Variation in genetic traits of the Baltic clam Macoma balthica from a tidal gradient in the subarctic

Abstract

In a subarctic tidal gradient, strong heterogeneity in genetic traits of the Baltic clam Macoma balthica was found. The heterogeneity was stronger within the intertidal gradient, over a distance of only about GO mi than along a horizontal gradient over a distance of 1200 km in clams from the west European coast. For the locus Idh1 and the average heterozygosity, a tidal dine was found. The frequency of allele Idh1-B decreased with tidal level, whereas the frequency of allele Idh1-C, as well as the average heterozygosity, increased. The possibility is discussed that the strong genetic heterogeneity and tidal dines are caused by differential selection related to the (subarctic) temperatures to which the higher tidal zones are more exposed. [KEYWORDS: Allele frequency cline; mytilus-edulis; population-genetics wadden sea; electrophoretic data; allozyme variation; systematics; settlement; pollution; selection]