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QUANTITATIVE VARIATION AND CHROMOSOMAL ARRANGEMENTS IN A POPULATION OF DROSOPHILA PERSIMILIS FROM THE REDWOODS

Chromosomal arrangements (inversions) with stable frequencies (either "rigid" or "flexible") in natural populations of Drosophila are expected to hold particular alleles of linked loci in relatively unrecombining blocks which are most likely to be adaptive to their possessors (Dobzhansky, 1961, 1962). It follows that, for such populations under local conditions, the suppression of recombination constrains a portion of the potential genetic variability and maximizes whatever benefit of heterozygosity plus epistatic interaction may exist between relevant portions of the genome. For populations in which arrangements are stabilized we would expect the karyotypes to control particular fitness properties by which they should differ in some degree (unless their stability is derived from a frequency dependency with no selective differences at the point of equilibrium). Thereby versatility to meet seasonal or geographic changes throughout the population's distribution may well be gained, either if the karyotypes have different niche optima or if heterokaryotypes confer heterotic or homeostatic integrative properties on their carriers. (See also recent discussions by Crumpacker and Salceda, 1968; Marinkovic et al., 1969). In ascertainment of those fitness properties it has been found useful in the past to use the technique of randomizing the genetic background through strain crossing and comparing the karyotypes for those constant features distinguishable from the "noise" of background variation. The previous work of the senior author in searching for fitness properties of chromosomal polymorphs in Drosophila persimilis has concentrated on testing strain cross F1 individuals for fecundity, viability, rate of development, cold temperature resistance of early stages, and mating propensity (Spiess and Schuellein, 1956; Spiess, 1958; Spiess and Langer, 1961, 1964; Mohn and Spiess, 1963). The present report extends these studies in certain ways: