McKenzie David J, Vergnet Alain, Chatain Béatrice, Vandeputte Marc, Desmarais Erick, Steffensen John F, Guinand Bruno
UMR5119, Ecologie des systèmes marins côtiers (ECOSYM), Place Eugène Bataillon, Université Montpellier 2, 34095 Montpellier Cedex 5, France
Ifremer, Station expérimentale d'aquaculture, chemin de Maguelone, 34250 Palavas-les-Flots, France.
J Exp Biol. 2014 Sep 15;217(Pt 18):3283-92. doi: 10.1242/jeb.101857.
Although food deprivation is a major ecological pressure in fishes, there is wide individual variation in tolerance of fasting, whose mechanistic bases are poorly understood. Two thousand individually tagged juvenile European sea bass were submitted to two 'fasting/feeding' cycles each comprising 3 weeks of food deprivation followed by 3 weeks of ad libitum feeding at 25°C. Rates of mass loss during the two fasting periods were averaged for each individual to calculate a population mean. Extreme fasting tolerant (FT) and sensitive (FS) phenotypes were identified that were at least one and a half standard deviations, on opposing sides, from this mean. Respirometry was used to investigate two main hypotheses: (1) tolerance of food deprivation reflects lower mass-corrected routine metabolic rate (RMR) in FT phenotypes when fasting, and (2) tolerance reflects differences in substrate utilisation; FT phenotypes use relatively less proteins as metabolic fuels during fasting, measured as their ammonia quotient (AQ), the simultaneous ratio of ammonia excretion to RMR. There was no difference in mean RMR between FT and FS over 7 days fasting, being 6.70±0.24 mmol h(-1) fish(-1) (mean ± s.e.m., N=18) versus 6.76±0.22 mmol h(-1) fish(-1) (N=17), respectively, when corrected to a body mass of 130 g. For any given RMR, however, the FT lost mass at a significantly lower rate than FS, overall 7-day average being 0.72±0.05 versus 0.90±0.05 g day(-1) fish(-1), respectively (P<0.01, t-test). At 20 h after receiving a ration equivalent to 2% body mass as food pellets, ammonia excretion and simultaneous RMR were elevated and similar in FT and FS, with AQs of 0.105±0.009 and 0.089±0.007, respectively. At the end of the period of fasting, ammonia excretion and RMR had fallen in both phenotypes, but AQ was significantly lower in FT than FS, being 0.038±0.004 versus 0.061±0.005, respectively (P<0.001, t-test). There was a direct linear relationship between individual fasted AQ and rate of mass loss, with FT and FS individuals distributed at opposing lower and upper extremities, respectively. Thus the difference between the phenotypes in their tolerance of food deprivation did not depend upon their routine energy use when fasting. Rather, it depended upon their relative use of tissue proteins as metabolic fuels when fasting, which was significantly lower in FT phenotypes.
尽管食物匮乏是鱼类面临的主要生态压力，但鱼类对禁食的耐受性存在广泛的个体差异，其机制基础却知之甚少。两千条单独标记的欧洲鲈鱼幼鱼经历了两个“禁食/投喂”周期，每个周期包括3周的食物剥夺，随后在25°C下自由采食3周。计算每个个体在两个禁食期的体重损失率平均值，以得出总体平均值。确定了极端耐禁食（FT）和敏感（FS）表型，它们与该平均值的偏差至少为一个半标准差，且位于相反两侧。采用呼吸测定法研究了两个主要假设：（1）食物剥夺耐受性反映了禁食时FT表型较低的体重校正常规代谢率（RMR）；（2）耐受性反映了底物利用的差异；以氨商（AQ）衡量，即禁食期间氨排泄与RMR的同时比率，FT表型在禁食期间作为代谢燃料使用的蛋白质相对较少。禁食7天期间，FT和FS的平均RMR没有差异，校正至130 g体重后，分别为6.70±0.24 mmol h(-1) 鱼(-1)（平均值±标准误，N = 18）和6.76±0.22 mmol h(-1) 鱼(-1)（N = 17）。然而，对于任何给定的RMR，FT的体重损失率明显低于FS，7天总体平均值分别为0.72±0.05和0.90±0.05 g day(-1) 鱼(-1)（P<0.01，t检验）。在接受相当于体重2%的食物颗粒作为定量投喂20小时后，FT和FS的氨排泄和同时的RMR均升高且相似，AQ分别为0.105±0.009和0.089±0.007。在禁食期结束时，两种表型的氨排泄和RMR均下降，但FT中的AQ显著低于FS，分别为0.038±0.004和0.061±0.005（P<0.001，t检验）。个体禁食AQ与体重损失率之间存在直接线性关系，FT和FS个体分别分布在相对的下端和上端。因此，表型在食物剥夺耐受性上的差异并不取决于它们禁食时的常规能量使用情况。相反，它取决于它们在禁食时作为代谢燃料对组织蛋白质的相对利用情况，FT表型中的这种利用情况明显较低。
