Sea surface temperature, rather than land mass or geographical distance,
may drive genetic differentiation in a species complex of
highly-dispersive seabirds
Abstract
Seabirds, particularly Procellariiformes, are highly mobile organisms
with a great capacity for long dispersal, though simultaneously showing
high philopatry, two conflicting characteristics that may lead to
contrasted patterns of genetic population structure. Landmasses were
suggested to explain differentiation patterns observed in seabirds, but
philopatry, isolation-by-distance, segregation between breeding and
non-breeding zones, and oceanographic conditions (sea surface
temperatures) may also contribute to differentiation patterns. No study
has simultaneously contrasted the multiple factors contributing to the
diversification of seabird species, especially in the grey zone of
speciation. We conducted a multi-locus phylogeographic study on a
widespread shearwater species complex (Puffinus lherminieri/bailloni),
showing highly homogeneous morphology. We sequenced three mitochondrial
and six nuclear markers on all extant populations (five nominal
lineages, 13 populations). We found sharp differentiation among
populations separated by the African continent with both mitochondrial
and nuclear markers, while only mitochondrial markers allowed
characterizing the five nominal lineages. No differentiation could be
detected within these five lineages, questioning the strong level of
philopatry showed by these shearwaters. Finally, we propose that
Atlantic populations likely originated from the Indian Ocean. Within the
Atlantic, a stepping-stone process accounts for the current
distribution. Based on our divergence times estimates, we suggest that
the observed pattern of differentiation mostly resulted from variation
in sea surface temperatures.