Abstract
During the 1960s, the midge, Eretmoptera murphyi, was transferred from sub-Antarctic South Georgia (55oS 37oW) where it is endemic to a single location on maritime Antarctic Signy Island (60oS 45oW). 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.
Highlights
Over the last 200 years, human presence in the Antarctic has risen as a result of seal and whale hunting, scientific research and, more recently, tourism (Tin et al, 2009; Chwedorzewska, 2009)
We investigated the strength of the rapid cold hardening (RCH) response in E. murphyi and its relevance in the context of the maritime Antarctic climate, and examined whether RCH has any effect on the whole body freezing temperature, commonly known as the supercooling point (SCP)
Eretmoptera murphyi is only the second freeze-tolerant insect found to possess RCH, the other being another midge from the Antarctic, B. antarctica (Lee et al, 2006a,b)
Summary
Over the last 200 years, human presence in the Antarctic has risen as a result of seal and whale hunting, scientific research and, more recently, tourism (Tin et al, 2009; Chwedorzewska, 2009). Humans, via their cargo, vehicles and themselves, are a carrier of organisms (Hughes et al, 2005, 2010). In the maritime and continental Antarctic, instances of establishment of alien (or introduced) species remain limited (Hughes and Convey, 2012), best explained by the severity and isolation of their habitats eclipsing the alleviation of recent warming. If an organism is to colonize, establish and spread in the maritime or
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