Whether or not Daphnia is typical of eukaryotes with respect to intron gain (and loss), IU Bloomington evolutionary biologist Michael Lynch, the project's principal investigator, agreed that the discovery of parallelism will surprise his colleagues.
"Remarkably, we have found many cases of parallel intron gains at essentially the same sites in independent genotypes," Lynch said. "This strongly argues against the common assumption that when two species share introns at the same site, it is always due to inheritance from a common ancestor."
A unique and important aspect of the scientists' work is that they focused on one species (Daphnia pulex). Past studies have looked at a few introns shared by vastly different species. In doing so, geneticists have almost certainly missed the ephemeral appearance of new introns, and therefore would come to the wrong conclusions about how introns are gained, why they are lost, and how frequently either occurs.
That many introns are not acquired from a common ancestor but are the result of separate insertion events, the scientists say, means that the rates of intron gain in any species' lineage could be considerably higher than currently estimated.
Even if the rates of intron gain and loss of introns in Daphnia pulex are unlike those found in humans, sunflowers, and mushrooms, the Science report suggests geneticists and genome biologists take another look at introns, some of which could have been the result of hot spot insertion events in separate lines.
"The immediate question will be whether our findings can readily be extended to other species," Lynch said. "We are, in fact, doing that now. In addition, there is need for some solid molecular work to test our hypothesis about the mechanism of intron origin."
Intron is short for "intrageni
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