Bennett Valerie A, Sformo Todd, Walters Kent, Tøien Øivind, Jeannet Kennan, Hochstrasser Ronald, Pan Qingfeng, Serianni Anthony S, Barnes Brian M, Duman John G
Department of Biological Sciences, University of Notre Dame, Notre Dame, IN 46556, USA.
J Exp Biol. 2005 Dec;208(Pt 23):4467-77. doi: 10.1242/jeb.01892.
The beetle Cucujus clavipes is found in North America over a broad latitudinal range from North Carolina (latitude approximately 35 degrees N) to near tree line in the Brooks Range in Alaska (latitude, approximately 67 degrees 30' N). The cold adaptations of populations from northern Indiana (approximately 41 degrees 45' N) and Alaska were compared and, as expected, the supercooling points (the temperatures at which they froze) of these freeze-avoiding insects were significantly lower in Alaska insects. Both populations produce glycerol, but the concentrations in Alaska larvae were much higher than in Indiana insects (approximately 2.2 and 0.5 mol l(-1), respectively). In addition, both populations produce antifreeze proteins. Interestingly, in the autumn both populations have the same approximate level of hemolymph thermal hysteresis, indicative of antifreeze protein activity, suggesting that they synthesize similar amounts of antifreeze protein. A major difference is that the Alaska larvae undergo extreme dehydration in winter wherein water content decreases from 63-65% body water (1.70-1.85 g H2O g(-1) dry mass) in summer to 28-40% body water (0.40-0.68 g H2O g(-1) dry mass) in winter. These 2.5-4.6-fold reductions in body water greatly increase the concentrations of antifreeze in the Alaska insects. Glycerol concentrations would increase to 7-10 mol l(-1) while thermal hysteresis increased to nearly 13 degrees C (the highest ever measured in any organism) in concentrated hemolymph. By contrast, Indiana larvae do not desiccate in winter. The Alaska population also undergoes a diapause while insects from Indiana do not. The result of these, and likely additional, adaptations is that while the mean winter supercooling points of Indiana larvae were approximately -23 degrees C, those of Alaska larvae were -35 to -42 degrees C, and at certain times Alaska C. clavipes did not freeze when cooled to -80 degrees C.
叩甲科昆虫Cucujus clavipes在北美洲分布广泛，其纬度范围从北卡罗来纳州（北纬约35度）到阿拉斯加布鲁克斯山脉接近林木线的地区（北纬约67度30分）。对来自印第安纳州北部（北纬约41度45分）和阿拉斯加的种群的耐寒适应性进行了比较，不出所料，这些避免结冰的昆虫的过冷却点（它们结冰时的温度）在阿拉斯加昆虫中显著更低。两个种群都会产生甘油，但阿拉斯加幼虫体内甘油的浓度远高于印第安纳州的昆虫（分别约为2.2和0.5摩尔/升）。此外，两个种群都会产生抗冻蛋白。有趣的是，在秋季，两个种群的血淋巴热滞效应水平大致相同，这表明抗冻蛋白具有活性，说明它们合成的抗冻蛋白量相似。一个主要差异是，阿拉斯加幼虫在冬季会经历极端脱水，其含水量从夏季时占体重63% - 65%的体水（每克干重含1.70 - 1.85克水）降至冬季时的28% - 40%体水（每克干重含0.40 - 0.68克水）。体水含量2.5至4.6倍的降低极大地提高了阿拉斯加昆虫体内抗冻剂的浓度。甘油浓度会增至7 - 10摩尔/升，而在浓缩的血淋巴中，热滞效应会增至近13摄氏度（这是在任何生物体中测量到的最高值）。相比之下，印第安纳州的幼虫在冬季不会脱水。阿拉斯加种群还会经历滞育，而印第安纳州的昆虫则不会。这些以及可能的其他适应性变化的结果是，印第安纳州幼虫冬季的平均过冷却点约为 - 23摄氏度，而阿拉斯加幼虫的过冷却点为 - 35至 - 42摄氏度，在某些时候，阿拉斯加的Cucujus clavipes冷却至 - 80摄氏度时也不会结冰。
