Yeasts in floral néctarcommunity ecology and interactions with insect pollinators and host plants

Abstract

While yeast presence in floral nectar has been known to science at least since the nineteenth century, it has more recently focused scientific attention from an ecological perspective. Under this new approach, nectarivorous yeasts have been related with a density-dependent degradation of nectar quality. However, quantitative information on the magnitude of occurrence of yeast contamination in floral nectar is scattered geographically and incomplete from the perspective of plant phylogenetic affiliation. Here, we document yeast frequency and abundance in nectar by examining microscopically nectar from 105 plant taxa for a single mountainous area in SE Spain. This 105 species corresponded to 25 families and 15 orders. Yeasts occurred regularly in the floral nectar of many species, as they were detected in the 37% of all nectar samples analysed microscopically. Nectar-living yeasts sometimes reached very high densities in individual nectar samples (up to 10 5 cells/mm ), although the averaged yeast abundance in nectar for the study area was 4x10 3 3 cells/mm . Almost the 40% of the species surveyed contained yeasts, and there were significant differences in the magnitude of yeast colonization among plant species. The strongest component of 3 variance in yeast abundance in nectar samples was caused by interspecific variation in the magnitude of yeast colonization, but significant patterns of variance in nectar yeast abundance also takes place at the intraspecific level. As a result, we were unable to find a clear phylogenetic signal in the described patterns of yeast incidence. We discuss the relevancy of these results in the context of evolution of the three-way interaction among Angiosperms, their pollinators and the nectarivorous yeasts.