Population crash, population flush and genetic variability in cage populations of Drosophila melanogaster

Abstract

SummaryA large increase in the total phenotypic variance of thorax size was observed in a cage population of Drosophila melanogaster, maintained at 28 °C, a few months after it had been the victim of a naturally occuring population crash, the number of individuals in the population having, at a given moment, been reduced to half a dozen. In order to ascertain whether that increase in total phenotypic variance was due to an increase in environmental or in genetic variance that population was submitted, together with five other normally developing cage populations, to a selection programme for high and low bristle number. The additive genetic variance of these various populations was thereafter estimated. The additive genetic variance of the 28 °C cage population, victim of a population crash, was found to be highly significantly larger than all the other ones. The consequences of that unexpected observation on the theories of evolution are discussed. It is argued that that result confirms some of the predictions of the genetic revolution (genetic transilience) hypothesis of speciation.

Effects of bottlenecks on quantitative genetic variation in the butterfly Bicyclus anynana

“…With the exception of the statistically problematic experiment of Lints & Bourgois (1984) who measured an increase in V A for sternopleural bristle number following an extended bottleneck induced by high temperature, this possibility has not been explored by any of the empirical studies aiming to assess the consequences of bottlenecks for V A . If, for example, the more heterozygous genomes are favoured, for which there is increasing evidence (Keller et al, 1994 ;Saccheri et al, 1998), V A for the selected traits themselves or for those traits in linkage disequilibrium with the selected regions may increase, or decrease less than predicted by the neutral additive model.…”

“…The most influential of these empirical studies was that of Bryant et al (1986), followed up in Bryant & Meffert (1993), showing that V A for some morphological characters of Musca domestica can increase substantially after bottlenecks. Bottleneckinduced increases in V A have also been shown for sternopleural bristle number (Lints & Bourgois, 1984), viability (Lo! pez-Fanjul & Villaverde, 1989 ;Garcı!…”

Phenotypic and genotypic differentiation in cage populations of Drosophila melanogaster. I. Duration of development, thorax size and weight

“…They could be due to the fact that 28 °C is too high a temperature for Drosophila melanogaster, as shown by the failure of all the attempts made to create a subpopulation at 29 °C. They could also be due to the origin of that 028 subpopulation which, presumably due to maladjustment to the temperature, suffered a severe bottleneck and therefore started from as few as half a dozen individuals (for further details, see LINTS & B OURGOIS , 1984). On the other hand -and this is the only comparison which can be made with other studies -six years after the foundation of Vetukhiv's cages, raised at 19°, 25° and 27 °C, A NDERSON (1966) did observe that the wing length of the flies raised at 19 °C was larger than that of the flies raised at 25 ° and 27 °C, but he could not detect any difference between the 25° and 27 °C flies.…”

The founder effect theory: quantitative variation and mdg-1 mobile element polymorphism in experimental populations of Drosophila melanogaster

“…The theoretical expectations under additive models, i.e., a decrease of genetic variance during the first generation (Lande, 1980), is not in accordance with our results. Lints and Bourgois (1984) also reported an increase in heritability in experimental founded populations. Nevertheless, their experimental procedure could not discriminate between the respective roles of the bottleneck and the environmental changes.…”