National University of Singapore: Spider findings

Spiders court the girls with UV rays
Researchers from NUS and China find that female jumping spiders spend more time ogling males with ray reflectors
Lim Heng Liang, Straits Times 2 May 08;

ULTRAVIOLET rays cause sunburn, cataracts and skin cancer. But the UV beams, which are invisible to the human eye, are also part of a courting spider's calling card, researchers here have found.

National University of Singapore Associate Professor Li Daiqin has discovered that the rays are very much visible to arachnids and essential for eight-legged courtship rituals.

He has proven, for the first time, that a particular type of UV ray, ultraviolet B (UVB), is used in animal communication.

Its purpose? To get the girls.

Female jumping spiders spent twice the amount of time ogling males with UVB-reflecting markings on their body, compared to situations where the light wave had been filtered out.

The findings were published in the latest issue of the international scientific journal Current Biology, which comes out today.

UV light is divided into various groups categorised according to their wavelengths. UVB light has a much smaller wavelength range compared to other groups.

Dr Li, who is with the university's department of biological sciences, said the scientific community had long assumed that animals could not detect UVB light due to its small wavelength range and because such rays can harm the eyes.

In fact, UVB receptors needed to see such light have still not been found in animals.

A fellow spider expert, NUS honorary research associate David Court, offered a possible reason for the myopic view: 'People themselves are not sensitive to UV light. That's why it took so long to discover animals that used it for communication.'

The discovery was made after a three-year collaboration among researchers from China and Singapore to determine why male spiders of the species Phintella vittata had UVB-reflecting markings on their bodies.

Prof Li noted that the discovery opened the gates to further investigation on the role of UVB light in animal communication. He expects more studies on UVB light to be made in the future.

Prof Li, who is known as the Spider Man of NUS, hopes to further his research by investigating how the spiders are able to reflect UVB light.

He is also looking at how they protect their eyes from the damaging effects of UVB rays.

Such work could one day lead to the development of better sunscreens or treatments for eye damage.

Study sheds light on spider sex
Eebecca Morelle, BBC News 2 May 08;

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Mating behaviour in jumping spiders

Spiders "talk" to potential mates using a type of light not visible to the human eye, scientists report.

A team found that male jumping spiders ( Phintella vittata ) are using ultraviolet B (UVB) rays to communicate with females.

While UVA rays are often used in animal communication, this is the first evidence that UVB light is also being used, the researchers said.

The study is published in the journal Current Biology.

The team found that male spiders were reflecting the ultraviolet B rays from their bodies.

The researchers discovered that females were more likely to mate with males that could "talk" to them with UVB compared with spiders sitting in chambers where UVB light had been blocked with filters.

Professor Daiqin Li, from the National University of Singapore, said: "UVA and UVB make up a small fraction of the Sun's rays, but humans cannot see them.

"Most previous studies have focused on UVA in animal communication, but this is the first study of UVB on any animal.

"Until now, scientists have assumed that animals cannot 'see' UVB, but we have found that this is not the case."

Spiders have complex eyes and although scientists know that they have UVA receptors, it remains unclear how they can detect the ultraviolet B light.