Sonja Schmitz completed her doctoral work on the systematics of the circumpolar legume Lathyrus japonicus in our lab. The species is of interest in the larger context of our lab's emphasis on the evolutionary biology of Lake Champlain sandy beach disjunct species, including Ammophila breviligulata and Hudsonia tomentosa. All of these species we hypothesize to have reached our own Champlain Basin at the time when the Champlain Sea was a marine arm of the St. Lawrence ca. 10,000 years ago.
Sonja's work has documented the genetic structure and divergence of Lathyrus
throughout its circumpolar range, but with particular focus on the
northeastern part of North America. Using a
combination of chloroplast DNA data and allozyme variation, she was
able to show that there are two major clades in the species, one
Arctic-Pacific and the other Atlantic-Great Lakes, and that each of
these has recently yielded, by peripheral isolation, genetically
distinct southern and inland lineages. The genetic
structure of the Atlantic-Great Lakes clade strongly suggests that it
occupied a refugium on the exposed North-Atlantic coastal plain off New
England and the maritimes in the last ice age. The map below
shows the areas with greater genetic diversity in darker shades; these
Sonja inferred to be areas of longer residency by the beachpeas.
Of particular interest is an apparent suture zone at the mouth of the
St. Lawrence, where the two major clades have come into contact,
apparently quite recently. A synopsis of this work is
available in Barrington and Paris (2007) -- available as a pdf via a
link on Barrington's home page.
|Sonja at a lakeshore beachpea site.||Beachpea in its native element.|