Landscape genetics of insect-pollinated forest herbs in changing agricultural landscapes

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Most of the biodiversity in agricultural landscapes can be found in small fragments of semi-natural habitats. However, many species are not adapted to live in small habitat islands. For instance, typical deciduous forest herbs evolved during times when the landscape was more or less continuously forested. Long-term survival in habitat fragments requires habitat specialists to exchange regularly individuals or diaspores among local populations, as common in meta-populations. Whether at all and under which circumstances forest herbs form a metapopulation is unclear. Since gene flow among plant populations occurs via seed and pollen dispersal rather than active plant movement, the answer to these questions will depend on how the associated seed and pollen dispersal vectors are influenced by the landscape structure.In this project, we will combine population genetic and landscape ecological approaches to study the regional population genetic structure of forest herbs and their associated pollinators in the context of agricultural landscapes. We have three main objectives: (1) We will elucidate the role of the herb's mating strategy in shaping the regional population genetic structure (selfing vs. outcrossing; short vs. long forage distance of the associated pollinator species). (2) We will determine the effects of the landscape matrix on the regional population genetic structure. In particular, we are interested in the role of some crop species that are expected to influence seed dispersal by mammals (maize) or pollen transfer by insects (oilseed rape) and in linear landscape elements that may act as corridor (e.g., hedgerows) or barrier (e.g., roads). (3) We will detect legacies of the past in present-day plant population genetic structures. Here, we expect the current population genetic structure to reflect the landscape structure of some decades ago better than the current landscape structure.Our research will focus on three forest herb species, which will be surveyed in seven different agricultural landscapes spread across northwestern Europe. In addition, we will study the population genetic structure of two associated pollinator species, a bumblebee and a hoverfly species, in three of the landscapes. Genetic analyses will comprise amongst others the genotyping of plant and pollinator individuals based on microsatellite markers, paternity analysis to quantify the contemporary pollen-mediated gene flow, sibship reconstruction to assign bumblebee workers to colonies and the estimation of the historical gene flow rates based on coalescent theory. Landscape ecological approaches will include the mapping of the current and historical landscape composition and configuration, the calculation of landscape metrics in circular zones and landscape strips around and between the plant populations, respectively, the quantification of land-use changes since 1950, and the modelling of population genetic measures as a function of landscape(-change) metrics.