As you reap, so shall you sow: coupling of harvesting and inoculating stabilizes the mutualism between termites and fungi

At present there is no consensus theory explaining the evolutionary stability of mutualistic interactions. However, the question is whether there are general ‘rules’, or whether each particular mutualism needs a unique explanation. Here, I address the ultimate evolutionary stability of the ‘agricultural’ mutualism between fungus-growing termites and Termitomyces fungi, and provide a proximate mechanism for how stability is achieved. The key to the proposed mechanism is the within-nest propagation mode of fungal symbionts by termites. The termites suppress horizontal fungal transmission by consuming modified unripe mushrooms (nodules) for food. However, these nodules provide asexual gut-resistant spores that form the inoculum of new substrate. This within-nest propagation has two important consequences: (i) the mutualistic fungi undergo severe, recurrent bottlenecks, so that the fungus is likely to be in monoculture and (ii) the termites ‘artificially’ select for high nodule production, because their fungal food source also provides the inoculum for the next harvest. I also provide a brief comparison of the termite–fungus mutualism with the analogous agricultural mutualism between attine ants and fungi. This comparison shows that—although common factors for the ultimate evolutionary stability of mutualisms can be identified—the proximate mechanisms can be fundamentally different between different mutualisms.

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Symmetry-based reciprocity: evolutionary constraints on a proximate mechanism

PeerJ ◽

10.7717/peerj.1812 ◽

2016 ◽

Vol 4 ◽

pp. e1812 ◽

Cited By ~ 5

Author(s):

Marco Campennì ◽

Gabriele Schino

Keyword(s):

Social Relationships ◽

Group Living ◽

Evolution Of Cooperation ◽

Evolutionary Constraints ◽

Agent Based ◽

Cooperative Interactions ◽

Proximate Mechanism ◽

Proximate Mechanisms ◽

Emergent Features ◽

Selfish Agents

Background.While the evolution of reciprocal cooperation has attracted an enormous attention, the proximate mechanisms underlying the ability of animals to cooperate reciprocally are comparatively neglected. Symmetry-based reciprocity is a hypothetical proximate mechanism that has been suggested to be widespread among cognitively unsophisticated animals.Methods.We developed two agent-based models of symmetry-based reciprocity (one relying on an arbitrary tag and the other on interindividual proximity) and tested their ability both to reproduce significant emergent features of cooperation in group living animals and to promote the evolution of cooperation.Results.Populations formed by agents adopting symmetry-based reciprocity showed differentiated “social relationships” and a positive correlation between cooperation given and received: two common aspects of animal cooperation. However, when reproduction and selection across multiple generations were added to the models, agents adopting symmetry-based reciprocity were outcompeted by selfish agents that never cooperated.Discussion.In order to evolve, hypothetical proximate mechanisms must be able to stand competition from alternative strategies. While the results of our simulations require confirmation using analytical methods, we provisionally suggest symmetry-based reciprocity is to be abandoned as a possible proximate mechanism underlying the ability of animals to reciprocate cooperative interactions.

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Garden substrate preparation behaviours in fungus-growing ants

The Canadian Entomologist ◽

10.4039/n06-105 ◽

2007 ◽

Vol 139 (6) ◽

pp. 841-849 ◽

Cited By ~ 14

Author(s):

D.M. Mangone ◽

C.R. Currie

Keyword(s):

Fungal Pathogens ◽

Food Source ◽

The Other ◽

Filamentous Bacteria ◽

Fungus Garden ◽

Substrate Preparation ◽

Attine Ants ◽

Leaf Cutting ◽

Main Food Source ◽

Fungus Growing Ants

AbstractFungus-growing ants (Hymenoptera: Formicidae: tribe Attini) engage in mutually beneficial symbioses with fungi (Basidiomycota) that serve as their main food source. The leaf-cutters (genera Acromyrmex Mayr and Atta Fabricius), the most derived attine ants, employ elaborate nest-hygiene behaviours, including substrate preparation. By preparing substrate prior to its incorporation into the fungus garden, workers facilitate the physical breakdown of leaf material while reducing the abundance of potentially harmful microbes that contact their fungal mutualist. Despite its importance in ant fungiculture, substrate preparation has not been investigated in other genera of fungus-growing ants. We examined substrate-preparation procedures used by five genera of fungus-growing ants (Apterostigma Mayr, Cyphomyrmex Mayr, Trachymyrmex Forel, Acromyrmex, and Atta) representing most of the phylogenetic range of the Attini. Behavioural observations revealed that all five genera engage in substrate-preparation behaviours. Furthermore, these behaviours vary by genus, with Trachymyrmex, Acromyrmex, and Atta engaging in more elaborate preparation behaviours than the other genera. Additionally, we found that during substrate preparation, leaf-cutting ants inoculate leaf fragments with actinomycetous bacteria. These filamentous bacteria are known to produce antibiotics that suppress fungal pathogens, which suggests that inoculation with the bacterial mutualist during substrate preparation helps protect the fungus gardens of leaf-cutter ants from these parasites. Our finding that substrate-preparation behaviours occur across the phylogenetic range of attine ants suggests that these behaviours are a critical component of successful fungiculture by ants.

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SEM Observations on the Germination of Euonymous Americanus

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100119363 ◽

1985 ◽

Vol 43 ◽

pp. 508-509

Author(s):

D.R. Hill ◽

J.R. McCurry ◽

L.P. Elliott ◽

G. Howard

Keyword(s):

Electron Microscopy ◽

Scanning Electron Microscopy ◽

Light Microscopy ◽

Filter Paper ◽

Room Temperature ◽

Food Source ◽

Environmental Chamber ◽

Dormant Stage ◽

Scanning Electron

Germination of Euonymous americanus in the laboratory has previously been unsuccessful. Ability to germinate Euonymous americanus. commonly known as the american strawberry bush, is important in that it represents a valuable food source for the white-tailed deer. Utilizing the knowledge that its seeds spend a period of time in the rumin fluid of deer during their dormant stage, we were successful in initiating germination. After a three month drying period, the seeds were placed in 25 ml of buffered rumin fluid, pH 8 at 40°C for 48 hrs anaerobically. They were then allowed to dry at room temperature for 24 hrs, placed on moistened filter paper and enclosed within an environmental chamber. Approximately four weeks later germination was detected and verified by scanning electron microscopy; light microscopy provided inadequate resolution. An important point to note in this procedure is that scarification, which was thought to be vital for germination, proved to be unnecessary for successful germination to occur. It is believed that germination was propagated by the secretion of enzymes or prescence of acids produced by microorganisms found in the rumin fluid since sterilized rumin failed to bring about germination.

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