Abstract
The UNESCO world heritage sub-Antarctic terrestrial ecosystems are unique.
They have been isolated for over 30 million years by constant circum-polar
currents and winds, and shaped by climatic cycles that surpass the
tolerance limits of many species. Despite this recognition, surprisingly
little is known about how these ecosystems acquired their native
terrestrial fauna and how it changed over deep time scales. Here the
patterns and timing of colonization and speciation in the largest and
dominant arthropod predators in the Eastern sub-Antarctic – spiders of the
genus Myro – are demonstrated for the first time. Our results indicate
that this lineage originated from Australia before the Plio-Pleistocenic
glacial cycles and underwent an adaptive radiation on the Crozet
archipelago. We discuss the gain and loss of pre-adaptations acting as
filter that enabled only one of four Myro species native to the Crozet
islands to repeatedly disperse via the Antarctic circum-polar current,
resulting in an outstanding distribution range over 9000 kilometres. The
results highlight the outstanding role of the volcanic Crozet archipelago
for the evolution of arthropod life in the sub-Antarctic, and the
potential of terrestrial macro-invertebrates to achieve rare but
ecologically influential trans-oceanic dispersal events over thousands of
kilometres under hostile conditions.