Genetic variation in a semi-natural Drosophila population after a bottleneck I. Lethals, their allelism and effective population size

Abstract

A semi-natural Drosophila melanogaster population was twice forced through a genetic bottleneck and allowed to recover naturally. In one case additional variation was introduced to the recovering population. The percentage of lethal chromosomes, the level of allelism between these lethals, and the effective population size calculated from the allelism of these lethals all rose sharply in the few generations following each bottleneck, though this was not t~,e case in the very first generation. Thereafter this rise decelerated rapidly and never returned to pre-bottleneck levels. Additional introduced variation had little effect. The reasons for and implications of this pattern have been considered.

Evolution of Chilean colonizing populations of Drosophila subobscura: lethal genes and chromosomal arrangements

“…This is an order of magnitude higher than the rate estimated for independently arising lethal genes, which is 0.0041 ± 0.0019 for the O chromosome (Loukas et al 1980) and 0.0029 ± 0.0009 for the second chromosome of D. melanogaster (Begon et al 1985). The lethal genes responsible for the allelism between the Chilean populations analyzed were the lethal genes completely associated with the O 5 inversion, the lethal gene partially associated with the O 3?4?7 arrangement, and a lethal gene found once in both populations and located in an O 3?4?2 chromosome.…”

“…Most probably, the linkage disequilibrium for the inversions O 3?4 and O 7 is due to an extreme reduction of crossing over in the region between them (Sperlich and Feuerbach-Mravlag 1974 (Mestres et al 1990(Mestres et al , 1992(Mestres et al , 1995Solé et al 2000) presented only two kinds of allelic (Loukas et al 1980) and in chromosome II of D. melanogaster (p ? = 0.0029) (Begon et al 1985). Overall, out of 99 lethal genes studied in the American continent, 49 proved to be different.…”

“…Effective population size (N e ) was estimated as described by Nei (1968) and also by Begon et al (1985): both methods gave very similar values. Lethal heterozygote fitness reduction was estimated following Crow and Temin (1964) and Nei (1968).…”

Impact of clonal growth on effective population size in Hymenoxys herbacea (Asteraceae)

“…While demographic methods are frequently used and reasonably robust for a wide range of mating systems and dispersal patterns (Heywood, 1986;Basset et al, 2001), few comparisons of N e involving both demographic and genetic approaches exist (but see Begon et al, 1980;Husband and Barrett, 1992). Husband and Barrett (1992) found that demographic estimates of effective population size were between 2 and 500 times larger than genetic estimates.…”

Genetic variation in a semi-natural Drosophila melanogaster population after a bottleneck II. The relative fitnesses of second chromosomes

“…The population under study was a Drosophila melanogaster population which occupied a large isolated greenhouse, and has been described in a companion paper (Begon et al, 1984b). The 'prebottleneck' phase of the population lasted from the beginning of the study in October 1979 until 23 April 1980.…”