Supervising team: Matthias Rillig, Jasmin Joshi, Florian Jeltsch
Workplace: FU Berlin
0. Brief expected profile of PhD student
Candidates must have a completed MSc in Ecology, Microbiology or a related field. Previous experience in microbiological lab work is desirable, as well as a solid background in community ecology, and an interest in quantitative approaches and modelling.
1. Short Abstract
This project uses nectar yeast model systems to address in a combination of modelling and lab experiments how metacommunities and local communities of nectar yeasts are maintained by movement of yeasts.
2. Background and previous work (focus on PhD cohort 1)
The nectar of flowers is a sugar-rich ephemeral habitat for microorganisms like bacteria and yeasts. Nectar microorganisms are known to affect plant-pollinator interactions. Bacteria in the nectar mainly decrease the attractiveness of flowers to pollinators while yeasts do not (Vannette, Gauthier and Fukami 2013) or even increase pollinator visitation rate (Herrera, Pozo and Medrano 2013; Schaeffer et al. 2014). Our project will focus on the movement ecology of nectar yeasts and not bacteria, because nectar yeasts depend on pollinators for dispersal (Pozo et al. 2015), are mainly restricted to the flower habitat (Lievens et al. 2015) and strengthen the plant-pollinator interaction. Nectar yeasts can also change nectar chemistry (Herrera, Garcia and Pérez 2008; Vannette, Gauthier and Fukami 2013), flower temperature (Herrera and Pozo 2010), pollen transfer rates (Schaeffer and Irwin 2014) and seed production (Herrera, Pozo and Medrano 2013).
The nectar yeast metapopulation consists of thousands of flowers representing temporal island habitats that are linked by pollinators. The pollinator is a key element in this system with a complex set of roles including dispersal agent, competitor for nectar resources and likely incidental predator (Fig.1). Nectar yeast systems can also be conceptualized as metacommunities, and this perspective will be the focus of the PhD project.
To describe community structure of flower-occupying yeast communities, we have previously isolated and identified yeasts from flowers in the AgroScapeLabs. These are now available for laboratory experiments. In a combination of modelling and empirical measurements of key processes, we could determine that for the maintenance of a local nectar yeast population, the yeasts need to both be able to grow fast and adhere to flower surfaces; one feature alone is likely not enough. Additionally, we described what species of nectar yeasts are moved by different pollinators.
The project pursues the following aims:
1) Establish a metacommunity test system in the lab using nectar yeast strains, in which transfers between local populations mimic pollinator behavior.
2) Develop a corresponding modelling framework to derive specific predictions for experimental program.
3) Test selected traits of nectar yeasts isolates for importance in attachment for floral structures, and for interaction with other yeasts (e.g. mutual invasion).
4. Outline work program
We will build on the cultured strains we now have for use in laboratory experiments, coupled with modelling, to examine the effects of equalizing factors in a metacommunity framework. Pollination events (which in this system represent mobile links as well as a massive disturbance) are represented implicitly in the lab (i.e. without insects), and only the aspect as mobile links (as done in other studies). Laboratory studies will include testing ‘increase-when-rare’ mechanisms in pairwise interactions among yeast isolates (mutual invasion criterion). In these experiments, we will add small propagule numbers into established cultures and observe the resulting behaviour. The project will also include the measurement of yeast traits favouring attachment to the flower surface, as this was shown in cohort 1 to be instrumental in maintaining populations of nectar yeasts. Such traits may be chemical in nature (e.g. production of polysaccharides or other substances), but also structural (e.g., cell formations like in Metschnikowia species), or may be related to surface charge.
5. Linkage to ‘BioMove’ hypotheses, objectives and concepts
This project relates to testing in a microbial system the role of mobile linkers (here: pollinators, which also serve as disturbance agents) as means of metacommunity maintenance. We explore tradeoffs between growth rate, attachment and competitiveness, which can represent a source of equalizing effects in nectar yeast community maintenance. Our project mainly addresses BioMove Hypothesis 1, and Question 1 and 3.