Journal Article

The cost of myrmecophytism: insights from allometry of stem secondary growth

Rumsaïs Blatrix, Delphine Renard, Champlain Djieto-Lordon and Doyle McKey

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 110, issue 5, pages 943-951
Published in print October 2012 | ISSN: 0305-7364
Published online August 2012 | e-ISSN: 1095-8290 | DOI: http://dx.doi.org/10.1093/aob/mcs164
The cost of myrmecophytism: insights from allometry of stem secondary growth

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  • Ecology and Conservation
  • Evolutionary Biology
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Background and Aims

Plant defence traits against herbivores incur production costs that are usually difficult to measure. However, estimating these costs is a prerequisite for characterizing the plant defence strategy as a whole. Myrmecophytes are plants that provide symbiotic ants with specialized nesting cavities, called domatia, in exchange for protection against herbivores. In the particular case of stem domatia, production of extra wood seems to be the only associated cost, making this indirect defence trait a particularly suitable model for estimating the cost of defence.

Methods

Measurements were made of growth pattern and cumulative production cost of domatia over secondary growth in the myrmecophyte Leonardoxa africana subsp. africana, whose internodes display both a solid basal segment and a hollow distal part (the domatium), thus allowing paired comparison of investment in wood.

Key Results

Previous studies showed that ‘overconstruction’ of the hollow part of internodes during primary growth is needed for mechanical support. In this study, it is shown that the relationship between the woody cross-sectional area of the solid and hollow parts of internodes is negatively allometric at the beginning of secondary growth and nearly isometric later on. Thus, in hollow stems, the first phase of slow secondary growth compensates for the ‘overconstruction’ of the ring of wood during primary growth. Moreover, the cumulative production cost of a domatium (estimated as the additional volume of wood required for a hollow stem compared with a solid one) is very high at the beginning of secondary growth and then quickly tends to zero.

Conclusions

Making domatia incurs high costs early in ontogeny, costs that are then amortized later in development of stems and of individual plants. Characterizing ontogenetic variation of the net cost of this peculiar defence mechanism will help us build more accurate theoretical models of resource allocation in myrmecophytes.

Keywords: Ontogenetic trade-off; resource allocation; plant defence; symbiosis; mutualism; ant-plant; Leonardoxa africana; caulinary domatia; allometry

Journal Article.  7098 words.  Illustrated.

Subjects: Ecology and Conservation ; Evolutionary Biology ; Plant Sciences and Forestry

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