Fungus-growing ants

Evolution and Colony Foundation:
– Early ancestors of attine ants were insect predators.
– Higher attines evolved in Central and North America about 20 million years ago.
– Generalized fungus farming in ants evolved about 55–60 million years ago.
– Leaf-cutting ants likely arose as active herbivores about 10 million years later.
– Attine ants evolved cuticular cultures to suppress mycopathogens.
– After mating flights, queens create a chamber and start their colony’s garden.
– Queens fertilize the garden with their fecal liquid and energy comes from consuming eggs.
– Workers feed on the garden while larvae are fed malformed eggs.
– Colonies grow slowly for the first two years, then accelerate for the next three.
– Newly founded colonies have low survival rates, with some species more likely to survive.

Caste System and Workers:
– Attines have seven castes performing tasks.
– Reproductive caste includes male drones and female queens.
– Queens have larger ovaries than working caste females.
– Queens stay in a centralized fungal garden while workers move eggs.
– Worker caste size differences develop after colony establishment.
– Lower attines have minor polymorphism within minor workers.
– Higher attines have significant size differences between worker castes.
– Worker head width is important for determining tasks.
– Workers care for delicate fungus hyphae with their antennae and mouths.
– Foragers have larger mandibles powered by strong muscles.

Habitat and Farming:
– Lower attines live in nests with 100–1000 ants and small fungus gardens.
– Higher attines live in colonies of 5–10 million ants in interconnected chambers.
– Some colonies are visible from satellites, measuring up to 600m.
– Lower attines prefer dead vegetation, seeds, fruits, and insect feces for their gardens.
– Specific ant species have been found farming particular fungus species.
– Attine ants mostly farm fungi from the Agaricaceae family.
– Some species cultivate yeast, like Cyphomyrmex rimosus.
– Ants transmit cultures vertically or laterally to other colonies.
– Different ant species cultivate specific fungi in unique ways.

Worker Recruitment and Harvesting Vegetation:
– Leaf cutting recruitment varies based on leaf quality, species, and location.
– Pheromones from poison gland sacs are used for marking foraging trails.
– Chemical structures of trail recruitment pheromones have been identified.
– Pheromones like MMPC are potent and attract ants over long distances.
– Ants follow specific pheromones for recruitment and orientation.
– Ants cut vegetation by anchoring one mandible and moving the other.
– Leaf fragment sizes vary based on ant size and cutting techniques.
– Ants stridulate while cutting vegetation to make a noise and cut smoothly.
– Ants have high metabolic rates while cutting vegetation.
– Foraging behavior varies among ant species, with different strategies for carrying material back to the nest.

Gardening Process and Nutrition:
– Foragers bring vegetation back to the nest for the gardening process.
– Ants deposit the harvested material in specific locations within the nest.
– The gardening process involves cultivating fungus in specialized chambers.
– Ants tend to the fungus gardens, ensuring optimal growth conditions.
– The success of the ant colony depends on the efficiency of the gardening process.
– Higher attine fungi grow gongylidia rich in carbohydrates and lipids.
– Ants prefer eating staphylae over hyphae for longer lifespan.
– Cellulose is poorly degraded by fungus, ants rely on xylan, starch, and other sources for nutrition.
– Fungal enzymes in ant guts help digest laminarin.
– Only 5% of workers’ energy needs are met by fungal staphylae.

Bacterial Symbionts and Impact of Farming:
– Pseudonocardia bacterium acquired by pupae from workers for protection.
– Bacteria produce molecules to prevent specialized fungus garden pathogen growth.
– Specialized diets of attine ants reduce microbiotic diversity.
– Bacteria stored in crypts in ant exoskeletons.
– Ant farming scale comparable to human industrialized farming.
– Ant colonies can defoliate a mature eucalyptus tree overnight.
– Ecological impact significant in subtropical regions.
– Large colonies feed on tree sap in addition to fungus.
– Queens obtain energy from eggs laid by nonqueen females.