Occam’s Razor Cuts Both Ways: Endophytes, Resource Allocation, Herbivory, and Mutualism: A Reply to Rudgers et al.

Faeth, Stanley H.

doi:10.1086/652997

Cited by 7 publications

(4 citation statements)

References 42 publications

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“…In light of such theory, those who would argue that these strictly vertically transmitted fungi are not mutualists must provide a mechanism that explains how the fungus is maintained within a plant population, in the face of lifetime fitness costs to the plant. Faeth and Sullivan (2003) offer four possible explanations for their claim that "mutualistic asexual endophytes in a native grass are usually parasitic" (see also Faeth 2010). We briefly summarize these here.…”

Section: Non-hybridmentioning

confidence: 99%

Costs, Benefits, Parasites and Mutualists: The Use and Abuse of the Mutualism–Parasitism Continuum Concept for “Epichloë” Fungi

Newman

Gillis

Hager

2022

Philosophy, Theory, and Practice in Biology

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The species comprising the fungal endophyte genus Epichloë are symbionts of cool season grasses. About half the species in this genus are strictly vertically transmitted, and evolutionary theory suggests that these species must be mutualists. Nevertheless, Faeth and Sullivan (e.g., 2003) have argued that such vertically transmitted endophytes are “usually parasitic,” and Müller and Krauss (2005) have argued that such vertically transmitted endophytes fall along a mutualism-parasitism continuum. These papers (and others) have caused confusion in the field. We used a systematic review to show that close to half of the published papers in this field incorrectly categorize the interaction. Here, we develop the argument that advantages and disadvantages are not the same things as mutualism and parasitism and that experimental evidence must be interpreted in the context of theory. We argue that, contra Faeth and Sullivan, it is highly unlikely that such strictly vertically transmitted endophytes can be parasites, and that, contra Müller and Krauss, it is inappropriate to apply the continuum concept to strictly vertically transmitted endophytes. We develop a mathematical model to support and illustrate our arguments. We use the model to clarify that parasitism requires some degree of horizontal transmission, and that while it is appropriate to use the continuum concept when referring to the genus as a whole, or to species that possess horizontal transmission, we argue that it is inappropriate to use the concept when referring to species that are strictly vertically transmitted.

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Section: Non-hybridmentioning

confidence: 99%

Costs, Benefits, Parasites and Mutualists: The Use and Abuse of the Mutualism–Parasitism Continuum Concept for “Epichloë” Fungi

Newman

Gillis

Hager

2022

Philosophy, Theory, and Practice in Biology

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“…Furthermore, hormonal manipulation that increases the production of seeds might not always be beneficial to plant long‐term fitness. For example, a seed‐transmitted symbiont might enhance its fitness by making a plant flower earlier than would be optimal for the plant's total lifetime fitness (Faeth, 2010 ) or for the total yield of perennial crops. Fungi that benefit more from vegetative or clonal growth of their hosts than from seed production can suppress sexual reproduction (Clay, 1991 ).…”

Section: Comparing Benefits and Costs To Crop Plants From Different S...mentioning

confidence: 99%

An evolutionary perspective on increasing net benefits to crops from symbiotic microbes

Denison

Muller

2022

Evolutionary Applications

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Plant‐imposed, fitness‐reducing sanctions against less‐beneficial symbionts have been documented for rhizobia, mycorrhizal fungi, and fig wasps. Although most of our examples are for rhizobia, we argue that the evolutionary persistence of mutualism in any symbiosis would require such sanctions, if there are multiple symbiont genotypes per host plant. We therefore discuss methods that could be used to develop and assess crops with stricter sanctions. These include methods to screen strains for greater mutualism as resources to identify crop genotypes that impose stronger selection for mutualism. Single‐strain experiments that measure costs as well as benefits have shown that diversion of resources by rhizobia can reduce nitrogen‐fixation efficiency (N per C) and that some legumes can increase this efficiency by manipulating their symbionts. Plants in the field always host multiple strains with possible synergistic interactions, so benefits from different strains might best be compared by regressing plant growth or yield on each strain's abundance in a mixture. However, results from this approach have not yet been published. To measure legacy effects of stronger sanctions on future crops, single‐genotype test crops could be planted in a field that recently had replicated plots with different genotypes of the sanction‐imposing crop. Enhancing agricultural benefits from symbiosis may require accepting tradeoffs that constrained past natural selection, including tradeoffs between current and future benefits.

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“…In the face of such theory, those who would argue that these strictly vertically transmitted fungi are not mutualists must provide a mechanism that explains how the fungus is maintained within a plant population, in the face of lifetime fitness costs to the plant. Faeth and Sullivan (2003) offer four possible explanations for their claim that “mutualistic asexual endophytes in a native grass are usually parasitic” (see also Faeth, 2010). We briefly summarize these here.…”

Section: Introductionmentioning

confidence: 99%

Costs, Benefits, Parasites and Mutualists: The Use and Abuse of the Mutualism–Parasitism Continuum Concept forEpichloëFungi

Newman

Gillis

Hager

2021

Preprint

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The species comprising the fungal endophyte genus Epichloë are symbionts of cool season grasses. About half the species in this genus are strictly vertically transmitted, and evolutionary theory suggests that these species must be mutualists. Nevertheless, Faeth and Sullivan (e.g. 2003) have argued that such vertically transmitted endophytes are “usually parasitic,” and Müller and Krauss (2005) have argued that such vertically transmitted endophytes fall along a mutualism–parasitism continuum. These papers (and others) have caused confusion in the field. We used a systematic review to show that close to half of the published papers in this field incorrectly categorize the interaction. Here, we develop the argument that advantages and disadvantages are not the same things as mutualism and parasitism and that experimental evidence must be interpreted in the context of theory. We argue that, contra Faeth and Sullivan, it is highly unlikely that such strictly vertically transmitted endophytes can be parasites, and that, contra Müller and Krauss, it is inappropriate to apply the continuum concept to strictly vertically transmitted endophytes. We develop a mathematical model to support and illustrate our arguments. We use the model to clarify that parasitism requires some degree of horizontal transmission, and that while it is appropriate to use the continuum concept when referring to the genus as a whole, or to species that possess horizontal transmission, we argue that it is inappropriate to use the concept when referring to species that are strictly vertically transmitted.

show abstract

Occam’s Razor Cuts Both Ways: Endophytes, Resource Allocation, Herbivory, and Mutualism: A Reply to Rudgers et al.

Cited by 7 publications

References 42 publications

Costs, Benefits, Parasites and Mutualists: The Use and Abuse of the Mutualism–Parasitism Continuum Concept for “Epichloë” Fungi

Costs, Benefits, Parasites and Mutualists: The Use and Abuse of the Mutualism–Parasitism Continuum Concept for “Epichloë” Fungi

An evolutionary perspective on increasing net benefits to crops from symbiotic microbes

Costs, Benefits, Parasites and Mutualists: The Use and Abuse of the Mutualism–Parasitism Continuum Concept forEpichloëFungi

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