Tag Archives: ants

The queenless parthenogenetic ant Cerapachys biroi (subfamily Cerapachyinae) shows army ant-like behavior and is one of the main study systems in our group. The species is a native of Asia and has been introduced globally on tropical and subtropical islands.

Ant executions for the good of the colony

Researchers at The Rockefeller University and Paris University 13 have been studying a peculiar, yet highly fascinating ant species called Cerapachys biroi. The scientists were startled to find that many ants who had stepped out of line and laid eggs at an improper timing were executed by other ants belonging to the same colony, in order to improve efficiency.

C. biroi, along with a few other similar ant species, distinguish themselves by the fact that all worker ants can lay eggs, meaning there are no queens. This most likely caused all members of the species to share completely identical genetic mark-up. This also means something else, that from an evolutionary perspective at least, there would be no reason for ants to compete with one another for breeding rights.

“Similar policing behavior has been observed in several other ant species, and over the past decade it has been debated whether the behavior is a way to repress reproductive conflicts between individuals, or if it serves as a regulatory mechanism to increase efficiency of the whole group,” says Kronauer. “These two factors are very difficult to disentangle in other species. But by examining the behavior in Cerapachys biroi we can conclude that, at least in this species, the executions are a colony-level mechanism, because individual differences that might lead to conflict are controlled for.”

The queenless parthenogenetic ant Cerapachys biroi (subfamily Cerapachyinae) shows army ant-like behavior and is one of the main study systems in our group. The species is a native of Asia and has been introduced globally on tropical and subtropical islands.

The queenless parthenogenetic ant Cerapachys biroi (subfamily Cerapachyinae) shows army ant-like behavior and is one of the main study systems in our group. The species is a native of Asia and has been introduced globally on tropical and subtropical islands. (c) Rockefeller University

For the hive

The researchers studied 11 such colonies over the course of 13 months, and over this period they’ve found that ants were executed by other members of the colony after these failed to “stick to the plan”. The C. biroi ants have a reproductive cycle by which all members hatch at the same time, or as supposed to, and once the larvae hatch from the eggs, the ants stop laying eggs and begin to forage for food to feed the hungry larvae. Some worker ants, however, stray away and lay eggs during hatching. Several ants would ambush the perpetrator and bite and sting it for several hours or even days until it died.

“It appears this is an evolutionary mechanism to eliminate individuals who do not respond properly to the normal social cues that tell the ants when to start laying eggs and when to stop,” says Kronauer.

The researchers involved in the study, which was recently reported in a paper published in the journal Current Biology, describe this behavior akin to how the immune system fights cancer cells in the body, making for a fantastic example of how individual creatures join to collectively form one massive social structure, like a complex organism.

“This system in C. biroi shows striking analogies to immunosurveillance on cancer cells,” says Kronauer. “In both cases, the individuals — single ants and cells, respectively — that are not responsive to regulatory signals proliferate uncontrollably and are attacked and removed to protect the higher-level unit. It’s a fascinating example of how evolution converges on analogous solutions to similar problems at different levels of biological organization.”

source

Zombie-ant fungus infection

Hyper-parasite defends ant colonies from zombie-ant fungus

Last year, we reported on one of the most gruesome and horrific acts that goes on in nature; it seems so unreal, like if some sort of SciFi monstrous scenario transcended into the realm of reality, that one has a hard time wrapping his head around it. Yes, as some of you might have read previously, I’m talking about the zombie-ant fungus or Ophio­cordy­ceps. These parasite fungi infect tropical ants, literary taking control of their actions, ultimately leading the infected ant to march to its death at a mass grave near the ant colony, where the fungus spores erupt out of the ant’s head so it can spread even further.

Zombie-ant fungus infection Now, scientists at Penn State University who have been studying interactions between the zombie-fungus and their host ants have found that there’s a third player at work. Coming to the rescue of the tropical ants, it seems, is another fungi – a parasite of parasite, typically referred to as an hyper-parasite. So, the counter-par­a­sites keep the first one in check and help pre­vent it from over­run­ning en­tire ant col­o­nies.

