Résumé
Knowledge of the main drivers of population differentiation is crucial for
understanding evolutionary processes and preserving biodiversity. While
primarily studied in terrestrial habitats, the mechanisms operating in the
marine realm are less well understood. This study reconstructed the
phylogeographic history of a tropical seabird to identify relevant marine
barriers promoting intraspecific diversity in the Western Indian Ocean.
Three subspecies of tropical shearwater: Puffinus bailloni bailloni, P. b.
*nicolae, P. b. colstoni. *We used restriction site-associated DNA
sequencing and applied population genomics to birds from six breeding
colonies to assess intraspecific diversity, population genetic structure,
and connectivity in the tropical shearwater. Results were complemented
with data from six oceanographic variables and effective migration
surfaces to evaluate the role of oceanographic factors in driving
population differentiation. All analyses consistently separated the birds
from the northern colonies (subsp. nicolae and colstoni) from those of the
southern islands (subsp. bailloni), but failed to assign the colstoni
birds as a different taxon. Results revealed remarkable levels of genetic
differentiation within an ocean basin in a highly vagile species, and
suggested higher levels of gene flow at the northern limit of the species’
distribution compared to the southern range. Our study suggests that ocean
surfaces and sea surface temperature may constitute an important barrier
to gene flow for the tropical shearwater, and potentially other marine
species in the region. This study does not support the colstoni form as a
different subspecies, highlighting the need for further taxonomic
reassessment. Ultimately, the results allowed us to identify Europa and
Aldabra as the most threatened management units and propose conservation
strategies directly applicable to these most at-risk colonies.