Environmental differences are correlated with the distribution pattern of cytotypes in Veronica subsection Pentasepalae at a broad scale

Abstract

Background and Aims The distribution of cytotypes and its potential correlation with environmental variables represent a cornerstone to understanding the origin and maintenance of polyploid lineages. Although many studies have addressed this question in single species at a regional scale, only a few have attempted to decipher this enigma in groups of closely related species at a broad intercontinental geographical scale. Here, we consider ca. 20 species of a diploid-polyploid complex (Veronica subsect. Pentasepalae) of recent and rapid diversification represented in Europe and North Africa to study the frequency and distribution of cytotypes and its relationship with environmental variables. Methods A total of 680 individuals (207 populations) were sampled. Ploidy levels were determined using flow cytometry. Ecological differentiation among cytotypes was tested using climatic and environmental variables related to temperature, precipitation, vegetation and biogeographical region, among others, and by performing univariate and multivariate (constrained PCoA) analyses. Key Results Four ploidy levels (2x, 4x, 6x, 8x) were found and genome downsizing was observed to occur within the group. Plants of different ploidy level are ecologically differentiated, with hexaploids and octoploids occurring in wetter and colder habitats with a higher seasonality than diploids. A south-to-north distribution pattern was found, with diploids occupying southern refugial areas and octoploids being more frequent in northern regions of Europe above the permafrost boundary. Conclusions The distribution of cytotypes can be explained by ecological differentiation, the geographical position of refuge areas during the Quaternary climatic oscillations, as well as by ice and permafrost retreat patterns. The Balkan Peninsula constitutes the most important contact zone between cytotypes. This work provides the first comprehensive ploidy screening within V. subsect. Pentasepalae at a broad scale and indicates that polyploidy and genome downsizing might have contributed to the colonization of new habitats in a recently diverged polyploid complex.

Comparative Phylogeography of Veronica spicata and V. longifolia (Plantaginaceae) Across Europe: Integrating Hybridization and Polyploidy in Phylogeography

“…subg. Pseudolysimachium , but see also Bardy et al, 2010 ; Padilla-García et al, 2018 ; Rojas-Andrés et al, 2020 ; López-González et al, 2020 ). However, we produced some triploids in our greenhouse from interploidal crosses ( Table 3 ), although we did not yet grow them to maturity to check for fertility.…”

Intricate Distribution Patterns of Six Cytotypes of Allium oleraceum at a Continental Scale: Niche Expansion and Innovation Followed by Niche Contraction With Increasing Ploidy Level

“…Existence of diverse global and local distribution patterns of cytotypes within polyploid complexes, ranging from sympatry through more common parapatry with cytotype-mixed populations over contact zones to allopatry (Lewis, 1980 ; reviewed by Stebbins, 1985 ; Thompson and Lumaret, 1992 ; Petit et al, 1999 ; Levin, 2002 ; Martin and Husband, 2009 ; Husband et al, 2013 ; Kolář et al, 2017 ) suggest that cytotype distributions are the results of complex processes and that certain distribution patterns (e.g., local sympatry, large-scale allopatry) can be generated by processes other than niche evolution (Šingliarová et al, 2019 ; Wos et al, 2019 ) or that some of these processes (e.g., reproductive isolation) could reinforce niche differentiation between cytotypes (Rausch and Morgan, 2005 ; Rojas-Andrés et al, 2020 ). Modification of the reproductive system toward autogamy, apomixis, or vegetative propagation to secure reproduction in polyploids (Barringer, 2007 ; Paule et al, 2011 ; Herben et al, 2017 ) can be a key advantage in their local establishment irrespective of their initial minority status (Kao, 2007 , 2008 ).…”

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

“…In contrast to populations with 2n = 30, those with 2n = 32 grow at higher (sub)alpine sites in the Alps and were recorded also in northern Spain . We therefore suggest that the polyploids of C. pratensis may have arisen via both single and multiple origins, and probably in earlier (glacial or interglacial) as well as in later (postglacial) periods, as has been documented also in other polyploid complexes (e.g., Brandrud et al, 2020;Rojas-Andrés et al, 2020). Nevertheless, details regarding polyploid origins, such as their source geographic areas, specific diploid or lower-ploidy ancestral lineages and the time of their origin, remain largely unresolved.…”

“…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).…”