“In a case where biology is stranger than fiction, the parasite of the zombie-ant fungus is itself a fungus — a hyperparasitic fungus that specializes in attacking the parasite that turns the ants into zombies,” Hughes said. The research will be published in the journal PLoS ONE.

“The hyperparasitic fungus effectively castrates the zombie-ant fungus so it cannot spread its spores,” said Hughes, who is an assistant professor of entomology and biology, and a member of the Center for Infectious Disease Dynamics at Penn State. “Because the hyperparasitic fungi prevents the infected zombie-ant fungus from spreading spores, fewer of the ants will become zombies.”

The team of biologists, lead by Hughes, created a detailed model which offered extra insights regarding the fungus-infected ants and the parasite-infected zombie-ant fungus interaction. Previously, scientists had known that ants ward off infections by carefully grooming each other, now the model reveals the effect of ant behavior on limiting infection. Nature often sends in unexpected allies to aid those threatened by atypical enemies.

“Interest­ingly, be­yond the well-known ef­fect of de­fen­sive ant be­hav­ior, our new re­search re­veals the added ef­fect of the cas­trat­ing ac­tions of the hyperpar­a­site fun­gi, which may re­sult in sig­nif­i­cantly lim­it­ing the spread of the zom­bie-ant fun­gus,” Hughes said.

The sci­en­tists re­port that only about 6.5 per­cent of the spore-producing or­gans of the zom­bie-ant fun­gus were vi­a­ble.

“Even though there are a lot of dead and in­fected zom­bie ants in the neigh­bor­hood, only a few of the spores of the zom­bie-ant fun­gus will be­come ma­ture and able to in­fect healthy ants,” Hughes said. “Our re­search in­di­cates that the dan­ger to the ant col­o­ny is much smaller than the high dens­ity of zom­bie-ant ca­dav­ers in the gra­veyard might sug­gest. This com­plex in­ter­ac­tion be­tween ant col­o­nies, their brain-mani­pu­lat­ing par­a­sites, and oth­er fun­gi capa­ble of lend­ing as­sis­tance to the col­o­ny un­der­scores the need to study so­cial in­sects un­der nat­u­ral con­di­tions.”

The findings were reported in the journal PLoS ONE.

source: Penn State University

Ants use bacteria to grow gardens

leafAnts are most amazing creatures, and there’s so much we could learn from them I wouldn’t even know where to start. As it is, we’ve just started to scratch the surface of what we know about ants, and strangely enouch, researchers are discovering more and more things human and ant societies have in common.

Leaf cutter ants are one of the most remarkable ant species, and scientists have recently found a new quality (or ‘skill’, if you wish) to add to their inventory: they use nitrogen-fixing bacteria to make their gardens grow. You know who else does something similar? Humans.

The finding was reported on 20 November in Science by bacteriologist Cameron Currie from the University of Wisconsin-Madison and analyzes a previously unknown very interesting symbiosis between ants and bacteria, providing a totally new insight on leaf cutter ants and how they managed to be the dominant ant species in the American tropics and subtropics.

“Nitrogen is a limiting resource,” says Garret Suen, a UW-Madison postdoctoral fellow and a co-author of the new study. “If you don’t have it, you can’t survive.”

Indeed, this ‘business relationship’ allows the ants to be impressively successful, while the bacteria thrives too.

“This is the first indication of bacterial garden symbionts in the fungus-growing ant system,” says Currie, a UW-Madison professor of bacteriology.

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The fungus growing ants are technically herbivores, but without the bacteria, there is absolutely no way they could get the necessary nutrients.

“Without nitrogen, there is no way these guys could achieve such large colony sizes. These ants are one of the most dominant insects in the Neotropics. The ability to have colonies with millions of ants is predicted to require a tremendous amount of nitrogen.”

So how do they do it ? The gardens in question are initially sowed by the ants, which bring leaf pieces into their underground nests. From the leaf, a fungus called Leucoagaricus gongylophorus starts growing – which was traditionally viewed as the ants’ food, ever since 1890s research; only recently did researchers start taking into consideration the more complex interactions between the fungus, the bacteria and ants.

