Final Report Summary - ANTS (Attine ANT SymbiomeS)
The attine fungus-growing ants are prime models for understanding phenotypic adaptations in social evolution and symbiosis and their genetic underpinning. Our 5-year research project aimed to use a series of cutting-edge omics methods to address unexplored questions of social insect mating system evolution (WP1), the extent of functional co-adaptation between farming ants and their fungal cultivars (WP2), the adaptive functional significance of microbes domesticated as endosymbionts in the ant guts and surrounding organs, and ectosymbionts on the cuticles of farming ant workers (WP3), and the extent to which advanced superorganismal colony-life is affected by intragenomic and social conflicts that emanate from and shape genome-wide variation (WP4). We achieved encompassing protein-level and experimental understanding of sperm competition between ejaculates of males inseminating the same leaf-cutting ant queens and of the elimination of sperm competition by proteins in the secretions of queen sperm storage organs (WP1). We also resolved the functions of several proteins ingested with fungal-cultivar food to be transferred as manure for new garden growth via the fecal fluid of the farming ants, and we showed that the most evolutionarily advanced ant farmers rear polyploid fungal cultivars (WP2). We reconstructed the evolutionary histories of a number of bacterial symbionts of the attine ants and used genome sequencing to infer their mutualistic functions in the farming symbiosis (WP3). After obtaining a series of reference genomes and transcriptomes of representatives of the entire crown group of the attine ant phylogeny and their fungal cultivars, we embarked on genome-level studies of Acromyrmex leaf-cutting ants and some of their social parasitic sister lineages, which included a yet unfinished population genomics study to investigate genome rearrangements and loss of genetic diversity following specialization on a socially parasitic life style (WP4). Many of our studies found molecular evidence for ongoing co-adaptation between male and female interests in mating system evolution, and between the farming ants and their fungal and bacterial cultivars in fine-tuning mutualistic interactions and defense against disease.