For tens of millions of years, the wingless gnat Antarctic Belgium has perfected the art of freezing itself to weather Antarctica’s darkest and coldest winter months, carving out an exclusive niche for itself as the continent’s only native insect.
As climate change drives up polar temperatures, this set of hard-earned survival skills could ironically harm its very existence, potentially driving it to the brink of extinction.
Laboratory experiments by a team of researchers from the United States, United Kingdom and South Africa have shown that warmer winters in the frozen south have a significant impact on the movements and energy reserves of the insect, jeopardizing his chances of seeing another summer.
Usually smaller than a centimeter from tip to tail, the tiny arthropod also occupies the unlikely position of being the largest animal on earth to never set foot in the ocean. Its entire life cycle – spent mostly in one of four larval states – takes place amid moist beds of moss and algae, munching on decaying greenery and trash.
Even these humble havens freeze over in harsh Antarctic winters, trapping precious moisture and threatening to turn the tiny creatures into popsicles. So to resist the cold, the midge has developed a clever strategy to avoid death and bide its time.
To guard against the trauma caused by the ice crystals piercing its tissues, the gnat slowly dries out. In the right conditionsindividuals have a good chance of surviving the summer, even after losing up to three quarters of its moisture.
Much of this good luck depends on moisture and whether it rehydrates using water vapor from the air or absorbs it directly from liquid water. Even small changes in environmental conditions could make a big difference in survival rates.
In the Antarctic Peninsula – a region relatively rich in biodiversity – microclimates like those occupied by the midge tend to hover between -5 and 0 degrees Celsius (23 and 32 Fahrenheit). Protected by layers of snow and ice, temperatures can drop in the atmosphere above, with little effect on the midge’s mossy garden.
With temperatures steadily rising by up to half a degree per decade on the peninsula, these relatively sheltered conditions could change. Higher temperatures could mean more precipitation, which means more snow, creating thicker insulation and less risk of winter frost.
To see exactly what effect it would have on B. Antarcticathe researchers collected midge larvae near a station on Anvers Island, at the tip of the Antarctic Peninsula.
These specimens were then returned to a laboratory in the United States where they spent six months living in subtly different winter conditions, ranging from cold -5 degrees Celsius to mild -1 degrees. Different types of substrates, such as moss and algae, were also tested.
Upon thawing in ice water, survivors were examined for signs of movement, tissue damage, and energy stores of carbohydrates, fats, and proteins.
This slight difference in temperature had a profound effect on the midge’s recovery. Under typical conditions, about half of the insects survived. Warmed by only a few degrees, barely a third survived. Energy stores also varied significantly, with more fat and protein stores retained in cold conditions than in warmer conditions.
“These results correspond to locomotor activity levels, where larvae in the warm winter diet were slowest, potentially due to energy loss,” the researchers said. note in their report.
“With a limited time before pupation after winter, and in adulthood B. Antarctica lack functional mouthparts, depletion of energy reserves during the later larval stages would likely have irreversible consequences on the energy available for reproduction.
It’s hard to say exactly what kind of long-term impact this would have if temperatures continue to rise. Depending on the stresses posed by climate change, this could be a minor inconvenience or a blow that wipes out entire populations.
There is a possible silver lining though: warmer winters could also be shorter, giving the gnat more time to collect larger stores during the summer months.
It remains to be seen whether this behavioral control compensates for the negative impact of a warming environment.
With record-breaking heat waves crushing the poles, the only insect to call Antarctica home could become yet another victim of our rapidly changing climate.
This research was published in Functional ecology.