Deep-diving insect larvae are challenging a long-held idea about why there are no insects in the ocean, thanks to sturdy air sacs.
Daily dive to dodge death
In Lake Malawi in East Africa, billions of lake fly larvae (Chaoborus edulis), make an unusual commute: By day, they sink more than 200 metres into the lake's oxygen-starved "dead zone" to hide from predators. By night, they rise to safely feed – but not before passing through a horde of waiting fish.
UBC researchers Drs. Philip Matthews and Evan McKenzie deployed a sonar system at the bottom of the lake to map these daily dives.
Dissecting the larvae, the team found they had turned part of their respiratory system into two pairs of tiny air sacs that function like ballast tanks to control their buoyancy.
They also found that the air sac wall contains a material called resilin which expands or contracts when the larvae change the wall's pH. This mechanism allows the larvae to control the volume of their sacs and so, their own buoyancy.
Under pressure
The researchers placed larvae in tiny pressure chambers to find the maximum depths they could endure before their air-sacs imploded.
They proved remarkably tough, holding out to the equivalent of more than 400 metres deep, far beyond the larvae's daily dives.
Insects thrive on land and fresh water, but the open ocean is insect-free. One popular explanation is the insects' air-filled respiratory systems would collapse under the pressure of the depths. These larvae puncture that idea.
pH-powered engines
Resilin has been studied in other insects as a nearly perfect biological rubber in wear-and-tear-resistant wing hinges and tendons.
In the future, the research could add to work aimed at creating pH-powered resilin smart materials or artificial muscles activated on chemical command.
This project was partially funded by Natural Sciences and Engineering Research Council of Canada Discovery and Accelerator grants
