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Keywords:

  • Antarctica;
  • historical biogeography;
  • Hydrozoa;
  • Leptothecata;
  • Oswaldella;
  • PAE;
  • palaeocurrents;
  • Southern Ocean

Abstract

Aim  The aim of this study is to investigate areas of endemism within the distribution of Oswaldella species in the Southern Ocean, thereby testing previous hypotheses and proposing alternative scenarios for Antarctic evolution.

Location  Southern Ocean, Antarctic and sub-Antarctic waters of southern South America.

Methods  We prepared a database for the 31 currently known species of the Antarctic genus Oswaldella, which includes geographical locations gathered from published taxonomic studies as well as materials from museums and expeditions. A parsimony analysis of endemicity (PAE) was used to test hypotheses of distribution patterns.

Results  Four areas of endemism are hypothesized: southern South America, two high Antarctic areas (eastern and western) and a larger area, mainly in western Antarctica at lower latitudes and including insular areas (but not the Balleny Islands).

Main conclusions  The results support, in part, previous hypotheses for the Southern Ocean region, while providing more detailed resolution. The areas of endemism may reflect both historical and ecological processes that influenced the Antarctic biota. The Magellanic area reflects the well-known affinities of the Antarctic biota with that of South America and may be a consequence of dispersal through deeper (and colder) waters, followed by speciation. The second area, the largest one, encompasses most of the insular faunas and may also be associated with deeper waters formed since 43 Ma. The third area may be explained by the development of seaways in the circum-Antarctic region beginning 50 Ma. Finally, the fourth zone, with a very poor fauna, coincides with the opening of the Tasman Strait and the formation of the Australo-Antarctic Gulf, associated with a minor wind-driven current.