Symbiont fidelity and the origin of species in fungus-growing ants

Abstract

A major problem in evolutionary biology is explaining the success of mutualism. solving this problem requires understanding the level of fidelity between interacting partners. Recent studies have proposed that fungus-growing ants and their fungal cultivars are the products of 'diffuse' coevolution, in which single ant and fungal species are not exclusive to one another. Here we show for ants and associated fungi in the Cyphomyrmex wheeleri species group that each ant species has been exclusively associated with a single fungal cultivar 'species' for millions of years, even though alternative cultivars are readily available, and that rare shifts to new cultivars are associated with ant speciation. such long-term partner fidelity may have facilitated 'tight' ant-fungus coevolution, and shifts to new fungal cultivars may have had a role in the origin of new ant species.

Ant-fungal species combinations engineer physiological activity of fungus gardens

“…Although vertical transmission of symbionts and generalized fidelity between clades of ants and clades of fungi is the norm, horizontal transmission is quite extensive, especially among the phylogenetically early branching lineages (Green et al, 2002;Kellner et al, 2013;Mehdiabadi et al, 2012;Mikheyev et al, 2010;Mueller et al, 2010;Mueller et al, 1998;Schultz and Brady, 2008). One of the more profound evolutionary and ecological transitions occurred in the derived lineages (the 'higher Attini'), the most complex of which are found in the clade containing leaf-cutting ants (genera Atta and Acromyrmex).…”

“…leaf-cutter ants tend to cultivate Attamyces; Trachymyrmex ants tend to cultivate Trachymyces), several observations are inconsistent with a strict 1:1 co-evolution. Colonies can be experimentally switched to nonnative fungi, and surveys indicate that switches can occur naturally on ecological and evolutionary scales (Mehdiabadi et al, 2012;Mikheyev et al, 2010;Mueller et al, 2011b;Mueller et al, 1998;Seal and Tschinkel, 2007a;Stradling and Powell, 1986;Weber, 1956) (supplementary material Fig. S1).…”

Examination of graphs in Multiple Agent Genetic Networks for Iterated Prisoner's Dilemma

“…Farmer ants, such as Cyphomyrmex wheeleri, have been known to become attached to specific species of fungi for millions of years, even when other food sources are available [19]. These species have experienced a form of 'lock-in'.…”

Nest Biology and Demography of the Fungus-Growing Ant Cyphomyrmex lectus Forel (Myrmicinae; Attini) at a Disturbed Area Located in Rio Claro, SP, Brazil

“…According to Leal et al (2011), the fungus garden in Cyphomyrmex colonies was usually characterized by yeast nodules scattered among the superficial soil and leaf litter, in Brazilian savanna (Cerrado). In this biome, the same authors detected three basic types of fungus garden in six Attines genera: (1) pieces of substrate enveloped by yeast (Cyphomyrmex, rimosus group), (2) laminar fungus suspended in the chamber ceiling or plant roots (Mycetarotes, Mycocepurus, and Myrmicocrypta), and (3) amorphous fungus on the floor of the chamber (Sericomyrmex and Trachymyrmex; see also Solomon et al, 2004;Rabeling et al, 2007;Mehdiabadi et al, 2012).…”