Evolution and biodiversity of Antarctic organisms: a molecular perspective

Abstract

The Antarctic biota is highly endemic, and the diversity and abundance of taxonomic groups differ from elsewhere in the world. Such characteristics have resulted from evolution in isolation in an increasingly extreme environment over the last 100 Myr. Studies on Antarctic species represent some of the best examples of natural selection at the molecular, structural and physiological levels. Analyses of molecular genetics data are consistent with the diversity and distribution of marine and terrestrial taxa having been strongly influenced by geological and climatic cooling events over the last 70 Myr. Such events have resulted in vicariance driven by continental drift and thermal isolation of the Antarctic, and in pulses of species range contraction into refugia and subsequent expansion and secondary contact of genetically distinct populations or sister species during cycles of glaciation. Limited habitat availability has played a major role in structuring populations of species both in the past and in the present day. For these reasons, despite the apparent simplicity or homogeneity of Antarctic terrestrial and marine environments, populations of species are often geographically structured into genetically distinct lineages. In some cases, genetic studies have revealed that species defined by morphological characters are complexes of cryptic or sibling species. Climate change will cause changes in the distribution of many Antarctic and sub-Antarctic species through affecting population-level processes such as life history and dispersal.

Figure 1

Map of the Antarctic and sub-Antarctic showing sites and areas referred to in the text. Dark grey area is the Southern Ocean south of the average position of the Polar Frontal Zone. Adapted from the map of the Census of Antarctic Marine Life Sampling Area (http://www.caml.aq/data-maps/index.html).

Figure 2

Schematic diagram showing pulses of species range contraction and expansion during periods of (a) glaciation and (b) glacial retreat. Glaciation is characterized by extinction of taxa and range contraction into refugia on the Antarctic or on the sub-Antarctic islands or southern continents. Glacial retreat is characterized by range expansion, secondary contact of populations or sister species and radiation of clades.