How to start a termite 'orgy'

February 12, 2013 by Angela Herring
New research from Northeastern investigators Rebeca Rosengaus and Tamara Hartke (above) turns a decades-old theory of termite behavior on its head. Credit: Rebeca Rosengaus

There are more than 3,000 species of ter­mites in the world, all living in social colonies with dis­tinct hier­ar­chies. They can be dev­as­tating pests, with the ability to destroy entire build­ings. But they're also an impor­tant com­po­nent of nat­ural ecosys­tems, with much to teach us about soil nutrient recy­cling. Still, nei­ther of these facts is what gets Rebeca Rosen­gaus, an asso­ciate pro­fessor of biology in the depart­ment of marine and envi­ron­mental sci­ences, out of bed in the morning. As she put it, "I'm inter­ested in them because they're neat."

In the vast majority of ter­mite colonies, a single king-​​queen pair is respon­sible for repro­duc­tion. But in the early 1980s, researchers dis­cov­ered some­thing very odd when they looked inside the mature arbo­real nests of one species, Nasu­titermes corniger: About 20 per­cent of the colonies were headed by what looked like "mini-​​orgies," said Rosen­gaus, who has been studying like ter­mites and ants for 30 years.

Many show sim­ilar polyg­a­mous ten­den­cies, said Rosen­gaus, but not ter­mites. "In ants, those colonies that are started by mul­tiple repro­duc­tive females have cer­tain ben­e­fits," she explained. "So they grow faster or pro­duce workers at a faster rate." This behavior of estab­lishing colonies in groups is called pleomet­rosis and for 30 years, researchers have assumed it was how the handful of polyg­a­mous ter­mite colonies formed.

Rosen­gaus and her stu­dent Tamara Hartke, now a Sir Keith Mur­doch Fellow at the Center for Inte­gra­tive Bee Research in Aus­tralia, tip that long-​​held assump­tion on its head in work recently pub­lished in the journal Proceedings of the Royal Society B.

Of the world’s 3000-​​plus ter­mite species, only a few are known to form colonies led by polyg­a­mous groups. Credit: Rebecca Rosengaus.

With funding from a National Sci­ence Foun­da­tion Career Award, Hartke and Rosen­gaus col­lab­o­rated with the Smith­sonian Trop­ical Research Insti­tute in Panama to study the polyg­a­mous N. corniger colonies. The team sorted more than 16,000 repro­duc­tive ter­mites into petri dishes. Some had just one repro­duc­tive pair, but others had as many as five kings and queens.

They sup­ple­mented these arti­fi­cial exper­i­ments with obser­va­tions of both sem­i­nat­ural and nat­u­rally estab­lished colonies, which the team dug out of the Pana­manian forest floor. The results of each of the exper­i­ments were the same: Ter­mite colonies started by more than one repro­duc­tive pair were much less suc­cessful than their single-​​pair coun­ter­parts, ruling out pleomet­rosis as the route by which mature polyg­a­mous colonies get their start.

Young ter­mite colonies start out in microbial-​​rich envi­ron­ments like soil or a dead or rot­ting wood, according to Rosen­gaus. If the eggs aren't kept clean and moved often, they become infected with fungus. "Ter­mite par­ents are really very con­sci­en­tious about cleaning their baby eggs and keeping them in a pile all together," she explained. "They spend a lot of time doing this type of parental care."

Hartke and Rosen­gaus spec­u­late that repro­duc­tives in pleometrotic colonies spend less time on egg care than monog­a­mous pairs. Instead, the mem­bers of a founding group seem to be engaging in subtle repro­duc­tive com­pe­ti­tion, diverting energy toward inter­acting with each other rather than toward their own off­spring. This, said Rosen­gaus, may explain why pleometrotic groups have lower hatching rates.

"There should, the­o­ret­i­cally and based on obser­va­tions of other social organ­isms, be sur­vival or colony-​​growth ben­e­fits to estab­lishing a colony with more repro­duc­tives, so in that sense it was sur­prising to find more costs than ben­e­fits," said Hartke.

The authors sus­pect that neigh­boring ter­mite colonies even­tu­ally merge into one as they grow and mature. The king-​​queen pairs of each indi­vidual colony persist—and now that workers take care of the parental duties, the com­pe­ti­tion seen in nascent pleometrotic colonies disappears.

Rosen­gaus hopes to con­tinue pur­suing her work with what she calls these "weird" colonies, adding impor­tant genetic data to the mix. "Any ques­tion about evo­lu­tion of sociality needs to be ana­lyzed by using a variety of methods, including mol­e­c­ular and genetic tech­niques to better under­stand the system," she said.

Explore further: 3Qs: Analyzing the cybersecurity threat posed by hackers

More information: rspb.royalsocietypublishing.org/content/280/1756/20122563.abstract?sid=2ef4e581-8cb9-4534-8531-e96b77018639

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