Keller L., Gordon E. The Lives of Ants

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So what’s so special about

the genome of ﬁre ants?

As we have already said, there is no need to know the

whole story of ants’ genome to investigate the genetic

basis of their behaviour, though the task would certainly

be greatly facilitated and accelerated if we did know the

complete repertory of their genes, in other words if their

genome was deciphered.

Deciphering it would not in fact be impossible. Quite a few

genomes, some of which belong to living organisms that are

much more complex than an ant, for instance chickens, chim-

panzees, and even humans, have already been mapped. Com-

pared to the three billion ‘letters’ making up human genome, the

800 million or so likely to be found in the DNA of ants look like

small beer indeed. Reading them, however, will require the

bringing together of many different skills and a substantial

amount of funds.

At present, the genomes of only a small number of highly

social species, human beings, chimpanzees, and bees, have been

deciphered, so it would be nice to be able to add ants to the list.

Because they are the most social of social insects, they are the

perfect model for studying links between genetics and behaviour.

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Furthermore, a comparison of their genome with that of bees

should make it possible to identify certain genetic features under-

lying the development of sociality in insects to begin with, then

in vertebrates.

Close investigation of the DNA of an ant is thus required. But

which ant? The most logical choice would be the ﬁre ant Sole-

nopsis invicta, the worst type of invasive species. Traditional

methods for halting their advance having failed, genomics

could possibly lead to the discovery of other ways of dealing

with them. This might help us to identify the genes that govern

reproduction or perhaps even those that make it possible for

social harmony to exist inside colonies, thus giving us a weapon

against them. If it should prove possible, say, to prevent the

queens from reproducing or to affect the mechanism of caste

determination, this might well offer some hope of exterminating

the reproductive caste, thereby destroying their colonies.

There are further reasons for taking an interest in the genome

of Solenopsis invicta. Because of the damage they cause, these ants

have already been thoroughly studied. All over the world, dozens

of teams of myrmecologists have investigated their biology,

habits, and behaviours, making it one of the ants best known

to science. So it would appear logical to take things further by

analysing the totality of its genome. It should be added that the

main function of the red imported ﬁre ant would be as a model,

since the deciphering of their genome is expected to supply

information applicable to many other species.

Genes and castes

Another beneﬁt of sequencing the genome of Solenopsis invicta

would be that it could help us to understand the origin of

polymorphism in ant colonies. It was recognized long ago that

queens are unlike their workers: they are larger and they have

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sexual organs. It is also known that there are great morphological

differences among workers in some species, including as it happens

Solenopsis invicta. The occurrence of several morphological castes

is the source of much speculation. What is the process that turns

a larva into a queen rather than a worker? What are the mechan-

isms that make one worker a normal worker and another a soldier?

We know that the way the workers feed the brood has an inﬂuence

on the development of the larvae and that, though this holds

good for most species, there are some exceptions to the rule. In

Pogonom yrmex, for example, it is now clear that genetic factors

and maternal effects, including changes made by females to the

hormonal content of their eggs, also inﬂuence the process of caste

determination. Identiﬁcation of which factors they are could en-

lighten us on how genes and environment interact during the

development of individuals.

Great things are also expected from a comparison of the ﬁre

ant genome not only with that of another social insect, the bee,

but with that of the parasitic wasp Nasonia, which is solitary.

Analysis of genetic features shared or not shared by these three

Hymenoptera would provide a good way of identifying potential

genes for sociality, some of which it is not fanciful to think may

also be present in human beings.

Understanding ageing

It might be thought that the gulf between ants and humans is so

vast as to be unbridgeable. But, genetically speaking, the speci-

ﬁcity of our own species is really quite slight: we share 99 per

cent of our genes with chimpanzees and about 40 per cent with

mice! The future will tell what similarities there are between our

DNA and the DNA of ﬁre ants. One thing is already established,

that there are features common to both humans and ants; and

identiﬁcation of them could improve our understanding of some

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THE LIVES OF ANTS

biological mechanisms, ﬁrst and foremost those involved in

human ageing.

Understanding why and how living things age has become a

real challenge for scientists in many different disciplines. Special-

ists in evolution would like to know what underlies the enor-

mous disparities in the longevity of living creatures, why, for

instance, some turtles can live for 100 years, while the life

expectancy of mice is at best three. Biologists and doctors, too,

take an interest in this: faced with the conundrum of ageing in

industrialized societies, they would be glad to be able to delay or

even counter the effects on organisms of living longer. They are

investigating the cellular, molecular, and genetic origins of sen-

escence, work in which they focus on model organisms. Hith-

erto, they have relied essentially on the worm Caenorhabditis

elegans, the fruit ﬂy Drosophila melanogaster, or the yeast Sacchar-

omyces cerevisiae, all of which are well known and easy to study.

