Amaurobioides is a genus of coastal spiders found on three Southern Hemisphere continents: Australasia, Africa and South America. It was previously unclear how they got to these continents; an ancestral population may have existed on the ancient supercontinent Gondwana and become geographically separated when Gondwana broke up into modern-day continents. Or, Amaurobioides may have arisen on a single modern continent and later dispersed across oceans to reach others.
To address this question, F. Sara Ceccarelli from Museo Argentino de Ciencias Naturales and her colleagues analyzed gene fragments in mitochondria and nuclei from spider cells. They used DNA from 45 Amaurobioides specimens and 60 specimens from related taxa, as well as DNA sequences from previous studies, to construct an Amaurobioides evolutionary tree.
In their recently published PLOS ONE study, the researchers suggest that an ancestor of Amaurobioides may have dispersed eastward during the Miocene epoch from South America to South Africa, likely aided by the establishment of the Antarctic Circumpolar Current. The Amaurobioides genus originated in South Africa, the authors say, 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 other Southern Hemisphere species have come to be distributed across continents.
Research Article: Ceccarelli FS, Opell BD, Haddad CR, Raven RJ, Soto EM, Ramírez MJ (2016) Around the World in Eight Million Years: Historical Biogeography and Evolution of the Spray Zone Spider Amaurobioides (Araneae: Anyphaenidae). PLoS ONE 11(10): e0163740. doi:10.1371/journal.pone.0163740
Image Credit: Ceccarelli et al (2016)