Abstract
BackgroundUnderstanding 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.ResultsBased 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.ConclusionPlant 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.
Highlights
Understanding the mechanisms that control species genetic structure has always been a major objective in evolutionary studies
Plant traits correlated with generation time affect both inbreeding depression and mating system
We recently showed that when accounting for phylogenetic signal and covariation between traits, the only species trait that consistently predicted genetic structure was the mating system: selfing species tend to build up more genetic structure than outcrossing species [6]
Summary
Understanding the mechanisms that control species genetic structure has always been a major objective in evolutionary studies. One achievement of empirical population genetic studies is the survey of the genetic diversity of thousands of plant and animal species using molecular markers, first on the basis of proteins and of DNA This "immense outpouring of data on genetic variation" has been considered to be both a milestone, because any type of organism could be investigated using standardised molecular methods, and a "millstone around our neck", because it resulted in the "depauperization of the diversity of empirical work in evolutionary genetics" [1]. We revisit the interrelations between population genetic structure, mating system and plant traits using a quantitative estimate of the mating system (i.e. outcrossing rate), while controlling phylogenetic signal and using traits as covariates
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