Data from: Are heritability and selection related to population size in nature? meta-analysis and conservation implications

It is widely thought that small populations should have less additive genetic variance and respond less efficiently to natural selection than large populations. Across taxa, we meta-analytically quantified the relationship between adult census population size (N) and additive genetic variance (proxy: h2) and found no reduction in h2 with decreasing N; surveyed populations ranged from four to one million individuals (1735 h2estimates, 146 populations, 83 species). In terms of adaptation, ecological conditions may systematically differ between populations of varying N; the magnitude of selection these populations experience may therefore also differ. We thus also meta-analytically tested whether selection changes with N, and found little evidence for systematic differences in the strength, direction, or form of selection with N across different trait types and taxa (7344 selection estimates, 172 populations, 80 species). Collectively, our results (i) indirectly suggest that genetic drift neither overwhelms selection more in small than in large natural populations, nor weakens adaptive potential/h2 in small populations, and (ii) imply that natural populations of varying sizes experience a variety of environmental conditions, without consistently differing habitat quality at small N. However, we caution that the data are currently insufficient to determine whether some small populations may retain adaptive potential definitively. Further study is required into (i) selection and genetic variation in completely isolated populations of known N, underrepresented taxonomic groups, and non-generalist species, (ii) adaptive potential using multidimensional approaches, and (iii) the nature of selective pressures for specific traits.

学界普遍认为，相较于大种群，小种群的加性遗传方差（additive genetic variance）更低，且对自然选择的响应效率也更弱。本研究针对各类生物类群（taxa），通过元分析（meta-analysis）量化了成年个体普查种群大小（adult census population size，记为N）与加性遗传方差的关联，以狭义遗传力h²作为其代理指标；结果未观测到随种群大小降低而出现h²下降的现象。本次调研覆盖的种群个体数跨度为4至100万，共包含1735个h²估计值、146个种群以及83个物种。从适应性进化角度而言，不同种群大小的生境生态条件可能存在系统性差异，因此这些种群所经历的选择强度也可能存在差异。为此，我们同样通过元分析检验了选择效应是否随种群大小发生变化，结果未发现足够证据表明，在不同性状类型与生物类群之间，选择的强度、方向或形式会随种群大小出现系统性差异（共包含7344个选择效应估计值、172个种群以及80个物种）。综合而言，本研究结果（i）间接显示，相较于大种群，自然小种群中的遗传漂变（genetic drift）并未更强地压制自然选择，也未削弱小种群的适应潜力（adaptive potential）与加性遗传方差；（ii）表明不同种群大小的自然种群虽面临多样的环境条件，但小种群的生境质量并未普遍更低。但需注意的是，当前数据尚不足以判定部分小种群是否能够持久保留适应潜力。未来仍需开展以下方向的研究：（i）已知种群大小的完全隔离种群、代表性不足的生物类群以及特化物种中的选择效应与遗传变异情况；（ii）采用多维度方法探究适应潜力；（iii）特定性状所受选择压力的本质。