Key questions: Does land-use change, e.g. the increased cultivation of energy crops, increase landscape resistance to plant gene flow (i.e. seed dispersal and
pollen dispersal) and therefore alters the functioning of mobile links for biodiversity emergence and maintenance? Can observations of contemporary gene flow be related to
population genetic patterns? Does contemporary gene flow act as an equalizing or stabilizing mechanism influencing local plant species richness? Are patterns of plant gene flow and genetic diversity correlated with variability in plant-species diversity at habitat islands such as permanent and ephemeral kettle holes within the agricultural matrix?
Background, methods and work plan: The majority of landscape genetic studies have been conducted using animal species as model systems but rarely plants. If gene flow (i.e. pollen and seed dispersal, either by wind or by mobile links) is not restricted by migration barriers, it may generally enhance genetic diversity within populations of competing plant species, but decrease genetic differentiation among populations and act as an equalizing element contributing to the maintenance of local biodiversity. The main obstacles of studying contemporary plant gene flow within an isolation-with–migration framework, i.e. analysing the influence of major landscape elements on plant gene flow, are the difficulty (i) to conduct direct observations of individual pollen and seed dispersal between populations and (ii) to infer gene flow from patterns of genetic diversity that are also influenced by other mechanisms such as genetic drift and ancestral polymorphisms. This possible mismatch between direct observations of gene flow and population genetic patterns has been identified as ‘Slatkin’s paradox’ (Slatkin 1987). Whereas species richness seems generally not be related to genetic diversity within populations, species richness and neutral genetic diversity were found to positively correlate in island situations such as forest patches
or isolated sand dunes.
The AgroScapeLab-Quillow provides an ideal landscape setting to perform a landscape resistance analysis on contemporary plant gene flow and investigate (i) whether land-use change, i.e. the increased cultivation of energy crops increases landscape resistance to plant gene flow (i.e. seed and insect mediated pollen dispersal) and therefore alters the importance of mobile links for biodiversity emergence and maintenance, (ii) whether contemporary gene flow matches with population genetic patterns and (iii) whether these patterns of genetic diversity within and among competing plant populations are correlated with patterns of plant-species diversity. These questions can be ideally addressed focusing on habitat islands, such as the kettle holes (infield ponds) found across the AgroScapeLab-Quillow. These form patches of wetland vegetation within the agricultural matrix. Two main types of kettle holes are present in this landscape: ephemeral flat infield ponds that are only present in years with sufficient precipitation and permanent steep infield ponds that differ from ephemeral ones in species richness, in a higher amount of long-lived species and a lower fraction of species with seed dormancy. In contrast to permanent infield ponds, the species richness of ephemeral ponds is positively influenced by the number of neighbouring ponds within a 500 m radius. This indicates differences in seed establishment, but also putative differences in seed dispersal and pollen flow between these two types of infield ponds.
Our workplan for a PhD consists of three steps: (i) Using a set of plant species typical for the wetland communities of infield ponds (e.g. Alisma plantago-aquatica, Bidens tripartita, Lythrum salicaria, Oenanthe aquatica) but differing in flower types, pollinator species and self-incompatibility, we will experimentally and spatially explictly assess pollenflow across different landscapes differing in land-use types surrounding the infield ponds (energy crops, grasslands, grain fields). (ii) We will genotype seedlings and putative mother plants for paternity analyses as well as use potted plants placed along a spatial gradient with increasing distances from infield ponds across the agricultural matrix. UV fluorescent dyes will be used to mark pollen grains, as well as direct pollinator observations on model plants within wetland communities and adjacent agricultural matrix to correlate the direct observational data with data on neutral genetic diversity (using single nucleotide polamorphism (SNP) loci) of the model species. (iii) Using a multi-species approach, the data will enable us to correlate patterns of within- and among-population genetic diversity with patterns of species richness to assess the importance of landscape elements on an integral part of biodiversity.
Innovation and link to overarching questions: The proposed landscape-scale approach will investigate how landscape structures influence plant gene flow and movement-mediated habitat connectivity maintaining genetic diversity and putatively population viability and species richness. To better understand possible consequences of gene flow patterns on biodiversity, we will combine bottom-up and top-down approaches in studying the influence of individual gene flow movement patterns on biodiversity and try to infer these movement mechanisms (influenced by landscape structures) from biodiversity patterns. We will link land use structure to gene flow patterns of habitat specialist’ and generalist’ plant species to identify common factors that influence biodiversity patterns. Our approach will help to identify (i) the role of gene flow as putatively equalizing or even stabilizing effect on biodiversity, (ii) key scales at which movement impacts biodiversity, and (iii) the role of specific landscape features and human impact on those for the linkage between individual movement and biodiversity.
Marco Donat (Msc 2018) - Gene flow of Typha latifolia between habitat islands in Brandenburg (northeast Germany)