Abstract

Despite the scarcity of geographical barriers in the ocean environment, delphinid
cetaceans often exhibit marked patterns of population structure on a
regional scale. The European coastline is a prime example, with species
exhibiting population structure across well-defined environmental boundaries.
Here we undertake a comprehensive population genetic study on the
European common dolphin (Delphinus delphis, based on 492 samples and 15
loci) and establish that this species shows exceptional panmixia across most
of the study range. We found differentiation only between the eastern and
western Mediterranean, consistent with earlier studies, and here use
approximate Bayesian computations to explore different scenarios to explain
the observed pattern. Our results suggest that a recent population bottleneck
likely contributed significantly to the differentiation of the Eastern Mediterranean
population (in Greek waters). This interpretation is consistent with
independent census data that suggest a sharp population decline in the
recent past. The implication is that an unperturbed population may currently
show panmixia across the full study range. This exception to the
more typical pattern of population structure seen for other regional dolphin
species (and for common dolphin populations elsewhere in the world)
suggests particular ecological or life-history traits distinct to this species in
European waters.