Résumé
Human activities are responsible for the translocation of vast amounts of
organisms, altering natural patterns of dispersal and gene flow. Most
research to date has focused on the consequences of anthropogenic
transportation of non-indigenous species within introduced ranges, with
little research focusing on native species. Here, we compared genetic
patterns of the sessile marine invertebrate, Ciona intestinalis, which has
highly restricted dispersal capabilities. We collected individuals in a
region of the species' native range where human activities that are
known to facilitate the artificial spread of species are prevalent. Using
microsatellite markers, we revealed highly dissimilar outcomes. First, we
found low levels of genetic differentiation among sites separated by both
short and large geographical distances, indicating the presence of
anthropogenic transport of genotypes, and little influence of natural
geographical barriers. Second, we found significant genetic
differentiation in pairwise comparisons among certain sites, suggesting
that other factors besides artificial transport (e.g. natural dispersal,
premodern population structure) may be shaping genetic patterns. Taken
together, we found dissimilar patterns of population structure in a highly
urbanized region that could not be predicted by artificial transport
alone. We conclude that anthropogenic activities alter genetic composition
of native ranges, with unknown consequences for species' evolutionary
trajectories.