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Studying Factors that Determine an Ant's Destiny (Worker or Queen)

NSF Award:

The genetic architecture of reproductive caste determination in ants  (Arizona State University)

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The fate of most ant larvae—that is, whether an individual insect grows up to be a worker or a queen—depends largely on the quality and the amount of food they receive from the other ants in the colony. But in a few rare species, an ant’s future social “caste’’ rests solely within its genes.

All ant species establish colonies ruled by a queen, sometimes several queens, who are the only members of the colony who can mate and reproduce.  For most ants, the destiny of the queens’ offspring usually is determined by food, possibly with some input from genes. But in a few “minority’’ ant groups—ant scientists have discovered only five species so far—genetic composition alone is the deciding factor.

“Workers just work; they don’t produce offspring.  Only the queen reproduces,’’ said Juergen Gadau, associate professor of biology in Arizona State University’s school of life sciences. “From an evolutionary standpoint, it is hard to understand how something can evolve that foregoes reproduction.  At the core of their ‘society’ is the division of reproductive and non-reproductive individuals.’’

Gadau is studying these rare ant populations, focusing on Harvester ants, with the goal of identifying the individual genes responsible for producing either queens or workers. Ultimately, he hopes to use his findings to reveal which of those genes also are involved in the case of the other ants—those largely influenced by food—and how, for example, the differences in food are involved in turning on the worker or queen genes.  

The information produced from studying both groups could enhance the understanding of evolutionary biology, including how all ant species grow and develop, and also might unravel a few similar mysteries about humans, since the latter also are a product of the interaction between their genes and the environment.

“Ants are a model system of phenotype plasticity, meaning the same genome can produce dramatically different phenotypes (observable traits and physical characteristics) in queens and workers, depending on environment,’’ he said. “With humans, for example, if you don’t receive enough food when you are young, you can’t grow to the size you should, which is why, when you look at developing nations, individuals are usually smaller. But if you take the same genotype, and give them enough food, they grow taller; that is, they realize their genetic potential.

“In ants, the same genome can produce a worker or a queen,’’ he added. “So one of the big questions in evolutionary biology is how, if you have the same genomes, do you get different phenotype classes?’’

The work is being funded by a $500,000 grant over four years from the National Science Foundation as part of the American Recovery and Reinvestment Act of 2009.  Nearly half of the stimulus dollars have gone to the university for buildings and hiring, while about $80,000 of the grant went to a Houston technology company to run DNA sequences involved in the research project, Gadau said.      

With these rare ant species, here’s how it works: There are two types of queens, call them A and B. Each has its own unique genetic makeup. Similarly, there also are two types of males, A and B. When an A queen mates with an A male, or a B queen mates with a B male, the offspring all will become queens. When two different types of ants mate—A and B—their progeny all will become workers. 

The researchers are isolating the ants’ DNA, and examining genotypes from workers and queens from the same colony.  They then combine these results with their knowledge of the ant genome, that is, the location of the genes responsible for the observed differences between workers and queens. Later, they will compare what they have found with the ant species that use differential feeding (“food’’ ant group) to generate workers or queens.

“We want to first understand the genetics, then see if the food issue prompts the same gene expression in the other ant population,’’ Gadau said.  “Once I have the gene, then I can go back and see how it is involved in the regulatory network, and test whether the introduction of food changes the regulation of the genome in the same way.’’

Harvester ants usually are found in dry climates in the West, and exist mostly by eating seeds. “They are considered a pest species because they clear out wheat fields, or, if in meadows, they deter cattle and a cut off parts of vegetation there,’’ Gadau said. “They can be very disturbing at golf courses or public parks. And they have a very painful sting, which lasts longer than that of a wasp or a honeybee.’’

Gadau, who has been stung multiple times, believes that this basic research eventually could lead to improved agriculture practices—protecting crops from destruction by ants—as well as possible new disease treatment approaches, individualized medicine, for example. Moreover, it also could provide a clearer picture of human development.

“Understanding how ants modify the regulation of their gene expression to produce different phenotypes will help us understand how humans develop into different phenotypes.  For example, why do some people become alcoholics, or obese?’’ he said. “Anything not innate has to be an interaction between the environment and the genes.  If we understand these processes at the level of ants, we may gain a more enhanced understanding of how these differences evolve in humans.’’


  • rough harvester ants at nest entrance, pebbly ground
The researchers are studying Harvester ants with the goal of identifying the genes responsible for producing either queens or workers.
Whitney Cranshaw, Colorado State University,

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