19
June
2015
|
15:14
Asia/Singapore

Web of intrigue

A new species of Sinothela, which is a "primitive spider, found in Hebei Province, China (Photo: Dr Xu Xin)

The geographical distribution of the most "primitive spiders existing today may provide new insights into the movement of Earth's land masses, reported NUS biologists in Proceedings Of The Royal Society B. Their study also proved genetically that the current spiders diverged from their ancestors much more recently than previously believed.

The group of spiders named liphistiids, regarded as "living fossils as they closely resemble their extinct ancestors with segmented abdomen and spinnerets located in the middle of the lower abdomen, inhabit East Asia and Southeast Asia. However, the only fossil of their ancient relatives dating back some 295 million years old was found only in France. The researchers are convinced that the cross-continental migrating arachnids could shed light on continental drift, the widely held belief of the Earth's beginnings as a supercontinent that broke up and shifted.

The multinational team, involving members from China, Japan, Malaysia, Slovenia, Spain, Vietnam and the Smithsonian Institution in the US, is led by Associate Professor Li Daiqin from the NUS Department of Biological Sciences and Dr Matjaz Kunter from the Slovenian Academy of Sciences and Arts.

The scientists examined about 2,000 liphistiid specimens in Asia. With a "molecular clock method using DNA analysis, they could determine the timing when the extant spiders originated and diversified.

Assoc Prof Li said the test shows for the first time that the original liphistiid branched out from their ancestors about 39 to 58 million years ago, rather than much older as popularly thought. This "new group started diversifying to eight genera between four and 24 million years ago, giving rise to some 89 species. Only one genus is found in Southeast Asia while the rest are in East Asia.

The relatively "recent branching and quick evolution coincided with the time when the subcontinent of India collided with Eurasia, he pointed out. As this group of burrow-dwelling spiders cannot be dispersed over water, he believes they must have travelled with the land masses.

Assoc Prof Li and his colleagues proposed three possible hypotheses explaining the eastward dispersal routes of the spiders' ancestors from Europe. The first, "Out of Gondwana, travelled along the southern supercontinent of Gondwana and then drifted north. The second, "Stepping-on Middle East, means the animals traversed south of the ancient northern supercontinent Laurasia via the Middle East to Southeast Asia. "Silk road, the third route, crossed Central Asia to China. The team's results refute the earlier idea that short-term land bridges, formed during the glacial cycles between the mainland and southern Japanese islands such as Kyushu and Okinawa, allowed migration of the creatures to these islands.

The latest findings arm scientists with important intelligence for studying the arachnid "Tree of Life, which traces the origin and species diversity of the spiders. It may also provide clues for unearthing fossils along the hypothesised paths, to unveil what caused their extinction.

As this work focused on East Asian liphistiid spiders, the team plans to further examine the little-known Southeast Asian species. Research on the phylogeny and biogeography of these two groups of spiders will provide valuable knowledge on how historical geological and climatic events might have shaped their present-day diversity and distribution.