March 2011

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English summaries

    • pdf downloaden Genetics in nature management: an undervalued tool
    • H.P. Koelewijn & A.T. Kuiters
    • Genetic diversity is the base of our existence. Without genetic diversity a population or species cannot adapt to changing conditions. Current changes in land use, fragmentation of the landscape and increasing traffic intensity pose threats to the existence of plant and animal populations and cause a decline in genetic diversity. Researchers have therefore emphasized, amongst others, the relationships between population size and genetic diversity. Genetic diversity is used in these cases as an indicator of the state of a population. Genetic diversity can also be used as a diagnostic marker, since all individuals are unique. This uniqueness is reflected in the DNA molecules, our ultimate forensic record. In this sense genetic diversity can be used as a tool for identifying individuals and processes in small populations. In this article we explore the possibilities that genetic diversity studies offer for ecological research. By embedding genetic techniques in ecological research, a much more detailed picture of the whereabouts of a population can be obtained. This is illustrated by examples from research on Otter, Common hamster and Black grouse in The Netherlands. We also argue that a decline in genetic diversity can be used as an early warning signal: changes at the level of genetic diversity already occur before it is even visible at the population level. Finally, we indicate how genetic research can help to support the evaluation of the effectiveness of faunal corridors. All in all we think that advanced genetic techniques, including non-invasive genetic monitoring, can have a distinct added value in ecological research for nature conservation purposes.

    • pdf downloaden How fragmentation and genetic erosion undermine the adaptive potential and persistence of populations: experimental evidence
    • R. Bijlsma, J. Bakker, D. Joubert & M.E.C. van Rijswijk
    • Biodiversity is increasingly subject to human induced stresses like climate change, chemical pollution and habitat destruction. To cope with such stressful conditions organisms should be sufficiently tolerant and able to adapt to these challenges. However, due to extensive fragmentation of habitats many, often endangered, species are subjected to genetic erosion: loss of genetic variation and a decrease in fitness. This might impair their tolerance and adaptive responses considerably. Using Drosophila melanogaster as model organism we investigated the consequences of fragmentation and genetic erosion in this respect. We observed that: 1) Inbreeding does not only cause decreased fitness but inbred populations also suffer significantly more from stress than non-inbred populations. 2) Populations that have a history of fragmentation show a lower evolutionary adaptive response than non-fragmented populations. 3) As a result, genetically eroded populations have a significantly more increased extinction probability under stress than non-eroded populations. In conclusion, due to genetic erosion, fragmented populations (of endangered species) are expected to be even less able to cope with changing and deteriorating environments.

    • pdf downloaden How genetic studies of freshwater fishes can support nature conservation
    • J.A.M. Raeymaekers, K. De Gelas, A. Kobler, M.H.D. Larmuseau, G.E. Maes, J.K.J. Van Houdt, W. Van Neer & F.A.M. Volckaert
    • Freshwater environments are vulnerable ecosystems, and anthropogenic pressures often degrade their intrinsic value. Fishes are often the most visible victims of anthropogenic impacts, such as pollution, habitat degradation and  migration barriers. Nature restoration programs focus on restoring habitats and connectivity. While costs are high, restoration projects also have to be compatible with other aspects of water management, such as water treatment and flood control. A sound knowledge of the population genetics of freshwater fish represents an important basis for nature conservation and may provide guidelines for restoration and management. Here we illustrate how the understanding of the genetic structure of healthy, vulnerable, extinct, reintroduced and exotic fish populations may contribute to nature conservation. In the long run, population genetic studies should become a fixed component of an integrated management of fish populations.

    • pdf downloaden Genetic barcoding reveals multiple cryptic invasions in Water frogs
    • J. Mergeay, G. Holsbeek, F.A.M. Volckaert & L. De Meester
    • Trade in water frogs results in the importation of non-native species of unknown origin in Europe and with poor information on the risk of invasion by these species. Since many water frog species are very hard to distinguish from native species based on morphological criteria alone, we used a DNA-barcoding approach to identify water frogs (Pelophylax spp.) caught in a series of ponds and lakes in N-Belgium. We found that more than half of the water bodies contain non-native species, belonging to at least four species. In three of them we have clear evidence for a causal relationship with trade in frogs. We discuss the role of the current legislation in Europe and its member states in the fight against non-native invasive species.

    • pdf downloaden Hybridisation and gene flow in poplar: implications for the restoration of floodplain forests
    • A. Vanden Broeck & S.M.G. de Vries
    • It is recognized that introgressive hybridization and gene flow from domesticated species into their wild relatives can have a profound effect on the persistence and evolution of wild populations. Poplar is one of the most planted tree species worldwide. Hybridization and genetic swamping by planted exotic Populus taxa is supposed to threaten native resources of Populus species. We investigated the cross-compatibility relationship between exotic Populus x canadensis and its wild relative, the European black poplar (Populus nigra ), by analyzing the outcome of a series of hand-pollination cross experiments carried out in the greenhouse. The results of this study suggest that mixed pollen loads could break down the incompatibility system of P. x canadensis. In the wild, where mixed pollen loads are common, mentor effects could play a critical role in determining hybridization frequencies and may enhance the invasiveness of exotic P. x canadensis. Threat and possible consequences of gene flow from cultivated poplars are discussed in order to finally suggest conservation strategies for the restoration of floodplain forests.

    • pdf downloaden Genetic diversity and connectivity in House sparrows across an urbanization gradient
    • C. Vangestel, J. Mergeay & L. Lens
    • During the last decades House sparrows have shown steep population declines for reasons that are not yet fully understood. The difference in timing, magnitude and progress of decline and the highly sedentary nature of House sparrows have led to the general belief that urban and rural populations comprise two distinct and independent units and hence call for separate conservation strategies. Here we analyze 26 House sparrow populations with respect to neutral genetic diversity along an urban-rural gradient. Analyses revealed lower levels of genetic diversity in urban populations compared to the surrounding suburban populations. Genetic differentiation among populations was larger than among urbanization classes. This indicates that genetic drift in populations is the main source of genetic differentiation, and that migration rates are lower than expected from a bird, even at a scale of a few kilometers. There was no support, for an urban-rural dependency or other source-sink dynamics.

    • pdf downloaden Environment and Genetics, two sides of the same medal
    • P. Vergeer & N.J. Ouborg
    • The occurrence of species is determined by the interplay of environment and adaptation. A species is not passive in this process: a species can (genetically) adapt to suboptimal conditions. Despite the interacting roles of environment and genetics, management is traditionally focused on the environment and more specifically the restoration of the environment. In this manuscript we explain the role of genetics in the fitness of an individual and therewith the conservation of a species. We show by research on Succisa pratensis that environment and genetics are two sides of the same medal.