Transient equilibrium at the est 6 locus in wild populations of Drosophila melanogaster

Est-6 polymorphism was studied by extensive sampling of Drosophila melanogaster populations in different years and in different places in the Venetia region of North-East Italy. In many cases an unexpected excess of homozygous genotypes was found. The excess is relatively high in late August and early September and it is followed by a progressive decrease with time toward late autumn, when the population size undergoes a progressive increase. It is postulated that in late August an apparent natural population of D. melanogaster virtually consists of several micropopulations; in each of which geographic isolation induces a certain degree of inbreeding. The excess of homozygous genotypes decreases with time since the progressive increase of the effective population size gives progressively more opportunities to the original micropopulations of coming into contact and of intermizing. © 1977 Dr W. Junk BV Publishers.