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 maritimus 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.