Population genetic structure is a key parameter in evolutionary biology. Earlier comparative studies have shown that genetic structure depends on species ecological attributes and life history traits, but species phylogenetic relatedness had not been accounted for. Here we reevaluate the relationships between genetic structure and species traits in seed plants. Each species is characterized by a set of life history and ecological features as well as by its geographic range size, its heterozygote deficit (FIS) and its genetic structure (GST) at nuclear and organelle markers, to distinguish between pollen- and seed-mediated gene flow. We use both a conventional regression approach and a method that controls for phylogenetic relationships among taxa. Related species are shown to have similar levels of genetic structure. As a consequence of this phylogenetic conservatism, many relationships between ecological traits and GST observed in conventional analyses vanish when using phylogenetically independent contrasts. Once covariation among traits is taken into account, genetic structure is shown to be related with only a few traits such as mating system for nuclear markers and seed dispersal mode or geographic range size for organelle markers. Along with studies on invasiveness, diversification rate or extinction risk, our study of plants genetic structure illustrates the fact that few simple traits can predict the fate of species across a broad taxonomic assemblage, a testimony of the highly contingent nature of evolution.

Photo: Montane forest in SE Sapin, with Taxus bacatta, Prunus mahaleb, and Pinus nigra ssp. salzmannii.