Leaf-Cutter Ant EcosystemSlide 2Ants in BiosphereLeaf-Cutter AntsLeaf-Cutter Ant GardenersLeaf-Cutter Ant Caste SystemLeaf-Cutter Ant EcosystemSlide 8Nitrogen fixation in gardensExperimental deviceExperimental resultsNitrogen fixing bacteriaPhylogeny of the bacteriaLeaf-Cutter Ant Ecosystem Workers of Atta cutting down a whole plant. From Wikipedia by C.R. Linder (1999)Science article on Leaf-Cutter Ants (2009)Ants in Biosphere1/3 of all insect biomass on Earth>4/5 of arthropods in tropical forestsOne genus, Atta, are the leaf cutter antsPictures and information from Nature article by Pinto-Tomas et al. (vol 326, pp 1120-3)Leaf-Cutter AntsDominant herbivores in tropical forestRecycle nutrients which maintains ecosystemLargest insect colony of 8 million workersPeruvian tropical rain forest (publicly available image from Wikipedia)Leaf-Cutter Ant GardenersHarvest hundreds of pounds of leaf material per yearHarvests a fungus which feeds on leavesAnts eat the fungusQueen ant surrounded by fungus gardenLeaf-Cutter Ant Caste SystemAt top are queens (rightmost: winged form); others are workers and soldiers. From Wikipedia by Sarefo (2007).Leaf-Cutter Ant EcosystemFungus is a mutual with antsSecond mutual is ActinobacteriaActinobacteria produces antibiotics which defends fungus from parasitesLeaf-Cutter Ant EcosystemResearcher thought nitrogen fixing bacteria a third mutualNitrogen is a limiting resource for fungus feeding on leavesExperiments showed the fungus gardens have more nitrogen than in leaves (so must come from nitrogen in air)Nitrogen fixation in gardensNitrogen content of different ecosystem componentsMeasurement of nitrogen fixation activity in different componentsExperimental deviceMeasure an isotope of nitrogen gas (GC is fungus garden chamber and FC is the feeding chamber joined by tube)Experimental resultsGrey bars have enriched nitrogen atmosphere while white bars do not. Bar chart shows that the extra nitrogen is taken up by the fungus garden & ants.Nitrogen fixing bacteriaKlebsiella and Pantoea are the nitrogen fixing bacteria detected in fungus gardens. However, Pantoea only in one-third of colonies. The grey bar is a control to verify design of experiment.Phylogeny of the bacteriaPhylogeny to determine the genus of N-fixing