THE GENETIC-STRUCTURE OF BETA-VULGARIS SSP MARITIMA (SEA BEET) POPULATIONS .2. DIFFERENCES IN GENE FLOW ESTIMATED FROM RFLP AND ISOZYME LOCI ARE HABITAT-SPECIFIC

In a previous paper, isolation by distance at RFLP loci was demonstrat ed in 10 populations of sea beet growing on the Dorset (U.K.) coast. I n the same populations there was no evidence of isolation by distance at isozyme loci. Here, the data are reanalysed to reduce biases result ing from nonrandom mating within the populations; the contrast between RFLPs and isozymes remains very clear. Separate analysis of cliff-top populations shows strong isolation by distance at both RFLP and isozy me loci, whereas in populations on sea walls around the perimeter of P oole Harbour there is isolation by distance at RFLP loci but not isozy me loci. Thus, whatever the cause of the difference between RFLP and i sozyme loci, it occurs in the harbour populations only. There was no e vidence that founder effects are a significant source of variation bet ween populations on the perimeter of the harbour. This is very differe nt from a previous finding of strong founder effects between populatio ns on Furzey Island (in Poole Harbour).