School of Biosciences, University of Birmingham, Edgbaston, Birmingham, UK.
J Insect Physiol. 2012 Aug;58(8):1104-11. doi: 10.1016/j.jinsphys.2012.05.009. Epub 2012 Jun 7.
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.
20 世纪 60 年代，Eretmoptera murphyi 摇蚊从南乔治亚亚南极地区（55°S 37°W）转移到了航海南极的 Signy 岛（60°S 45°W）的一个单一地点，而南乔治亚亚南极地区是 E. murphyi 的特有栖息地。自此之后，它的分布范围显著扩大，这表明它已经预先适应了更恶劣的南部环境。为了测试其预先适应水平的一个方面，研究了该物种的快速冷驯化（RCH）反应。当 E. murphyi 的幼虫（L1-L2 和 L3-L4）直接暴露于逐渐降低的温度 8 小时时，它们分别表现出 10-20%个体存活的鉴别温度（DTemp）为-11.5°C 和-12.5°C。两个幼虫群体的平均 SCP 均高于-7.5°C，这证实了之前的研究发现，该物种具有抗冻能力。在逐渐冷却（0.2°Cmin(-1))的情况下，两个幼虫群体的 DTemp 存活率显著更高。该反应很强，将最低致死温度（LLT）降低了多达 6.5°C，并在 DTemp 下至少 22 小时内保持了 80%以上的存活率。在生态相关的温度周期（+4°C 至-3°C）的冷却阶段也表现出了 RCH。从机制上讲，该反应不会影响冻结，因为在逐渐冷却后，没有发现过冷却点（SCP）的改变，并且在生物体处于冻结状态时，也不会诱导 RCH。这些结果在 E. murphyi 预先适应 Signy 岛条件及其在航海南极更南部地区的潜在殖民化方面进行了讨论。
