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Cool Creatures, Spineless Wonders

Ants, Ants Everywhere: and a lot more than you think

Ants are everywhere: so much so that they often heralded as one of evolution’s success stories. Recently, three open access papers have exposed secrets behind these social insects’ triumph—by unearthing their routes to new habitats; comparing how the workers measure-up to one another; and by dissecting the source of the ant’s ‘superhero’ strength.

Ants have colonised almost every landmass on Earth, and can survive at the extremes of the natural world. In the Sahara desert, shiny silver ants search the scorching desert sands to scavenge corpses of heat-stricken animals, before racing back to their nests to avoid overheating themselves. At the opposite extreme near the Arctic Circle, thatch ants build and live in their own ‘centrally-heated’ rotting compost heap. Furthermore and whilst there are no truly aquatic ants—when floodwaters from the Amazon River submerge their rainforest homes, fire ants will grasp each other to form a living raft that floats the colony to safety: and the mangrove mud-nesting ant of northern Australia is believed unique amongst ant species in that it can actually swim underwater.

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The Saharan silver ant is one of the most heat tolerant animals on the planet | Image: ©BBC from the absolutely, awesome “Africa” series

In addition to being everywhere, ants are typically found in large numbers. Large ant colonies can contain millions, if not billions, of individuals. If you were to weigh all the living animals in a terrestrial ecosystem, an impressive 15% of that mass would be ants—which when scaled up would mean that the weight of all the ants on Earth would be roughly equal to that of all the people on Earth.

“There are more species of ants in a square kilometre of Brazilian forest than all the species of primates in the world, more workers in a single colony of driver ants than all the lions and elephants in Africa”.

 —E. O. Wilson (1975)

This abundance of ants around the world—which outnumber us 1.5 million to one—makes them a dominant force in nature. Like us, ant colonies have the power to engineer their own world around them. Many build elaborate underground nests, complete with chambers and connecting tunnels—and ants may, in fact, have a very long history of living underground. Work published in PLOS ONE at the end of last year and conducted by Dr. Andrea Lucky—an evolutionary biologist from the University of Florida—and co-workers suggests that the ancestor’s of ants likely evolved when living in soil. Subsequently, some ant species have moved up through leaf litter to exploit other habitats. The weaver ants, for example, have now climbed to the dizzying heights of the rainforest canopy and make their nests by weaving together leaves using silk produced by their own larvae.

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The underground nests of some ant colonies contain gardens of a cultivated fungus that is used to feed the colony | Image credit: ©Alex Wild

These weaver ants have fastened together leaflets of a tree to form a hanging nest. The white parts are silk spun by the ants' larvae | Image credit Alex Wild

These weaver ants have fastened together leaflets of a tree to form a hanging nest. The white parts are silk spun by the ants’ larvae | Image credit: ©Alex Wild

Ants can have such a big impact on the world around them because they work together and share out the jobs between them. Males in ant colonies (drones) tend to be short-lived and only serve one purpose, but female ants make up the bulk of a colony and fulfil different roles. Queen ants are responsible for reproduction; and are larger and have wings (for at least part of their lives). Worker ants are smaller and wingless, and devote themselves to building the nest and feeding the young larvae.

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A queen and worker Argentine ant: a species that is invasive in many countries around the world and forms ‘megacolonies’ | Image credit ©Alex Wild

A few ant species—typically those that live in the tropics—have other castes of female ants with bodies adapted to match more specialised roles. The soldier castes uses their large and powerful jaws to protect the rest of the colony: whilst some honeypot ants are overfed to the point that their abdomens become distended and bloated with food and are used as a ‘living larder’.

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The mighty jaws of the driver ant soldier serve to protect the rest of the colony | Image credit: ©Alex Wild

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Honeypot ants grotesquely bloated abdomens store excess nutrients for the colony | Image credit: ©Alex Wild

However, having a specialised body shape to match a specialised job within the colony appears the exception rather than the rule—according to a paper published last year. In PeerJ, Dr. Marcio Pie and Marcel Tschá from the Universidade Federal do Paraná in Brazil reported that, following measuring the bodies of worker ants from over 100 species and relating these measurements to the ant’s evolutionary family tree—they discovered that ants only rarely evolved new body shapes and were much more likely to simply evolve to become bigger or smaller.

However, more recent work, conducted by Dr. Roberto Keller—from the Instituto Gulbenkian de Ciência in Portugal—and co-workers, and published in eLife this month, revealed that even the bodies of the seemingly most unremarkable worker ant shows a unique feature that helps it to work for the good of the colony. Again they measured over 100 ant species, but looked at both workers and queens. This revealed that workers have a disproportionately larger neck than the queens of the same species. Taking a closer look, by dissecting the necks of some workers and queens, Keller and colleagues revealed that the worker ants’ necks contained powerful muscles and skeletal parts that had not seen in other insects.

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Careful dissection of the thorax segments of worker and queen ants reveals some unique features that link form to function | Image adapted from Keller et al. (2014) DOI: http://dx.doi.org/10.7554/eLife.01539.008

A strengthened neck appears to be an adaptation that allows workers to perform their famous feats of strength, and lift and carry objects many times heavier than themselves. It also appears to be a universal feature of worker ants, and probably evolved in the earliest ancestor of all ants. As such it was likely one of the innovations that contributed to the evolutionary success of these miniature, yet mighty, creatures.

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Interesting Link:

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References:

RESEARCH ARTICLES :

Lucky et al. (2013). Tracing the Rise of Ants – Out of the Ground. PLOS ONE DOI: http://dx.doi.org/10.1371/journal.pone.0084012 (OPEN ACCESS)

Pie and Tschá. (2013) Size and shape in the evolution of ant worker morphology. PeerJ  DOI: http://dx.doi.org/10.7717/peerj.205  (OPEN ACCESS)

Keller et al. (2014). Evolution of thorax architecture in ant castes highlights trade-off between flight and ground behaviors eLife DOI: http://dx.doi.org/10.7554/eLife.01539 (OPEN ACCESS)

RELATED INSIGHT :

Tautz (2014). Evolutionary morphology: One size does not fit all, eLife, DOI: http://dx.doi.org/10.7554/eLife.02088 (OPEN ACCESS)

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About StuartKing

Hi, I'm Stuart, an Assistant Features Editor at eLife and recent life sciences PhD graduate. I blog about evolution and its weird and wonderful creations.

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