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).