PHYSIOLOGICAL PROPERTIES OF GENE ARRANGEMENT CARRIERS INDROSOPHILA PERSIMILISIII. CYTOPLASMIC INFLUENCE ON FECUNDITY OF ARRANGEMENT HETEROZYGOTES

Abstract

Competition experiments utilizing artificial populations designed to measure adaptive values of chromosomal variants from various Drosophila species have demonstrated in many instances that each arrangement from any particular locality at a single point in time may possess particular genetic properties maintained principally by the action of natural selection. Such genetic properties often must be perpetuated by a co-adaptation between two separate arrangements, that is, by the incorporation of higher net fitness in arrangement heterozygotes (Wright and Dobzhansky, 1946; Dobzhansky, 1952). In seeking for physiological properties which are determined by the gene contents of certain chromosomal arrangements from D. persimilis native to the Yosemite area of California, the author has found that the properties of the two most common arrangements (Whitney and Klamath of chromosome III) generally differed when comparing homozygotes, and heterozygotes often displayed heterosis (Spiess, Ketchel, and Kinne, 1952: Spiess, Terrile, and Blumenheim, 1952). It was in the egg-laying capacity experiments that a number of interesting facts lending support to expectations from competition experiments appeared (Spiess, 1950). 1) Flies homozygous for Whitney or Klamath differed in fecundity; 2) heterozygotes maintained a higher rate of production than either homozygote but differed in their production depending upon which arrangement was derived from the female parent. This difference in reciprocally derived heterozygotes though slight was nevertheless significant. Apparently while increased egg production was characteristic of the heterozygotes, an influence from cytoplasmic factors conditioned by the chromosomal arrangement of the female parent effected a detectable amount of difference in expression of heterosis. It was decided to test further this cytoplasmic conditioning effect in inversion heterozygotes by measuring the egg-laying capacity of Standard arrangement females and their heterozygotes with Whitney.