Supervising team: Ralph Tiedemann/Florian Jeltsch, Jasmin Joshi, Matthias Rillig
Workplace: University of Potsdam
0. Brief expected profile of PhD student
We are looking for a highly motivated candidate holding a Master’s degree in ecology or a related field. The candidate should have expertise in molecular and experimental plant ecology. The project will include population genetic analyses as well as field experiments. Hence, valuable skills are knowledge in molecular genetics (preferably NGS application), experimental design and analyses, scientific writing as well as high motivation for working in a team.
1. Short Abstract
The AgroScapeLabs provide an ideal model system to perform a landscape and local habitat-resistance analysis to investigate i) how habitat filtering as well as recruit-ment and dispersal limitations shape population genetic patterns within and among populations within an agricultural landscape; ii) whether ephemeral natural habitats within an intensively used agricultural matrix represent important stepping-stone habitats maintaining metapopulations and metacommunities; iii) whereas in contrast establishment bottlenecks are predominant in permanent natural kettle-hole habitats restricting plant establishment, iv) whether patterns of genetic diversity within populations are correlated with patterns of plant-species diversity within the two types of habitat islands, and v) how mobile animal linkers such as ducks and hares influence plant-gene flow and lead to the connectedness of metacommunities.
2. Background and previous work (focus on PhD cohort 1)
If gene flow, i.e. pollen and seed dispersal (often related to mobile links) at landscape level is not restricted by migration barriers, it may act as a stabilizing element main-taining local biodiversity. Migration barriers can either be landscape elements hindering gene flow i.e. by restricting pollinator movement across landscapes or by limiting seed-dispersal distance; or they can be the result of abiotic or biotic seed-recruitment limitation. In this case, seeds might be dispersed within a potential meta-community, but germination is restricted by plant-plant competition, stressful abiotic conditions or by pathogen or herbivore attacks at local habitat patches. Hence, when comparing genetic patterns of plant metapopulations, a lack of gene flow may either reflect dispersal limitations across a landscape or be the result of habitat filtering and recruitment limitations of dispersed seeds.
In the first phase of this project, we used a system of small wetlands (kettle holes) embedded in an intensively managed, agri-cultural matrix to test how population genetic and plant-species diversities of kettle-hole communities is affected by spatial isolation favouring species with high colonisation abilities. Results of the first phase of this project revealed within the same, clonal, species either low genetic differentiation among geographically distant kettle holes, but also in some cases clear genetic differ-entiation between adjacent kettle holes. Moreover, we identified grasslands as barriers for gene flow for an insect pollinated species.
In addition, two types of plant communities were detected typical for kettle holes. Flat, ephemeral, kettle holes held a higher percentage of non-perennials, more short lived species and more species with dispersal abilities via animal vectors. In these flat kettle holes, species richness was negatively correlated with the degree of isolation, whereas no such pattern was found for the less frequently disturbed, steep, kettle holes that comprised more plant species than flat ones. Hence, the less permanent kettle holes can be regarded as meta-ecosystems that strongly depend on seed dispersal and recruitment from a seed bank, while permanent kettle holes had a more stable local plant community. To infer contemporary plant gene-flow within an isolation-with–migration framework from patterns of genetic diversity it is necessary to conduct direct observations of individual pollen and seed dispersal between populations.
We will therefore concentrate on obstacles of plant-gene flow in species relying on animal vectors (linked to projects P03 and P04). Special emphasis will also be put on establishment bottlenecks, i.e. on recruitment limitations that may lead to a mismatch between population genetic patterns and geographic proximity of plant populations within an agricultural landscape. The genetic data analysed during the first phase of the experiment point to relatively low genetic exchange between populations in the clonal species investigated in the permanent kettle holes.
During the follow-up period, we will enlarge our set of plant species by investigating plant species also occurring on ephemeral shallow kettle holes where movement (seed/ pollen flow) is more important due to higher disturbance making regeneration by seeds pivotal.
Can observations of contemporary gene flow be related to population genetic patterns?
How do habitat filtering as well as recruitment and dispersal limitations shape population genetic patterns within and among populations within a landscape?
Are patterns of genetic diversity correlated with plant-species diversity within permanent vs. ephemeral natural habitat islands within the agricultural matrix?
4. Outline work program
We will use a set of plant species typical for both types of kettle holes, but differring in the mode of seed dispersal (wind vs. zoochorus; e.g. Alisma plantago-aquatica, Bidens tripartita, Juncus buffonius are species commonly found at kettle holes that have been observed to be distributed by hare dung (by project P03)). With such model species we will experimentally and spatially explictly assess seed flow across landscapes differing in land-use types surrounding the kettle holes (energy crops, grasslands, grain fields).
Population genetic patterns within and among populations will be assessed using informative Single Nucleotide Polymorphisms (SNPs) to be established via ddRAD sequencing. In addition, we will conduct seed addition and seed bank exclusion experiments to test for putative establishment bottlenecks in the two types of habitats. Seed establishment traps placed at strategic points within our model agricultural landscape will provide information on gene flow by seed dispersal and data on pollinator community composition and diversity in our habitats collected in the first phase of this project will provide data on potential pollinator availability.
In addition, mobile animal linkers (birds, mammals) caught in projects P03, P04 and P07 as well as their faeces will be screened for seeds and pollen, both by visual inspection and genetic metabarcoding. These analyses may be extended to pollinators to assess pollen flow across the landscape.
5. Linkage to ‘BioMove’ hypotheses, objectives and concepts
We will perform a landscape and habitat resistance analysis investigating the effects of mobile links (here: genetic linkers) on biodiversity as putatively stabilizing elements for species coexistence in a meta-community context. Our approach will help to identify (i) the role of gene flow as putatively stabilizing effect on biodiversity, (ii) key scales at which movement impacts biodiversity, and (iii) the role of specific landscape features for the linkage between individual animal disperser movement and plant diversity.