Source: The Conversation – Canada – By Sabrina Rondeau, Postdoctoral Researcher in Pollinator Ecology, L’Université d’Ottawa/University of Ottawa
In most bumblebee species, the queens spend their winters buried underground in a tiny cavity the size of a grape. For six to nine months, they enter a deep sleep-like state called diapause, waiting for spring.
As climate change brings more intense rainfall in many regions, these overwintering queens face increasing risks of unstable underground conditions, including flooding.
It’s a good thing, then, that these insects can survive days underwater without drowning. Remarkably, our new research reveals they achieve this through a process of continually breathing while submerged for up to eight days.
It began with a lab accident
We initially discovered that overwintering bumblebee queens can survive submersion due to an accident.
During an experiment at the University of Guelph, some of the tubes in which queens were overwintering in the lab refrigerator inadvertently filled with water.
Initially, we assumed the queens had died. But after emptying out the water, they began to move and soon recovered. This suggested that bumblebee queens might be able to survive submersion.
(Charles-Antoine Darveau)
So, we designed a follow-up experiment involving 143 common eastern bumblebee queens (Bombus impatiens).
This confirmed it was no fluke: the queens withstood complete submersion for up to a week.
This raised an intriguing question: how can this terrestrial insect pollinator survive underwater? Answering it required a different approach — we needed to study their physiology.
The heart of the colony
The queen is the heart of a bumblebee colony and its only chance of producing the next generation. While we often hear the buzz of workers visiting flowers during the summer, queens are rarely seen. They spend much of the season inside the nest, laying eggs that will become workers and, later in the summer, males and new queens.
When winter comes, most members of the colony die and only the newly produced queens survive. After mating, these new queens disperse and burrow underground, each settling into a tiny cavity where they enter diapause.
When spring finally returns, the queens that survived their long underground sleep emerge from their burrows and begin the important task of founding a new colony.
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Breathing underwater
To understand how these queens can survive submersion, we studied their breathing and metabolism in our lab at the University of Ottawa.
During diapause, queens are already in extreme energy-saving mode. The energy they need to stay alive (known as their metabolic rate) drops by more than 99 per cent. When submerged, energy needs drop even further. With such tiny oxygen demands, underwater breathing becomes possible.
But how did we determine whether queens are actually breathing underwater? One way is by measuring the gases exchanged with the surrounding water. We did this and the results were striking: queens continuously consumed oxygen and released carbon dioxide underwater throughout an eight-day period of submersion.
(Sabrina Rondeau)
Many aquatic insects use a simple trick to breathe underwater. A thin layer of air clings to their body, allowing them to use their normal air-breathing system — the tracheal system. Oxygen from the surrounding water slowly diffuses into this air layer. Bumblebee queens likely rely on the same mechanism.
Still, underwater respiration alone does not fully meet the queen’s energy needs. To bridge the gap, queens also produce some energy through anaerobic metabolism — a process that does not require oxygen. This pathway produces lactic acid, which we detected in queens during submersion.
These physiological tricks allow queens to survive underwater, but come at a cost. After resurfacing, queens spend several days recovering, using far more energy than they would have if they had never taken the plunge.
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An unexpected resilience
Bumblebee queens spend the winters alone, buried underground and relying on stored energy to survive until spring. Their ability to tolerate days of submersion — and even breathe underwater — reveals an unexpected resilience to one of the hazards of life below ground.
This matters because bumblebee colonies depend entirely on the survival of overwintering queens. If a queen dies during winter, the colony she would have founded the following spring will never exist.
This ability to survive submersion could play an important — and previously overlooked — role in the resilience of threatened bumblebee populations.
Even in terms of familiar and comparatively well-studied insects like bumblebees, there is still so much to learn about the surprising ways they cope with environmental challenges.
Sabrina Rondeau received funding from the Natural Sciences and Engineering Research Council of Canada, the Fonds de recherche du Québec—Nature et technologies and the Weston Family Foundation.
Charles-Antoine Darveau receives funding from the Natural Sciences and Engineering Research Council Discovery Grants program.
Nigel Raine receives funding from the Natural Sciences and Engineering Research Council, the Horizon Europe ProPollSoil project, the Canada Foundation for Innovation Innovation Fund, the Ontario Ministry of Agriculture, Food and Agribusiness, the Canadian Wildlife Federation and the Weston Family Foundation.
– ref. Queen bumblebees can breathe underwater — for days. We discovered how – https://theconversation.com/queen-bumblebees-can-breathe-underwater-for-days-we-discovered-how-278175