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Latest update: Communication through UVB: First evidence in spiders ALL-SEEING EYES: The Phintella vittata can see UVB rays. To date, no other animals are able to do this. For the first time, scientists led by Assoc Prof Li Daiqin, Department of Biological Sciences, have shown that Ultraviolet B rays (UVB) play a significant role in a species of female Chinese jumping spiders (Phintella Vittata) when they are selecting their spouse. According to Assoc Prof Li, they prefer mates that reflect UVB versus those that do not. This process of selection could be related to greater survivability of the species — products of such union are more fertile — said Assoc Prof Li. To date, no other animal is known to have UVB photo receptors. Their findings were published in Current Biology (1 May 2008), a leading international biology journal. “Many animals, particularly butterflies, have body parts that reflect UVB light, showing UVB colouration, but no studies have been carried out to investigate the adaptive significance of UVB vision and UVB colouration because it has long been assumed that animals cannot see UVB due to its direct deleterious effects. In our studies of UV vision in jumping spiders, we found that some jumping spiders reflect both UVA and UVB while others reflect only UVB light. This has led us to explore the possibilities of UVB in animal communication,” said Assoc Prof Li. Earlier findings on the spiders and UV light were also published in Science (26 Jan 2007). Assoc Prof Li and his PhD student Matthew Lim discovered that female jumping spiders were aroused when their male counterparts reflect UV light. UV light has a wavelength shorter than that of visible light and cannot be seen by the human eye.  A natural source of UV light is the sun. "Most research has been based on observing animals through human eyes. But we have to realise that animals see things differently from us. We don't have UV vision but jumping spiders do. The way animals are studied should be reassessed," said Assoc Prof Li. The team plans to conduct more studies to understand how jumping spiders see UVB and whether other animals also exhibit this trait. They also plan to determine how UVB colouration is produced, as this will have implications for developing biomaterials that are capable of reflecting UVB radiation.

Spiders with brains

Look into the eyes of a spider… and you may be looking into the mind of an unexpectedly intelligent creature. Can a spider with a pinhead of a brain (estimated to have about 600,000 neurons compared to a human brain with 100 billion brain cells and a honeybee's one million) actually form a mental picture of its prey? But Associate Professor Li Daiqin at his Behavioural Ecology & Sociobiology Laboratory of the NUS Department of Biological Sciences has made a startling discovery. He has found that a genus of jumping spiders, called Portia, is able to do an image search of its prey — based on mental templates. This kind of spider makes intelligent decisions and choices — going about its day-to-day business not entirely through instinctive behaviour.

	SUPER BUG: Associate Professor Li Daiqin with Portia on his palm. Inset shows closeup of Portia labiata from Malaysia.

This research was noted in an article, Smarter than the average bug in New Scientist, May 2006: "Research experiments by behavioural ecologist Li Daiqin at the National University of Singapore have demonstrated yet more startling cognitive abilities. He has found that after Portia makes a kill, it finds it easier to spot prey of the same species and becomes less attuned to other types of prey. This looks very much like selective attention…"

And they only need to make only one encounter for them to remember the image. Bees, even eagles need several encounters before they could come out with a mental template, said Associate Professor Li. Way back in the 60s, scientists have argued that a predator, after discovering a particular type of prey, develops "an eye" for it. The predator then forms "search images" for this particular prey. So far, this hypothesis holds true only for higher vertebrates, especially birds. But Associate Professor Li and his team have taken the hypothesis a few steps further — applying them on Portia which belongs to the jumping spider family that has extremely good eyesight.

They set off with proving four hypotheses: that the predators have evolved an innate predisposition to form search images for prey from the preferred category (Portia have shown a preference for spitting spiders as opposed to other insects such as houseflies); they rely on optical cues (as opposed to chemical cues); they become more dangerous to the type of prey which they have formed search images of; and while using a search image for one prey type, the predator's attention to other prey types is diminished.

They have proven all four hypotheses — and their findings were published in Animal Cognition in April 2004, co-authored by Associate Professor Li and Professor Robert Jackson of the University of Canterbury. They were the first to demonstrate search-image use by a spider.

Portia is indeed, a very clever spider. "Portia is both a web builder as well as a hunter. While it stalks its prey like cats and tigers, it also uses webs to catch its food. It also invades the webs of other spiders and imitate the vibrations made by usual prey, luring the master of the web to approach it so that it can make its kill," said Associate Professor Li.

Spitting spiders

The jumping spiders' preferred food — spitting spiders, are equally smart. Not only that, they are social species and show parental care like higher forms of animals, said Associate Professor Li. They move around carrying their egg sacs in their mouths, even feeding the babies when they are hatched.  

What spitting spiders lack in eyesight, they make up by having quick and accurate response to sensing chemical cues and vibrations. For all their poor eyesight, they could spit accurately to kill a predator at the length of six centimetres, with judgement based on other senses.

Associate Professor Li has found that when the egg-carrying female spiders sense danger, they could make their eggs hatch earlier so that they don't have to be encumbered by the load when running away from dangers. Baby spiders hatched prematurely in such conditions are found to be smaller than normal. The team is still trying to find whether these babies will grow up to be healthy adults — after tender, loving care from their mothers. They are also researching how the mothers could regulate the hatching period of the eggs.

Currently, a PhD student under Associate Professor Li is also looking into the hormones secreted by spiders during communication — identifying the compounds produced when picking up chemical cues. "Our findings may be useful in pest control programmes where predators can be triggered by hormones to kill pests such as mosquitoes and cockroaches," he said.

Models can also be built based on their findings on the search-image ability of jumping spiders, and used as comparison in the cognition process of vertebrates. In fact, Associate Professor Li's explorations into the world of spiders have yielded other research spinoffs. For example, studying jumping spiders' unique characteristics to reflect UV light may offer an all-natural sunblock — or materials which can keep UV rays away. Spider silk which is extremely strong (spider silk bunched together into the thickness of a pencil can pull a Boeing 747) is also being studied.

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