1983. A chromosomal inversion polymorphism in Scandinavian populations of the seaweed fly, Coelopa frigida. -Hereditas 99: 135-145. Lund, Sweden. ISSN 0018-0661. Received November 29, 1982 British populations of the seaweed fly Coelopa frigida are polymorphic for the large a@ inversion on chromosome I (BUTLIN et al., Heredity48: 45-55). Flies from Norway, Swedenand Denmark are shown to possess the same inversion polymorphism, and to exhibit similar though not identical polymorphisms at two enzyme-determining loci associated with this inversion. There is a cline in inversion frequencies from the North Sea, through the Skagerrak and Kattegat, into the Raltic Sea. This cline correlates with salinities, the algal composition of seaweed beds in which Coelopa breeds: and with the presence of the sibling species C. pilipes.It is suggested that heterokaryotypic advantage is the major selective force maintaining this polymorphism, and that genotype-related differences in generation times, and the longevity of seaweed beds, may constitute lesser forces acting on the inversion frequencies.

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SUMMARYPopulations of the seaweed fly Coelopa frigida are polymorphic at three loci determining the enzymes peptidase-1 (Pep-i), alcohol dehydrogenase (Adh) and larval esterase-2 (Es-2). Alleles at these loci have been shown by others to be non-randomly associated with each other. In the present paper we report non-random associations between the Adh and Es-2 loci and inversions on chromosome I. The two common alleles Adh-B and D are in strong linkage disequilibrium with the a and /3 inversions, but the Adh-A and C alleles are not so. The X and Y alleles at the Es-2 locus show weak, but still significant, associations with the inversions. We consider possible linkage relationships of the loci on the chromosomal arrangements, and discuss the hypothesis that they constitute part of a coadapted gene complex whose members code for functionally related enzymes.

SUMMARYThe rate at which the seaweed fly, Coelopaftigio'a, develops from egg to adult is shown to be associated with the presence of alternate alleles at the alcohol dehydrogenase locus. Evidence for this correlation is presented for animals in laboratory culture and in natural populations. The relevance of the association to the maintenance of genetic polymorphism is discussed.

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