Species integrity in trees

From California sequoia, to Australian eucalyptus, to the outstanding diversity of Amazonian forests, trees are fundamental to many processes in ecology and evolution. Trees define the communities that they inhabit, are host to a multiplicity of other organisms and can determine the ecological dynamics of other plants and animals. Trees are also at the heart of major patterns of biodiversity such as the latitudinal gradient of species diversity and thus are important systems for studying the origin of new plant species. Although the role of trees in community assembly and ecological succession is partially understood, the origin of tree diversity remains largely opaque. For instance, the relative importance of differing habitats and phenologies as barriers to hybridization between closely related species is still largely uncharacterized in trees. Consequently, we know very little about the origin of trees species and their integrity. Similarly, studies on the interplay between speciation and tree community assembly are in their infancy and so are studies on how processes like forest maturation modifies the context in which reproductive isolation evolves. In this issue of Molecular Ecology, Lindtke et al. () and Lagache et al. () overcome some traditional difficulties in studying mating systems and sexual isolation in the iconic oaks and poplars, providing novel insights about the integrity of tree species and on how ecology leads to variation in selection on reproductive isolation over time and space

Data from: Genome-wide analysis of allele frequency change in sunflower crop-wild hybrid populations evolving under natural conditions

Crop-wild hybridization occurs in numerous plant species, and could alter the genetic structure and evolutionary dynamics of wild populations. Studying crop-derived alleles in wild populations is also relevant to assessing/mitigating the risks associated with transgene escape. To date, crop-wild hybridization has generally been examined via short-term studies, typically within a single generation, focusing on few traits or genetic markers. Little is known about patterns of selection on crop-derived alleles over multiple generations, particularly at a genome-wide scale. Here, we documented patterns of natural selection in an experimental crop × wild sunflower population that was allowed to evolve under natural conditions for two generations at two locations. Allele frequencies at a genome-wide collection of SNPs were tracked across generations, and a common garden experiment was conducted to compare trait means between generations. These data allowed us to identify instances of selection on crop-derived alleles/traits and, in concert with QTL mapping results, test for congruence between our genotypic and phenotypic results. We found that natural selection overwhelmingly favors wild alleles and phenotypes. However, crop alleles in certain genomic regions can be favored, and these changes often occurred in parallel across locations. We did not, however, consistently observe close agreement between our genotypic and phenotypic results. For example, when a trait evolved towards the wild phenotype, wild QTL alleles associated with that trait did not consistently increase in frequency. We discuss these results in the context of crop allele introgression into wild populations and implications for the management of GM crops

Appendix A. Environmental correlates of core and edge habitat in five Gilia tricolor habitats.

Environmental correlates of core and edge habitat in five Gilia tricolor habitats

Appendix C. Changes in the frequency of Gilia plants along experimental transects in the Calcium Seep population.

Changes in the frequency of Gilia plants along experimental transects in the Calcium Seep population

Appendix B. Changes in soil attributes across the boundary of the central G. tricolor population.

Changes in soil attributes across the boundary of the central G. tricolor population