Prof. Dr. John Edward Carlson
Coordination: Oliver Gailing
Even though
Darwin’s central idea that natural
selection drives speciation is widely accepted, the mechanisms by which it may
lead to reproductive isolation and the origin and maintenance of species
integrity in the face of ongoing gene flow are still largely unknown. This
project addresses this central question in evolutionary biology to provide
additional evidence that divergent selection towards different optima can maintain
species integrity in the face of gene flow and could have resulted in the
evolution of new species (ecological speciation). Sympatric, multispecies oak
(Fagaceae: Quercus) communities are
model systems to study processes of ecological speciation with gene flow at the
genome level. Thus, hybridization is common among oaks, and species boundaries
in European white oaks (Quercus
section Quercus) and in the North
American red oaks (Quercus section Lobatae) are notoriously weak. However,
recurrent gene flow among these species has not led to a loss of genetic
cohesiveness or adaptive distinctness, and there is evidence that
ecologically-driven selection plays an important role in limiting effective
interspecific gene flow. Screening of gene-based microsatellite markers and
genome scans revealed genes under strong divergent selection with potential
effect on both adaptive divergence and reproductive isolation between species. This
project will focus on the two hybridizing sister species of the white oak
group, Quercus robur and Quercus petraea, and of the red oak
group, Q. ellipsoidalis and Q. rubra,
that have distinct and varied adaptations to drought. The project will be
generating genome-wide data across multiple population pairs using Whole Genome
Resequencing (1) to characterize genome-wide patterns of divergent selection
and (2) to identify candidate genes for adaptive divergence and reproductive
isolation between species the shaped lineage divergence across the oak tree of
life. Studies identifying genes involved in speciation and maintenance of
species integrity are rare, but ongoing gene flow in our Quercus model system, coupled with divergent selection, allows for
the identification of genes under selection (outlier loci) and of linked
genomic regions that resist the homogenizing force of interspecific gene flow.
Integrating genome-wide outlier screens with high density genetic linkage maps
that are currently constructed in Q.
robur and in Q. rubra we will
characterize the genome-wide distribution of outlier loci. For this purpose,
both Q. robur and Q. rubra linkage maps will be anchored
to scaffolds of the sequenced and annotated Q.
robur genome to identify the genomic location of outlier genes and of
physically linked candidate genes with putative role in reproductive isolation
between species. The proposed project forms the foundation for the
identification of genes involved in adaptive divergence and reproductive
isolation in oaks and for understanding adaptive divergence across the oak tree
of life.