Rapid radiation of Southern Ocean shags in response to receding sea ice

Aim:

Understanding how wild populations respond to climatic shifts is a fundamental goal of biological research in a fast-changing world. The Southern Ocean represents a fascinating system for assessing large-scale climate-driven biological change, as it contains extremely isolated island groups within a predominantly westerly, circumpolar wind and current system. The blue-eyed shags (Leucocarbo spp.) represent a paradoxical Southern Ocean seabird radiation; a circumpolar distribution implies strong dispersal capacity yet their speciose nature suggests local adaptation and isolation. Here we use genetic tools in an attempt to resolve this paradox.

Location:

Southern Ocean.

Taxa:

17 species and subspecies of blue-eyed shags (Leucocarbo spp.) across the geographical distribution of the genus.

Methods:

Here we use mitochondrial and nuclear sequence data to conduct the first global genetic analysis of this group using a temporal phylogenetic framework to test for rapid speciation.

Results:

Our analysis reveals remarkably shallow evolutionary histories among island-endemic lineages, consistent with a recent high-latitude circumpolar radiation. This rapid sub-Antarctic expansion contrasts with significantly deeper lineages detected in more temperate regions such as South America and New Zealand that may have acted as glacial refugia. The dynamic history of high-latitude expansions is further supported by ancestral demographic and biogeographic reconstructions.

Main conclusions:

The circumpolar distribution of blue-eyed shags, and their highly dynamic evolutionary history, potentially make Leucocarbo a strong sentinel of past and ongoing Southern Ocean ecosystem change given their sensitivity to climatic impacts.