But things get even more complicated from here on – genetic analysis of proteins found in bacteria revealed even more complex interactions.

“Our results show that calling these ‘fungal gardens’ is pretty misleading; ‘fungus-bacterial communities’ would be far more accurate,” said Kristin Burnum, a bioanalytical chemist at the Department of Energy’s Pacific Northwest National Laboratory. . “Bacteria are not only integral residents of these communities, but they perform essential tasks that keep the communities — and the ants that help cultivate them — living.”

 

Researchers hope that understanding how this (sort of) symbiosis works can not only boost our understanding of complex ant societies and biological mechanism, but also lead to more effective development of biofuels.

Ants – more rational than humans

Researchers from Arizona State University and Princeton University conducted a study that goes to show that our ‘multimodal, egg-headed, tool-using, bipedal, opposing-thumbed‘ selves come way behind ants when it comes to ration. That doesn’t actually mean that we are dumber than ants, but rather that we sometimes make irrational decisions, especially when faced with very difficult and important decisions.

“This paradoxical outcome is based on apparent constraint: most individual ants know of only a single option, and the colony’s collective choice self-organizes from interactions among many poorly-informed ants,” says Pratt, an assistant professor in the School of Life Sciences in ASU’s College of Liberal Arts and Sciences.

The insight came frin examining the process of choosing a new home. The major hints come when the ants are faced with making a decision between two possibilities with very similar advantages.

“Rationality in this case should be thought of as meaning that a decision-maker, who is trying to maximize something, should simply be consistent in its preferences.” Pratt says. “For animals trying to maximize their fitness, for example, they should always rank options, whether these are food sources, mates, or nest sites, according to their fitness contribution. Which means that it would be irrational to prefer choice ‘A’ to ‘B’ on Tuesday and then to prefer ‘B’ to ‘A’ on Wednesday, if the fitness returns of the two options have not changed.”

“Typically we think having many individual options, strategies and approaches are beneficial,” Pratt adds, “but irrational errors are more likely to arise when individuals make direct comparisons among options.”

How house ants pick their dream home

Photo by Mark W. Moffet

Photo by Mark W. Moffet

Seeing all the available houses in the neighborhood and then choosing is not necessarily the best option, at least if you’re an ant. These house-hunting rock ants manage to make a decision together even without going through the options they have.

In this recent study conducted by Dr Elva Robinson and colleagues from the Bristol University, they put tiny radio-frequency identification tags on the ants; each of these small tags was about “1/2000” as big as a postage stamp. What they wanted to observe was how they made the difference between a poor house nearby and a better house further away. They were pretty surprised to find out the ants have a pretty sophisticated way of choosing, and location isn’t all that matters.

When a colony of ants decides there’s a need for a new nest, they first send out scouts to smell out the nearby nests. If the scout fancies the respective site, he, as an informed ant, briefs some other greenhorn. Then this greenhorn goes to the site and if he thinks it’s all good, he goes out to another and so on, until they reach a certain number. When they reach a quorum, they start moving the necessary materials for a new nest. This may result in a temporary split of the ant population, as some may pick a different place than the majority, or they can split into more than 2 places.

In the Bristol experiment, very few ants made actual direct comparisons between different options. They discovered that they choose the better place even if it’s location is 9 times further away.
Dr Robinson said:

“Each ant appears to have its own ‘threshold of acceptability’ against which to judge a nest individually. Ants finding the poor nest were likely to switch and find the good nest, whereas ants finding the good nest were more likely to stay committed to that nest. When ants switched quickly between the two nests, colonies ended up in the good nest. Individual ants did not need to comparatively evaluate both nests in order for the entire colony to make the correct decision.
“On the other hand, animals – including humans – who use comparative evaluation frequently make ‘irrational’ decisions, due to the context in which options are compared or by inconsistently ranking pairs of options, (for example option A preferred to B, B preferred to C but C preferred to A).
“The ants’ threshold rule makes an absolute assessment of nest quality that is not subject to these risks, and circumvents the necessity for memorization and comparison of every site visited. Thus, simple individual behaviour substitutes for direct comparison, facilitating effective choice between nest sites for the colony as a whole.”