Population genetics in Littorina striata on a microgeographical scale
De Wolf, H.; Backeljau, T.; Breugelmans, K.; Brito, C. (1993). Population genetics in Littorina striata on a microgeographical scale. Belg. J. Zool. 123(Suppl. 1): 22-23
In: Belgian Journal of Zoology. Koninklijke Belgische Vereniging voor Dierkunde = Société royale zoologique de Belgique: Gent. ISSN 0777-6276; e-ISSN 2295-0451, more
The periwinkle Littorina striata is a planctotrophic developer. According to Scheltema (1) and Crisp (2), it is expected to have great dispersal abilities resulting in a high degree of gene flow. Scheltema (1) and Crisp (2) consider gene flow as a homogenising force, diminishing population differentiation in both genetic and phenotypic traits. In contrast to these ideas L.striata exhibits a high degree of shell variation even on a rnicrogeographical scale. On I1heu de Vila Franca, which is a volcanic crater in the Açores, different rnorphotypes of L.striata are found. The shell surface of the periwinkle can be smooth or nodulous. A white band on the last whirl can be present or absent. In addition all morphotypes can be erodated. Although different morphotypes do co-occur, nodulous animals are mostly found on the sheltered inside, whereas the other rnorphotypes are found on the exposed outside of the crater. Six populations of L.striata from Ilheu de Vila Franca and Vila Franca (Sao Miguel, Açores) were surveyed for electrophoretic variation at four enzyme loci (GPI, PGD, MDH and MPI). All six populations were found being in Hardy Weinberg equilibrium. Only at locus MPI, a significant genetic heterogeneity was observed. No genetic heterogeneity was found between smooth, nodulous and males and females. Wright's F-statistics showed no population differentiation (Fst=0.014). Based on the value of Fst, gene flow was estimated: Nm=17.06. This preliminary study does not find a convincing genetic basis for the observed morphological heterogeneity. Therefore phenotypic plasticity could account for the observed morphological differences. Natural selection can however not be ignored since only a small part of the genome was investigated.(1) R.S. SCHELTEMA (1971). Biological Bulletin 140:284-322.(2) D. CRISP (1978). Ecology and Evolution. Plenum Press, New York.
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