Abstract:
Due to their worldwide distribution and occupancy of different types of environments,
bottlenose dolphins display considerable morphological variation. Despite limited understanding
about the taxonomic identity of such forms and connectivity among them at
global scale, coastal (or inshore) and offshore (or oceanic) ecotypes have been widely
recognized in several ocean regions. In the Southwest Atlantic Ocean (SWA), however,
there are scarce records of bottlenose dolphins differing in external morphology according
to habitat preferences that resemble the coastal-offshore
pattern observed elsewhere.
The main aim of this study was to analyze the genetic variability, and test for
population structure between coastal (n = 127) and offshore (n = 45) bottlenose dolphins
sampled in the SWA to assess whether their external morphological distinction is consistent
with genetic differentiation. We used a combination of mtDNA control region
sequences and microsatellite genotypes to infer population structure and levels of genetic
diversity. Our results from both molecular marker types were congruent and revealed strong levels of structuring (microsatellites FST = 0.385, p < .001; mtDNA FST =
0.183, p < .001; ΦST = 0.385, p < .001) and much lower genetic diversity in the coastal
than the offshore ecotype, supporting patterns found in previous studies elsewhere.
Despite the opportunity for gene flow in potential “contact zones”, we found minimal
current and historical connectivity between ecotypes, suggesting they are following discrete
evolutionary trajectories. Based on our molecular findings, which seem to be consistent
with morphological differentiations recently described for bottlenose dolphins in
our study area, we recommend recognizing the offshore bottlenose dolphin ecotype as
an additional Evolutionarily Significant Unit (ESU) in the SWA. Implications of these results
for the conservation of bottlenose dolphins in SWA are also discussed.
