Variation of Scutellar Bristles in Drosophila IV. Effects of Selection

Abstract

A series of experiments of selection of scutellar bristles in D. melanogaster is described. The evidence suggest that there are three levels at which artificial selection is relatively ineffective and that these levels are not necessarily a function of homozygosity but rather of natural selection maintaining the line at a new equilibrium value. Crosses between the initial set (A set) of selection lines led to the conclusion that there is a consistent dominance of the parent with the lower scutellar value.Inversion-marked chromosomes were used to determine the location of selection advance on chromosomes I, II, and III. In the lines which had reached the highest level of selection advance the most effective chromosomes were chromosomes I and III or a combination of each of these. The lines which had reached the second level showed a marked heterogeneity of response, which included large negative components resulting from interchromosomal interactions.

Studies on The Scutellar Bristles of Drosophila Melanogaster I. Basic Variability, Some Temperature and Culture Effects, and Responses to Short-Term Selection in the Oregon-Rc Strain

“…The results of selection in wild-type populations are also relevant to this subject and have been studied by Payne (1918), Sismanidis (1942), Fraser (1963), Latter (1964Latter ( , 1966, Fraser et al (1965), and Scowcroft (1966aScowcroft ( , 1966b. This report deals with a similar study in the Oregon-RC wild-type strain.…”

Effects of temperature on selection for scutellar Bristles

“…Thus it is possible that the inverse correlation between temperature and scutellar bristle number may be associated with changes in the size of flies cultured at different temperatures. However, Fraser, Erway and Brenton (1968) Artificial selection can alter the responsiveness of scute populations to temperature (Druger, 1967;Kindred, 1965) and can reverse the relationship between scutellar bristle number and temperature. Natural selection affected the responsiveness of the present control lines to culture temperature but a more pronounced effect occurred in the line selected at 20° C. The pattern of extra bristles produced when the Athens base population was first cultured at 20° C. was replaced under selection for increased scutellar bristle number at 20° C. by a different pattern, with a higher proportion of extra bristles at anterior sites.…”

Variation of Scutellar Bristles in Drosophila V. Components of Selection Advance

“…The mating procedure and conditions to which these matings were exposed were similar to those employed by Fraser et al (1965) in their chromosomal analyses. All matings were carried out in half-pint cream jars at a constant temperature of 23°C.…”

“…Rendel (1959), Rendel and Sheldon (1960), and Latter (1964) have shown that pro bit analysis is extremely useful in the transformation of data, and it has been applied to this data in an attempt to resolve the nature of chromosomal interactions, since if these were due wholly to the threshold effect then the probit transformation would remove them. Fraser et al (1965) have suggested from their data that there are complex relationships between scutellar number and reproductive fitness. The extensive data of our analyses make it possible to compare the relative survivals of the different genotypic classes, and to correlate survival with scutellar number.…”

“…Fraser et al (1965) have used a similar method to dissect the advances produced by selection for extrascutellars and for missing scutellars. They found that interchromosomal interactions were a major component of selection advances in some lines, and they suggested that the interactions could be an artefact due to the canalization of scutellar number at four.…”