But all of these organisms have a very brief lifespan, which is why

they are not ideal for studying the mechanics of ageing.

Ants would be much better suited to this purpose. For one

thing, their longevity can be remarkable (some queens have been

known to reach the age of twenty-nine); and on average they live

100 times longer than most other insects. For another thing,

within a single species there are wide variations among the

different castes: a queen, for instance, may live 500 times longer

than the males and twenty times longer than her workers.

Disparities of this sort can even be apparent within the worker

caste, something that we have demonstrated with Michel

Chapuisat in weaver ants, among whom lifespan is a function

of specialization, little nursemaids living statistically a few weeks

longer than the large hunter-warriors. What is especially surpris-

ing about this ﬁnding is that, in most animal species, smaller

individuals do not live as long as larger ones. Among weaver ants,

therefore, the tendency is inverted, even when colonies are

housed in a labor atory, away from natural dangers. This must

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mean that differences in gene expression between weaver ants of

different size directly affect the difference in their longevity.

The fact remains that queens and their worker daughters share

a good part of their genome, as do the workers of any given

colony. The differences observed in their longevity cannot there-

fore be explained by the nature of their genes, but rather by the

way the genes are expressed, that is ‘activated’ by external and

environmental factors. This hypothesis could be proved, or per-

haps disproved, by analysis of the ﬁre ant’s genome, added to

which is the possibility that, in a more general way, deciphering

the genome could also reveal the existence of genes linked to

ageing that might be peculiar to organisms with long lifespans.

Walking chemical plants

The implications could go even further, in that there could be

medical beneﬁts to be derived from the genome of the ﬁre ant,

ﬁrst and foremost the development of new antibiotics. After all,

ﬁre ants live in an environment favourable to the growth of

pathogens, the humid warmth of the nest providing an excellent

culture medium. In addition, their living conditions inside the

nest entail much close bodily contact and they often exchange

food with each other. This way of life is ideal for tr ansmitting

microbes throughout the colony—despite which, and despite

being susceptible to certain diseases, ﬁre ants, like all other

ants, seem to have developed protection against micro-organ-

isms, probably because of the substances secreted by their glands

and their stings. So it is entirely possible that work on these

walking chemical plants could produce recipes for new bacteri-

cides or even fungicides, herbicides, and insecticides.

Another source of inspiration might be the venom used by

Solenopsis invicta for a variety of purposes. They use it, for

example, to defend their nest against predators, vertebrate or

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invertebrate, and for keeping other ants out of their territory. It

also ser ves as a toxin for overcoming their prey and even, as it

appears, as an antiseptic against the growth of micro-organisms

in the soil which might infect the nest. Not bad going for a single

substance! It is also a further reason, if further reasons are

required, for trying to understand the mechanisms via which

the ants can synthesize this do-all venom. Here, too, information

from their genome would be likely to lead to a breakthrough.

It can be seen that the full sequencing of the Solenopsis invicta

genome would provide enough data for scientists in many dif-

ferent disciplines to work on for many years. Entomology for

one, of course, would make great strides. Once deciphered, the

genome of ﬁre ants would provide new tools to elucidate some

of the mysteries surrounding their lives and their exceptional

social organization.

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Part VIII

High-tech Ants

Drawing 8 Ant robots Engineers are devising teams of mini-robots

based on the social behaviour of ants.

Computer-modelling behaviour

That a great many entomologists take a close interest in

ants, in their behaviour and their genes, is only to be

expected. But it may be more surprising that engineers

such as computer scientists and specialists in robotics

should also ﬁnd them of interest and even try to borrow

ideas from their social arrangements. The fact is that

experts in artiﬁcial systems are now drawing upon our

knowledge of ants to help them in their development of

automated devices for speeding up telecommunications

or even for designing teams of robots to send to Mars.

At ﬁrst sight, there is nothing in common between the future

miracles of the technologists and creatures that appeared on

earth millions of years ago. Nor are ants, with their tiny br ains,

gifted with great intelligence. Workers, taken individually, spend

their time doing very simple and repetitive tasks and can even act

in completely disorganized ways, not infrequently undoing the

work done just a few moments before by a nestmate. Neverthe-

less, collectively, they are capable of great achievements. They

can construct nests of sophisticated architecture which are verit-

able cathedrals on an entomological scale; and they can come up

with solutions to complex problems.

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