The existence and break-up of the Antarctic land bridge as indicated by both amphi-Pacific distributions and tectonics

摘要

Amphi-Pacific disjunct distributions between South America and Australasia are correlated with the breakup and changing palaeo-climate of Gondwana. For a long period, with a temperate climate, Antarctica formed a land bridge between Australia and South America, allowing species to disperse/vicariate between both continents. Dated phylogenies in the literature, showing sister-clades with a distribution disjunction between South America and Australia, were used for the correlation. The initiation of the Antarctic Circumpolar Current, and a change to a colder Antarctic climate is associated with the opening of the Drake Passage between South America and Antarctica at c. 30 Ma, and the final separation of Australia and Antarctica along the South Tasman Rise at c. 45 Ma. The distribution data highlighted the existence of a “southern disjunct distribution” pattern, which may be the result of continental vicariance/dispersal. This is strongly indicative of a connection between Antarctica, South America and Australia; which later provided a dispersal pathway and facilitated vicariance after break up. The taxa that likely dispersed/vicariated via Antarctica included all species with a more (sub)tropical climate preference. Twelve distributions, younger than 30 Ma, are interpreted as the result of long distance dispersal between South America and Australia; these taxa are suited to a temperate climate. The climatic signal shown by all taxa is possibly a consequence of the Australian plate's asynchronous rifting over tens of millions of years in combination with climate changes. These events may have provided opportunities for tropical and sub-tropical species to disperse and speciate earlier than what we observe for the more temperate taxa.