Supersoldier ants created in the lab by reactivating ancestral genes

Jan 06, 2012 by Lin Edwards report
A supersoldier communicates with a minor worker from the hyper-diverse ant genus Pheidole. Photo courtesy of Alex Wild/alexanderwild.com

(PhysOrg.com) -- There are over 1100 species of Pheidole genus ants, and most individual ants belong to either the worker or soldier caste. In only eight of the Pheidole species, some individuals can belong to a "supersoldier" subcaste instead, and these ants fight off predatory army ant species and bar their way by blocking off the entrances to the nest using their over-sized heads. Now, scientists have managed to create supersoldiers in other species by reactivating ancestral genes.

The international team of scientists, led by Dr Ehab Abouheif of the Department of Biology at McGill University in Montreal, Canada, looked at the genomes of two that produce supersoldiers. They identified the genetics behind the supersoldier caste and were able to activate the genes by treating ant larvae with methoprene, a growth hormone. As expected, the ant larvae became supersoldiers.

They then treated in the same way larvae of Pheidole morrisi, an ant species which lives in New York and that does not normally produce supersoldiers, but which lead author, Dr Abouheif, had previously noted produced large-headed ants resembling supersoldiers on rare occasions. The treated larvae grew to become large headed and jawed ants resembling supersoldiers. The same effect was produced in two other Pheilode species, which are not known to produce supersoldiers.

Dr Abouheif and colleagues report, in their paper published in the journal Science, that ant larvae normally develop into soldiers or workers depending on the levels of the "": if levels are high the ants become soldiers, while if they are low they become the smaller . In the species that produce supersoldiers there is a second high threshold of the juvenile hormone, above which the larvae develop into the larger supersoldiers. The methoprene, used in the experiments, mimics the effects of juvenile hormone.

The results of the experiments suggest that even those species that do not produce supersoldiers must have been able to do so in the distant past, some 35 to 60 million years ago, and that they still retain the genetic information for supersoldier production that can be reactivated under certain environmental or nutritional states. The researchers say that retaining the ancestral tools could be important for the evolution of new physical traits.

Supersoldier ants occur naturally in species found in Mexico and the south-west of the USA. They were also known in ancestral species, and Abouheif and the team suggest the common ancestor of the entire Pheidole had the ability to produce supersoldiers.

It is not known why only eight of the species retain the ability and the remainder simply abandon the nests if they are invaded by predatory army ants, but Abouheif said the might have been repeatedly reactivated. This would explain anomalies such as the rare instances of supersoldiers he noted in the P. morrisi ants, which is a species not threatened by army ants.

Dr. Abouheif and colleagues think that their work in unlocking ancestral features could find application in fields such as agriculture, where it might be used to breed crops with greater nutritional value. Abouheif also suggests the work might also shed some light on the growth of cancers, which he said could be "the unleashing of some kind of ancestral potential," which might be reversible if it could be identified.

Explore further: First sex determining genes appeared in mammals 180 million years ago

More information: Ancestral Developmental Potential Facilitates Parallel Evolution in Ant, Science 6 January 2012: Vol. 335 no. 6064 pp. 79-82. DOI:10.1126/science.1211451

ABSTRACT
Complex worker caste systems have contributed to the evolutionary success of advanced ant societies; however, little is known about the developmental processes underlying their origin and evolution. We combined hormonal manipulation, gene expression, and phylogenetic analyses with field observations to understand how novel worker subcastes evolve. We uncovered an ancestral developmental potential to produce a “supersoldier” subcaste that has been actualized at least two times independently in the hyperdiverse ant genus Pheidole. This potential has been retained and can be environmentally induced throughout the genus. Therefore, the retention and induction of this potential have facilitated the parallel evolution of supersoldiers through a process known as genetic accommodation. The recurrent induction of ancestral developmental potential may facilitate the adaptive and parallel evolution of phenotypes.

