Larson James H, Eckert Nathan L, Bartsch Michelle R
U.S. Geological Survey, Upper Midwest Environmental Sciences Center, La Crosse, Wisconsin, United States of America.
U.S. Fish and Wildlife Service, Genoa National Fish Hatchery, Genoa, Wisconsin, United States of America.
PLoS One. 2014 Nov 20;9(11):e112252. doi: 10.1371/journal.pone.0112252. eCollection 2014.
Freshwater mussels are ecologically and economically important members of many aquatic ecosystems, but are globally among the most imperiled taxa. Propagation techniques for mussels have been developed and used to boost declining and restore extirpated populations. Here we use a cohort of propagated mussels to estimate the intrinsic variability in size and growth rate of Lampsilis siliquoidea (a commonly propagated species). Understanding the magnitude and pattern of variation in data is critical to determining whether effects observed in nature or experimental treatments are likely to be important. The coefficient of variation (CV) of L. siliquoidea soft tissues (6.0%) was less than the CV of linear shell dimensions (25.1-66.9%). Size-weight relationships were best when mussel width (the maximum left-right dimension with both valves appressed) was used as a predictor, but 95% credible intervals on these predictions for soft tissues were ∼145 mg wide (about 50% of the mean soft tissue mass). Mussels in this study were treated identically, raised from a single cohort and yet variation in soft tissue mass at a particular size class (as determined by shell dimensions) was still high. High variability in mussel size is often acknowledged, but seldom discussed in the context of mussel conservation. High variability will influence the survival of stocked juvenile cohorts, may affect the ability to experimentally detect sublethal stressors and may lead to incongruities between the effects that mussels have on structure (via hard shells) and biogeochemical cycles (via soft tissue metabolism). Given their imperiled status and longevity, there is often reluctance to destructively sample unionid mussel soft tissues even in metabolic studies (e.g., studies of nutrient cycling). High intrinsic variability suggests that using shell dimensions (particularly shell length) as a response variable in studies of sublethal stressors or metabolic processes will make confident identifications of smaller effect sizes difficult.
淡水贻贝是许多水生生态系统中具有生态和经济重要性的成员，但在全球范围内却是最濒危的类群之一。贻贝的繁殖技术已经得到开发并用于增加数量下降的种群和恢复已灭绝的种群。在这里，我们使用一组繁殖的贻贝来估计椭圆光壳蚌（一种常见的繁殖物种）大小和生长速率的内在变异性。了解数据变化的幅度和模式对于确定在自然环境或实验处理中观察到的影响是否可能具有重要意义至关重要。椭圆光壳蚌软组织的变异系数（CV）为6.0%，低于线性壳尺寸的CV（25.1 - 66.9%）。当使用贻贝宽度（两壳紧闭时的最大左右尺寸）作为预测指标时，大小 - 重量关系最佳，但这些软组织预测的95%可信区间约为145毫克宽（约为平均软组织质量的50%）。本研究中的贻贝处理方式相同，来自同一组群体，但特定大小等级（由壳尺寸确定）的软组织质量变化仍然很大。贻贝大小的高变异性通常是公认的，但在贻贝保护的背景下很少被讨论。高变异性将影响放流幼体群体的生存，可能影响实验检测亚致死应激源的能力，并可能导致贻贝对结构（通过硬壳）和生物地球化学循环（通过软组织代谢）的影响之间出现不一致。鉴于它们濒危的状态和长寿特性，即使在代谢研究（例如营养循环研究）中，人们通常也不愿意对蚌科贻贝的软组织进行破坏性取样。高内在变异性表明，在亚致死应激源或代谢过程研究中使用壳尺寸（特别是壳长）作为响应变量将难以可靠地识别较小的效应量。
