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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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Related in: MedlinePlus

Phylogenetic trees of isolated strains. Maximum-likelihood trees of LSU (D1/D2 domains) sequences of isolated strains and their closest NCBI-BLAST hits of (A) ascomycetes and (B) basidiomycetes. Shaded areas illustrate species delimitation used in the study, when more than one strain identified. The numbers given on branches are frequencies (>70%) with which a given branch appeared in 1000 bootstrap replications. The scale indicates the number of expected substitutions accumulated per site.
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Fig6: Phylogenetic trees of isolated strains. Maximum-likelihood trees of LSU (D1/D2 domains) sequences of isolated strains and their closest NCBI-BLAST hits of (A) ascomycetes and (B) basidiomycetes. Shaded areas illustrate species delimitation used in the study, when more than one strain identified. The numbers given on branches are frequencies (>70%) with which a given branch appeared in 1000 bootstrap replications. The scale indicates the number of expected substitutions accumulated per site.

Mentions: Several studies acknowledge only ascomycetes from the order Metschnikowiaceae and phylogenetically related species of the genus Candida as specialized nectar-dwelling yeasts [24,25,28]. The high number of isolates per species in this group underlines the expected specialization (Figure 6). The repeated isolation of a broader diversity of yeast and yeast-like species from flowers contrasts this view and suggests that additional groups of organisms might have exploited the vast number of different floral microhabitats evolved within the multitude of pollination syndromes in Angiosperms [22,58]. This hypothesis is supported by the high frequencies and within-flower abundances of ‘allochthonous’ species in this study (Additional file 1). Total cell densities of almost all isolated yeast species, measured as CFUs per flower show a considerable inter- and intraspecific variability, as has also been reported from other plants [18,58,59]. Interestingly, high yeast colony numbers were not restricted to fermenting ascomycetes in our study, but were also common for several basidiomycetous species in ornithophilous flowers (Additional file 1).Figure 6


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)

Phylogenetic trees of isolated strains. Maximum-likelihood trees of LSU (D1/D2 domains) sequences of isolated strains and their closest NCBI-BLAST hits of (A) ascomycetes and (B) basidiomycetes. Shaded areas illustrate species delimitation used in the study, when more than one strain identified. The numbers given on branches are frequencies (>70%) with which a given branch appeared in 1000 bootstrap replications. The scale indicates the number of expected substitutions accumulated per site.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Fig6: Phylogenetic trees of isolated strains. Maximum-likelihood trees of LSU (D1/D2 domains) sequences of isolated strains and their closest NCBI-BLAST hits of (A) ascomycetes and (B) basidiomycetes. Shaded areas illustrate species delimitation used in the study, when more than one strain identified. The numbers given on branches are frequencies (>70%) with which a given branch appeared in 1000 bootstrap replications. The scale indicates the number of expected substitutions accumulated per site.
Mentions: Several studies acknowledge only ascomycetes from the order Metschnikowiaceae and phylogenetically related species of the genus Candida as specialized nectar-dwelling yeasts [24,25,28]. The high number of isolates per species in this group underlines the expected specialization (Figure 6). The repeated isolation of a broader diversity of yeast and yeast-like species from flowers contrasts this view and suggests that additional groups of organisms might have exploited the vast number of different floral microhabitats evolved within the multitude of pollination syndromes in Angiosperms [22,58]. This hypothesis is supported by the high frequencies and within-flower abundances of ‘allochthonous’ species in this study (Additional file 1). Total cell densities of almost all isolated yeast species, measured as CFUs per flower show a considerable inter- and intraspecific variability, as has also been reported from other plants [18,58,59]. Interestingly, high yeast colony numbers were not restricted to fermenting ascomycetes in our study, but were also common for several basidiomycetous species in ornithophilous flowers (Additional file 1).Figure 6

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
Related in: MedlinePlus