Greenbeard genes are selfish genetic elements (SGEs) that favor their own transmission by increasing the fitness of other carrying individuals. Such a phenotype, can only occur if a gene or a group of tightly linked genes produce (1) a conspicuous phenotype, (2) the ability to recognize this phenotype, allowing the bearer individual to discriminate carriers from non-carriers and (3) a nepotistic behavior in favor of carriers. These extraordinary SGEs can have profound evolutionary consequences on genomes and social behavior. The first identified Greenbeard haplotype was in the fire ant Solenopsis invicta. In this species, the Social b (Sb) supergene, an 11 Mb non-recombining region is associated with a Greenbeard effect. Discriminating on cuticular chemical profiles, carrier ant workers spread the Sb supergene by killing non-bearer queens. In this project I aim to identify the genetic basis of the queen-discrimination ability of Greenbeard-carrier ant workers. I will first compare the molecular evolution of the Sb supergene with the non-driving homologous haplotype over multiple bearer and outgroup species. Then I will compare patterns of expression of Sb supergene genes in antennae and brains between workers. Lastly, I will functionally validate candidate genes by genetically altering their sequence in workers. I will assay the impact of the knock out on the Greenbeard effect by testing the queen-discrimination ability of transformed workers. Using this combination of techniques and analyses, the GreenAnt project will tackle the molecular basis and evolution of Greenbeard genes in metazoan organisms.
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