Ah, the Australian trapdoor spider. Just one of the fears of shoe-less country kids, popping out from its burrow to scare the bejeezus out of you at dusk. It’s a bit of a homebody, living out its life no further than a couple of metres from where it was hatched.
But hold on to that thought – because now research from University of Adelaide shows this hard-bodied eight-legged tank must have travelled to Australia over the Indian Ocean from South Africa.
Turns out the Australian Moggridgea rainbow actually belongs to a genus of trapdoor spiders otherwise found only in South Africa.
“Conventional wisdom had suggested the spiders became split from their South African relations with the separation of Africa from Gondwana around 95 million years ago,” says University of Adelaide PhD candidate Sophie Harrison, who also works as a Natural Resources Officer with the Department of Environment, Water and Natural Resources.
“But our research showed that the divergence of M. rainbowi from African Moggridgea trapdoor spiders occurred sometime between two and 16 million years ago, well after the Africa-Gondwana separation. Likewise, the timing of divergence rules out the other alternative theory for the spiders arrival in Australia – that of being transported with humans, who arrived in Australia much later.”
The remaining – and amazingly – most logical theory of dispersal is long-distance ocean travel across the Indian Ocean from Africa to Australia.
“At first thought, this does seem incredible,” says Professor Andrew Austin, Ms Harrison’s PhD supervisor. “But there are precedents of such ocean travel. Moggridgea are also found on the Comoros volcanic islands, 340 km from mainland Africa, however this is a relatively short distance compared with the 10,000 kms from South Africa to Kangaroo Island.”
The researchers suggest that a spider colony could have travelled across the oceans on a land “raft” – a large chunk of land and vegetation washed out to sea.
“The burrows they live in are quite stable and they would have been quite secure in their silk-lined tubes with their trapdoors closed – it was probably quite a safe way to travel,” says Ms Harrison.
To establish the connections between the Australian and South African trapdoors the researchers generated DNA sequences from six molecular markers (genes) to compare the Australian and South African species, which showed they belong to the same genus.
“Molecular clock” dating technology showed the inter-specific divergence time of 2-16 million years ago with separate populations on Kangaroo Island diverging between 1 and 6 million years ago.