Callobius_nevadensis_(Amaurobiidae)_adult_female By Marshal Hedin - Flickr_ Callobius nevadensis (F Amaurobiidae) adult female CC BY 2_0

Swashbuckling spiders took a round-the-world trip

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The ancestors of coastal spiders probably found their eight sea legs and swashbuckled across oceans from South America to South Africa, Australia and New Zealand, according to international scientists, including an Australian. The coastal spiders genus Amaurobioides is found in Australasia, Africa and South America, but scientists weren't sure whether they originated on the ancient supercontinent of Gondwana before it split up, or if they evolved on one continent and then travelled to reach the others. Reconstructing the evolutionary family tree of the spiders suggests the latter is true. It looks like the spiders dispersed eastward from South Africa to Australia and New Zealand before completing the loop back to South America. They say the spiders could have rafted across oceans on mats of vegetation.

Journal/conference: PLOS One

Organisation/s: Queensland Museum, Museo Argentino de Ciencias Naturales, Argentina

Media Release

From: PLOS

Dispersal of coastal spider ancestors may have occurred eastward across oceans around Southern Hemisphere

Phylogenetic analysis supports long-distance transoceanic dispersal of Amaurobioides genus, possibly by "rafting"

Coastal spiders may have undergone transoceanic dispersal eastward from South America to South Africa, Australia and New Zealand as the Amaurobioides genus evolved, according to a study published October 12, 2016 in the open-access journal PLOS ONE by F. Sara Ceccarelli from Museo Argentino de Ciencias Naturales, and colleagues.

Amaurobioides is a genus of coastal spiders found on three Southern Hemisphere continents: Australasia, Africa and South America. It was previously unclear whether an ancestral population existed on the ancient supercontinent Gondwana and was geographically separated when Gondwana broke up into modern day continents, or whether Amaurobioides arose on a single continent and later underwent long-distance, transoceanic dispersal to reach others.To address this question, Ceccarelli and colleagues considered mitochondrial and nuclear gene fragments, using DNA from 45 Amaurobioides specimens and 60 specimens from related taxa, as well as sequences from previous studies, to construct an Amaurobioides evolutionary tree.

The researchers suggest that an ancestor of Amaurobioides may have dispersed eastward during the Miocene era from South America to South Africa, likely aided by the establishment of the Antarctic Circumpolar Current. The Amaurobioides genus originated in South Africa and dispersed further eastward to Australia and New Zealand in the early and mid-Pliocene. Finally, Amaurobioides species recolonized South America at the end of the Pliocene, completing the eastward circle of long-distance dispersal around the Southern Hemisphere.

The coastal habitats of Amaurobioides species may have been conducive to this unusually large scale transoceanic dispersal, which the authors propose occurred by “rafting” across oceans on mats of vegetation. While there are other possible explanations for the present day distribution of Amaurobioides species, this study may shed light on how Southern Hemisphere species have come to be distributed across continents.

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