Some ants live longer than others—way longer. And the mapping of the first full genome sequences of ants helps to reveal how two ants from the same colony, and with much the same genetic material, can have such different life histories. The work may also provide insights into longevity in another social species with which ants share about one third of their genes: humans.
Researchers sequenced the genomes of two ant species: Jerdon's jumping ant (Harpegnathos saltator) and the Florida carpenter ant (Camponotus floridanus), which have quite different levels of social—and hence, biological—mobility. Carpenter ants live in large colonies that revolve around a queen that lays all of the fertilized eggs. Once the queen dies, the colony perishes as well. Jerdon's jumping ants, on the other hand, have smaller colonies in which worker ants can replace the queen after she dies. These so-called gamergate queens change physically and behaviorally as they take on the queen's duties.
All of these ant castes seem to start with the same basic genetic blueprint, yet end up looking—and behaving—very differently. Scientists point to epigenetics, the change in gene expression (rather than direct alterations in the DNA code), as a likely explanation. "It's not changes in the genome," says Shelley Berger, a professor of cell and developmental biology at the University of Pennsylvania School of Medicine and co-author of the new paper. "It seems to me this was an epigenetic question of how they took on these different forms," she says of the ants.
The genome sequencing, published in the August 27 issue of Science, reveals that the carpenter ant has about 240 million base pairs and 17,064 genes, whereas the jumping ant has some 330 million base pairs and 18,564 genes (compared with about three billion base pairs and 23,000 genes in humans). Berger notes that the group could only sequence the genomes of male ants, but based on that data they had little reason to think the females would be radically different.
The first two ant genomes "are going to be incredibly useful to compare against other genomes," says Christopher Smith, a cell and molecular biologist at San Francisco State University, who was not involved in the recent research. He calls the new work "a really forward-looking study."
Long live the queen—and her replacements
The sequenes provide clues that explain why queen ants can live as much as 10 times as long as female worker ants, and researchers are keen to figure out what factors go into determining this extreme longevity.
When a queen from an H. saltator colony dies, female worker ants fight to decide who will take over. Once a new queen is selected, her form and function change. She shifts from workaday laborer to fertile egg layer, adjusting body and life history in the process.
The researchers found that in the ants expression of telomerase, enzymes that help to protect the genetic information at the end of chromosomes, changed as gamergate queens transformed from worker to egg-layer. "That gamergate queen, she starts expressing higher level of telomerase," and her life span increases from that of an average worker ant, Berger explains. She and her colleagues are interested in finding the "aspects of longevity that correlate with this genetic switch."