The genetics and evolution of the mariner transposable element in Drosophila simulans: worldwide distribution and experimental population dynamics

We have studied both the frequency and biogeographical distribution of the transposable DNA element mariner in natural populations of Drosophila simul ans and the short-term evolutionary characteristics of mariner in experimen tal populations. The mariner element has been identified in natural populat ions of D. simulans from Africa, Europe, the Middle East, Japan, Australia, several Pacific islands, North America, and South America. Only four lines out of 296 were devoid of active mariner elements, as measured by the pres ence of functional mariner transposase. A slight correlation was found betw een the latitudinal coordinate of the collection sites and the level of mar iner activity in the population; this correlation became highly significant in Australia where a cline in mariner activity was observed along the east ern coast of the continent. We also observed that wild-type laboratory stra ins kept for several years as small populations might lose mariner activity over time. Using experimental populations, we modeled what might happen wh en naturally occurring populations exhibiting high and low levels of marine r activity encounter one another. We found that active mariner elements eit her will tend to lose their activity over time and gradually become inactiv e or possibly will be lost from the population; in either case, this will l ead to the pattern seen in this experiment of a significant loss of mariner activity over time.