Largest orb-weaving spider discovered in South Africa

October 21st, 2009 - 12:40 pm ICT by ANI  

Washington, October 21 (ANI): Scientists from the United States and Slovenia have discovered the largest orb-weaving spider in South Africa.

The spider belongs to the Nephila species, and researchers have shown that on average, it is the largest orb weaver known.

Nephila spiders are renowned for being the largest web-spinning spiders. They make the largest orb webs, which often exceed 3 feet (1 meter) in diameter.

They are also model organisms for the study of extreme sexual size dimorphism and sexual biology.

Giant golden orb weavers are common throughout the tropics and subtropics. Thousands of Nephila specimens that have been collected are in natural history museums.

“It was surprising to find a giant female Nephila from South Africa in the collection of the Plant Protection Research Institute in Pretoria, South Africa, that did not match any described species,” said Matjaa Kuntner, chair of the Institute of Biology of the Slovenian Academy of Sciences and Arts and a Smithsonian research associate, who first examined the specimen in 2000.

Kuntner, senior scientist Jonathan Coddington, and colleagues launched several expeditions to South Africa specifically to find this species, but all were unsuccessful, suggesting that perhaps the Nephila specimen, first collected in 1978, was a hybrid or perhaps an extinct species.

In 2003, a second specimen from Madagascar suggested it was not a hybrid. No additional specimens turned up among more than 2,500 samples from 37 museums.

The species seemed extinct.

Then, a few years ago, a South African colleague found a male and two females in Tembe Elephant Park, and it became clear that the specimens were indeed a valid new species.

Kuntner and Coddington described N. komaci as a new species, now the largest web-spinning species known, and placed it on the evolutionary tree of Nephila.

They then modeled evolution to test if natural selection had affected body size. They found strong evidence that it had, but only in females.

Nephila females consistently through time increased in size and, mainly in Africa, a group of giant spiders evolved.

Nephila males, in contrast, did not grow larger, but instead remained about five times smaller than their mates.

Kuntner and Coddington have urged the public to find new populations of N. komaci in Africa or Madagascar, both to facilitate more research on the group, but also because the species seems to be extremely rare. (ANI)

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