The phylogenetic distribution of extrafloral nectaries in plants - PubMed (original) (raw)

The phylogenetic distribution of extrafloral nectaries in plants

Marjorie G Weber et al. Ann Bot. 2013 Jun.

Abstract

Background and aims: Understanding the evolutionary patterns of ecologically relevant traits is a central goal in plant biology. However, for most important traits, we lack the comprehensive understanding of their taxonomic distribution needed to evaluate their evolutionary mode and tempo across the tree of life. Here we evaluate the broad phylogenetic patterns of a common plant-defence trait found across vascular plants: extrafloral nectaries (EFNs), plant glands that secrete nectar and are located outside the flower. EFNs typically defend plants indirectly by attracting invertebrate predators who reduce herbivory.

Methods: Records of EFNs published over the last 135 years were compiled. After accounting for changes in taxonomy, phylogenetic comparative methods were used to evaluate patterns of EFN evolution, using a phylogeny of over 55 000 species of vascular plants. Using comparisons of parametric and non-parametric models, the true number of species with EFNs likely to exist beyond the current list was estimated.

Key results: To date, EFNs have been reported in 3941 species representing 745 genera in 108 families, about 1-2 % of vascular plant species and approx. 21 % of families. They are found in 33 of 65 angiosperm orders. Foliar nectaries are known in four of 36 fern families. Extrafloral nectaries are unknown in early angiosperms, magnoliids and gymnosperms. They occur throughout monocotyledons, yet most EFNs are found within eudicots, with the bulk of species with EFNs being rosids. Phylogenetic analyses strongly support the repeated gain and loss of EFNs across plant clades, especially in more derived dicot families, and suggest that EFNs are found in a minimum of 457 independent lineages. However, model selection methods estimate that the number of unreported cases of EFNs may be as high as the number of species already reported.

Conclusions: EFNs are widespread and evolutionarily labile traits that have repeatedly evolved a remarkable number of times in vascular plants. Our current understanding of the phylogenetic patterns of EFNs makes them powerful candidates for future work exploring the drivers of their evolutionary origins, shifts, and losses.

Keywords: Extrafloral; angiosperms; asteriids; distribution; extrafloral nectary; extranuptial; foliar; mutualism; nectary; phylogeny; rosids; taxonomy.

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Figures

Fig. 1.

Fig. 1.

EFNs are diverse within and between taxa, and are found throughout vascular plants. (A) Ants feeding on the foliar nectaries of a fern frond, Dyrnaria quercifolia. (B, C) Monocots: sepal nectaries on Dendrobium gatton (B) and an unidentified orchid (C). (D) Malvales: sepal nectaries on Hibiscus sp. (E, F) Solanales: ant feeding on the foliar/petiolar nectaries on Ipomoea carnea (E) and sepal nectaries on Ipomoea alba (F). (G–I) Dipsacales: foliar nectaries on Viburnum coriaceum (G), marginal nectaries on V. cinnamomifolium (H) and petiolar nectaries on V. opulus (I). Photographs: (A) by Eric Belita; (B) by Suzanne Koptur; (C–F) by K.H.K., (G, H) by Patrick Sweeney, copyright 2011 Peabody Museum of Natural History; (I) by Gary Fawless, Cofrin Center for Biodiversity.

Fig. 2.

Fig. 2.

The phylogenetic distribution of plant families containing species reported to have EFNs (Angiosperm Phylogeny Working Group, 2009). Branch lengths are according to fossil information from Wilkström et al. (2001). Family names are only given for those families with EFNs. Ancestral branches leading only to families containing reports of EFNs are coloured in red. Branches whose daughters include EFNs and non-EFN families are indicated in black. Blue boxes surrounding the phylogeny are shaded according to the number of species with EFNs in that family (inner ring), and the percentage of species with EFNs in that family (outer ring), with light shading representing low numbers and dark shading representing high numbers. The number of species with EFNs in a family (inner ring) range from 1069 species (Fabaceae) to 0 species. The percentage of species with EFNs (outer ring) ranges from 100 % (Cephalotaceae, Thomadersiaceae, Drosophyllaceae) to 0 %.

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