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Caterpillars and fungal pathogens: two co-occurring parasites of an ant-plant mutualism.

Roux O, Céréghino R, Solano PJ, Dejean A - PLoS ONE (2011)

Bottom Line: This probable temporal priority effect also allows female moths to lay new eggs on trees that already shelter caterpillars, and so to occupy the niche longer and exploit Cecropia resources before colonization by ants.Although no higher herbivory rates were noted, these caterpillars are ineffective in protecting their host trees from a pathogenic fungus, Fusarium moniliforme (Deuteromycetes), that develops on the trichilium in the absence of mutualistic ants.The cost of greater FB production plus the presence of the pathogenic fungus likely affect tree growth.

View Article: PubMed Central - PubMed

Affiliation: CNRS, Écologie des Forêts de Guyane (UMR-CNRS 8172), Campus Agronomique, Kourou, France. olivier.roux@ird.fr

ABSTRACT
In mutualisms, each interacting species obtains resources from its partner that it would obtain less efficiently if alone, and so derives a net fitness benefit. In exchange for shelter (domatia) and food, mutualistic plant-ants protect their host myrmecophytes from herbivores, encroaching vines and fungal pathogens. Although selective filters enable myrmecophytes to host those ant species most favorable to their fitness, some insects can by-pass these filters, exploiting the rewards supplied whilst providing nothing in return. This is the case in French Guiana for Cecropia obtusa (Cecropiaceae) as Pseudocabima guianalis caterpillars (Lepidoptera, Pyralidae) can colonize saplings before the installation of their mutualistic Azteca ants. The caterpillars shelter in the domatia and feed on food bodies (FBs) whose production increases as a result. They delay colonization by ants by weaving a silk shield above the youngest trichilium, where the FBs are produced, blocking access to them. This probable temporal priority effect also allows female moths to lay new eggs on trees that already shelter caterpillars, and so to occupy the niche longer and exploit Cecropia resources before colonization by ants. However, once incipient ant colonies are able to develop, they prevent further colonization by the caterpillars. Although no higher herbivory rates were noted, these caterpillars are ineffective in protecting their host trees from a pathogenic fungus, Fusarium moniliforme (Deuteromycetes), that develops on the trichilium in the absence of mutualistic ants. Therefore, the Cecropia treelets can be parasitized by two often overlooked species: the caterpillars that shelter in the domatia and feed on FBs, delaying colonization by mutualistic ants, and the fungal pathogen that develops on old trichilia. The cost of greater FB production plus the presence of the pathogenic fungus likely affect tree growth.

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Trichilium infested by Fusarium moniliforme.Percentages of Cecropia obtusa saplings whose trichilia were attacked by Fusarium moniliforme in three situations: saplings sheltering an Azteca colony, saplings sheltering Pseudocabima guianalis caterpillars, and unoccupied saplings (N = number of saplings in each case). Statistical comparisons; Kruskal-Wallis test: H3610 = 338.1; P<0.001; Dunn's multiple comparison test, different letters indicate significant differences at P<0.001.
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pone-0020538-g002: Trichilium infested by Fusarium moniliforme.Percentages of Cecropia obtusa saplings whose trichilia were attacked by Fusarium moniliforme in three situations: saplings sheltering an Azteca colony, saplings sheltering Pseudocabima guianalis caterpillars, and unoccupied saplings (N = number of saplings in each case). Statistical comparisons; Kruskal-Wallis test: H3610 = 338.1; P<0.001; Dunn's multiple comparison test, different letters indicate significant differences at P<0.001.

Mentions: Fusarium moniliforme was present on 323 of the 610 C. obtusa saplings (53.0%), sometimes completely covering the trichilia (Fig. 1C). The percentage of infested individuals was significantly lower among saplings sheltering an Azteca colony than those sheltering P. guianalis caterpillars or not occupied, while the difference between the latter two cases was not significant (Fig. 2).