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DavidMcC
4.9 / 5 (7) Jan 06, 2012
If P. morrisi ants were to be experimentally threatened by army ants, they would presumably rapidly regain their super-soldier caste, without any genetic evolution, by the epigenetic process mentioned in the article, triggered by some pheromone produced by the army ants. In other words, the caste isn't really lost, even to those species that don't regularly express it at present, due to not regularly being threatened by their enemy.
El_Nose
5 / 5 (4) Jan 06, 2012
@David
not necessarily true -- they would probably be wiped out due to the fact they don't currently have any super soldier active. The issue isn't that they could produce this other variety the issue is that they just don't ... colonies have soldiers even if there is no predator - so the lack of this type suggest strongly that that instinct to produce more of this hormone is lost.
DavidMcC
3.8 / 5 (4) Jan 06, 2012
@David
not necessarily true -- they would probably be wiped out due to the fact they don't currently have any super soldier active. The issue isn't that they could produce this other variety the issue is that they just don't ... colonies have soldiers even if there is no predator - so the lack of this type suggest strongly that that instinct to produce more of this hormone is lost.


No, the real reason the "super-soldierless" species don't currently produce them isn't because they can't, it's because they have evolved to exploit the opportunity presented by a lack of army ants to avoid producing useless super-soldiers, while retaining the ability to quickly "resurrect" them epigenetically when they're needed. Again, an experiment would show whether this is really the case, as I suspect.
DavidMcC
4.7 / 5 (3) Jan 06, 2012
... If they had really "lost the instinct", then it would be strange if they could, at the same time, actually produce them on cue from the appropriate hormone, which (whilst not a protein itself) must be indirectly made by the genetic structure associated with the supposedly "lost instinct". It's not lost, it's merely suppressed, I bet. It's a case of the evolution of an active genetic switch, IMO, because you never know when army ants will show up.
Telekinetic
3.7 / 5 (9) Jan 06, 2012
These researchers are using methoprene as a growth hormone to unleash the super soldier genes in the ants. Wouldn't you know that methoprene is used in Frontline flea and tick repellant, and this chemical is everywhere besides your pet's neck. The killer ants ARE coming. Then when they march through Fukushima...
Sinister1811
2.3 / 5 (9) Jan 07, 2012
Imagine the other species they could do this with. If they can reactivate ancient genes in animals, then they could resurrect the dead ancestors of today's animals.

In fact, I read an article where scientists were attempting to turn a chicken into a dinosaur, by reactivating ancient genes buried during the transition from dinosaurs to birds.
DavidMcC
5 / 5 (2) Jan 07, 2012
Sinister, I doubt that the relevant genes are dead at all. All that has been shown so far points to a surviving mechanism for producing super-soldiers whenever soldier ants become a threat. Any species within the clade that may occasionally encounter soldier ants would benefit from not producing them when they are not needed, hence the epigenetically activated switch is a reasonable hypothesis, though not yet verified. (We have to assume that soldier ants were, indeed, a threat in the recent evoluitionary past, otherwise the ability to produce super-soldiers would have disappeared by random mutation, turning some of the genes involved into pseudo-genes.)
Isaacsname
5 / 5 (2) Jan 07, 2012
Thought-provoking, to say the least.

Especially in light of the work being done with implantation in insects. Implants in " superbugs " would be very interesting.
hagger
1.3 / 5 (3) Jan 07, 2012
will they..like countless other times introduce them to an area where non exist to screw up that ecology..evolution cut these out for a reason best known to it's self..
C_elegans
5 / 5 (2) Jan 07, 2012
It irks me that you keep assuming there's an epigenetic switch. If that were the case, the ants would be extremely related species, if not the same species, with the only difference between them being their geographic location. This is not the case. The ants have diverged genetically over a great history of time while emigrating. Many of the species appeared to have lost the ability to activate the growth hormone, or lost the the ability to respond to it in a way that activates supersoldiers. The scientists here used an artificial application of synthetic hormone to activate a transcriptional pathway that is otherwise irrelevent to the species. The Lamarkian idea of epigenetics, while resurging, has not been able to discout genetic divergence of species. Evolution still occurs, and those with biological adaptations to their specific niche environments survive while others dont, eliminating colonies that are able to activate supersoldiers in environments that dont require such luxuries
C_elegans
5 / 5 (2) Jan 07, 2012
"otherwise the ability to produce super-soldiers would have disappeared by random mutation, turning some of the genes involved into pseudo-genes."

