Large-scale mitochondrial COI gene sequence variability reflects the complex colonization history of the invasive soft-shell clam, Mya arenaria (L.) (Bivalvia)
Résumé
The aim of the study was to determine genetic diversity in the soft-shell clam Mya arenaria on a wide
geographical scale using mtDNA COI gene sequences. Low levels of genetic diversity was found, which
can most likely be explained by a bottleneck effect during Pleistocene glaciations and/or selection. The
geographical genetic structuring of the studied populations was also very low. The star-like phylogeny of
the haplotypes indicates a relatively recent, rapid population expansion following the glaciation period
and repeated expansion following the founder effect(s) after the initial introduction of the soft-shell clam
to Europe. North American populations are characterized by the largest number of haplotypes, including
rare ones, as expected for native populations. Because of the founder effect connected with initial and
repeated expansion events, European populations have significantly lower numbers of haplotypes in
comparison with those of North America. We also observed subtle differentiations among populations
from the North and Baltic seas. The recently founded soft-shell clam population in the Black Sea
exhibited the highest genetic similarity to Baltic populations, which confirmed the hypothesis that
M. arenaria was introduced to the Gulf of Odessa from the Baltic Sea. The most enigmatic results were
obtained for populations from the White Sea, which were characterized by high genetic affinity with
American populations.