Pre-adapted to the maritime Antarctic?--rapid cold hardening of the midge, Eretmoptera murphyi.
During the 1960s, the midge, Eretmoptera murphyi, was transferred from sub-Antarctic South Georgia (55°S 37°W) where it is endemic to a single location on maritime Antarctic Signy Island (60°S 45°W). Its distribution has since expanded considerably, suggesting that it is pre-adapted to the more severe conditions further south. To test one aspect of the level of its pre-adaptation, the rapid cold hardening (RCH) response in this species was investigated. When juvenile (L1-L2) and mature (L3-L4) larvae of E. murphyi were directly exposed to progressively lower temperatures for 8h, they exhibited Discriminating Temperatures (DTemp, temperature at which there is 10-20% survival of exposed individuals) of -11.5 and -12.5°C, respectively. The mean SCP was above -7.5°C in both larval groups, confirming the finding of previous studies that this species is freeze-tolerant. Following gradual cooling (0.2°Cmin(-1)), survival was significantly greater at the DTemp in both larval groups. The response was strong, lowering the lower lethal temperature (LLT) by up to 6.5°C and maintaining survival above 80% for at least 22h at the DTemp. RCH was also exhibited during the cooling phase of an ecologically relevant thermoperiodic cycle (+4°C to -3°C). Mechanistically, the response did not affect freezing, with no alteration in the supercooling point (SCP) found following gradual cooling, and was not induced while the organism was in a frozen state. These results are discussed in light of E. murphyi's pre-adaptation to conditions on Signy Island and its potential to colonize regions further south in the maritime Antarctic.
School of Biosciences, University of Birmingham, Edgbaston, Birmingham, UK.
M J
MJ
Everatt
M R
MR
Worland
J S
JS
Bale
P
P
Convey
S A L
SA
Hayward
D000222:Adaptation, Physiological; D025041:Animal Migration; D000818:Animals; D000864:Antarctic Regions; D004175:Diptera / Q000254:growth & development / Q000502:physiology*; D005615:Freezing; D007814:Larva / Q000254:growth & development / Q000502:physiology