Ant biology: November 2012 Archives

Hello,

How come when it gets really hot ants are still able to run around on bitumen and pavers without burning their feet?

Regards
Anna W
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Dear Anna,

Although the thermotolerance of ant tarsi (feet) on hot bitumen or pavement has not been directly studied, there are a few biomechanic studies out there that can help us make some educated guesses.

Part of the reason ants may be able to run quickly over hot pavement is that their tarsi are composed of sclerotized chitin, which is a really tough polymer of many connected glucose molecules. The toughness of this biomaterial is often compared to the keratinized tissue seen in vertebrate hooves--such as horse hooves--many of which are also able to walk on hot bitumen and pavement. This is very different than human feet, which have many nerves and soft, burnable tissue on the bottom of our feet. Yet, even humans can walk on hot pavement if repeated friction and pressure forces the formation of calluses that insulate the sensitive tissue in your foot from the pavement.

While this explanation helps us understand how ants don't burn their tarsi (feet), it does not get around the larger of issue of how the ants on hot pavement deal with the increased body temperature (ants are small!). Well, as it turns out, there are some extremely interesting studies on ants that have adapted to hot, dry environments. One ant in particular--the Sahara Desert ant (Cataglyphis bicolor)--has adapted such a high thermotolerance that its proteins can operate at higher temperatures (4-5 degrees Celsius) and it can forage normally at body temperatures above 50C or 122F. Considering this ant makes a living by running on the hot sand to find and consume insects that have died of heat exhaustion, it makes sense that it can withstand this heat. While you wouldn't commonly find Cataglyphis running on pavement, there has been recent research showing that ants found in urban and suburban areas are more likely to come from hotter, drier habitats because of the prevalence of open areas in the urban and suburban landscape. Thus, it is logical that the ants you see running around on pavement might have also have some thermotolerance themselves!

Thanks for your question,

Max Winston & the AskAnt Team

Acacia-ant mutualism?


Hi there.

I am a science teacher who traveled to Northern Kenya in July. While in Ndonyo Wasin (near Archer's Post), I observed many ant mounds under acacia trees. I was wondering if you could identify the type of ant that built this mound. I am also interested in learning more about their mutualism. I am writing a science curriculum about the environment that surrounds our sister school there, and would really love to learn more about the ants that inhabit the region. Any help would be greatly appreciated.

Thanks,
Maria
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Dear Maria,

The mounds in your pictures were made by termites, not ants. They are potentially interesting for their complicated caste system and symbiosis with certain fungi, similar to Attine leaf-cutting ants in the Americas.

However, I am guessing that the mutualism you are referring to is that between acacia trees and ants, not between termites and fungi. Such relationships do occur in Kenya between Acacia drepanolobium and three species of ant in the genus Crematogaster and one species in the genus Tetraponera. Unfortunately, the plant pictured here is not an Acacia drepanolobium, but that does not mean they are not present in the area. These plants typically grow on "black cotton" soils and are often the only overstory plant in the area.

Acacia drepanolobium trees are very easy to identify because they are full of hollow swollen thorns and are typically rife with ants, as in the picture below.

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Photo by Eric Denemark

The basic idea behind the mutualism is that the plants grow the hollow thorns pictured as well as extra-floral nectaries and protein-rich food bodies. Ants nest in the thorns and feed on the nectar and food bodies and in exchange, they aggressively protect their host plants against herbivores. The ants are so effective that they can even protect their plants against elephants (Goheen and Palmer 2010)! The ants will not nest anywhere else and without ant residents, the acacias are quickly destroyed, making the mutualism obligate. Both organisms involved are completely dependent on each other. However, when researchers (Palmer et al. 2008) used fences to exclude large herbivores from a plot of acacias for a period of ten years, the plants actually stopped producing resources for the ants, because they no longer needed their protection. Without their host plants, these ants have nowhere to nest. This is yet more evidence that the extinction of single species can have wide-ranging and unexpected results.

In reality, the acacia-ant mutualism is much more complex than what I have outlined. For example, there is a high level of competition between ants of both the same and different species for nesting space because nearly every tree is occupied and founding new colonies or expanding current colonies necessarily means that confrontation must occur. The dominance hierarchy between species is closely related to average colony size (Palmer et al. 2000). No single ant of a species involved here is much better at fighting than any other ant so the largest colony usually wins. Ants also provide differing levels of protection to their hosts so plants experience different benefits depending on who is nesting in their thorns.

If you do find these plants and ants in the area, I would strongly encourage you to incorporate them into your curriculum. The four species of ant are easy to tell apart by the shape of their body and coloration of segments. See how the first two segments are red and the last segment is black in the ants in the picture? That means they are C. mimosae. C. nigriceps is black, black, red and C. sjostedti is all black. The single Tetraponera species, T. penzigi is also all black but has a long and thin body unlike the stocky Crematogaster species.

As you may have guessed, a lot of research has been done on the Kenyan acacia-ant relationship, predominantly by Todd Palmer's research group at the University of Florida and Maureen Stanton's group at the University of California Davis. I have listed a number of their publications below but you should definitely check out their websites as well. They have been featured in quite a few popular science articles that may be useful.

Thanks for your question and good luck,
Ben Rubin, James Trager & the AntAsk Team

Goheen JR, Palmer TM. 2010. Defensive plant-ants stabilize megaherbivore-driven landscape change in an African savanna. Current Biology 20, 1768-1772.
Palmer T. 1994. Wars of attrition: colony size determines competitive outcomes in a guild of African acacia ants. Animal Behaviour, 68, 995-1004.
Palmer TM, Brody AK. 2007. Mutualism as reciprocal exploitation: African plant-ants defend foliar but not reproductive structures. Ecology 88, 3004-3011
Palmer TM, Stanton ML, Young TP, Goheen JR, Pringle RM, Karban R. 2008. Breakdown of an ant-plant mutualism follows the loss of large herbivores from an African savanna. Science. 319, 192-195.
Palmer TM, Young TP, Stanton ML, Wenk E. 2000. Short-term dynamics of an acacia ant community in Laikipia, Kenya. Oecologia, 123, 425-435.
Stanton ML, Palmer TM. 2010. The high cost of mutualism: effects of four species of East African ant symbionts on their myrmecophyte host tree. Ecology 92, 1073-1082
Stanton ML, Palmer TM, Young TP. 2002. Competition-colonization trade-offs in a guild of African acacia-ants. Ecological Monographs, 72, 347-363.

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