Caterpillars and fungal pathogens: two co-occurring parasites of an ant-plant mutualism.

Roux O, Céréghino R, Solano PJ, Dejean A - PLoS ONE (2011)

Trichilium infested by Fusarium moniliforme.Percentages of Cecropia obtusa saplings whose trichilia were attacked by Fusarium moniliforme in three situations: saplings sheltering an Azteca colony, saplings sheltering Pseudocabima guianalis caterpillars, and unoccupied saplings (N = number of saplings in each case). Statistical comparisons; Kruskal-Wallis test: H3610 = 338.1; P<0.001; Dunn's multiple comparison test, different letters indicate significant differences at P<0.001.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3105098&req=5

pone-0020538-g002: Trichilium infested by Fusarium moniliforme.Percentages of Cecropia obtusa saplings whose trichilia were attacked by Fusarium moniliforme in three situations: saplings sheltering an Azteca colony, saplings sheltering Pseudocabima guianalis caterpillars, and unoccupied saplings (N = number of saplings in each case). Statistical comparisons; Kruskal-Wallis test: H3610 = 338.1; P<0.001; Dunn's multiple comparison test, different letters indicate significant differences at P<0.001.
Mentions: Fusarium moniliforme was present on 323 of the 610 C. obtusa saplings (53.0%), sometimes completely covering the trichilia (Fig. 1C). The percentage of infested individuals was significantly lower among saplings sheltering an Azteca colony than those sheltering P. guianalis caterpillars or not occupied, while the difference between the latter two cases was not significant (Fig. 2).

Bottom Line: This probable temporal priority effect also allows female moths to lay new eggs on trees that already shelter caterpillars, and so to occupy the niche longer and exploit Cecropia resources before colonization by ants.Although no higher herbivory rates were noted, these caterpillars are ineffective in protecting their host trees from a pathogenic fungus, Fusarium moniliforme (Deuteromycetes), that develops on the trichilium in the absence of mutualistic ants.The cost of greater FB production plus the presence of the pathogenic fungus likely affect tree growth.

View Article: PubMed Central - PubMed

Affiliation: CNRS, Écologie des Forêts de Guyane (UMR-CNRS 8172), Campus Agronomique, Kourou, France. olivier.roux@ird.fr

ABSTRACT
In mutualisms, each interacting species obtains resources from its partner that it would obtain less efficiently if alone, and so derives a net fitness benefit. In exchange for shelter (domatia) and food, mutualistic plant-ants protect their host myrmecophytes from herbivores, encroaching vines and fungal pathogens. Although selective filters enable myrmecophytes to host those ant species most favorable to their fitness, some insects can by-pass these filters, exploiting the rewards supplied whilst providing nothing in return. This is the case in French Guiana for Cecropia obtusa (Cecropiaceae) as Pseudocabima guianalis caterpillars (Lepidoptera, Pyralidae) can colonize saplings before the installation of their mutualistic Azteca ants. The caterpillars shelter in the domatia and feed on food bodies (FBs) whose production increases as a result. They delay colonization by ants by weaving a silk shield above the youngest trichilium, where the FBs are produced, blocking access to them. This probable temporal priority effect also allows female moths to lay new eggs on trees that already shelter caterpillars, and so to occupy the niche longer and exploit Cecropia resources before colonization by ants. However, once incipient ant colonies are able to develop, they prevent further colonization by the caterpillars. Although no higher herbivory rates were noted, these caterpillars are ineffective in protecting their host trees from a pathogenic fungus, Fusarium moniliforme (Deuteromycetes), that develops on the trichilium in the absence of mutualistic ants. Therefore, the Cecropia treelets can be parasitized by two often overlooked species: the caterpillars that shelter in the domatia and feed on FBs, delaying colonization by mutualistic ants, and the fungal pathogen that develops on old trichilia. The cost of greater FB production plus the presence of the pathogenic fungus likely affect tree growth.

Show MeSH
Related in: MedlinePlus