Abstract
BackgroundStudies 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.ResultsIn 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.ConclusionsThere 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.Electronic supplementary materialThe online version of this article (doi:10.1186/s12898-015-0036-x) contains supplementary material, which is available to authorized users.
Highlights
Studies on the diversity of yeasts in floral nectar were first carried out in the late 19th century
Most widespread yeast taxa were Metschnikowia gruessii and Cryptococcus carnescens, each isolated from flowers of six different host plants during the two years
M. reukaufii was found in five, while Starmerella bombicola and Cryptococcus heimaeyensis were found in nectars of four host plants
Summary
Studies on the diversity of yeasts in floral nectar were first carried out in the late 19th century. Despite the importance of these nectar dwelling yeasts, knowledge of the factors that drive their diversity and species composition is scarce. Several recent studies have invoked a resurgent interest in the importance of pollination to plant reproductive success and fertility [1,2]. Research in the past years added knowledge on functionality [13], population structure [14] and epigenetic variability of Metschnikowia reukaufii [15]. Studies on flowers all over the world strengthened the impression of a narrow and highly specific nectarivorous yeast community [16,17,18], which may consist up to 85% of fast growing ascomycetous specialists [19], adapted to sugar rich, temporally and spatially fragmented nectar environments
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