Genomics of mutualism in plant-ants

Pseudomyrmex spinicola on their host acacia plant.

Pseudomyrmex spinicola on their host acacia plant.

Acacia-ants in the genus Pseudomyrmex are iconic examples of plant-ant mutualism. These ants obligately nest in the hollow thorns grown by acacias and feed exclusively on the extra-floral nectar and Beltian food bodies produced by their plants. In exchange for this nesting space and food, the ants aggressively protect their hosts against herbivores, pathogenic fungi, and encroaching plants. The ants are incredibly effective and plants without resident ants are quickly overrun by herbivory and disease.

phylogeny

Dendrogram representing species targeted for genome sequencing. Note the convergence of mutualistic behaviors within the group.

 

Plant-ant mutualism has evolved at least three times within Pseudomyrmex, making this an ideal group in which to study the evolution of this behavior. Utilizing next-generation Illumina sequencing, I have successfully assembled and annotated the genome of P. gracilis, a non-mutualistic species. I have used this reference sequence to assist in the assembly of representative species from each mutualistic clade and the most closely related non-mutualistic clades. Together, these data will show the consistent differences in genomes between mutualists and generalists and help us understand how this amazing behavior evolved. Many of these results are now published here.