Lee Carol Eunmi, Petersen Christine H
Department of Zoology, 430 Lincoln Drive, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
Physiol Biochem Zool. 2003 May-Jun;76(3):296-301. doi: 10.1086/375433.
Invasive species are commonly thought to have broad tolerances that enable them to colonize new habitats, but this assumption has rarely been tested. In particular, the relative importance of acclimation (plasticity) and adaptation for invasion success are poorly understood. This study examined effects of short-term and developmental acclimation on adult salinity tolerance in the copepod Eurytemora affinis. This microcrustacean occurs in estuarine and salt marsh habitats but has invaded freshwater habitats within the past century. Effects of short-term acclimation were determined by comparing adult survival in response to acute versus gradual salinity change to low salinity (fresh water). Effects of developmental acclimation on adult tolerance were determined using a split-brood 4 x 2 factorial experimental design for one brackish-water population from Edgartown Great Pond, Massachusetts. Twenty full-sib clutches were split and reared at four salinities (fresh, 5, 10, and 27 practical salinity units [PSU]). On reaching adulthood, clutches from three of the salinity treatments (no survivors at fresh) were split into low- (fresh) and high- (40 PSU) salinity stress treatments, at which survival was measured for 24 h. Short-term acclimation of adults did not appear to have a long-term affect on low-salinity tolerance, given that gradual transfers to fresh water enhanced survival relative to acute transfers in the short term (after 7 h) but not over a longer period of 8 d. Developmental acclimation had contrasting effects on low- versus high-salinity tolerance. Namely, rearing salinity had a significant effect on tolerance of high-salinity (40 PSU) stress but no significant effect on tolerance of low-salinity (freshwater) stress. In addition, there was a significant effect of clutch on survival under freshwater conditions, indicating a genetic component to low-salinity tolerance but no significant clutch effect in response to high salinity. While developmental acclimation might enhance survival at higher salinities, the minimal effect of acclimation and significant effect of clutch on low-salinity tolerance suggest the importance of natural selection during freshwater invasion events.
入侵物种通常被认为具有广泛的耐受性，这使它们能够在新栖息地定殖，但这一假设很少得到验证。特别是，对于适应（可塑性）和适应性在入侵成功中的相对重要性，人们了解甚少。本研究考察了短期和发育适应对桡足类近缘真宽水蚤成体耐盐性的影响。这种微型甲壳动物出现在河口和盐沼栖息地，但在过去一个世纪内已侵入淡水栖息地。通过比较成体在急性与逐渐盐度变化至低盐度（淡水）时的存活率，确定短期适应的影响。使用来自马萨诸塞州埃德加敦大池塘的一个咸淡水种群的裂巢4×2析因实验设计，确定发育适应对成体耐受性的影响。将20个全同胞的卵块分开，在四个盐度（淡水、5、10和27实用盐度单位[PSU]）下饲养。成年后，将来自三个盐度处理（淡水中无存活个体）的卵块分成低盐度（淡水）和高盐度（40 PSU）胁迫处理组，在这两种处理下测量24小时的存活率。鉴于在短期内（7小时后）相对于急性转移，逐渐转移到淡水可提高存活率，但在8天的较长时间内则不然，因此成体的短期适应似乎对低盐度耐受性没有长期影响。发育适应对低盐度和高盐度耐受性有不同影响。具体而言，饲养盐度对高盐度（40 PSU）胁迫的耐受性有显著影响，但对低盐度（淡水）胁迫的耐受性没有显著影响。此外，卵块对淡水条件下的存活率有显著影响，表明低盐度耐受性存在遗传成分，但对高盐度的反应没有显著的卵块效应。虽然发育适应可能会提高在较高盐度下的存活率，但适应的最小影响以及卵块对低盐度耐受性的显著影响表明了淡水入侵事件中自然选择的重要性。
