Pechenik JA, Berard R, Kerr L
Biology Department, Tufts University, 02155, Medford, MA, USA
J Exp Mar Biol Ecol. 2000 Nov 1;254(1):19-35. doi: 10.1016/s0022-0981(00)00261-6.
Physiological adjustment to water of reduced salinity requires energy expenditure. In this study we sought to determine the fitness costs associated with such adjustment in the euryhaline polychaete Capitella sp. I, and the extent to which such costs could be explained by increased rates of energy expenditure. In a series of experiments conducted at 20 degrees C, salinity was reduced from 30 per thousand to either 25, 20, 15, 12, or 10 per thousand within 72 h after the larvae had been induced to metamorphose. Juveniles were reared on fine, organic-rich sediment. Over the next 15-30 days, we determined survival, growth, fecundity, and rates of respiration and feeding (via fecal pellet production). Larval salinity tolerance was also determined. Juvenile survival at salinities as low as 12-15 per thousand was comparable to that at 30 per thousand. The lower limit of salinity tolerance was 10-12 per thousand at 20 degrees C for both larvae and juveniles. Juveniles grew significantly more slowly at 12-15 per thousand in six of the seven experiments. Fecundity, however, was generally highest at intermediate salinities of 20-25 per thousand, and comparable at 30 and 15 per thousand. No individuals released embryos at 12 per thousand over the approximately 30-day observation periods in any of the three experiments in which the worms were reared at this low salinity. Reduced growth rates were not explained by differences in rates of respiration at different salinities: at reduced salinity, respiration rates were either statistically equivalent to (P>0.10) or significantly below (P<0.05) those recorded for animals maintained at 30 per thousand. Lower growth rates at lower salinities were best explained by reduced feeding rates. Further studies are required to determine whether digestive efficiency, growth hormone concentrations, or reproductive hormone concentrations are also altered by low salinity in this species.
对盐度降低的水进行生理调节需要消耗能量。在本研究中，我们试图确定广盐性多毛纲小头虫Capitella sp. I进行这种调节所带来的适合度代价，以及这种代价在多大程度上可以通过能量消耗率的增加来解释。在一系列于20摄氏度进行的实验中，在幼虫被诱导变态后的72小时内，盐度从千分之30降至千分之25、20、15、12或10。幼体在富含有机物质的细沉积物上饲养。在接下来的15 - 30天里，我们测定了存活率、生长率、繁殖力以及呼吸和摄食率（通过粪便颗粒产生量）。还测定了幼虫的盐度耐受性。在低至千分之12 - 15的盐度下，幼体的存活率与在千分之30时相当。在20摄氏度时，幼虫和幼体的盐度耐受下限均为千分之10 - 12。在七个实验中的六个实验里，在千分之12 - 15盐度下幼体生长明显更慢。然而，繁殖力通常在千分之20 - 25的中等盐度下最高，在千分之30和千分之15时相当。在将蠕虫饲养在这种低盐度的三个实验中的任何一个实验中，在大约30天的观察期内，没有个体在千分之12的盐度下释放胚胎。不同盐度下呼吸率的差异并不能解释生长率的降低：在盐度降低时，呼吸率在统计学上要么与维持在千分之30的动物所记录的呼吸率相当（P>0.10），要么显著低于（P<0.05）。较低盐度下生长率降低的最佳解释是摄食率降低。需要进一步研究来确定该物种中低盐度是否也会改变消化效率、生长激素浓度或生殖激素浓度。
