Invasive Species Can Produce "Hotspots of Evolutionary Novelty"

   This hypothesis underlies the emerging view that invasions are not singular chance events, but rather reflect a long-term change in migration regimes, involving repeated intercontinental exchanges, on which the evolutionary fate of invasive populations heavily depends. However, up to now, empirical data have failed to provide unequivocal evidence for this view. In no single example we are aware of, the role of multiple introductions in accumulating sufficiently large genetic variance for adaptive traits to evolve was clearly established.

   In the study reported in the March 11 Current Biology , analysing the invasion of the Martinique Island (French West Indies) by a freshwater snail (Melanoides tuberculata), we document how a spectacular genetic diversity for key-ecological traits such as fecundity, juvenile size and age at first reproduction, can be accumulated in invasive populations. Such levels of genetic variation for as fundamental a life-history trait as fecundity are among the highest ever recorded, not only in invasive populations, but generally in animal populations. We provide the first direct evidence that multiple introductions are primarily responsible for this accumulation, and that sexual reproduction amplifies this effect by generating novel trait combinations. This finding means that these key-ecological traits have a remarkably large potential for evolutionary change in the invasive area.

   The perception of biological invasions by scientists and the general public has up to now focused on their destructive impact, ranging from economic loss to the threat of homogenization of earth biota and uniform domination by a few winning genotypes or species [18].

   Our study adds to the growing body of evidence that invasions may also be creative and bring together original assemblages of genotypes or species, making them hotspots of evolutionary and ecological novelty. In order to predict the consequences of increased international trade and long-distance introductions, future studies will have to consider the two faces of biological invasions.