Effects of glaciation and whole genome duplication on the distribution of the Campanula rotundifolia polyploid complex

Abstract

Premise Of The StudyBoth intrinsic and extrinsic factors contribute to a species distribution. Among plants, the extrinsic effects of glaciation and intrinsic effects of whole genome duplication are powerful drivers of biogeographical patterns, but the interplay of these factors is poorly understood. Here, we investigate the roles glaciation and whole‐genome duplication have played in the evolution of the widespread polyploid complex Campanula rotundifolia.MethodsWe assessed the cytotype of 37 populations that spanned the geographic and cytotypic range of the C. rotundifolia complex. We constructed a chloroplast phylogeny for these populations and used RAD‐seq to create nuclear phylogenies and networks for a subset of 23 populations; and estimated divergence times of major clades using Bayesian estimation of substitution rates.Key ResultsCampanula rotundifolia originated in south‐central Europe and underwent range expansion throughout much of Europe and North America. Multiple genome duplications have occurred in C. rotundifolia—at least two tetraploid and three hexaploid formations.ConclusionsNuclear and chloroplast phylogenies are largely congruent with a history of populations surviving glacial maxima in known Pleistocene refugia in Europe and North America. Divergent European clades are consistent with two disjunct glacial refugia within Europe. North America was colonized by hexaploids derived from Western European lineages. A glacial refugium in Midwestern North America likely facilitated post‐glacial recolonization of North America and limited genetic divergence. These results implicate both glaciation and whole‐genome duplication as contributing factors to the extant biogeography of C. rotundifolia.

Westward range expansion from middle latitudes explains the Mississippi River discontinuity in a forest herb of eastern North America

“…Recently, refugia have also been inferred outside of the southeastern United States (Bemmels et al, 2019). Such inferences suggest that some North American populations may have persisted near the extent of glaciers even during harsh conditions (Rowe et al, 2004;Sutherland & Galloway, 2018;Willi et al, 2018).…”

“…Recently, refugia have also been inferred outside of the southeastern United States (Bemmels et al., 2019). Such inferences suggest that some North American populations may have persisted near the extent of glaciers even during harsh conditions (Rowe et al., 2004; Sutherland & Galloway, 2018; Willi et al., 2018). Hereafter, we will define refugia as ancient repositories of genetic diversity, often with high among‐population genetic variation caused by historical subdivision during glacial maxima (Gavin et al., 2014; Hewitt, 2000, 2004; Keppel et al., 2012; Lewis & Crawford, 1995; Tzedakis et al., 2013).…”

Strength in numbers? Cytotype frequency mediates effect of reproductive barriers in mixed‐ploidy arrays

“…Cytotypes are nonrandomly distributed throughout the range; tetraploids are widespread on both continents, whereas diploids occur primarily in Central and Northern Europe, and hexaploids have distributions in central Europe, the British Isles, and Central and Western North America (Kovanda 1977; Shetler 1982; Stevens et al. 2012, Sutherland and Galloway 2018; Wilson et al. 2020).…”

“…2020). Zones of contact exist in both North America and Europe, and occur between diploids and tetraploids, or tetraploids and hexaploids (McAllister 1972; Sutherland and Galloway 2018).…”

“…Four populations, comprising two diploid‐tetraploid pairs, were selected from central Europe—one parapatric pair from the Czech Republic, and two populations in eastern Germany separated by approximately 50 km. Two tetraploid‐hexaploid pairs were chosen from North America: parapatric populations from Manitoulin Island in southern Ontario and populations from Massachusetts and Ontario (approximately 740 km apart), chosen for genetic divergence similar to that found in other heteroploid contact zones (Sutherland and Galloway 2018). Wild‐collected seeds from 20 to 30 families (mean 24 ± 3.5 families) for each of the eight populations were sown in the University of Virginia greenhouse, multiple siblings/family were transplanted as rosettes into 10‐cm pots, and grown to flowering.…”