Isolation by Disruptive Selection

Effects of disruptive selection XI: gene flow and divergence

“…In each of these experiments total variance rapidly increased, the subpopulations rapidly diverged in mean, and they rapidly became isolated from one another because the "hybrid" flies ceased to be included amongst those selected. (These experiments are not to be confused with those reported by Thoday and Gibson (1962) in which mating choice was allowed and strong reproductive isolation developed). Though Gibson and Thoday's second experiment involved relatively weak selection, it seemed desirable to test the effectiveness of still weaker selection, and that was the prime purpose of the present experiments.…”

Assortative mating for a metrical characteristic in Drosophila

“…There may also be behavioural differences between flies of different sizes leading to minor modifications in courtship. Thoday and Gibson (1962) found that disruptive selection based on sternopleural chaeta number may lead to isolation, i.e. the splitting of a population into discrete sub-populations.…”

Disruptive selection in crop development

“…The intermediate position on the frequency diagrams is occupied by hybrids between the wild and cultivated sorghums. There is a clear resemblance between our first three text-figures and those obtained for Drosophila by Thoday and Gibson (1962) and by Thoday (1964, fig. 6).…”

“…Secondly, when Millicent and Thoday (1961) Thoday (1961) show that differences developed under disruptive selection between the wild and cultivated sorghums would still be maintained. Thirdly, divergence in Drosophila had occurred after only 12 generations in one trial, and after only 7 generations in another, under a regime of disruptive selection with opportunity for random mating Thoday, 1964). This demonstrates that the time required for the development of the sorghum crop from the wild type by disruptive selection need not have been great.…”

“…Mather (1953Mather ( , 1955 defined disruptive selection and deduced that its application should result in the development of polymorphism, with the production of reproductive isolation barriers within the population under the appropriate conditions. Thoday and his co-workers (Thoday, 1958(Thoday, , 1959(Thoday, , 1960(Thoday, , 1964Boam, 1959, 1961;Millicent and Thoday, 1961;Thoday and Gibson, 1962;Gibson and Thoday, 1962), working Our results show that the behaviour of Drosophila in the laboratory of Thoday and his co-workers parallels the development of the sorghum crop in Africa during the past 5000 years, and it presents a model applicable to A From U.S.A., collected originally in Ethiopia.…”