Phylogeography constrains chromosome number distribution in the
western Mediterranean Carex gr. laevigata
Phylogeographic and phylogenetic inference in C. gr.laevigata has remained obscure in previous studies based on
Sanger sequencing of a few DNA regions, especially for the C.
laevigata -C. binervis species pair (Escudero et al., 2008, 2010;
Escudero & Luceño, 2009). On one hand, systematic studies focused on
the Carex sect. Spirostachyae based on ITS and 5’trn K
intron (Escudero et al., 2008, 2010; Escudero & Luceño, 2009) retrieved
non-monophyly and intermingled phylogenetic relationships for C.
laevigata -C. binervis . On the other hand, the only previous
attempt to elucidate the phylogeographic structure of the group, based
on two plastid DNA regions (5′trn K and the intergenictrn V-ndh C) and a wide population sampling, obtained a
highly intricate haplotype network (Escudero et al., 2013b). Previously
inferred ribotype additivities and haplotype sharing between C.
laevigata -C. binervis have been attributed to hybridisation
(Escudero et al., 2008, 2013b; Escudero & Luceño, 2009) or incomplete
lineage sorting (Escudero et al., 2013b). The phylogenetic resolution
provided by the highly increased amount of loci obtained across the
entire genomes of the study species with the RAD-seq approach (1761 loci
here vs. 1–2 in previous studies) allowed us to shed light on the main
phylogeographic patterns of C. gr. laevigata . While the
phylogenetic relationships for C. camposii and C.
paulo-vargasii are congruent with previous studies, we uncovered a
previously unknown genetic lineage for C. binervis from the
Eurosiberian part of its range, and distinct from the clade includingC. binervis samples from the Iberian Peninsula. Overall, the
southern Iberian peninsula-north Africa displayed higher phylogenetic,
taxonomic (all four species of C. gr. laevigata present)
and cytogenetic (most chromosome number range) diversities (Figs. 1–2).
Besides, endemics from that region (C. paulo-vargasii from
Morocco and C. camposii from Sierra Nevada), as well as southern
populations of C. binervis and C. laevigata appeared as
successive sisters to the rest of the lineages (Fig. 2). On the other
hand, only C. laevigata and C. binervis are distributed in
the northern Iberian Peninsula and the rest of western Europe, where a
reduced subset of their phylogenetic diversity (Fig. 2) and chromosome
numbers are found (2n = 70–74, Fig. 1). Therefore, the
taxonomic, molecular and cytogenetic evidence points to southern
Iberia-north Africa (especially the region around the Strait of
Gibraltar) as the evolutionary cradle for C. gr.laevigata . These phylogeographic and karyotypic patterns are
compatible with the signature of Pleistocene glaciations, including
southern refugia and northwards postglacial recolonization (e.g. Hewitt,
2011). This temporal-geographic scenario, which frequently caused
speciation (e.g. Kadereit & Abbott, 2021), has been previously reviewed
for many plant groups (Rodríguez-Sánchez et al., 2008; Lavergne et al.,
2013; Nieto Feliner, 2014; Molina-Venegas et al., 2017).