Are Drosophila melanogaster populations under a stable geographical differentiation due to the presence of P elements?

Abstract

In order to simulate the outcome of the P-M status of Eurasian populations of Drosophila melanogaster, the evolution of experimental mixed-strains was monitored for up to 50 generations. The results were compared with the evolution in natura of European populations sampled in 1981-83 and 1986-87 over a similar period of time. Different combinations of P and M' strains, Q and M' strains, M' and M' strains and M and M' strains were set up at 25°Cand duplicated at 13°C night-21°C day. The possibility of a change towards a P type only appeared with the introduction of the strong P strain Harwich into Eurasian strains. Strains with strength similar to that of Harwich are not currently found in wild populations. With the introduction of weak P and Qstrains of the strength presently observed in western Europe, experimental populations evolved slowly towards a Qstate or a weak M' state. M'-M' mixed populations resulted in strong M' strains, as was the case for M-M' populations. In these cases. P sequences were not eliminated. In wild populations both genetic and molecular analyses showed no significant differences, over a five year period, for GD sterility potentials, for total P copy number or for distribution of the full-sized and KP elements. Changes in Eurasian populations are probably taking place at a very low rate and may even have stopped, leading to a quasi-stable differentiation over the continent. During the different steps of progressive invasion of P transposable elements, several deleted elements developed and natural selection may have acted on them. The possibility of the selection of different types of regulatory mechanisms according to the presence of different kinds of derivative elements, leading to a world-wide differentiation between P-Q and M' strains is discussed. INTRODUCTIONIn the P-M system of Drosophila melanogaster, the syndrome of hybrid dysgenesis (inducing gonadal sterility, high mutation level, etc.) is understood to be related to the activity of the P element family of transposons (reviewed by Engels, 1989). P element structures can be classified into two broad types: autonomous (complete) elements of 2.9 kb, and non-autonomous elements that usually have sustained internal deletions of varying sizes.Strains of Drosophila may be characterized on the basis of two properties related to the phenotypic effects of their P elements. Strains are specific in their ability for mobilizing P elements that are in an unregulated state. This ability is referred to as "P activity potential". Strains may also vary in their property to regulate or suppress the activity of the autonomous P elements present in their genomes. This property is referred to as "P susceptibility". It covers the joint action of all mechanisms affecting P element regulation, including that of cytotype (Engels, 1979).Based on these properties, strains may be classified into four broad types, according to their phenotypic characteristics in diagnostic test crosses and the number of P elements they possess.P strains have low to high...

DrosophilaP element: Transposition, regulation and evolution

“…This event cannot be precisely dated because P elements may have been maintained in small isolated populations during a long period before their spread to other populations. A hypothesis on the process of P element invasion may be postulated, given data on the evolution of experimental mixed populations (Anxolab6h~re et al, 1986;Periquet, Hamelin & Ronsseray, 1989). Anxolab6h~re, Kidwell and Periquet (1988) proposed the model of 'innovative stepping-stone' invasion.…”

Comparative evolution of P–M system and infection by the sigma virus in French and Spanish populations ofDrosophila melanogaster

“…In Eurasia, a gradient can be traced from Western Europe, where most strains are Q, to mid-Asian areas where M' strains predominate (Anxolabehere et al 19886). A similar gradient was also found in the Languedoc area, over a distance of 250 km, with weak P populations in the north, Q populations in the centre and M' populations in the south (Anxolabehere et al 1988 a) raising the question of the stability of this geographical distribution (Periquet et al 1989).…”

“…The spread of these elements in the southern populations during the 1987-1991 period and the mixing with the other elements may explain the fate of these populations. This interpretation assumes that the complete elements have a slight advantage, as generally observed in experimental evolution (Anxolabehere et al 1986) and from the general model of the invasion hypothesis of D. melanogaster by P elements (Kidwell, 1983;Anxolabehere et al 19886;Periquet et al 1989;Daniels et al 1990). This model suggests that the invasion of the Americas preceded that of Europe by about a decade.…”

Domesticated P Elements in the Drosophila montium Species Subgroup Have a New Function Related to a DNA Binding Property

“…This is illustrated by the invasion of the genome of D. melanogaster by the canonical P element. Complete P element copies able to transpose cannot invade genomes that have deleted copies able to regulate transposition (Periquet et al 1989). Alternatively, coexistence may not result from horizontal transfer, but from the divergence of two subfamilies from a common ancestor in the same genome.…”