Duminil Jérôme, Hardy Olivier J, Petit Rémy J
Université Libre de Bruxelles, Faculté des Sciences, Service Evolution Biologique et Ecologie, CP 160/12, 50 Av. F. Roosevelt, 1050 Bruxelles, Belgium.
BMC Evol Biol. 2009 Jul 27;9:177. doi: 10.1186/1471-2148-9-177.
Understanding the mechanisms that control species genetic structure has always been a major objective in evolutionary studies. The association between genetic structure and species attributes has received special attention. As species attributes are highly taxonomically constrained, phylogenetically controlled methods are necessary to infer causal relationships. In plants, a previous study controlling for phylogenetic signal has demonstrated that Wright's FST, a measure of genetic differentiation among populations, is best predicted by the mating system (outcrossing, mixed-mating or selfing) and that plant traits such as perenniality and growth form have only an indirect influence on FST via their association with the mating system. The objective of this study is to further outline the determinants of plant genetic structure by distinguishing the effects of mating system on gene flow and on genetic drift. The association of biparental inbreeding and inbreeding depression with population genetic structure, mating system and plant traits are also investigated.
Based on data from 263 plant species for which estimates of FST, inbreeding (FIS) and outcrossing rate (tm) are available, we confirm that mating system is the main influencing factor of FST. Moreover, using an alternative measure of FST unaffected by the impact of inbreeding on effective population size, we show that the influence of tm on FST is due to its impact on gene flow (reduced pollen flow under selfing) and on genetic drift (higher drift under selfing due to inbreeding). Plant traits, in particular perenniality, influence FST mostly via their effect on the mating system but also via their association with the magnitude of selection against inbred individuals: the mean inbreeding depression increases from short-lived herbaceous to long-lived herbaceous and then to woody species. The influence of perenniality on mating system does not seem to be related to differences in stature, as proposed earlier, but rather to differences in generation time.
Plant traits correlated with generation time affect both inbreeding depression and mating system. These in turn modify genetic drift and gene flow and ultimately genetic structure.
了解控制物种遗传结构的机制一直是进化研究的主要目标。遗传结构与物种属性之间的关联受到了特别关注。由于物种属性在分类学上受到高度限制，因此需要采用系统发育控制方法来推断因果关系。在植物中，先前一项控制系统发育信号的研究表明，赖特氏FST（一种衡量种群间遗传分化的指标）最好由交配系统（异交、混合交配或自交）来预测，并且多年生性和生长形式等植物性状仅通过它们与交配系统的关联对FST产生间接影响。本研究的目的是通过区分交配系统对基因流和遗传漂变的影响，进一步概述植物遗传结构的决定因素。同时还研究了双亲近交和近交衰退与种群遗传结构、交配系统和植物性状的关联。
基于263种植物的数据（这些数据可用于估计FST、近交系数（FIS）和异交率（tm）），我们证实交配系统是FST的主要影响因素。此外，使用一种不受近交对有效种群大小影响的FST替代指标，我们表明tm对FST的影响是由于其对基因流（自交时花粉流减少）和遗传漂变（由于近交自交时遗传漂变增加）的影响。植物性状，特别是多年生性，对FST的影响主要是通过它们对交配系统的作用，但也通过它们与对近交个体选择强度的关联：平均近交衰退从短命草本植物增加到长命草本植物，然后再到木本植物。多年生性对交配系统的影响似乎与先前提出的植株高度差异无关，而与世代时间差异有关。
与世代时间相关的植物性状会影响近交衰退和交配系统。这些反过来又会改变遗传漂变和基因流，最终影响遗传结构。
