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

Abstract

AimUnderstanding 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.LocationSouthern Ocean.Taxa17 species and subspecies of blue-eyed shags (Leucocarbo spp.) across the geographical distribution of the genus.MethodsHere 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.ResultsOur 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 conclusionsThe 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.

Progressing delineations of key biodiversity areas for seabirds, and their application to management of coastal seas

“…This underrepresentation is likely because both the absence of local (i.e. breeding locations with abundance estimates, Figure 2) and global population estimates (Table 2), coupled with taxonomic uncertainty for the shag populations (Rawlence et al, 2021; Schrimpf et al, 2018), meant analyses for certain species were limited by available quantitative data. Further baseline population census work will be particularly critical for Brown Skuas, Dolphin Gulls, Imperial Shags, Rock Shags, Magellanic Penguins, Slender‐billed Prions and Sooty Shearwaters (Appendix S1: Future research and monitoring and Survey record types for species – status and overview).…”

“…. Nevertheless, with marine management considerations underway at the Falkland Islands, the globally important sites we identified-with their expected stability in space-support recognition of key areas within Falklands waters against internationally recognized standards(Rose et al, 2020).Figure2) and global population estimates (Table2), coupled with taxonomic uncertainty for the shag populations(Rawlence et al, 2021;Schrimpf et al, 2018), meant analyses for certain species were limited by available quantitative data. Further baseline population census work will be particularly critical for Brown Skuas, Dolphin Gulls,…”