Cryptic speciation in Frullania asagrayana

ajb_coverSynopsis: Frullania asagrayana is a leafy liverwort found on tree trunks and rocks along the east coast of the United States and Canada. We sampled collections of F. asagrayana at DNA sequences (2 chloroplast and 1 nuclear) and microsatellites (10 loci). Despite no distinguishing morphological characteristics or DNA sequences, F. asagrayana sorts neatly into two very distant genetic clusters based on microsatellites. These groups roughly correspond to a Southern group extending from Mississippi to Maryland, and a Northern Group from Newfoundland south to North Carolina. However, in the southeastern US, the Northern group is restricted to the mountains. Admixture analysis using Structure showed limited mixing between the groups, but migration was shown to be asymmetrical, from the northern group into the south. Genetic diversity at very small scales (one tree or rock) was very low, but diversity at one forest site was overall very similar to the diversity seen on continental scales.

My role: This was the research of Megan Ramaiya, an undergraduate in the Shaw Lab who collected, extracted, and analyzed all of the molecular data. I was responsible for running the population genetic analyses, including Migrate, IM, and Structure, and creating figures showing the results. Some of the scripts I used for this paper, to convert between popgen program formats, can be found on my¬†Programming page. One lesson I take from this study is that these cryptic species are only distinguishable at the microsatellite level. We have been classifying life based on morphological distinctiveness or DNA sequence divergence, but potentially much more diversity is undiscovered because we aren’t using specific enough tools. Plus, we got the cover of AJB, woohoo!

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