Abstract
Geographic isolation and chromosome evolution are two of the major
drivers of diversification in eukaryotes in general, and specifically,
in plants. On one hand, range shifts induced by Pleistocene glacial
oscillations deeply shaped the evolutionary trajectories of species in
the Northern Hemisphere. On the other hand, karyotype variability within
species or species complexes may have adaptive potential as different
karyotypes may represent different recombination rates and linkage
groups that may be associated with locally adapted genes or supergenes.
Organisms with holocentric chromosomes are ideal to study the link
between local adaptation and chromosome evolution, due to their high
cytogenetic variability, especially when it seems to be related to
environmental variation. Here, we integrate the study of the
phylogeography, chromosomal evolution and ecological requirements of a
plant species complex distributed in the Western Euro-Mediterranean
region (Carex gr. laevigata , Cyperaceae). We aim to
clarify the relative influence of these factors on population
differentiation and ultimately on speciation. We obtained a
well-resolved RADseq phylogeny that sheds light on the phylogeographic
patterns of molecular and chromosome number variation, which are
compatible with south-to-north postglacial migration. In addition,
landscape genomics analyses identified candidate loci for local
adaptation, and also strong significant associations between the
karyotype and the environment. We conclude that karyotype distribution
in C. gr. laevigata has been constrained by both range
shift dynamics and local adaptation. Our study demonstrates that
chromosome evolution may be responsible, at least partially, for
microevolutionary patterns of population differentiation and adaptation
in Carex .
Keywords: Carex , Cyperaceae, chromosomal speciation,
hybrid dysfunction, landscape genomics, suppression recombination