The secret of invasive species鈥� notoriously destructive power may have been discovered. Genetic analysis of an introduced snail suggests that successive waves of invasion create a 鈥渉otspot鈥� of evolutionary potential that means conservationists should be even more vigilant against invading species.
of France鈥檚 National Center for Functional and Evolutionary Ecology in Montpellier and colleagues examined key physiological and behavioural attributes, or 鈥溾�� of an invasive population of freshwater snails (Melanoides tuberculata), found on the French Caribbean island of Martinique.
The snails, which are often sold in pet shops, probably arrived on the island in recent decades via plants and gravel used in household aquariums.
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Multiple invasions
David鈥檚 team sequenced key genes affecting fertility, juvenile size, and age at first reproduction in a number of snails, and found huge differences between them. The findings suggest the invading gastropods have strong potential for evolutionary change.
鈥淭he genetic variation for life history traits in these snails are among the highest ever observed for any kind of animal,鈥� David says. Such genetic variance, he contends, contradicts prior theories suggesting invasive populations are 鈥渆volutionary dead ends鈥�, lacking enough genetic diversity to evolve in their new environment.
The Martinique snails derive from five successive invasions of genetically distinct individuals arriving from different parts of Asia. David says that because of increased human traffic between continents, such multiple introductions from multiple locations are now common for species invasions.
鈥淚ntroductions are not single, chance events but repeated invasions which can accumulate diversity in these invasive populations,鈥� David says. 鈥淭his makes invasive populations really full of evolutionary potential.鈥�
Renewed vigilance
David Lodge of the University of Notre Dame in Indiana, US, says such potential is cause for alarm: 鈥淚t shows why multiple introductions of an invasive species can contribute to a particularly invasive genotype.鈥�
Lodge says that when the first few individuals of a given species invade, the group often lacks the genetic diversity needed for the population to thrive in their new environment.
As a result, invasive species often languish in small numbers in a localised area after their initial introduction. Lodge says that in showing high levels of genetic diversity after multiple invasions, David鈥檚 work should be seen as a call for renewed vigilance against invasion.
鈥淚t provides a reason to limit introduction even if a species is already established in a given environment,鈥� Lodge says. 鈥淎dditional introductions can be just the trigger that causes the invasive to spread like it was shot out of a cannon.鈥�
Journal Reference: (DOI: 10.1016/j.cub.2008.01.063)
