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Nectar sugars and bird visitation define a floral niche for basidiomycetous yeast on the Canary Islands.

Mittelbach M, Yurkov AM, Nocentini D, Nepi M, Weigend M, Begerow D - BMC Ecol. (2015)

Bottom Line: Our results show these basidiomycetes are significantly associated with ornithophilous flowers.There are two conclusions from this study: (i) a shift of floral visitors towards ornithophily alters the likelihood of yeast inoculation in flowers, and (ii) low concentrated hexose-dominant nectar promotes colonization of flowers by basidiomycetes.This challenges the current understanding that nectar is an ecological niche solely occupied by ascomycetous yeasts.

View Article: PubMed Central - PubMed

Affiliation: Department of Geobotany, - LS Evolution & Biodiversity of Plants, Ruhr-University Bochum, ND 1/150 / Universitaetsstr, 150, Bochum, 44780, Germany. moritz.mittelbach@rub.de.

ABSTRACT

Background: Studies on the diversity of yeasts in floral nectar were first carried out in the late 19th century. A narrow group of fermenting, osmophilous ascomycetes were regarded as exclusive specialists able to populate this unique and species poor environment. More recently, it became apparent that microorganisms might play an important role in the process of plant pollination. Despite the importance of these nectar dwelling yeasts, knowledge of the factors that drive their diversity and species composition is scarce.

Results: In this study, we linked the frequencies of yeast species in floral nectars from various host plants on the Canary Islands to nectar traits and flower visitors. We estimated the structuring impact of pollination syndromes (nectar volume, sugar concentration and sugar composition) on yeast diversity.The observed total yeast diversity was consistent with former studies, however, the present survey yielded additional basidiomycetous yeasts in unexpectedly high numbers. Our results show these basidiomycetes are significantly associated with ornithophilous flowers. Specialized ascomycetes inhabit sucrose-dominant nectars, but are surprisingly rare in nectar dominated by monosaccharides.

Conclusions: There are two conclusions from this study: (i) a shift of floral visitors towards ornithophily alters the likelihood of yeast inoculation in flowers, and (ii) low concentrated hexose-dominant nectar promotes colonization of flowers by basidiomycetes. In the studied floral system, basidiomycete yeasts are acknowledged as regular members of nectar. This challenges the current understanding that nectar is an ecological niche solely occupied by ascomycetous yeasts.

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Partitioning tree of yeast diversity. Recursive binary partitioning tree calculated for yeast diversity predicted by nectar traits (volume + sugar concentration + nectar type), pollinator compositions (visitation frequencies of each functional group), and year. Stopping criteria were set to α = 0.01 and minimum sizes of terminal nodes restricted to 30 L. Nodes are numbered and respective critical splitting variable values are provided on the lines. Bar-plots show weights of species in the respective node assemblages. Light bars illustrate basidiomycetes and dark bars ascomycetes. Number of isolates (n), Functional dispersion (FDis), Shannon index (H), and mean pairwise distances compared to patterns expected under the selected  model (Zphy) are provided for each species assemblage. Asteriks refer to significanes (* p < 0.05, *** p < 0.001) as calculated to the  model with default iterations and randomizations.
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Fig4: Partitioning tree of yeast diversity. Recursive binary partitioning tree calculated for yeast diversity predicted by nectar traits (volume + sugar concentration + nectar type), pollinator compositions (visitation frequencies of each functional group), and year. Stopping criteria were set to α = 0.01 and minimum sizes of terminal nodes restricted to 30 L. Nodes are numbered and respective critical splitting variable values are provided on the lines. Bar-plots show weights of species in the respective node assemblages. Light bars illustrate basidiomycetes and dark bars ascomycetes. Number of isolates (n), Functional dispersion (FDis), Shannon index (H), and mean pairwise distances compared to patterns expected under the selected model (Zphy) are provided for each species assemblage. Asteriks refer to significanes (* p < 0.05, *** p < 0.001) as calculated to the model with default iterations and randomizations.

Mentions: In addition to the nectar sugar concentration, frequencies of visitors to flowers (birds, bees, bumblebees) influence yeast diversity (Figure 4). Although specialized nectar dwelling members of the Metschnikowiaceae lineage are ubiquitous, they form a phylogenetically clustered node assemblage in flowers with high sugar concentrations and are responsible for a reduced functional yeast diversity (FDis) in this substrate. The occurrence of these yeasts varied substantially between sampling years, with most pronounced fluctuation being observed for M. reukaufii. Nonetheless, this species was isolated from a total of 27 samples of host plants, which were not part of the analysis in 2012.Figure 4


Nectar sugars and bird visitation define a floral niche for basidiomycetous yeast on the Canary Islands.

