Picture an Antarctic animal and most people think of penguins, but there is a flightless midge, the only known insect native to Antarctica, that somehow survives the extreme climate. How the Antarctic midge (Belgica antarctica) copes with freezing temperatures could hold clues for humans about subjects like cryopreservation, but there remain many mysteries about the tiny insect.
One mystery appears to have been solved by an Osaka Metropolitan University-led international research team. Graduate School of Science Professor Shin G. Goto and Dr. Mizuki Yoshida, a graduate student at the time of the research who is now a postdoc at Ohio State University, found that the midge deals with the seasons during its two-year life cycle by undergoing quiescence in its first year and obligate diapause in its second.
Quiescence is a form of dormancy in immediate response to adverse conditions, and when conditions improve, the organism becomes active again. Obligate diapause is a dormant period naturally induced at a fixed time in an organism's life cycle, a rare form seen in insects in temperate regions.
"We were able to establish a method for rearing the Antarctic midge over a period of six years to find out some of their environmental adaptation mechanisms," Dr. Yoshida explained.
The team found that Antarctic midge larvae usually grow to their second instar by the first winter and undergo quiescence so that they can quickly resume development at any moment when it suddenly becomes warmer. As the second winter approaches, the larvae reach the final fourth instar, but they do not pupate. Instead, they enter obligate diapause so that they all emerge as adults when summer arrives. As adults, they have only a few days of life and need to find a mate, so this timing mechanism is key to their survival.
"We determined that for the Antarctic midge obligate diapause ends with the onset of low temperatures in winter so that the larvae all pupate at the same time and emerge as adults at the same time," Professor Goto stated. "Although seasonal adaptation strategies involving overwintering multiple times using both quiescence and obligate diapause have not been reported in other organisms, we believe that insects inhabiting harsh environments such as the Arctic and high altitudes might be employing similar strategies."
