By Tom Beal
Arizona Daily Star
Tucson, Arizona | Published: 10.13.2009
Villanova University student Christopher Meehan made good use of his January 2007 trip to the beach south of CancÃºn â€” documenting behavior of the first spider known to science to be deliberately and almost totally vegetarian.
Meehan, now a first-year graduate student in the department of ecology and evolutionary biology at the University of Arizona, is the lead author in a study published Monday in Current Biology on Bagheera kiplingi, a jumping spider that will pass up a tasty fly for a sip of nectar and a salad.
It’s not a bad start for a young man who was just looking to do a “quick and dirty” field study to find something interesting to say about the much-researched mutualistic arrangement between acacias and ants â€” the biological equivalent of finding a new angle for a term paper on Shakespeare’s “Hamlet.”
Meehan’s focus was easily steered from ants to spiders when he made his first visit to the acacia shrubs.
“It was pretty early, a beautiful morning and I was walking down the beach. I saw these little silken shelters studding the plants and these spiders that evidently lived in the shelters.”
That sent him running back to his adviser and co-author, Robert L. Curry, a biology professor at Villanova.
“He came back and said, ‘Can I study the spider?’” recalled Curry. “I said, ‘What spider?’ ”
These acacias, you see, aren’t supposed to have spiders or beetles or caterpillars on them. The ants who inhabit them “are known for being very aggressive, vicious defenders,” said Meehan. The deal is they defend the plant from other predators, and the plant makes these nutrient-rich leaf parts called Beltian bodies for them to eat.
Meehan began observing.
“So I was following this spider around, trying to see why it was there while all these vicious ants were trying to bite and sting it,” Meehan said. “I saw it approach a group of ants guarding one of these Beltian bodies. It took a strike, but not at the ant â€” at the vegetable body. I knew that it was something new to the literature. I knew spiders shouldn’t eat plants.”
He reported back to Curry.
“I said, ‘Oh my God,’ ” Curry recalled.
Spiders are known to inadvertently ingest a little pollen along with their prey, and they do a small bit of nectar-feeding, said Curry, but none of the 40,000 species of spider was known to deliberately eat plants.
Meehan’s lab director at UA, Judith Bronstein, said it’s the kind of discovery that requires fresh eyes.
“There is a large community of scientists who study spiders, and they all know spiders eat other insects,” she said. “One is not supposed to see vegetarian spiders.”
Bronstein, a professor of ecology and evolutionary biology, said Meehan “has this very naive, honest approach about what theory says nature should look like, and because of that, he goes from discovery to discovery.”
“It’s a symptom of the kind of biologist he is, and this is the first of many things he’ll find,” Bronstein said.
Meehan had a bit of a letdown when he returned to Villanova, found someone who could identify the spider for him and learned he wasn’t the first to note this spider’s behavior.
Eric Olson of Brandeis University had observed similar behavior in Costa Rica in 2001, but results of his study were never published. Meehan called Olson, and the two at first “held our cards close to our vests,” said Meehan.
Curry said Olson’s research was not conclusive. The spiders he had observed were not as numerous and not as herbivorous.
Meehan and Olson decided to merge their research.
Olson became a co-author, as did Curry, and Matthew W. Reudink and T. Kurt Kyser of Queens University in Ontario. Reudink and Kyser performed the analysis that found that the spiders, the ants and the acacias had virtually identical ratios of certain isotopes of carbon and nitrogen â€” laboratory proof that the spiders’ diet came from the plants.
Meehan changed his master’s thesis topic.
Curry said the spiders were a better fit for his student than the birds he had him studying at Villanova. “He was never that much a bird person anyway,” he said. “He was the kid in the backyard, mucking around, looking at creepy-crawly things.”
Jumping spiders have always intrigued him, said Meehan. “They look at you and seem superficially curious,” he said.
These spiders proved infinitely interesting and entertaining.
Meehan made four more trips to Mexico, observing and recording the spiders’ behavior.
He discovered they build their nests on the tips of the oldest foliage, which are less patrolled by the ants.
He observed male spiders who “guard their nests and attack any intruder â€” spiders will smack it off,” he said.
“It’s the first case of spiders being Mr. Mom,” he said.
He hopes to make a case for the spiders’ sociality, which would be another big deal, but he is “lacking systematic data,” at the moment.
“Think of our own societies,” he said, “a race of individually-oriented, clever hunter-gatherers who transitioned to farming, transitioned to civilization from year-round access to consistently available food.”
These spiders, “thousands or at least hundreds on a single plant, tolerate each other. The males are aggressive toward each other, but what else is new?”
The new grad student is hitting the books this semester and working in Bronstein’s lab.
His expanded research areas include the evolution of cooperation and conflict, mutualism and the evolution of sociality. He’s also signed on to study the effects of climate change on species interaction in Amazonia.
He’s been a graduate student for a month and he’s already afflicted with wanderlust.
“I’m just waiting for these classes to get over,” he said, “so I can get back in the field.”
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