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24 May 2007

Flexible genes allow ants to change destiny

The discovery of a flexible genetic coding in leaf-cutting ants sheds new light on how one of nature’s ultimate self-organising species breeds optimum numbers of each worker type to ensure the smooth running of the colony.

Research at the University of Leeds shows that despite an inherited genetic pre-disposition to grow into a particular worker caste, ant larvae can be triggered by environmental stimuli to switch development depending on colony’s workforce needs.

“Our previous research suggested that genetics did indeed play a part in caste determination - but not how much of a part,” says evolutionary biologist Dr William Hughes of the Faculty of Biological Sciences. “This left us with a conundrum: ant colonies are a model of social efficiency, yet if genetics ruled caste development, then this would be a very rigid - and therefore very inefficient - method of ensuring an optimum workforce balance.”

“It seems that ants have evolved their own solution to this problem. Given that it takes an ant eight weeks to develop from an egg into an adult, ant colonies have to predict the need for different types of worker well in advance, and a flexible combination of nature and nurture will help them do this.”

Dr Hughes’ research used colonies of Acromyrmex leaf-cutting ants, which have two distinct worker castes: large workers, which forage and build the nest and small workers, which care for the ant larvae and the fungus they eat. Worker ants are always female and the large workers are up to three times the size of the smaller ones. “Males don’t do much other than eat, fly off, mate and die,” says Dr Hughes.

As leaf-cutting queens mate with multiple males, they make good candidates for examining role of genetics in caste determination. With the same mother and rearing conditions, the only differences between workers within a colony will be the genes inherited from their different fathers.

To see if genetic pre-disposition was fixed, all the large workers were removed from a colony to stimulate the need for more larvae to develop into this caste. The results showed that genetic types that didn’t normally develop into large workers did so when the need for this caste was increased, proving that the genetic influence is adaptable.

Leaf-cutting ants have an enormous ecological impact because of the amount of leaves they harvest and are a significant pest for several crops. They particularly like citrus and Eucalyptus trees and a colony of the Atta species can defoliate a tree in a single night. They have been estimated to remove 17 per cent of leaf production in some tropical forests. Understanding how colonies function may well offer new opportunities to control their impact.

“We don’t yet know what environmental cues influence the caste destiny of the larvae – it could be the food they’re fed, the temperature, or even pheromones,” says Dr Hughes.

Dr Hughes’ research has been published online in Proceedings of the Royal Society B: Biological Sciences.

Further information from:

Clare Elsley, campuspr. Tel: 0113 258 9880 Mob: 07767 685168

Simon Jenkins, University of Leeds Press Office. Tel: 0113 343 5764


Dr Hughes is a Lecturer at the Institute of Integrative and Comparative Biology in the Faculty of Biological Sciences at the University of Leeds. The key theme of his work is evolutionary biology, looking at models of social, symbiotic and sexual relationships in insect species, including the leaf cutting ant.

The research has been carried out in collaboration with Dr Jacobus Boomsma, University of Copenhagen, and funded by the Carlsberg Foundation, Denmark.

The University of Leeds’ Faculty of Biological Sciences is one of the largest in the UK, with nearly 150 academic staff and over 400 postdoctoral fellows and postgraduate students. The Faculty’s current active research grant portfolio is around £77M and funders include charities, Research Councils, the European Union and industry. The Faculty has an outstanding research record and all major units of assessment were awarded Grade 5 in the last government (HEFCE) Research Assessment Exercise.

Leaf cutting ants: some facts

  • There are two types of leaf-cutting ant, Atta and Acromyrmex. Atta have large colonies of up to 7 million workers, with nests up to 7m deep and 10m across. Acromyrmex are much smaller with up to tens of thousands of workers.
  • Leaf-cutting ands are only found in the Neotropics, from Argentina in the south, to Texas in the north.
  • Leaf-cutting ants cut leaves which they use for growing a particular fungus they feed on. The ants need the fungus to feed on, and the fungus needs the ants to reproduce – neither can survive without the other.


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