Flowers as Islands: Spatial Distribution of Nectar-Inhabiting Microfungi among Plants of Mimulus aurantiacus, a Hummingbird-Pollinated Shrub

Abstract

Microfungi inhabiting floral nectar offer unique opportunities for the study of microbial distribution and the role that dispersal limitation may play in generating distribution patterns. Flowers are well-replicated habitat islands, among which the microbes disperse via pollinators. This metapopulation system allows for investigation of microbial distribution at multiple spatial scales. We examined the distribution of the yeast, Metschnikowia reukaufii, and other fungal species found in the floral nectar of the sticky monkey flower, Mimulus aurantiacus, a hummingbird-pollinated shrub, at a California site. We found that the frequency of nectar-inhabiting microfungi on a given host plant was not significantly correlated with light availability, nectar volume or the percent cover of M. aurantiacus around the plant, but was significantly correlated with the location of the host plant and loosely correlated with the density of flowers on the plant. These results suggest that dispersal limitation caused by spatially non-random foraging by pollinators may be a primary factor driving the observed distribution pattern.

Nectar bacteria, but not yeast, weaken a plant–pollinator mutualism

“…Bombus vosnesenskii and Xylocopa micans) may also visit M. aurantiacus flowers. Flowers can persist for approximately 6 -10 days [22] and contain up to 10 ml of nectar [21], in which both yeasts [23] and bacteria frequently attain densities of 10 4 CFUs (colony forming units) per ml, similar to densities reported in other systems [24]. At JRBP, bacterial densities ranged from 0 to 10 4 CFUs per ml, with an average of 350 CFUs per ml among flowers exposed to pollinators (n ¼ 82 flowers).…”

“…At JRBP, bacterial densities ranged from 0 to 10 4 CFUs per ml, with an average of 350 CFUs per ml among flowers exposed to pollinators (n ¼ 82 flowers). Previously, we found lower microbial densities when nectar was sampled from flowers in an experimental cage that excluded large pollinators like hummingbirds (but not bees and other smaller flower visitors) compared with flowers outside the cage, indicating that the micro-organisms mainly colonize flowers via large pollinators [23].…”

Metschnikowia drakensbergensis sp. nov. and Metschnikowia caudata sp. nov., endemic yeasts associated with Protea flowers in South Africa

“…The dominant yeasts recovered in those plant species were the small-spored Metschnikowia clade species Candida rancensis, M. reukaufii and M. koreensis. These three species appear to be cosmopolitan, being commonly isolated worldwide from floral nectar in plants pollinated by a diverse array of pollinators, primarily bees, butterflies and birds (BryschHerzberg, 2004;Pozo et al, 2011;Belisle et al, 2012;de Vega & Herrera, 2012). As nectar yeasts are thought to be vectored by the main animal visitors, and the newly described species appear associated with a small set of plant species visited by beetles, our findings suggests that the novel species are highly selective in terms of host and habitat requirements.…”

“…The genus Metschnikowia (and anamorphs in the genus Candida) is one of the dominant taxa found in these substrates (Lachance et al, 2001;Lachance, 2011). For example, the cosmopolitan Metschnikowia reukaufii, M. gruessii and M. koreensis have been isolated repeatedly from a wide diversity of flowers and associated bee, butterfly and bird pollinators in both the Old World and the New World (Hong et al, 2001;Pozo et al, 2011;Belisle et al, 2012). Interestingly, flowers visited by a distinct pollinator guild, the beetles, harbour different, highly specific yeast communities that are not found in plant species pollinated by other animals (Marinoni & Lachance, 2004;Lachance et al, 2005;Guzmán et al, 2013).…”

“…However, floral nectar is not used exclusively by pollinators. Its composition makes it a favourable environment for the growth of micro-organisms, and it is exploited by floricolous yeasts that are vectored from flower to flower by floral visitors (Brysch-Herzberg, 2004;Herrera et al, 2008;Belisle et al, 2012;de Vega & Herrera, 2013).…”