AOBPreview originally published online on February 10, 2009
Annals of Botany 2009 103(9):1415-1423; doi:10.1093/aob/mcp026
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This article appears in the following Annals of Botany issue: Special Issue: Plant-Pollinator Interactions [View the issue table of contents]
Yeasts in floral nectar: a quantitative survey
1 Estación Biológica de Doñana, Consejo Superior de Investigaciones Científicas (CSIC), Avenida Américo Vespuccio, E-41092 Sevilla, Spain
2 Centro de Investigación Científica de Yucatán (CICY), A.C. Calle 43 No. 130 Chuburná de Hidalgo, 97200 Mérida, Yucatán, México
* For correspondence. E-mail herrera{at}cica.es
Received: 22 September 2008 Returned for revision: 20 November 2008 Accepted: 5 January 2009 Published electronically: 10 February 2009
Background and Aims: One peculiarity of floral nectar that remains relatively unexplored from an ecological perspective is its role as a natural habitat for micro-organisms. This study assesses the frequency of occurrence and abundance of yeast cells in floral nectar of insect-pollinated plants from three contrasting plant communities on two continents. Possible correlations between interspecific differences in yeast incidence and pollinator composition are also explored.
Methods: The study was conducted at three widely separated areas, two in the Iberian Peninsula (Spain) and one in the Yucatán Peninsula (Mexico). Floral nectar samples from 130 species (37–63 species per region) in 44 families were examined microscopically for the presence of yeast cells. For one of the Spanish sites, the relationship across species between incidence of yeasts in nectar and the proportion of flowers visited by each of five major pollinator categories was also investigated.
Key Results: Yeasts occurred regularly in the floral nectar of many species, where they sometimes reached extraordinary densities (up to 4 x 105 cells mm–3). Depending on the region, between 32 and 44 % of all nectar samples contained yeasts. Yeast cell densities in the order of 104 cells mm–3 were commonplace, and densities >105 cells mm–3 were not rare. About one-fifth of species at each site had mean yeast cell densities >104 cells mm–3. Across species, yeast frequency and abundance were directly correlated with the proportion of floral visits by bumble-bees, and inversely with the proportion of visits by solitary bees.
Conclusions: Incorporating nectar yeasts into the scenario of plant–pollinator interactions opens up a number of intriguing avenues for research. In addition, with yeasts being as ubiquitous and abundant in floral nectars as revealed by this study, and given their astounding metabolic versatility, studies focusing on nectar chemical features should carefully control for the presence of yeasts in nectar samples.
Key words: Bumble-bees, floral nectar, microbial communities, pollination, yeasts
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