SELECTION INDROSOPHILA PSEUDOOBSCURAIN RELATION TO CROWDING

New evidence of heterosis in naturally occurring inversion heterozygotes in Drosophila pseudoobscura

“…In this species, the over-all fitness of the ST/CH heterozygotes was found to be no higher than that of the ST/ST homozygotes, hut much higher than that of the CH/CH homozygotes. However, the different components of fitness of these karyotypes arc known to vary in their relative values quite appreciably in different environments (Heuts, 1947(Heuts, , 1948Birch, 1955).…”

The fate of polymorphic inversions of Drosophila melanogaster transferred to laboratory conditions.

“…Birch (1955) found the case that natural selection was a function of larval density, and the selection at high density was favorable to the standard gene arrangement of D. pseudoobscura. Lewontin (1958) showed that a gene arrangement derived from a laboratory population after many generations of maintenance had increased in adaptive value due to natural selection acting on genes within the arrangement.…”

Effect of larval crowding on adult mating behaviour in Drosophila melanogaster

“…Most of these studies have focused upon the effect of larval density on eggadult viability, showing that, generally, larval crowding produces an important decrease on viability (Sang, 1949;Birch, 1955;Bakker, 1961;Bentvelzen, 1963;Lewontin and Matsuo, 1963;Barker, 1973; Barker and Podger, 1970a, b). It has also been shown that larval crowding acts to reduce adult body size and female fecundity (Alpatov, 1932;Pearl, 1932).…”