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.