Antarctica as an evolutionary arena during the Cenozoic global cooling

Abstract

It is striking to observe that species richness is not evenly distributed across the surface of the planet. Current species diversity indeed decreases toward the poles, with Antarctica for instance being depauperate compared to tropical regions. This ubiquitous pattern has long attracted the attention of naturalists and more recently of evolutionary biologists and paleontologists to understand why species diversity peaks at the equator. However, it remains poorly understood how polar biodiversity originated and diversified. Antarctica is currently defined as three large biogeographic regions: the Maritime Antarctic, the sub-Antarctic, and the Continental Antarctic. The Maritime Antarctic region is largely separated from the rest of the world’s oceans due to the Antarctic Circumpolar Current (ACC), differences in temperature along the Antarctic Polar Front (APF), and the presence of a deep sea surrounding the Antarctic shelf (1). The sub-Antarctic region consists of dozens of islands contained within the APF, generally characterized by the presence of tundra (absent from the Continental Antarctic) and fellfield habitats. As for the Continental Antarctic region, it is mostly uninhabitable, with less than 0.5% of its surface being ice-free. A long-standing idea is that biodiversity in Antarctica is low, and only constituted of old and poorly diversified lineages. In PNAS, a study (2)—relying on both microevolutionary and macroevolutionary approaches—challenges this idea and shows that terrestrial life can thrive there. Our understanding of the origin and evolution of Antarctic biodiversity has greatly improved in recent years, thanks in part to studies revealing high levels of cryptic diversity, especially for marine organisms for which species diversity is often underestimated (3). Several molecular studies also show evidence for recent colonization and high in situ diversification, thus challenging the view that Antarctica is an inhospitable frozen region where groups cannot adapt, thrive, and successfully diversify (1). Interestingly, elevated speciation rates have been recovered … [↵][1]1To whom correspondence may be addressed. Email: fabien.condamine{at}gmail.com. [1]: #xref-corresp-1-1