John Grahame

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Research interests - the shapes of shells

This page - research interests - differentiation at the DNA level

I'm interested in the evolution of differentiation in the wild, and being innately a marine invertebrate biologist I use a common, very variable intertidal snail, Littorina saxatilis, and its close relatives.


Some of the variation we see: snails from Thornwick Bay, Flamborough, on the Yorkshire coast. The thin-shelled H morph lives higher on the shore than the thicker, robust M, which is evidently adapted to resist predation by the green shore crab, Carcinus maenas. At least in Yorkshire, this variation is associated with a weak reproductive barrier (27) and assortative mating (15).



The most exciting recent findings are to do with evidence of selection in AFLP loci; the picture shows the sample of our 300 loci with those inferred to be influenced by selection lying well above the 99% quantile derived from a simulation (see below). This is written up in (7): Journal of Evolutionary Biology 14 : 611-619.



We have found evidence of a cline over just the few metres of vertical distance between the H, cliff-dwelling morphs, and the boulder field animals (M). The graph shows the data for the 15 AFLP loci inferred to be under selection. This is written up in Evolution 60: 278-278. These two papers (7, 1) discuss the evidence pertaining to selection and genomic differentiation in these morphs of the snail.




The interpretations in (7) depended on a simulation relying on theory provided by Beaumont & Nichols, 1996: Proc Roy Soc London B 263: 1619-1626. If you are interested you can download a description of the program and the zip file of the software from this site.

The work referred to above was funded by the NERC.

Developments: funded by the BBSRC, we have pursued the matter of what these AFLP loci, and their related sequence, may mean in terms of likely operation in the animals. Work on this is in preparation for publication now.



words about the program

program zip file