Résumé
Biological invasions offer interesting situations to observe how novel
interactions between closely related, formerly allopatric species may
trigger phenotypic evolution in situ. Assuming that successful invaders
are usually filtered to be competitively dominant, invasive and native
species may follow different trajectories. Natives may evolve traits that
minimize the negative impact of competition, while trait shifts in
invasives should mostly reflect expansion dynamics, through selection for
colonization ability and transiently enhanced mutation load at the
colonization front. These ideas were tested through a large-scale
common-garden experiment measuring life-history traits in two closely
related snail species, one invasive and one native, co-occurring in a
network of freshwater ponds in Guadeloupe. We looked for evidence of
recent evolution by comparing uninvaded or recently invaded with
long-invaded sites. The native species adopted a life history favoring
rapid population growth (i.e. increased fecundity, earlier reproduction
and increased juvenile survival) that may increase its prospects of
coexistence with the more competitive invader. We discuss why these
effects are more likely to result from genetic change than from maternal
effects. The invader exhibited slightly decreased overall performances in
recently colonized sites, consistent with a moderate expansion load
resulting from local founder effects. Our study highlights a rare example
of rapid life-history evolution following invasion.