Bigger, scarier weapons help spiders get the girl (w/ video)

Dec 12, 2011
The jumping spider's big eyes can be steered independently. The one on the right is aimed right at the camera and you can see the retina. The other one is looking somewhere else. (Cynthia Tedore)

(PhysOrg.com) -- If you're a red-headed guy with eight bulging eyes and a unibrow, size does indeed matter for getting the girl.

More specifically, the bigger a male jumping spider's weapons appear to be, the more likely his rival will slink away without a fight, leaving the bigger guy a clear path to the waiting female.

Duke University graduate student Cynthia Tedore, working with her dissertation advisor, visual ecologist Sönke Johnsen, wanted to know what visual signals matter most to magnolia green jumping spiders, which have an impressive array of eyes, including two giant green ones that face forward.

Vision is clearly important to these quarter-inch animals, which can be "very predaceous and aggressive," when love is in the air.

This video is not supported by your browser at this time.
Magnolia jumping spiders size each other up and sometimes bang heads, just like males of other species. Duke graduate student Cynthia Tedore says these behaviors aren't conscious or learned, but "they're following rules of some kind. I think of them more as robots."

Tedore's lab in the basement of Duke's biological sciences building is lined with wire shelves covered with row after row of Lucite boxes, each holding an individual chartreuse . Full-spectrum lights and squares of green paper mimic sunlight and leaves to keep the spiders calm between bouts. They're fed leftover fruit flies from other labs.

In pairs, 24 males squared off for 10 minutes in "the arena," a box festooned with female silk to put the males in a fighting frame of mind. Over the course of 68 of these cage matches, the male with the bigger chelicerae, heavy, bristling fangs hanging in front of their mouth parts, usually scared the other guy off without a fight.

"The males wave their forelegs at each other for a period, and then the smaller male runs off," Tedore said. "That's why we think they're using vision to size each other up. Most of the time, the smaller one will run away before it comes to blows."

On the rare occasion that a male with smaller won, he tended to have chelicerae which were less red. That's the opposite of what Tedore expected, and she's not sure what the color differences are about. It may be that the spiders who invest fewer resources into making red fangs gain some agility or endurance as a tradeoff.

Seven of the matches were scored as ties. Seventeen of the contests turned into shoving matches, with the butting chelicerae against each other. Occasionally one would flip an opponent on his back, then chase and pounce on him. Tedore had to break up a couple of contests before time expired so that nobody got hurt.

Tedore said her work provides another glimpse into how these creatures, which have tiny brains and never met their parents, manage to make decisions and navigate their world. "I don't really think of them as conscious, but they're following rules of some kind. I think of them more as robots."

In her next series of experiments, Tedore is pitting males against video images of other males that have artificially exaggerated chelicerae and altered colors.

Explore further: Deep sea fish eyesight similar to human vision

More information: "Weaponry, color, and contest success in the jumping spider Lyssomanes viridis," Cynthia Tedore, Sönke Johnsen. Behavioral Processes, 2011. Doi:10.1016/j.beproc.2011.10.017

Related Stories

Male black widows look for well-fed mates

Jul 07, 2011

(PhysOrg.com) -- According to a new study published in Animal Behaviour, a male black widow spider is able to identify a female spider that has eaten well by simply taking a few steps on the web she spins. ...

The eyes have it for perfect predator

Jul 09, 2010

(PhysOrg.com) -- The most striking feature of jumping spiders is their arsenal of big eyes. In contrast to web-building spiders, they rely on their excellent vision to actively hunt and catch their insect ...

In spiders, size matters: Small males are more often meals

Sep 10, 2008

Female spiders are voracious predators and consume a wide range of prey, which sometimes includes their mates. A number of hypotheses have been proposed for why females eat males before or after mating. Researchers ...

Recommended for you

Dogs hear our words and how we say them

Nov 26, 2014

When people hear another person talking to them, they respond not only to what is being said—those consonants and vowels strung together into words and sentences—but also to other features of that speech—the ...

Amazonian shrimps: An underwater world still unknown

Nov 26, 2014

A study reveals how little we know about the Amazonian diversity. Aiming to resolve a scientific debate about the validity of two species of freshwater shrimp described in the first half of the last century, ...

Factors that drive sexual traits

Nov 26, 2014

Many male animals have multiple displays and behaviours to attract females; and often the larger or greater the better.

User comments : 2

Adjust slider to filter visible comments by rank

Display comments: newest first

cmn
5 / 5 (1) Dec 13, 2011
So the male with the larger features ends up being dominant??? This must be a groundbreaking discovery.
gwrede
not rated yet Dec 13, 2011
Another case of a female pitting males against each other. This time the female is Mz. Tedore.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.