Mittelbach M, Yurkov AM, Nocentini D, Nepi M, Weigend M, Begerow D - BMC Ecol. (2015)

Partitioning tree of yeast diversity. Recursive binary partitioning tree calculated for yeast diversity predicted by nectar traits (volume + sugar concentration + nectar type), pollinator compositions (visitation frequencies of each functional group), and year. Stopping criteria were set to α = 0.01 and minimum sizes of terminal nodes restricted to 30 L. Nodes are numbered and respective critical splitting variable values are provided on the lines. Bar-plots show weights of species in the respective node assemblages. Light bars illustrate basidiomycetes and dark bars ascomycetes. Number of isolates (n), Functional dispersion (FDis), Shannon index (H), and mean pairwise distances compared to patterns expected under the selected  model (Zphy) are provided for each species assemblage. Asteriks refer to significanes (* p < 0.05, *** p < 0.001) as calculated to the  model with default iterations and randomizations.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4318194&req=5

Fig4: Partitioning tree of yeast diversity. Recursive binary partitioning tree calculated for yeast diversity predicted by nectar traits (volume + sugar concentration + nectar type), pollinator compositions (visitation frequencies of each functional group), and year. Stopping criteria were set to α = 0.01 and minimum sizes of terminal nodes restricted to 30 L. Nodes are numbered and respective critical splitting variable values are provided on the lines. Bar-plots show weights of species in the respective node assemblages. Light bars illustrate basidiomycetes and dark bars ascomycetes. Number of isolates (n), Functional dispersion (FDis), Shannon index (H), and mean pairwise distances compared to patterns expected under the selected model (Zphy) are provided for each species assemblage. Asteriks refer to significanes (* p < 0.05, *** p < 0.001) as calculated to the model with default iterations and randomizations.
Mentions: In addition to the nectar sugar concentration, frequencies of visitors to flowers (birds, bees, bumblebees) influence yeast diversity (Figure 4). Although specialized nectar dwelling members of the Metschnikowiaceae lineage are ubiquitous, they form a phylogenetically clustered node assemblage in flowers with high sugar concentrations and are responsible for a reduced functional yeast diversity (FDis) in this substrate. The occurrence of these yeasts varied substantially between sampling years, with most pronounced fluctuation being observed for M. reukaufii. Nonetheless, this species was isolated from a total of 27 samples of host plants, which were not part of the analysis in 2012.Figure 4

Bottom Line: Our results show these basidiomycetes are significantly associated with ornithophilous flowers.There are two conclusions from this study: (i) a shift of floral visitors towards ornithophily alters the likelihood of yeast inoculation in flowers, and (ii) low concentrated hexose-dominant nectar promotes colonization of flowers by basidiomycetes.This challenges the current understanding that nectar is an ecological niche solely occupied by ascomycetous yeasts.

View Article: PubMed Central - PubMed

Affiliation: Department of Geobotany, - LS Evolution & Biodiversity of Plants, Ruhr-University Bochum, ND 1/150 / Universitaetsstr, 150, Bochum, 44780, Germany. moritz.mittelbach@rub.de.

ABSTRACT

Background: Studies on the diversity of yeasts in floral nectar were first carried out in the late 19th century. A narrow group of fermenting, osmophilous ascomycetes were regarded as exclusive specialists able to populate this unique and species poor environment. More recently, it became apparent that microorganisms might play an important role in the process of plant pollination. Despite the importance of these nectar dwelling yeasts, knowledge of the factors that drive their diversity and species composition is scarce.

Results: In this study, we linked the frequencies of yeast species in floral nectars from various host plants on the Canary Islands to nectar traits and flower visitors. We estimated the structuring impact of pollination syndromes (nectar volume, sugar concentration and sugar composition) on yeast diversity.The observed total yeast diversity was consistent with former studies, however, the present survey yielded additional basidiomycetous yeasts in unexpectedly high numbers. Our results show these basidiomycetes are significantly associated with ornithophilous flowers. Specialized ascomycetes inhabit sucrose-dominant nectars, but are surprisingly rare in nectar dominated by monosaccharides.

Conclusions: There are two conclusions from this study: (i) a shift of floral visitors towards ornithophily alters the likelihood of yeast inoculation in flowers, and (ii) low concentrated hexose-dominant nectar promotes colonization of flowers by basidiomycetes. In the studied floral system, basidiomycete yeasts are acknowledged as regular members of nectar. This challenges the current understanding that nectar is an ecological niche solely occupied by ascomycetous yeasts.

Show MeSH