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Leafcutter ants retire when they grow old


Leaf-cutter ants "retire" from

their cutting role when they grow old, switching to carrying when their jaws

blunt with age.

Leaf-cutter ants start their lives with razor-like jaws, or

mandibles, to cut through the leaves they harvest.


But as these "wear out", the insects tend to carry

the leaves cut by their younger counterparts.


The findings suggest that individual ants can extend their

useful lifespan as their skills decline.


They are reported in the journal Behaviour Ecology and



The US-based scientists discovered that older ants were

significantly less efficient at cutting leaves.


leafcutter ant head

A close up shot of a leafcutter ant - Jeff Cremer


They estimated these older colony members' "worn-out

teeth" halved the speed at which the entire colony was able to harvest



The researchers, from the University of Oregon and the

Oregon State University, supports previous research showing the survival of a

leaf-cutter colony depends on the efficiency of its workers.

The leaf-disks collected by the forager ants are transported

back to the colony where the sap can be harvested for food.

The gathered leaves are also used as a surface to grow the

fungus that is consumed by the colony.


"Cutting leaves is hard work," explains the

University of Oregon's Dr Robert Schofield, who led the study.


leafcutter ant

A leafcutter ant carrying a leaf - Jeff Cremer



"Much of the cutting is done with a V-shaped blade

between teeth on their mandibles.


"This blade starts out as sharp as the sharpest razor

blade that humans have developed."


It is believed that leaf-cutter ants' mandibles also contain

zinc-enriched biomaterials, which strengthen them.


Over time, however, these razor-sharp blades become blunt

and less efficient.


The ants cut the leaves with a V-shaped blade on their jaw.


The researchers measured the wear on the mandible cutting

blade in the ant species Atta cephalotes from a colony in Soberania National

Park, Panama.


Dr Schofield and his team used electron microscopy to

compare the pristine teeth of laboratory-reared pupae with the worn teeth of

the wild forager ants.


By comparing the radius of the mandible teeth they found the

blade of a cutter ant to be 340 times duller than the pristine blade of a pupa.


The study revealed that leaf-cutter ants with highly worn

mandibles had difficulties cutting and anchoring leaves.


Individuals with the most worn teeth, which had less than

10% of the cutting blade, exclusively carried leaves rather than cut them


The team estimated that, because of this age-related wear, a

colony spent twice the energy cutting leaves than it would if all the ants had

sharp mandibles.


The findings support the idea that wear and fracture can be

significant problems for insects as well as larger animals.


Greater good


"This study demonstrates an advantage of social living

that we are familiar with," says Dr Schofield.


"Humans that can no longer do certain tasks can still

make very worthwhile contributions to society.


Leaf-cutter ants live in colonies that have a very developed

structure with a strict hierarchy.


This level of social organisation is described as eusocial.


As well as benefitting the colony, the researchers believe

that this ability to change jobs may also lead to longer life spans in social

insects compared to their solitary cousins.


Source: http://news.bbc.co.uk/earth/hi/earth_news/newsid_9306000/9306830.stm

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