This loss of directionality does not occur with the removal of contralateral middle and hind tarsi. However, M. americana lose their ability to use the alternating tripod gait to walk on water on the day of contralateral ablation. Remarkably, by the next day, M. americana adapt and regain the ability to walk on water using the alternating tripod gait. Our findings elucidate the specialized leg dynamics within the alternating tripod gait of M. americana, and their adaptability to tarsal loss. This research could guide the development and design strategies of small, adaptive, and resilient micro-robots that can adapt to controller malfunction or actuator damage for walking on water and terrestrial surfaces.more » « less
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1007/s00285-022-01740-4
