title: Nutrition mediates the expression of cultivar-farmer conflict in a fungus-growing ant.
abstract: Attine ants evolved farming 55-60 My before humans. Although evolutionarily derived leafcutter ants achieved industrial-scale farming, extant species from basal attine genera continue to farm loosely domesticated fungal cultivars capable of pursuing independent reproductive interests. We used feeding experiments with the basal attine Mycocepurus smithii to test whether reproductive allocation conflicts between farmers and cultivars constrain crop yield, possibly explaining why their mutualism has remained limited in scale and productivity. Stoichiometric and geometric framework approaches showed that carbohydrate-rich substrates maximize growth of both edible hyphae and inedible mushrooms, but that modest protein provisioning can suppress mushroom formation. Worker foraging was consistent with maximizing long-term cultivar performance: ant farmers could neither increase carbohydrate provisioning without cultivars allocating the excess toward mushroom production, nor increase protein provisioning without compromising somatic cultivar growth. Our results confirm that phylogenetically basal attine farming has been very successful over evolutionary time, but that unresolved host-symbiont conflict may have precluded these wild-type symbioses from rising to ecological dominance. That status was achieved by the evolutionarily derived leafcutter ants following full domestication of a coevolving cultivar 30-35 Mya after the first attine ants committed to farming.
authors.affiliation: Centre for Social Evolution, Department of Biology, University of Copenhagen, 2100 Copenhagen, Denmark; Smithsonian Tropical Research Institute, Apartado 0843-03092, Balboa, Ancon, Republic of Panama; jonathan.shik@gmail.com.
authors.forename: Jonathan Z
authors.initials: JZ
authors.lastname: Shik
authors.affiliation: Smithsonian Tropical Research Institute, Apartado 0843-03092, Balboa, Ancon, Republic of Panama;
authors.forename: Ernesto B
authors.initials: EB
authors.lastname: Gomez
authors.affiliation: Centre for Social Evolution, Department of Biology, University of Copenhagen, 2100 Copenhagen, Denmark; Jodrell Laboratory, Comparative Plant and Fungal Biology, Royal Botanic Gardens, Kew, Richmond TW9 3DS, United Kingdom;
authors.forename: Pepijn W
authors.initials: PW
authors.lastname: Kooij
authors.affiliation: Department of Biology, Brigham Young University, Provo, UT 84602.
authors.forename: Juan C
authors.initials: JC
authors.lastname: Santos
authors.affiliation: Smithsonian Tropical Research Institute, Apartado 0843-03092, Balboa, Ancon, Republic of Panama;
authors.forename: William T
authors.initials: WT
authors.lastname: Wcislo
authors.affiliation: Centre for Social Evolution, Department of Biology, University of Copenhagen, 2100 Copenhagen, Denmark;
authors.forename: Jacobus J
authors.initials: JJ
authors.lastname: Boomsma
mesh_terms: D000363:Agaricales / Q000187:drug effects* / Q000502:physiology; D000818:Animals; D001000:Ants / Q000145:classification / Q000502:physiology*; D005075:Biological Evolution; D050260:Carbohydrate Metabolism; D002241:Carbohydrates / Q000494:pharmacology; D010802:Phylogeny; D011506:Proteins / Q000378:metabolism / Q000494:pharmacology*; D013559:Symbiosis / Q000502:physiology*
chemical_list: D002241:Carbohydrates; D011506:Proteins
keywords: Mycocepurus smithii; crop domestication; geometric framework; social evolution; symbiosis