Penttinen Olli-Pekka, Holopainen Ismo J
Department of Biology, University of Joensuu, P.O.BOX 111, FIN-80101, Joensuu, Finland.
Oecologia. 1995 Sep;103(4):419-424. doi: 10.1007/BF00328679.
The rate of metabolism of laboratory reared Chironomus riparius was monitored by direct calorimetry over the entire life cycle from egg to adult stage. The metabolic response of the fourth instar larva to decreasing oxygen concentrations and anoxia was also measured. Normoxic measurements were carried out at 20°C and the hypoxic-anoxic experiments at 10°C. In larvae with body sizes ranging from 0.0028 to 0.645 mg ash-free dry mass (afdm), the rate of heat dissipation was related to body mass by a power function, with a mass exponent of 0.71±0.02 corresponding to an exponent of -0.29 for the relationship between mass-specific metabolic rate and body mass. However, the allometric equations applicable to larvae would not predict the metabolic rates of eggs, pupae and adults. Single egg batches used in the experiments consisted of 354±90 eggs, the individual egg with a mass of 0.99±0.01 μg (mean±SD). The mass-specific rate of heat dissipation of the egg (13.7±1.8 μ W mg afdm) was considerably lower than that of the first and second instar larvae (44-53 μ W mg) but equal to that of fourth instar larvae (13.1±3.9 μ W mg). Heat dissipation by a pupa shortly before adult emergence was high (14.8±1.8 μ W mg), probably due to high metabolism during metamorphosis. Emergence of the adult in the calorimeter was indicated by a short but intense burst of heat. The newly emerged imago had a ca. 20-35% higher metabolic rate than the pupa. In response to reduced O partial pressure the fourth instar larva of C. riparius displayed metabolic regulation. In continuously declining oxygen partial pressure, the fourth instar larva maintained its aerobic energy metabolism (4.2 μ W mg) with only a small decrease down to 0.8 kPa, corresponding to an oxygen concentration of 0.42 mg Ol HO. Below this critical oxygen concentration (P), the rate of heat dissipation decreased rapidly down to the anoxic level which was only 14-17% of the normoxic level. The high relative reduction of metabolic rate under anoxia gives a wrong impression of short-term tolerance of C. riparius to anoxia. The absolute energetic costs of C. riparius associated with anaerobic energy metabolism (0.64±0.11 μ W mg) are almost 6 times higher than those of more anoxia tolerant invertebrates such as sphaeriid bivalves.
通过直接量热法监测了实验室饲养的摇蚊从卵到成虫整个生命周期的代谢率。还测量了四龄幼虫对氧气浓度降低和缺氧的代谢反应。常氧测量在20°C下进行，低氧-缺氧实验在10°C下进行。对于体重范围从0.0028至0.645毫克无灰干重（afdm）的幼虫，散热率与体重呈幂函数关系，质量指数为0.71±0.02，对应于比代谢率与体重关系的指数为-0.29。然而，适用于幼虫的异速生长方程无法预测卵、蛹和成虫的代谢率。实验中使用的单个卵批次包含354±90枚卵，单个卵的质量为0.99±0.01微克（平均值±标准差）。卵的比散热率（13.7±1.8微瓦/毫克afdm）显著低于一龄和二龄幼虫（44 - 53微瓦/毫克），但与四龄幼虫（13.1±3.9微瓦/毫克）相等。成虫羽化前不久蛹的散热率较高（14.8±1.8微瓦/毫克），这可能是由于变态期间代谢率较高。量热计中成虫羽化表现为短暂但强烈的热脉冲。新羽化的成虫代谢率比蛹高约20 - 35%。作为对氧分压降低的反应，摇蚊四龄幼虫表现出代谢调节。在氧分压持续下降时，四龄幼虫维持其有氧能量代谢（4.2微瓦/毫克），直至氧分压降至0.8千帕时仅有小幅下降，对应氧浓度为0.42毫克/升H₂O。低于此临界氧浓度（P）时，散热率迅速下降至缺氧水平，仅为常氧水平的14 - 17%。缺氧条件下代谢率的高相对降低给人一种摇蚊对缺氧短期耐受性的错误印象。摇蚊与无氧能量代谢相关的绝对能量消耗（0.64±0.11微瓦/毫克）几乎是对缺氧耐受性更强的无脊椎动物（如球蚬双壳类）的6倍。
