Ants Assign Assignments According to Age
Everyone has seen the complex metropolis known as an ant farm and many more know about the complex structural organization involving the queen, worker ants, soldier ants and so forth. But did you know that ants divide their tasks according to age, hereby increasing the colony's fitness? It's this evolutionary mechanism that scientists believe has been a major factor in the success of social insects.
Dawid Moroń, Magdalena Witeka, and Michal Woyciechowskia created an experiment in which they tested colonies of the ant Myrmica scabrinodis, to see if the colonies would reassign risky jobs to less fit ants. The students did this by creating living environments for small artificially created hives and by treating a certain number of ants with carbon dioxide, another group they surgically removed propodeal spines, and the rest they left as control. The carbon dioxide greatly damaged the nerve membranes and increased haemolymph acidity, while removing the propodeal spines "provided an avenue of infection and/or uncontrolled desiccation". Desiccation is a fancy word for extreme dryness. The results of their experiment were as they hypothesised; the poisoned ants and the injured ants all started working riskier jobs earlier than the control ants did. Instead of working inside of the hive, where the safer jobs are, they were instead chosen to forage for food, a dangerous activity due to predators, competitors, and parasites.
The experimental data supports the original hypothesis, even though the experiment is testing for weakened/crippled ants, because generally speaking, the older the ant the weaker the ant becomes. This is not to say that 100% of the elderly ants would all have the same symptoms as the poisoned/maimed ants; we're merely making supporting a correlation between them.
Unfortunately, we are hopelessly ignorant about the actual ant behavior that leads to weakened ants being sacrificed for the colony and how the colonies determine the "fitness" of an ant. However, we do know that having the less fit ants do the dirty work, makes for a fitter colony.
The original document can be found at http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6W9W-4PT2FSP-R&_user=1516330&_coverDate=02%2F29%2F2008&_rdoc=4&_fmt=high&_orig=browse&_srch=doc-info(%23toc%236693%232008%23999249997%23679569%23FLA%23display%23Volume)&_cdi=6693&_sort=d&_docanchor=&_ct=48&_acct=C000053443&_version=1&_urlVersion=0&_userid=1516330&md5=31d2a104a94d1acb6f33b2130c4dcace.
Posted by David Byun (1)
Edited by David Byun on 9/21/08 @ 9:30pm
posted by PWH @ 4:05 PM
22 comments
22 Comments:
That's vey interesting. So, if weakness is a measure of age, does this mean that older ants are more likely to get the dangerous tasks? Why is that?
Cecelia Hunt
It's amazing how organized ants can be, being able to prioritize work for ants that are of a certain age or even ill. I'm interested however, in knowing how the ants that are poisoned/injured know that they need to start working their job earlier?
-Dan Hong
This comment has been removed by the author.
I have read about how an ant changes jobs in the colony as it ages, ending with the most dangerous. To me, the most interesting thing about ants is the evolution of a hive system. I wonder how evolution could favor sterile offspring to begin with. It seems completely illogical.
James Sullivan
If you wrote about how ants determine their age by physical ability in the beginning, then there would have been a better understanding of the experiment. How long was the experiment? Where were the students from? Where are the ant species Myrmica scabrinodis found?
You wrote that the weakened and crippled ants were chosen to forage for food. Is there a system where jobs are assigned to all the ants? This experiemnt made me think about what happens when the weakened ants return to their normal state, and how that affects what kind of job they do?
The weakened/crippled ants started working riskier jobs earlier than the control ants. Did the experiment include the amount of time? I think that this factor of time is important to perceive a colony's fitness and the organization of ant colonies.
SUSAN DUONG
So if the old are the ones that go out, and the young stay inside how do the young ones learn to do what the old ones did by the time they are old?
-Sasha
I forgot to put my whole name for my comment.
-Sasha Rogers
Its not so far fetched that older ants are the ones "assigned" with the riskier jobs. In many groups, the riskier tasks are undertaken by senior members of that group, mostly because they are less mundane, require more experience and are accompanied with prestige and respect. I am drawing this conclusion from experience in the human world, however ants have a social structure that is closer to that of humans than that of ,lets say, cats or squirrels. even in the context of a family, the older you get the more responsibility you carry. What fascinates me though is the intricacy of the end product of their work, especially when you take into consideration their size and anatomical structure.
Noam Pelleg (21997016)
this was very interesting. i just wonder, how do the poisoned and injured ants know they have to work the riskier jobs? is it a learned behavior or is it in their nature?
-Hessom Minaei
That's really interesting, but I'm a little confused. How exactly do we know that ants "determine age"? Maybe it's strictly a matter a weakness vs. strength..?
-Jane de Verges
I'm wondering why and how does adding CO2 and surgically removing the tested ants' propodeal spines made them taking riskier jobs faster than the control group?
- David Huynh
Phew, thanks for the comments!
To answer the question of how the colony knows to assign the tough jobs to the injured ants I have this quote from the article:
"The division of labour is caused by proximate internal and external factors (for a review see Gordon 1996). Internal factors include, for example, genetic and hormonal effects; external factors include, for example, perceived stimulus (Beshers & Fewell 2001). However, the ultimate factors involved in age polyethism, which is crucial to the division of labour in most social insects, are still unknown. Only Jeanne (1986) has demonstrated that performing risky tasks later in the lives of workers is profitable because it prolongs the mean longevity of workers (see also Tofilski 2006). It is well known that increasing worker longevity maximizes colony fitness ([Schmid-Hempel, 1987] and [Schmid-Hempel and Wolf, 1988]). Woyciechowski & Kozłowski (1998) showed that life expectancy, more accurately than age, explained why younger honeybees perform safer tasks compared to older ones."
