Invasion, isolation and evolution shape population genetic structure in Campanula rotundifolia

The genetic structure of British and Irish flora has been enduringly shaped by events during and since the last ice age ~27000 years ago. When the British–Irish ice sheet was at its maximum extent, only parts of southern and eastern England remained unglaciated, and grounded ice reached to the edge of the continental shelf along its whole boundary from Ireland to the Shetland Isles. The process of recolonization of deglaciated land resulted in distinctive genetic patterns, still evident today, and offered opportunities for species with adaptive strategies, such as genome doubling, to take advantage of the new space. As a result of this opportunistic polyploidisation, the herbaceous perennial Campanula rotundifolia has a distinctive distribution of tetraploid and hexaploid (and other more obscure) cytotypes in Britain and Ireland.

In a new study published in AoBP, Wilson et al. used a common garden experiment to examine the growth and flowering phenology of tetraploid, pentaploid and hexaploid cytotypes of C. rotundifolia and simulated a contact zone for the investigation of reproductive barriers. They found populations of different cytotypes to be mostly allopatric (occurring in separate non-overlapping regions). Analysis of the chloroplast genome showed allopatric hexaploids to be distinct from tetraploids, whereas sympatric hexaploids are not, and that allopatric hexaploids did not originate from British tetraploids. At a simulated contact zone, maternal tetraploids rarely produced progeny of other cytotypes, but maternal hexaploids produced many pentaploids and aneuploids. The authors conclude that present day distribution of this species reflects post-glacial recolonization events, now maintained by geographic separation, together with more recent occasional local in situ polyploidisation. Reproductive barriers favour the persistence of the tetraploid cytotype over the hexaploid, which is why the former is found across mainland Britain and the latter is limited to more westerly regions.

Researcher highlight

This paper reflects work by several generations of scientists from the Centre of Ecology and Hydrology in Edinburgh, UK; Julia Wilson (retired about 6 years ago), Jess Shepherd and Duran Castillo (MSc students), Mario Duran Castillo (PhD student), Annika Perry (a fairly recent PhD graduate), and Stephen Cavers (head of the genetics lab). A lot of the field collection and cytotyping in the lab was conducted by Julia after her retirement.

Mario Duran-Castillo was born in the Yucatán Peninsula, Mexico and in 2014 moved to Scotland to conduct a Masters in Biodiversity and Taxonomy of Plants at the Royal Botanic Gardens Edinburgh and later a PhD in Evolutionary Biology at the University of Edinburgh. Mario is currently a researcher in Botany at the National Institute for Forestry, Agricultural and Livestock Research (INIFAP) of Mexico where he is working in close proximity with local farmers and governmental authorities identifying areas of improvement in the management of natural resources (specifically native flora). Mario is an evolutionary biologist who is passionate about plant biology and has worked with hybridisation and speciation in plants. He is interested in conservation of genetic diversity of tropical forests in the south of Mexico. He is also interested in applying new genomic tools in the research of biodiversity in the tropics.

Since Jess Shepherd’s MSc she has specialised as a botanical artist – inky leaves – she does some impressive work. If you’re interested in her art please check out https://inkyleaves.com/.