A locust in flight. Photo credit: Edward Snelling.
Most insects have pretty sluggish metabolisms until they jump into the air; but when they take off, these animals are virtually on fire. Boosting their metabolic rates by as much as 100 times, fliers have to ensure that they can keep the furnace that powers flight well supplied with oxygen. Roger Seymour from the University of Adelaide, Australia, explains that insect bodies are plumbed with air capillaries – trachea – that supply oxygen directly to every tissue and this system is matched to the tissues that they supply: the tracheal system of the locust flight muscles is 6 times larger than that of the leg muscles, in line with the flight muscle's high energy consumption. However, the flight muscle contains 20 times more mitochondria – which consume oxygen during ATP production – than the leg muscles; could the muscle consume even more oxygen and if so could the tracheal system meet the demand? Seymour and graduate student Edward Snelling wondered how well the flight muscle's oxygen delivery system was matched to its oxygen demands.
Reasoning that the insects would be very sensitive to the amount of oxygen in the air at low concentrations if their oxygen delivery system and oxygen consumption were matched, Seymour realised that he could measure the locusts’ sensitivity by creating a variety of different atmospheres –oxygen mixed in different ratios with either nitrogen, light helium or heavy sulphur hexafluoride – and recording the insects’ oxygen consumption while they flew in the gases. If the insects’ performance dropped off below a specific oxygen concentration, then their respiratory system and muscle would be well matched.
Seymour assigned the task of designing the atmospheres to Honours student Rebecca Duncker and worked with her and Edward Snelling to figure out how to attach insects to a tether during flight via a tiny magnet glued to the insect’s back. However, he recalls that the locusts weren't always happy to fly in the unfamiliar atmospheres. ‘The difference in resistance of their wings… apparently stopped them from flapping’, he says.
Finally, Duncker plotted the metabolic rate of the insects against the fraction of oxygen in the air and realised that the metabolic rate of the insects plummeted below ∼21% oxygen: the oxygen delivery system was perfectly matched to the flight muscle. ‘The flight motor of locust seems to be either on or off, and it has only one gear. No excess oxygen supply is required’, says Seymour, who is keen to find out whether species that carry cargo can turn up oxygen delivery to power flight in a way that unburdened locusts cannot.
Having developed the novel atmospheres, the trio realised that altering the main gas component would also change how fast oxygen diffuses into the tissue and this could allow them to test whether oxygen was delivered to the flight muscle by diffusion through the trachea or by the contraction of the flight muscles pumping air through. Duncker scoured the literature to find out how to combine oxygen, helium and sulphur hexafluoride to create one atmosphere that had a normal density where oxygen diffused fast and a second where oxygen diffused at the normal rate but the atmosphere was relatively dense in order to find out whether increasing the diffusion rate of oxygen in the flight muscle trachea permitted the insects to increase their metabolic rate. However, when she compared the metabolic rates of the locusts flying in the two atmospheres, they were essentially identical, confirming that oxygen is pumped into the flight muscle by the muscle's own contraction.
- © 2017. Published by The Company of Biologists Ltd
References
Article navigation
Related articles
Cited by...
More in this TOC section
Similar articles
Other journals from The Company of Biologists
Editorial – The changing of the guard
In his Editorial, Hans Hoppeler announces that he will be stepping down as Editor-in-Chief of JEB in July 2020. He reflects on the history of JEB, why he has enjoyed his tenure as JEB’s Editor-in-Chief and the recent developments in the publishing world.
Big Biology podcast
JEB is partnering with the Big Biology podcast and in this sponsored episode, JEB Editor Michael Dickinson talks to the Big Biology team about the aerodynamic mechanisms of insect flight, how insects control flight with their tiny 100k neuron brain and his recent JEB paper showing how fruit flies navigate using the sun and polarized light as a compass.
Editors’ choice – An appetite for invasion: digestive physiology, thermal performance and food intake in lionfish (Pterois spp.)
Invasive lionfish are a colossal problem in the Mediterranean Sea and western Atlantic Ocean. Now it turns out that they are successful invaders because they invest more energy in digestion than moving about.
Travelling Fellowship – Anti-ageing in the Greenland Shark
Find out how Pierre Delaroche’s Travelling Fellowship grant from the Journal of Experimental Biology took him to Greenland, where he gathered data to further understand the ageing process in the longest-living vertebrate known to science. Don’t miss the next application deadline for 2020 travel, coming up on 29 November. Where will your research take you?
Commentary – Yank: the time derivative of force is an important biomechanical variable in sensorimotor systems
The derivative of force with respect to time does not have a standard term in physics. In their new Commentary, David C. Lin and his colleagues propose that the term ‘yank’ should be used to denote the time derivative of force.
Runners waste energy every time their legs stop swinging, but now a team of scientists from the US and Canada have shown that a springy ankle tether can reduce runners’ energy costs by 6.4%, which is nearly the entire cost of swinging the limbs. Read the full research article here.
Journal of Experimental Biology is pleased to announce a new partnership with Publons! This allows reviewers to easily track and verify every review by choosing to add the review to their Publons profile when completing the review submission form. Publons also makes it simple for reviewers to showcase their peer review contributions in a format that can be included in job and funding applications (without breaking reviewer anonymity). Read the official announcement here!
preLights – Oxygenation properties of hemoglobin and the evolutionary origins of isoform multiplicity in an amphibious air-breathing fish, the blue-spotted mudskipper (Boleophthalmus pectinirostris)
Charlotte Nelson highlights work in mudskippers suggesting that a diversity in expressed hemoglobin isoforms is not required for the switch between aquatic and aerial respiration.