Ants are one of the most extreme examples of the influence of nurture, rather than nature, in producing an individual's role in society. Each role, or "caste," is rigidly determined by environmental cues during their development. Now Earthwatch-supported scientists have discovered the origins of a startling example of genetic caste determination among harvester ants in southwestern New Mexico.
In the journal Nature , Drs. Sara Helms Cahan and Laurent Keller of the University of Lausanne reported that crosses between hybrid lineages give rise to workers, while queens develop from within-lineage matings. The hybrid lineages were the result of hybridization between two separate harvester ant species, Pogonomyrmex barbatus and P. rugosus . This is the first time such a unique arrangement has been reported in harvester ants, one of the best-studied groups of ants in North America.
"This study shows the power that genetics has to revolutionize our understanding of how organisms work, even in systems we thought we knew well," said Helms Cahan, principal investigator of an Earthwatch Student Challenge Awards Program (SCAP) project on the hybrid harvester ants.
Earthwatch SCAP fellows were instrumental in the collection of field samples from the hybrid populations, involving excavating the colonies to find the hidden queens and males. SCAP offers high school students with limited experience in the sciences an opportunity to expand their appreciation for science and conservation by working directly with leading scientists.
"It is anyone's guess how many other fascinating and unusual phenomena remain to be revealed in the many thousands of other species whose genetics have yet to be explored," continued Helms Cahan.
The researchers used genetic markers to identify two distinct pairs of interbreeding lineages in the hybrid zone between the harvester ant species, P. barbatus and P. rugosus . All 75 workers tested were the result of interbreeding between the lineages. None of the dozens of ant colonies sampled had queens that were the result of an inter-lineage mating.
"We show that this unusual system was originally a hybrid zone between two normal ant species that have since become dependent on hybrids to make workers," said Helms Cahan. "Thus, hybridization has played a pivotal and complex role in harvester ant evolution, leading to a fundamental shift in how reproduction is divided within their social groups."
For more information, see "Complex hybrid origin of genetic caste determination in harvester ants." Sara Helms Cahan and Laurent Keller. Nature (2003) 424: 306-309.
For information on the Student Challenge Awards Program ( SCAP), click here
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