Johns Hopkins scientists probe mystery of spider web-spinning
Researchers aim to unlock the mysterious brain function and genetic code that allows spiders to build webs from spatial memory
The spiders in Andrew Gordus' laboratory at Johns Hopkins University spin their webs in the dark under tight surveillance. Every movement of every one of their eight legs, every step through the two hours or so that it takes to create their circular web, is recorded under infrared light.
An assistant professor in the Department of Biology, Gordus is tracking this little spider in hopes of unlocking secrets of behavior: How is it shaped by genetics? How is it a response to surroundings? Gordus said the project could eventually shed light on higher animals, but for now, it's necessary to start small with a creature with a tiny brain and a relatively small genetic profile that performs one behavior over and over: web building.
The web is the tangible result of actions carried out over a relatively long stretch of time, and it stands apart among typical animal construction projects. Animals that build shelters tend to either displace an existing material in making burrows or gather material around themselves to build nests.
Spiders construct an abstract shape in space. They can sense where they are in relation to this complex shape they are making. They're not using their vision, Gordus said, but some sort of spatial memory.
It's a remarkable feat if you think about it, said Gordus. Imagine if you walked into the chimpanzee house at the zoo, he said, "and saw they had tied ropes together like that. You'd say those are pretty amazing chimps."
Spiders have considerably less brain power. They have no more than 100,000 brain neurons, which is about the same as a fruit fly. So how exactly do spiders—in this case, a species called Uloborus diversus, native to the American southwest, California, and Mexico—do this?
"How does a brain encode all these behaviors in the correct sequence?" Gordus asked.
Gordus and his laboratory crew are pursuing three main phases of a project designed to understand what specific behavior is driven by genetics and what behavior is a response to the environment.
For starters, the scientists are making videos of spiders spinning webs. Well-fed on a diet of fruit flies, a spider is placed onto a box-like frame inside a black box equipped with an infrared camera. The box is then closed and the spider gets to work in the darkness.
In the videos, the spiders appear ghostly white on a black background, and their legs twitch in what seems to be no particular pattern. The web itself is invisible, as the infrared light is set up to highlight the spider, so the movements of its legs will be as clear as possible.
Nick Wilkerson, a Johns Hopkins graduate working in the Gordus lab, is developing software to track the spider's web building activities, down to the movement of each leg. Movements will be computer cataloged and coded so that the researchers can break this complex sequence of behavior into small pieces.
At the same time, the Gordus team will create a genetic profile of the spider. The genomes of a number of animals, including humans, have been "sequenced" and published, but the spider's genome has not, so the Gordus lab scientists have to do it themselves.
Then comes the work of trying to link the behaviors to the genome to see what specific elements of the spider's web building are encoded in DNA. The researchers use drugs to disable specific genes to see how they affect the spider's behavior. As Gordus put it, they are trying to figure out what the genetic "players" are in the web-building sequence.
Gordus said he also plans to attach probes to the spider's brain to try to trace the behavior through nerve pathways or create a genetic and physiology map of behavior. Similar techniques could eventually be used to understand higher animal behavior, but this is just a start. One small spider step at a time.