Division of CBRN Defence and Security, Swedish Defence Research Agency, 901 82, Umeå, Sweden.
Department of Ecology and Environmental Science, Umeå University, 901 87, Umeå, Sweden.
Sci Rep. 2021 Apr 23;11(1):8834. doi: 10.1038/s41598-021-88128-4.
Inbreeding depression (ID) is a fundamental selective pressure that shapes mating systems and population genetic structures in plants. Although it has been shown that ID varies over the life stages of shorter-lived plants, less is known about how the fitness effects of inbreeding vary across life stages in long-lived species. We conducted a literature survey in the Pinaceae, a tree family known to harbour some of the highest mutational loads ever reported. Using a meta-regression model, we investigated distributions of inbreeding depression over life stages, adjusting for effects of inbreeding levels and the genetic differentiation of populations within species. The final dataset contained 147 estimates of ID across life stages from 41 studies. 44 Fst estimates were collected from 40 peer-reviewed studies for the 18 species to aid genetic differentiation modelling. Partitioning species into fragmented and well-connected groups using Fst resulted in the best way (i.e. trade-off between high goodness-of-fit of the model to the data and reduced model complexity) to incorporate genetic connectivity in the meta-regression analysis. Inclusion of a life stage term and its interaction with the inbreeding coefficient (F) dramatically increased model precision. We observed that the correlation between ID and F was significant at the earliest life stage. Although partitioning of species populations into fragmented and well-connected groups explained little of the between-study heterogeneity, the inclusion of an interaction between life stage and population differentiation revealed that populations with fragmented distributions suffered lower inbreeding depression at early embryonic stages than species with well-connected populations. There was no evidence for increased ID in late life stages in well-connected populations, although ID tended to increase across life stages in the fragmented group. These findings suggest that life stage data should be included in inbreeding depression studies and that inbreeding needs to be managed over life stages in commercial populations of long-lived plants.
近交衰退（ID）是塑造植物交配系统和种群遗传结构的基本选择压力。尽管已经表明，在寿命较短的植物的生命阶段中，ID 会发生变化，但对于在寿命较长的物种中，近交对适应性的影响如何在生命阶段中变化，人们知之甚少。我们对松科（Pinaceae）进行了文献综述，松科是一个已知具有最高突变负荷的树种之一。使用元回归模型，我们调查了近交衰退在生命阶段的分布情况，同时调整了近交水平和物种内种群遗传分化的影响。最终数据集包含了来自 41 项研究的 147 个跨生命阶段的 ID 估计值。为了帮助遗传分化模型的建立，从 40 项同行评议研究中收集了 44 个 Fst 估计值，涵盖了 18 个物种。使用 Fst 将物种分为碎片化和连接良好的群体，是在元回归分析中纳入遗传连接性的最佳方法（即模型对数据的拟合度高和模型复杂度降低之间的权衡）。包括生命阶段术语及其与近交系数（F）的相互作用极大地提高了模型的精度。我们观察到，在最早的生命阶段，ID 与 F 的相关性非常显著。尽管将物种种群划分为碎片化和连接良好的群体解释了研究之间的异质性很小，但包括生命阶段和种群分化之间的相互作用表明，与连接良好的种群相比，分布碎片化的种群在早期胚胎阶段的近交衰退程度较低。在连接良好的种群中，没有证据表明在晚期生命阶段会出现更高的 ID，尽管在碎片化的群体中，ID 倾向于随着生命阶段的增加而增加。这些发现表明，在近交衰退研究中应包括生命阶段数据，并且在商业寿命较长的植物种群中，需要在生命阶段管理近交。
