Selection for increased abdominal bristle number in Drosophila melanogaster with concurrent irradiation

Abstract

Replicate lines, each initially with one hundred pairs of parents selected at 50% intensity, were derived from the Canberra strain. In later generations population size was reduced and selection intensity increased. Three lines were selected without irradiation and five with 1000 r X-rays per generation for thirty generations. Selection was continued until generation 66. Long-term responses were similar in unirradiated and irradiated lines, and there was evidence that genes with large effects influenced response patterns in both groups of lines.

The Nature of Quantitative Genetic Variation in Drosophila. II* Average Dominance of Abdominal Bristle Polygenes

“…The selection lines were all derived from the Canberra (Can) population (Latter 1964) and are described in detail by Frankham et ai, (1968aFrankham et ai, ( , 1968b, Jones et al (1968) and Hollingdale and Barker (1971). They were all selected for increased abdominal bristle number for 50 or more generations.…”

The rate of polygenic mutation

“…As an aggregate, polygenic mutations often appear at a much higher frequency than macromutations (Mukai, 1979), and some evidence suggests that the mutation rate varies inversely with mutational effect (Gregory, 1965). Unlike macromutations, mutations with small effects often arise in a non-directional manner, having little or no average effect on the mean of a character in an unselected base population (Oka et al 1958;Gregory, 1965;Hollingdale & Barker, 1971;Mukai et al 1984). If the pleiotropic effects of mutant polygenes are also highly variable (and little information on this exists), then polygenic mutation would provide a potential mechanism for the evolution of adaptive suites of characters that is unlikely to be matched by macromutation.…”

Adaptation of Drosophila melanogaster to increased NaCl concentration due to dominant beneficial mutations

“…Yet, the magnitude of the role of preexisting variation vs. new mutations is unknown (Haldane 1932;Fisher 1930;Maynard Smith 1976;Hill 1982;Nei 2007;Gillespie 1991Gillespie , 2006Hartl and Taubes 1998;Orr 1998Orr , 2005aOrr , b, 2009Orr , 2010Orr and Betancourt 2001;Yedid and Bell 2002;Bull and Otto 2005;Rokyta et al 2005;Houle and Kondrashov 2006; Barrett and Schluter 2007;Lynch 2007;Brookfield 2009;Stoltzfus and Yampolsky 2009;Woodruff and Zhang 2009;Azad et al 2010;Lynch and Abegg 2010;Pritchard et al 2010 and references therein). To estimate the effect of mutation on adaptations, genetic variation in the founding populations should be eliminated by using homozygous isogenic stocks so that fitness changes and selection responses over generations can be attributed to new beneficial mutations (Knight and Robertson 1957;Hollingdale and Baker 1971;Caballero et al 1991;Hill and Caballero 1992;Mackay et al 1994;Bataillon 2000;Azad et al 2010).…”