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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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Height of Cecropia treelets.Mean height of trees (±SE) that sheltered colonies of one of the two Azteca species, Pseudocabima guianalis caterpillars, or that sheltered neither Azteca nor caterpillars during the experimental period. Statistical comparisons (normality and equal variance tests passed); ANOVA: F256 = 8.56; P<0.0001. Newman-Keuls' post-hoc test: different letters indicate significant differences at P<0.05.
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pone-0020538-g005: Height of Cecropia treelets.Mean height of trees (±SE) that sheltered colonies of one of the two Azteca species, Pseudocabima guianalis caterpillars, or that sheltered neither Azteca nor caterpillars during the experimental period. Statistical comparisons (normality and equal variance tests passed); ANOVA: F256 = 8.56; P<0.0001. Newman-Keuls' post-hoc test: different letters indicate significant differences at P<0.05.

Mentions: We did not note significant differences in the percentage of foliar surface eaten by defoliating insects between the C. obtusa sheltering an Azteca colony, caterpillars, or not occupied by either ants or caterpillars (Kruskal-Wallis test, H290 = 1.813; P>0.05). Nevertheless, caterpillar presence affected tree growth as those sheltering Azteca colonies during this experimental period were significantly taller at the end of the survey than those sheltering caterpillars or those that were unoccupied (Fig. 5). The differences were not significant between trees sheltering colonies of the two Azteca species, or between trees sheltering caterpillars or that were unoccupied.


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

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

Height of Cecropia treelets.Mean height of trees (±SE) that sheltered colonies of one of the two Azteca species, Pseudocabima guianalis caterpillars, or that sheltered neither Azteca nor caterpillars during the experimental period. Statistical comparisons (normality and equal variance tests passed); ANOVA: F256 = 8.56; P<0.0001. Newman-Keuls' post-hoc test: different letters indicate significant differences at P<0.05.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0020538-g005: Height of Cecropia treelets.Mean height of trees (±SE) that sheltered colonies of one of the two Azteca species, Pseudocabima guianalis caterpillars, or that sheltered neither Azteca nor caterpillars during the experimental period. Statistical comparisons (normality and equal variance tests passed); ANOVA: F256 = 8.56; P<0.0001. Newman-Keuls' post-hoc test: different letters indicate significant differences at P<0.05.
Mentions: We did not note significant differences in the percentage of foliar surface eaten by defoliating insects between the C. obtusa sheltering an Azteca colony, caterpillars, or not occupied by either ants or caterpillars (Kruskal-Wallis test, H290 = 1.813; P>0.05). Nevertheless, caterpillar presence affected tree growth as those sheltering Azteca colonies during this experimental period were significantly taller at the end of the survey than those sheltering caterpillars or those that were unoccupied (Fig. 5). The differences were not significant between trees sheltering colonies of the two Azteca species, or between trees sheltering caterpillars or that were unoccupied.

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