It seems that this did indeed occur, since the northern species of ants do not form supersoldiers de novo. They have mutated genes responsible for creating this hormone.
C_elegans
5 / 5 (2) Jan 07, 2012
You may have noticed that chickens do not turn into dinosaurs on their own, the developmental timing has been evolutionarily adjusted to produce a chicken rather than a raptor. The same concept applies to these ants. What would be the biological 'signal' that recreates supersoldiers in these northern ant species without altering the genetics that control this regulatory mechanism? Stress? I think northern ant species undergo stress and competition, just as southern supersoldier generating colonies. The difference is that their genetics causes them to adapt to that stress in different ways. Southerns make supersoldiers, northerns do not.
Servelan
2 / 5 (1) Jan 07, 2012
I like how they try to relate the research to useful things, possibly to make it look more worthwhile. (We didn't just make these awesome super-soldier ants! Our research could be used for... improving crops! Oh, and fighting cancer!) How is growing ant larvae with hormones connected to breeding better crops and shedding light on cancer?
C_elegans
5 / 5 (2) Jan 07, 2012
Cancerous cells contain lots of genomic rearrangements which are able to alter the expression profiles of their genes, activating previously dormant genetic material. This is somewhat analagous to the reactivation of ancient ant genes. Crops could be enhanced to live in new climates that the current species do not endure by altering the activation of ancient resistance genes. Just some thoughts for ya Servelan. Biology is intercalated. It is not many discontinuous unrelated topics, as often assumed, but rather a single integrated story of life on earth. We are all descended from a single cell, and hence, we all share similar biological processes on this planet. That is why we are able to expand biological findings beyond the immediate organism studied.
Mike44
4 / 5 (2) Jan 07, 2012
cool now go do the same thing with the human genome..
DavidMcC
2 / 5 (1) Jan 08, 2012
... Furthermore, C elegans, you have assumed that I think that NO ant species have lost the ability to produce super-soldiers. This is not logical. Clearly, only those species derived from the super-soldier-producing species could have llost it in the first place, and some of these could well have done so, if they have not encountered soldier ants sufficiently recently.
______

Regarding your reply to Servelan, this is OTT. You appear to be exaggerating the ability of pseudogenes to make a comeback. Therefore, you are downplaying the role of convergent evolution generally. Which is ironic, considering.
DavidMcC
2 / 5 (1) Jan 08, 2012
C elegans, where is your evidence that the non-super-soldier-producing ants have "lost the hormone"? The article says that a certain hormone acts as a MIMIC for one that can induce super-soldiers in these ants, which shows tha they have not lost the ability to produce them.
Also, arguments concerning chickens are irrelevant - chickens do not have epigenetic castes. Eusocial insects have castes, and these are what allow for supersoldier ants top be turned on and off, provided it occurs frequently enough not to be lost to pseudogenes.
Maybe it's you that needs to think more about the differences between chickens and ants.
______
NB, this post was submitted before my above post, but I did not realise that it had to be re-submitted.
DavidMcC
not rated yet Jan 08, 2012
... Sorry,I referred to army ants as "soldier ants" in some of my above posts. My bad.
DavidMcC
not rated yet Jan 09, 2012
Here's a better article on super-soldiers:
http://www.nature...s-1.9746
Apparently, super-soldiers can be induced in ALL ant species, and this has researchers puzzled. Maybe it's always handy to be able to block access by raiding ants - it protects the queen and the larvae, after all. Perhaps they are simply too expensive to produce as a matter of course, so colonies just take a chance on being raided, to reduce food use.
DavidMcC
not rated yet Jan 09, 2012
As for the issue of why their sisters feed the over-sized super-soldiers, that is simple - the instinct must be: if she's one of ours, feed her, no questions asked.
El_Nose
5 / 5 (1) Jan 09, 2012
my issue with the above comments

case 1:
a) colony is being attacked
b) deploy soldiers -- check
c) soldiers have been over run
d) deploy super soldiers
e) ahhh sir they will take 2 months to germinate
f) colony is dead

life is a little smarter than this --- yes I agree they could maybe make super soldier -- but since they DO NOT - this is suppressed to the point of being dead. Why - well if they could they would .. that simple. When life is fighting to survive it uses all tools - this is no longer a tool.. its suppressed into non existance -- i am not saynig there was no evolutionary pressure to suppress it -- I am just saying it's suppress so get over it and i probably won't come back

--- wait wait .. my forehead is getting bigger and my upper arms are getting stronger -- it would seems i am going cro-magnun -- forgtteign how to tpye toguh

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