We still don't know the exact reasons why this happens.
To Sasha Rogers
I believe that the ants are all genetically programed to understand all the jobs that they are required to do, nature not nuture in this case.
To Noam Pelleg
I would have to polietly disagree. I don't really think ants care that much about prestige and honor and I really hope that the social structure of ants is nothing like our social structure... Also if ants had "human feelings", then this organization would be closer to forcing your grandpa to work the dangerous jobs as he has less use for the family than anything related to prestige.
Thank you for your comments!
-David Byun
I'm wondering why and how does adding CO2 and surgically removing the tested ants' propodeal spines made them taking riskier jobs faster than the control group?
Quote from the article:
"The study confirmed (CD experiment) that M. scabrinodis workers treated with carbon dioxide had a significantly lower probability of survival in comparison to untreated workers from control groups. It is well known that carbon dioxide shortens the longevity of many insect species including social insects ([Annis and Morton, 1997], [Agnello et al., 2002] and Gunasekaran and Rajendran, 2005 N. Gunasekaran and S. Rajendran, Toxicity of carbon dioxide to drugstore beetle Stegobium paniceum and cigarette beetle Lasioderma serricorne, Journal of Stored Products Research 41 (2005), pp. 283–294. Article | PDF (243 K) | View Record in Scopus | Cited By in Scopus (1)[Gunasekaran and Rajendran, 2005]) as a result of an irreversible effect on the nerve membranes and by increasing haemolymph acidity (Gannon 2001). At high concentrations, as in our experiment, the effect of oxygen depletion may contribute to the toxicity (Gannon 2001). In PS experiment, the injured workers also had significantly lower survival rates in comparison to workers from control groups. The rupture in the cuticular integument provided an avenue of infection and/or uncontrolled desiccation."
-David Byun
This is an interesting topic. Is it an internal mechanism or a social aspect that alerts the ant that they need to work more dangerous jobs once they are injured? Is there a certain degree of injury that propels the ants to work outside of the colony?
Rob Lubenow
Interesting article! So does this hierarchical system apply to other social insects as well, or are ants the first to go by this evolutionary mechanism?
Helen Thi
I really like how you summarized the article, the way you included how the ants were tested and the outcome of the experiment. It is truly remarkable to learn of the organized and systematic lifestyle of the ants. I definitely agree that this mechanism is effective and beneficial to the ant colony but I am very curious about how being weakened/crippled is a clear reflection of age to the ants since the ants may be able to regain their form, energy, and strength. If they are able to regain their former selves do they just keep switching behaviors?
Posted by Tazneena Ishaque
To Helen Thi:
Indeed ants are not the only insects to go by such an evolutionary mechanism.
"Age polyethism has been frequently studied in bees (Seeley & Kolmes 1991), wasps (Jeanne 1991) and ants (Hölldobler & Wilson 1990)."
To Rob Lubenow:
Those are the next set of questions that researchers will be asking themselves.
I'm guessing that its more of a instinctual activity because I can't imagine someone willingly going along with it. On the other hand, I'm not an ant so I'm not qualified to answer such questions.
To Tazneena Ishaque:
You raise an interesting point that I didn't think about. However, I don't think there is that much focus on the individual in a colony. FYI I have no prior knowledge about this subject, just what I read in that article so it would be up to you to research it.
-David Byun
This was a great choice of article, I think, since we ended the last class briefly speaking about ants. I still think it is very interesting that such seemingly simple organisms have such practical and intricate social systems. What I would like to know, however is how they are assigned to a certain job or who exactly assigns them.
-Jen Kodela
wow, that is a sad yet amazing blog assignment. I was just wondering if the weaker and/or older ants are sent to do the more dangerous tasks then how does the ants that are weaker and/or older do these jobs? I mean isn’t lifting foods and running form predators require more strength and agility? So because of that wouldn’t they get less food then sending a more fit ant to do the work?
Tenzing Y. Dundutsang
I find this article very interesting.
I understand that the ants with carbon dioxide had a significantly lower probability of survival but at the same time, i wonder if it is accurate to assume that the logic we are assuming to be true (the older the weaker) is true. In some species, the animal will get stronger as it ages. Take anoles lizards for example, who have dewlaps that get bigger as they age, because they increase more and more testosterone. I wonder if assigning different tasks here matches the thinking that its because they are weaker, and better suited for one task over another.
-Ahmed Sandakli
Survival of the fittest? Another great example of how uncountable years of evolutions teach species to be more efficient. Such complex thinking coming out of such small creatures is pretty impressive. By letting the weaker ants in essence die for the colony it not only increases the Darwinian fitness of the colony generation after generation but it also provides the colony with a good defense from predators by having the stronger ants inside. There are a lot of benefits to this strategy.
Patrick Salome
very interesting article, my only question is that if the older/weaker ants are given the more risky jobs, does this mean that they also sacrifice themselves for the rest of the ants to consume or for the ants to use their body for something (maybe building a structure) when they are too weak to do even simple foraging, or do those old weak ants just go off into the woods and die?
-Joe Alonzo
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