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There is only one queen in most fungus-growing ant colonies. She only has an opportunity to mate with males once in her life, on her nuptial flight, and has to store all the sperm that she will need to fertilise the eggs she produces for the rest of her life. This may be another 10-20 years for the leaf-cutter ants. The queens of most ant species mate with only one or a few males, but research at the University of Aarhus has revealed that leaf-cutter ant queens often mate with many males on their nuptial flight. The evidence for multiple mating in fungus-growing ants. The evidence for mating with many males comes from recently developed techniques for looking at the DNA of worker ants using genetic markers. These markers allow the paternity worker ants to be determined. The same techniques are used for paternity analysis | |
 | Each worker gets one copy of her genes from her mother and another from her father. Genetic markers are chosen which have multiple alleles. This means that the same region of DNA (the same locus) in different members of the population may be made up of a different sequence of the four basic building blocks that make up DNA. Each different sequence at any locus is termed an allele.
If the alleles that a queen has at any one locus are known, then any allele that her offspring have at that locus which are not the same must have come from the male with which she mated. Therefore the number of different alleles that a sample of workers have for any locus which are different from those of their mother can be used to provide a minimum estimate of the number of males with which the queen has mated. |
| The picture above shows an analysis of one locus from six workers. There are three different alleles present in these six workers. If, from left to right, we call them A,B and C, then because we know that the queen has alleles A and B, then we can work out that she has mated with at least two males, one with another copy of the B allele and one with the C allele. The more alleles are present in the population, and the more loci that are used, the more accurate will be the estimate of mating frequency.
Research at the University of Aarhus has shown that the queens of the leaf-cutter ants mate with many more males than any other known group of ants. For example, Boomsma et al. (1999) have shown that queens of Acromyrmex octospinosus mate with at least 4 to 10 males. Among the social insects, only honeybees are known to have a higher mating frequency. Why do leaf-cutter ant queens mate with so many males? Mating with many males has several consequences for the colony produced by a queen ant. A major effect is to increase the genetic diversity of the workers in the colony, but this also means that the relatedness of the workers in the colony will be reduced. A reduction in relatedness could potentially reduce the cooperation between the individuals in an ant colony, as the benefits to each ant of cooperating with the others will depend on how closely related it is to the other workers and the reproductives produced by the colony. Hence it is important to understand the possible benefits of multiple paternity to the ant colony. A number of rather complex hypotheses have been produced to explain the advantage of mating with many males, which are set out on a separate web page. Research is currently underway at the Universities of Copenhagen and Aarhus that should allow us to distinguish between at least some of these hypotheses, as well as giving more information on mating frequencies within the fungus-growing ants. | |
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