What traits predispose the Band-rumped Storm-petrel, Oceanodroma castro, to ecological speciation in the absence of physical barriers to gene flow?

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Deane, Petra Elizabeth
Ecological Speciation , Parallel Evolution , Standing Variation
Evidence for the repeated, independent evolution of hot- and cool-season breeding populations across colonies of the Band-rumped Storm-petrel has garnered much interest from seabird ecologists and evolutionary biologists, alike. Sympatric seasonal populations have been shown to be each other’s closest relatives, implying that ecological divergence into two seasonal foraging types has taken place several times independently across the species’ range, each time in the absence of geographical barriers to gene flow. I present data on the molecular genetic characteristics of a unique year-round breeding population in the Cape Verde archipelago. Using mitochondrial control region sequence and five microsatellite loci, I characterized genetic relationships among 220 birds breeding in four different months (January, April, June and November) and tested for a relationship between temporal isolation and genetic differentiation. Birds breeding in April, June and November were genetically indistinguishable at microsatellite loci, but control region sequence suggested differentiation between January and other months (pairwise ΦST from 0.19 to 0.46, p≤0.05). No evidence for genetic isolation by time was found. A comparison of birds breeding in June and November revealed significant differences in a suite of morphological traits related to foraging strategy (tarsus length, bill length, bill depth, head length, wing length and tail shape), and even significant variation among birds breeding in the same month, despite evidence for gene flow between these groups. Interpreting these patterns in the context of Band-rumped Storm-petrel populations range-wide, I suggest that divergent selection on standing variation within ancestral populations may be an important mechanism explaining the repeated, independent evolution of conserved seasonal foraging types in this species.
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