Ecological segregation does not drive the intricate parapatric distribution of diploid and tetraploid cytotypes of theArabidopsis arenosagroup (Brassicaceae)

Abstract

Detailed knowledge of the geographic distribution of cytotypes is a prerequisite for any experimental or molecular study of ploidy-variable plant systems. The Arabidopsis arenosa group, an intricate di-tetraploid complex from the plant model genus Arabidopsis, has remained largely neglected regarding the distribution and habitat associations of its cytotypes. Using flow cytometry, we conducted a large population-level cytological screen across the A. arenosa group range, involving more than 2900 individuals from 194 populations. We characterized a largely parapatric distribution of the diploid (Southeast Europe) and tetraploid (Northwest Europe) cytotypes with two contact zones -a narrow contact zone in the Slovenian Forealps and a diffuse contact zone across the Carpathians. In addition, a previously unknown isolated diploid lineage with distinct ecology was revealed from sandy areas of the southeastern Baltic coast. We also recorded several adult triploid individuals for the first time in wild Arabidopsis arenosa. Particularly in the Western Carpathians, the diploid and tetraploid populations are largely intermingled, and both cytotypes are spread along the whole lowland-alpine gradient of habitats, exhibiting no signs of ploidy-linked habitat differentiation. In contrast with the complexity at the landscape scale, the within-population cytological homogeneity and the rare occurrence of triploids indicate that the contact zone is rather stable.

Northern glacial refugia and altitudinal niche divergence shape genome‐wide differentiation in the emerging plant model Arabidopsis arenosa

“…There are no extant diploid A. arenosa populations known from the areas between Baltic coast and Carpathians, which corresponds with the lack of suitable habitats in these flat landscapes (Kolář et al . ) and similar Carpathian – Baltic disjunctions documented for other plants preferring low‐competitive environments (Zając & Zając ). All current occurrences of A. arenosa in this area that are known to us come from non‐native stands and represent a different tetraploid lineage preferring man‐made habitats such as roadsides and railway tracks (Arnold et al .…”

“…In addition, there is virtually no chance of ongoing gene flow, as indicated by the nearly complete lack of naturally occurring triploid individuals, that is potential mediators of gene flow from tetraploids to diploids (Kolář et al . ).…”

“…We collected leaf material of ~10 individuals from 64 natural populations of diploid Arabidopis arenosa in 2011–2013 across the entire range of its diploid cytotype and checked ploidy level of all collected individuals using flow cytometry, as described in Kolář et al . () (for locality details see Table S1, Supporting information). Two populations (three individuals each) of the closely related (Hohmann et al .…”

“…All these populations have been sampled, georeferenced and cytotyped by means of flow cytometry by our team in years 2011–2015 (Kolář et al . and additional sampling, see the complete list in Table S1, Supporting information). The nongenotyped populations were assigned to the same major genetic group as their closest SNP‐genotyped counterpart (see Table S1, Supporting information), what was feasible due to mostly allopatric distribution of the major genetic lineages (Fig.…”

“…Native range of the diploid A. arenosa cytotype covers most of the eastern temperate Europe, spanning a 2500‐m altitudinal gradient from coastal habitats to alpine stands and a 1600‐km latitudinal gradient from the submediterranean Balkan Peninsula to previously glaciated Baltic Sea coast (Kolář et al . ). In contrast to other Arabidopsis species, little is still known about the rangewide patterns of genetic variation and evolutionary history of A. arenosa , particularly of its diploid cytotype.…”