Rob Jennings, 2004 - 2005 Graduate Student Researcher : CICOR

I have spent most of the past year investigating population genetic variation of the marine polychaete worm Clymenella torquata (a bamboo worm of the family Maldanidae). During the summer of 2002, I collected ~30 worms from each of several sites around Cape Cod (Buzzards Bay, Hyannisport, Stage Harbor, Pleasant Bay, and Barnstable Harbor), as well as from Pembroke, ME and Belmar, NJ. I sampled these sites again in the summer of 2003, and added samples from Chance Harbor, New Brunswick (Bay of Fundy) and Gloucester Point, VA. These worms comprise the study organisms for the first chapter of my dissertation, which consists of a gene flow analysis to determine 1) if the Cape Cod peninsula is an effective biogeographic or genetic barrier between the Gulf of Maine region and the middle Atlantic coast of the U.S., as has often been hypothesized, 2) whether the Cape Cod Canal allows transfer around this putative barrier, and 3) what the patterns of gene flow are in Cape populations of C. torquata. I have sequenced the mitochondrial gene ATP6 (involved in the synthesis of ATP) for approximately 3/4 of the worms collectedam investigating amplified fragment length polymorphism (AFLP) analyses for use as nuclear markers. The data obtained thus far indicate little to no contemporary gene flow (that is, each population bears a distinct genetic signature; see Figure One). There are two main genetic signatures (haplotypes) found in all locations, and rarer closely-related haplotypes specific to each location. The presence of only one genetic signature (haplotype) in New Brunswick and only 3 haplotypes in Maine (2 of them rare) indicate that C. torquata’s has recently re-colonized these sites, in contrast to the older populations on the Cape and in New Jersey, where there is considerably more haplotype diversity. This pattern of lower genetic diversity in northern sites is typical of glacially influenced dynamics, where ice sheet advances destroy northern populations, which then slowly return and rebuild genetic diversity during interglacial periods.

In addition to the adult collections described above, I collected juvenile (<3cm) worms from Barnstable Harbor for the second objective of my dissertation. These juveniles should provide a better estimate of dispersal (which involves only organism movement between locations, as opposed to gene flow which includes survival to adulthood and reproduction in the new location) because most benthic (soft-bottom) invertebrates experience extreme mortality (upwards of 90% in some cases) in the period just after dispersal and settlement. Population genetic studies traditionally sample adults, whose genetic diversity may already have been culled by this post-settlement mortality, thus underestimating the true amount of dispersal that occurred.

My third objective has been to develop a theoretical framework for the issues and complexities introduced by the second objective. No current population genetic models incorporate two-stage (i.e., juvenile and adult) dynamics, nor do they consider the possible effects of severe post-settlement mortality. The third objective thus seeks to interpret any differences seen between the gene flow estimate of the first objective (based on adults) and the dispersal estimate of the second objective (based on juveniles). To further develop the third objective, I traveled to Berkeley, CA, in May 2003 to visit Montgomery Slatkin. Dr. Slatkin is at the forefront of theoretical population genetics, and I discussed with him in general terms the issues and forces that would be important to such a model, as well as its general form. I am hoping this will lead to a more formal collaboration for this chapter of my dissertation.

In the fall semester of 2002, I was the TA for WHOI’s new Invertebrate Biology class. The course was designed as a pilot project; it was taught once a week in seminar style, in hopes that it could eventually be built into the sort of full-scale Invertebrate Biology class that WHOI has offered in the past. Professor Stace Beaulieu and I used my trips around the Cape last summer to collect marine invertebrates for the class. TAing this class was a great opportunity for me to help teach the type of class I had just attended in Friday Harbor. I think the course was a great launching point for what will hopefully become a full-time class; the students enjoyed the class thoroughly but cited lack of adequate class time as a serious drawback.