Genetic changes in New England Cichorium intybus since Thoreau’s times

Tomáš Závada discusses his recent paper ‘Radical shift in the genetic composition of New England chicory populations‘. Find out more about how genetic diversity and structure of Cichorium intybus populations have changed over time and the importance of herbarium specimens in this discovery.

Herbarium collections represent a goldmine of botanical data. These days, herbarium specimens allow us not only to trace distribution and morphology of plant species, but also zoom in on a genome level and study DNA changes over many plant generations. In our paper, we assayed the genetic make-up of historical and contemporary accessions of New England Cichorium intybus L. (chicory) over the last 170-year period.

Working with herbarium specimens transports you to other times.  Studying labels is like reading a book about a life that you will never occupy, a snapshot from past botanists’ adventures and trips. The oldest chicory plant in our study was collected in 1848 by the first full-time professor of botany at Harvard University. Asa Gray (1810 – 1888) was responsible for establishing systematic botany in the United States and advocating Charles Darwin’s work. When Asa Gray came to Cambridge, MA, in 1842, he brought with him a small collection of specimens. That rose to some 200,000 in 20 years and later became The Gray Herbarium. Currently the herbarium contains nearly two million specimens (Wood, 2010). When I became a member of New England Botanical Club (NEBC) as a graduate student and began attending NEBC meetings, I was introduced to these vast and diverse herbaria collections.

Asa Gray’s 1848 specimen. Photo: The Gray Herbarium (Harvard University Herbaria) © 2012 – 2015 President and Fellows of Harvard College. Record ID: 881c9381-30a7-4a61-b956-39fdeb43d145

My graduate research was focused on genotyping wild chicory, domesticated cultivars from native Eurasia and introduced North American populations (Závada et al., 2017).  While writing my dissertation proposal, I was influenced by several studies using Henry David Thoreau’s notes to document plant species loss and phenology since 1851 in Concord, Massachusetts. The fact that closely related, co-occurring species responded in many cases to climate very differently from one another (Willis et al., 2010; Willis et al., 2008) led me to pose a question ‘Are chicory plants we see today, genetically the same as those seen by Thoreau, or have these populations shifted with time?’ 

This research sort to answer the question ‘are chicory plants we see today genetically the same as those seen by Thoreau? Photo: Tomáš Závada

Archival plant DNA is usually well-preserved as long as the plant tissue has been dried properly. Glue can often complicate DNA extraction and no matter what adhesive was used, mounting specimens is a blend of science and art. Thoreau’s 648 preserved plant specimens inspired a recent exhibition “In Search of Thoreau’s Flowers: An Exploration of Change and Loss” exhibition at Harvard Museum of Natural History. We successfully extracted DNA from 84 herbarium specimens and 18 contemporary chicory populations and we used chloroplast DNA sequences and 12 chicory-specific microsatellite nuclear markers to assess the temporal genetic changes.

Contemporary Cichorium intybus (Chicory) was compared to the herbarium specimens. Photo: Tomáš Závada

The nuclear DNA markers showed a major shift in the genetic diversity and composition, with all historical herbarium collections belonging to a single genetic cluster and 16 out of 18 contemporary chicory populations belonging to different genetic clusters. Our results show that the genetic diversity and structure of Cichorium intybus populations have changed substantially since the founding populations in New England. While other studies linked the changes in New England plant distribution and phenology to climate change, our paper shows importance of cryptic genetic changes underlying the success of species adaptation to a rapidly changing landscape.

This study demonstrated the power of herbarium collections to help us understand global change. Photo: Tomáš Závada

Tomáš Závada Sterling College, Vermont, USA.

Read the full article online: ‘Radical shift in the genetic composition of New England chicory populations‘.

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