Overwintering strategies in polar copepods: Physiological mechanisms and buoyancy regulation by ammonium

个体发育的季节性迁移与滞育相关，是极地海洋中几种哲水蚤桡足类暂时逃离不利环境的一种适应。滞育的桡足类在较深的地方居住数月，在那里它们可能是中性浮力的。在几种海洋无脊椎动物中观察到的铵浮力从未在滞育桡足类中研究过。根据pH值，氨以NH3和NH 4+的形式存在于溶液中。由于NH3的毒性和较高的扩散性，需要低血淋巴pH值以促进铵（NH 4+）的形成。滞育的触发因素（发病、持续时间、终止）尚不清楚。在最近的一项研究中，我们检测到铵值高达500 mmol L-1的滞育南极桡足类Calanoides acutus和Rhincalanus gigas的血淋巴，以及滞育的哲水蚤桡足类Calanoides carinatus和Eucalanus sp。在本格拉电流上升流系统，表明氨浮力在这些物种。在滞育桡足类代谢抑制是明显的，降低代谢率和减少游泳活动。我们推测，低细胞外pH值滞育桡足类血淋巴中必要的形成NH 4+，并防止其扩散损失可能发挥根本性的作用，在调节代谢抑制，从而在控制滞育。这将导致氨浮力的季节性，高铵和低pH值滞育期间和高pH值和低铵的活跃期。

Ontogenetic seasonal migration associated with a diapause is known as an adaptation to escape temporally from an unfavourable environment in several calanoid copepod species in Polar Seas. Diapausing copepods reside for several months in greater depths where they are presumably neutrally buoyant. Ammonium buoyancy as been observed in several marine invertebrates has never been studied in diapausing copepods. Dependent on the pH, ammonia exists in solutions as both NH3 and NH4 +). Due to the toxicity and the higher diffusibility of NH3 a low haemolymph pH is required to favour the formation of ammonium (NH4 +). The trigger (onset, duration, termination) of diapause is yet unknown. In a recent study we detected ammonium values as high as 500 mmol L-1 in the haemolymph of the diapausing Antarctic copepods Calanoides acutus and Rhincalanus gigas, as well as in the diapausing calanoid copepods Calanoides carinatus and Eucalanus sp. in the Benguela Current upwelling system, indicating ammonia buoyancy in these species. In diapausing copepods metabolic depression is evident by reduced metabolic rate and reduced swim activity. We hypothesize that a low extracellular pH in the haemolymph of diapausing copepods necessary to form NH4 + and to prevent it from diffusive loss could play a fundamental role in the regulation of metabolic depression and thus in the control of diapause. This would lead to a seasonality of ammonia buoyancy with high ammonium and low pHe during diapause and high pHe and low ammonium in the active periods.