In order understand the evolution of complex societies, researchers are sequencing the genomes of social insects. The most recent data, published in the Early Edition of Proceedings of the National Academy of Sciences, come from several species of ants, including the red harvester ant, Pogonomyrmex barbatus.
A team, led by Arizona State University organismal and systems biology professor Juergen Gadau, sequenced one of the genomes and set out to decipher which genes might be responsible for defining which ants work and which ants reproduce in a red harvester ant colony.
Division of labor and reproduction are two crucial characteristics scientists think are important to the evolution of social structure. "Having multiple independently evolved social genomes helps us to better understand which genes are involved in crucial social traits, because those should be highly conserved," Gadau said.
In addition to specialization of roles within a colony, researchers argue that development of methods to communicate information is another key aspect of eusociality, the extreme form of social behavior exhibited by certain bees, termites and ants.
This study was funded by the Division of Integrative Organismal Systems, part of the National Science Foundation's Biology Directorate. The Developmental Systems Cluster within the division supports research aimed at understanding how interacting developmental processes give rise to the emergent properties of organisms.
Results from Gadau's study reveal that, compared to other insects, the red harvester ant genome has significantly more genes associated with the sense of smell, as well as detection and metabolism of chemical signals. This is consistent with the fact that ants use chemical signals to communicate.
Another difference appears in the genes of the ant's immune system. Previously, scientists hypothesized that ants may have evolved novel immune responses or specialized behaviors to avoid disease outbreaks within their dense populations. These results indicate the former may be a distinct possibility, however future comparisons with other insect genomes should yield more insight into the significance of the differences observed in this study.
"The diversity in social structure between the different ants sequenced will allow us to search for the genetic basis and the architecture underlying the observed social diversity in ants," Gadau explained. "A comparison with bees, a completely independent evolutionary lineage, will give us an opportunity to test whether there are multiple ways how a genome can become a sociogenome."
Finally, the team observed evidence of epigenetic differences--or changes in appearance that can be inherited--in genes related to division of labor and reproduction. In this case, the genes responsible for development of wings and ovaries, role-specific traits in a red harvester and colony, appear to show some differences.
According to the researchers, the finding implies that, although the genes themselves are present in both worker and queen ants, when and where the genes are expressed is highly regulated and heritable from one generation to the next.
"Everything we can learn about epigenetic modifications will probably have major implications for human health since these mechanisms are thought to be critical in the development of complex diseases of humans, such as mental illnesses and diabetes," said Gadau.
- C. R. Smith, C. D. Smith, H. M. Robertson, M. Helmkampf, A. Zimin, M. Yandell, C. Holt, H. Hu, E. Abouheif, R. Benton, E. Cash, V. Croset, C. R. Currie, E. Elhaik, C. G. Elsik, M.-J. Fave, V. Fernandes, J. D. Gibson, D. Graur, W. Gronenberg, K. J. Grubbs, D. E. Hagen, A. S. I. Viniegra, B. R. Johnson, R. M. Johnson, A. Khila, J. W. Kim, K. A. Mathis, M. C. Munoz-Torres, M. C. Murphy, J. A. Mustard, R. Nakamura, O. Niehuis, S. Nigam, R. P. Overson, J. E. Placek, R. Rajakumar, J. T. Reese, G. Suen, S. Tao, C. W. Torres, N. D. Tsutsui, L. Viljakainen, F. Wolschin, J. Gadau. Draft genome of the red harvester ant Pogonomyrmex barbatus. Proceedings of the National Academy of Sciences, 2011; DOI: 10.1073/pnas.1007901108
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