The farming ant Sericomyrmex amabilis nutritionally manages its fungal symbiont and its social parasite

Abstract

1. When parasites exploit mutualisms involving food exchange, they can destabilise the partnership with costs to interacting partners. For instance, the ant Sericomyrmex amabilis farms fungal symbionts to produce food, but, in so doing, attracts parasitic Megalomyrmex symmetochus guest ants that infiltrate fungus‐farming ant societies and live with their hosts their entire lives. 2. The present study examined whether host foraging in parasitised colonies shifts towards nutritional requirements of the parasitic guest ants as inferred from the parasite's elemental content (%C, %N, and C:N). 3. Laboratory feeding experiments with nutritionally defined diets indicated that S. amabilis ants harvest protein‐biased substrate, and more total substrate when hosting M. symmetochus relative to when provisioning their fungus gardens and nestmates. 4. Field surveys further showed that parasitised colonies incur reductions in fungus garden nutritional quality and quantity, brood mass, and host worker body condition. And yet these costs appear manageable across growing seasons, as parasitised fungal cultivars appear to provide sufficient nutrition for stable populations of host ants. 5. The approach developed here shows how behavioural strategies for nutrient regulation can extend beyond the needs of the individual to entire fungus‐farming systems, and implies that S. amabilis dynamically adjusts collective foraging strategies when parasitised to enhance long‐term symbiotic stability.

Mutualistic interactions between ants and fungi: A review

“…Other cases of food‐based ant‐fungus associations concern ants feeding on fungal hyphae as do the Attina. Ants in the Megalomyrmex silvestrii group (Myrmicinae) are social parasites that can also usurp the nests of the Attina of the genera Apterostigma , Cyphomyrmex , Trachymyrmex , and Sericomyrmex (Adams, Mueller, Holloway, et al, 2000 ; Adams, Mueller, Schultz, & Norden, 2000 ; Mueller et al, 2001 ; Shik et al, 2018 ; Wheeler, 1925 ). They feed on the fungal gardens of their host colonies and can participate in tending the gardens by readjusting their overall size and shape, but not by cultivating fungi, for example, by adding substrate (Mueller et al, 2001 ).…”

Using Nutritional Geometry to Explore How Social Insects Navigate Nutritional Landscapes

“…For more information on these mutualisms, see extensive reviews on bacteria [38,39], fungus [40,41], plants [33,42], and aphids [36]. We focus on mutualisms, while also noting that NG has been used to understand how parasites shape nutritional regulation in the ant colonies [43,44]. Figure 3C.…”