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Comparative analyses of basal rate of metabolism in mammals: data selection does matter
Biological Reviews ( IF 10.0 ) Pub Date : 2017-07-27 , DOI: 10.1111/brv.12350
Michel Genoud 1, 2 , Karin Isler 3 , Robert D. Martin 4, 5
Affiliation  

Basal rate of metabolism (BMR) is a physiological parameter that should be measured under strictly defined experimental conditions. In comparative analyses among mammals BMR is widely used as an index of the intensity of the metabolic machinery or as a proxy for energy expenditure. Many databases with BMR values for mammals are available, but the criteria used to select metabolic data as BMR estimates have often varied and the potential effect of this variability has rarely been questioned. We provide a new, expanded BMR database reflecting compliance with standard criteria (resting, postabsorptive state; thermal neutrality; adult, non‐reproductive status for females) and examine potential effects of differential selectivity on the results of comparative analyses. The database includes 1739 different entries for 817 species of mammals, compiled from the original sources. It provides information permitting assessment of the validity of each estimate and presents the value closest to a proper BMR for each entry. Using different selection criteria, several alternative data sets were extracted and used in comparative analyses of (i) the scaling of BMR to body mass and (ii) the relationship between brain mass and BMR. It was expected that results would be especially dependent on selection criteria with small sample sizes and with relatively weak relationships. Phylogenetically informed regression (phylogenetic generalized least squares, PGLS) was applied to the alternative data sets for several different clades (Mammalia, Eutheria, Metatheria, or individual orders). For Mammalia, a ‘subsampling procedure’ was also applied, in which random subsamples of different sample sizes were taken from each original data set and successively analysed. In each case, two data sets with identical sample size and species, but comprising BMR data with different degrees of reliability, were compared. Selection criteria had minor effects on scaling equations computed for large clades (Mammalia, Eutheria, Metatheria), although less‐reliable estimates of BMR were generally about 12–20% larger than more‐reliable ones. Larger effects were found with more‐limited clades, such as sciuromorph rodents. For the relationship between BMR and brain mass the results of comparative analyses were found to depend strongly on the data set used, especially with more‐limited, order‐level clades. In fact, with small sample sizes (e.g. <100) results often appeared erratic. Subsampling revealed that sample size has a non‐linear effect on the probability of a zero slope for a given relationship. Depending on the species included, results could differ dramatically, especially with small sample sizes. Overall, our findings indicate a need for due diligence when selecting BMR estimates and caution regarding results (even if seemingly significant) with small sample sizes.

中文翻译:

哺乳动物基础代谢率的比较分析:数据选择很重要

基础代谢率 (BMR) 是一个生理参数,应在严格定义的实验条件下进行测量。在哺乳动物之间的比较分析中,BMR 被广泛用作代谢机制强度的指标或能量消耗的代理。许多包含哺乳动物 BMR 值的数据库都可用,但用于选择代谢数据作为 BMR 估计值的标准往往各不相同,而且这种变异性的潜在影响很少受到质疑。我们提供了一个新的、扩展的 BMR 数据库,反映了对标准标准(静息、吸收后状态;热中性;成年、女性非生殖状态)的遵守情况,并检查了差异选择性对比较分析结果的潜在影响。该数据库包括 817 种哺乳动物的 1739 个不同条目,从原始来源编译。它提供了允许评估每个估计的有效性的信息,并为每个条目提供最接近适当 BMR 的值。使用不同的选择标准,提取了几个替代数据集,并将其用于 (i) BMR 与体重的比例以及 (ii) 脑质量与 BMR 之间的关系的比较分析。预计结果将特别依赖于样本量较小且关系相对较弱的选择标准。系统发育知情回归(系统发育广义最小二乘法,PGLS)被应用于几个不同进化枝(哺乳动物、Eutheria、Metatheria 或个别命令)的替代数据集。对于哺乳动物,还应用了“二次抽样程序”,其中从每个原始数据集中抽取不同样本量的随机子样本并依次进行分析。在每种情况下,都比较了两个具有相同样本量和物种但包含具有不同可靠性程度的 BMR 数据的数据集。选择标准对大型进化枝(哺乳动物、Eutheria、Metatheria)的缩放方程影响较小,尽管不太可靠的 BMR 估计通常比更可靠的估计大 12-20%。在更有限的进化枝中发现了更大的影响,例如 sciuromorph 啮齿动物。对于 BMR 和脑质量之间的关系,发现比较分析的结果强烈依赖于所使用的数据集,尤其是对于更有限的订单级进化枝。事实上,对于小样本量(例如 <100),结果经常显得不稳定。二次抽样表明,对于给定关系,样本大小对零斜率的概率具有非线性影响。根据包含的物种,结果可能会有很大差异,尤其是在样本量较小的情况下。总体而言,我们的研究结果表明,在选择 BMR 估计值时需要进行尽职调查,并对小样本量的结果(即使看似重要)保持谨慎。
更新日期:2017-07-27
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