Diversification and independent polyploid origins in the disjunct species Alyssum repens from the Southeastern Alps and the Carpathians

Abstract

Premise Disjunct distributions have been commonly observed in mountain plant species and have stimulated phylogeographic and phylogenetic research. Here we studied Alyssum repens, a member of the polyploid species complex A. montanum−A. repens, which exhibits SE Alpine‐Carpathian disjunctions with a large elevational span and consists of diploid and tetraploid populations. We aimed to investigate the species‘ genetic and cytotype structure in the context of its distribution patterns, to elucidate the polyploid origins and to propose an appropriate taxonomic treatment. Methods We combined AFLP fingerprinting markers, sequence variation of the highly repetitive ITS region of rDNA and the low‐copy DET1 nuclear gene, genome size, and morphometric data. Results We identified four geographically structured genetic lineages. One consisted of diploid populations from the foothills of the Southeastern Alps and neighboring regions, and the three others were allopatric montane to alpine groups comprising diploids and tetraploids growing in the Southeastern Carpathians and the Apuseni Mts. in Romania. Conclusions We inferred a vicariance scenario associated with Quaternary climatic oscillations, accompanied by one auto‐ and two allopolyploidization events most likely involving a northern Balkan relative. Whereas genetic differentiation and allopatric distribution would favor the taxonomic splitting of this species, the genetic lineages largely lack morphological distinguishability, and their ecological, cytotype and genome size divergence is only partial. Even though we probably face here a case of incipient speciation, we propose to maintain the current taxonomic treatment of Alyssum repens as a single, albeit variable, species.

Odontarrhena stridii (Brassicaceae), a new Nickel-hyperaccumulating species from mainland Greece

“…This marker has been widely used in previous analyses of Alysseae and Alyssum s.l. for its useful phylogenetic signal (Warwick et al 2008;Cecchi et al 2010Cecchi et al , 2013Rešetnik et al 2013;Li et al 2015;Salmerón-Sánchez et al 2018;Melichárková et al 2019), while cpDNA sequences have usually only limited value for species delimitation and phylogenetic inference, as in the case of the related genus Alyssum (Zozomová-Lihová et al 2014;Španiel et al 2017). All sequences were retrieved from GenBank except for typical O. baldaccii from Crete, not previously investigated.…”

So Closely Related and Yet So Different: Strong Contrasts Between the Evolutionary Histories of Species of the Cardamine pratensis Polyploid Complex in Central Europe

“…Although reproductive isolation is assumed between diploids and related polyploids, allowing for independent evolution and speciation of polyploid lineages even in sympatry, it may be incomplete and permits some inter-ploidy gene flow (Sonnleitner et al, 2013;Kolář et al, 2017;Sutherland and Galloway, 2017;Baduel et al, 2018). Recurrent polyploid formation and weak reproductive barriers between cytotypes or polyploid lineages generate intricate polyploid species complexes with reticulate evolutionary histories (e.g., Bardy et al, 2010;Ma et al, 2010;Frajman et al, 2016;Španiel et al, 2017;Mandák et al, 2018;Padilla-García et al, 2018;Melichárková et al, 2019). They frequently show weak genetic separation among polyploid species, discrepancies between morphological and genetic patterns, and shallow, largely unresolved phylogenetic structuring.…”

“…They frequently show weak genetic separation among polyploid species, discrepancies between morphological and genetic patterns, and shallow, largely unresolved phylogenetic structuring. Several studies of polyploid species complexes in Europe indicate their recent diversification, which has been dated to the Pliocene and, especially, the Pleistocene, driven by repeated cycles of glaciation-induced range shifts, and population isolation in refugia followed by range expansion and secondary contact (Franzke and Hurka, 2000;Bardy et al, 2010;Pachschwöll et al, 2015;Frajman et al, 2016;Dauphin et al, 2018;Melichárková et al, 2019;Rojas-Andrés et al, 2020). High species and genetic diversity has repeatedly been observed in Southern Europe, reflecting allopatric long-term survival in stable glacial refugia and only small-scale range shifts (Nieto Feliner, 2014), whereas a highly dynamic glacial and postglacial history can be expected in Central Europe, shaped by colonization of different lineages from southern refugia, their admixture in contact zones, as well as population survival and expansion from cryptic northern refugia (Hewitt, 2001;Birks and Willis, 2008;Stewart et al, 2010).…”

homologizer: Phylogenetic phasing of gene copies into polyploid subgenomes

“…Historically, groups with extensive polyploidy have been under-studied phylogenetically (Soltis et al, 2014). Often, polyploids are dropped from phylogenetic analyses, in a "diploids-first" (or diploids-only) approach (e.g., Beck et al, 2010;Govindarajulu et al, 2011;Lee et al, 2002) or, if polyploids are included, authors tend to infer gene trees for each locus individually and don't attempt true multilocus analyses (e.g., Rothfels et al, 2014;Sousa et al, 2016;Chrtek et al, 2019;Melichárková et al, 2019;Griffin et al, 2011;Sessa et al, 2012a;Fortune et al, 2008;Rousseau-Gueutin et al, 2009;Kao et al, 2020). By omitting polyploids from multilocus analyses, we're not just removing the information those accessions could provide about general evolutionary patterns.…”