Eretmoptera murphyi: pre-adapted to survive a colder climate
2010
WORLAND, MICHAEL ROGER
During the late 1960s, larvae of the flightless midge Eretmoptera murphyi Schaeffer were accidentally transferred from the sub-Antarctic island of South Georgia to Signy Island in the maritime Antarctic. Higher insects are rare in the Antarctic and the introduction and establishment of a new species is an unusual event. The fly has overcome the two major barriers to colonization of the Antarctic by new species: the geographical isolation of the region and its severe climate. Larvae of the flightless midge overwinter in the surface layers of soil on Signy Island where the temperature may fall to below -10 °C, compared with as little as -1.5 °C on South Georgia. This suggests the possession of a level of pre-adaption to colder conditions. Summer-collected larvae have a supercooling point (SCP or whole body freezing point) of approximately -5.0 °C but survive experimental exposure to -13 °C, giving them a level of freeze tolerance. After acclimation at -4 °C for 4 days, the SCP changes little but the temperature at which 50% of the population would die decreases to lower than -19 °C. Larvae are also resistant to dehydration. Under experimental conditions of 88% relative humidity at 5 °C, larvae lose water linearly (0.42% h⁻¹) over the first 30 h but resist further water loss once their water content decreases to approximately 1.4 g g⁻¹ dry weight. All larvae survive these conditions for the duration of the experiment (55 h). Eretmoptera murphyi is well adapted to survive on Signy Island, and these studies suggest that it has the ability to survive at more extreme locations at higher latitudes if it were to be inadvertently transferred to a suitable habitat.
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