How pirate spiders sailed around the world in eight million years

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This was published 7 years ago

How pirate spiders sailed around the world in eight million years

By Amy Mitchell-Whittington
Updated

Coastal spiders are tough little guys.

Not only do they live in the spray zone of rock faces off the coastlines of southern continents, they arrived there about 8 million years ago by "rafting" from South America eastward, stopping off at Africa and Australasia.

Images of one of the coastal spider species found by Dr Robert Raven off Flinders Island.

Images of one of the coastal spider species found by Dr Robert Raven off Flinders Island.Credit: Robert Whyte

An Argentinian-based study used DNA from 45 Amaurobioides (coastal spider) specimens and sequences from previous studies to construct an evolutionary tree and explore the movement of the genus through the South Pacific and Indian Oceans.

The study found the ancestral population, that existed on the ancient supercontinent Gondwana, did not disperse when Gondwana broke up into modern day continents but evolved on one continent (South America) and then crossed large bodies of ocean, aided by the establishment of the Antarctic Circumpolar Current, to reach Africa and Australasia.

A species of coastal spider found off Flinders Island.

A species of coastal spider found off Flinders Island.Credit: Robert Whyte

Queensland Museum senior curator of spiders Dr Robert Raven contributed to the study by providing a number of species from Flinders Island in Tasmania and said he fell in love with them instantly.

"They build an amazing thick bleached pure driven white silk, a strong silk that they seal up when the waves hit. They hunt from these rocks," he said.

"They surround themselves in a silken tube that is impervious to water.

"They are very tough, they are a little bit smaller than a redback [spider] and once you see them, your heart melts, mine does anyway – they're such fantastic animals to find."

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Illustration: Matt Golding

Illustration: Matt Golding

Each collected specimen was placed in a sequence and researchers "wound back through time" to see how old each species was to determine when they reached each continent.

Authors of the study propose the large scale transoceanic dispersal was made possible by the spiders "rafting" across oceans on mats of vegetation, which Dr Raven said was plausible given they lived off the coastline.

"[How they travelled across the oceans] is yet to be understood completely," he said.

"I suspect that large chunks of land have broken of from one time or another and floated, like a major mini island, and floated around the world and the spider has survived on them.

"They can survive months without food, but they would get lots of food on these things as well."

Dr Raven said understanding the movements of these sailing spiders was another piece in the puzzle to understanding how animals migrated and moved millions of years ago.

"It tells an ancient story, about relationships and on the one side it can work towards good management, we can prioritise conservation in land management," he said.

"It tells us how things have moved and we can use this information across groups governed by the sea."

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