Population genetics of the scallop Pecten maximus : morphological, allozyme electrophoresis and mitochondrial DNA approaches.
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Abstract
Although considerable evidence exists to suggest that certain populations of
scallops, Pecten maximus (L. ) are reproductively isolated, attempts to date to
differentiate populations using data from allozyme electrophoresis have been
unsuccessful. In order to further investigate the population structure of this
species, genetic differentiation was quantified using mitochondrial DNA (mtDNA)
markers and the results compared to morphological comparisons and allozyme
variation. A multivariate morphological study revealed little variation in shell shape
although animals from Brest and La Trinite (Brittany, France) appeared to have
longer hinges. A population from Saint Brieuc Bay, Brittany which exhibits
differences in reproductive cycle from neighbouring populations could not be
separated on the basis of shell shape although unquantified differences in shell
colour were noted. Allele frequencies at 7 loci assessed by allozyme
electrophoresis were essentially homogeneous throughout the sample range in
accord with previous studies and provided little evidence for population
subdivision. Length variation of the mtDNA was extensive, therefore variability
was assessed through a PCR approach in order that this did not cause analytical
problems. On the basis of sequence divergence data there was convincing evidence
that P. maximus from Mulroy Bay, Eire, a semi-enclosed sea lough, were
genetically differentiated from all other samples. This could not be unequivocally
attributed to a reduction in gene flow since the sample consisted of an ongrown
single spatfall. Although no distinct pattern of mtDNA haplotype frequencies was
apparent, the frequency of the commonest haplotype varied between sites with a
pattern similar to that of allozyme allele frequencies in Aequipecten opercularis, a
scallop species with a similar distribution and life history for which there is
evidence of considerable population subdivision. In comparisons of P. maximus
and the closely related P. jacobaeus no consistent differences were detected in
morphology, allozymes or mtDNA data. The taxonomic standing of P. jacobaeus
is brought into question