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Featured researches published by Klaus Schwenk.


Acta Oecologica-international Journal of Ecology | 2002

The Monopolization Hypothesis and the dispersal-gene flow paradox in aquatic organisms

Luc De Meester; Africa Gómez; Beth Okamura; Klaus Schwenk

Many aquatic organisms rely on passive transport of resting stages for their dispersal. In this review, we provide evidence pointing to the high dispersal capacity of both animals (cladocerans, rotifers and bryozoans) and aquatic macrophytes inhabiting lentic habitats. This evidence includes direct observation of dispersal by vectors such as wind and waterfowl and the rapid colonization of new habitats. Such high dispersal capacity contrasts with the abundant evidence of pronounced genetic differentiation among neighbouring populations in many pond-dwelling organisms. We provide an overview of the potential mechanisms causing a discrepancy between high dispersal rates and reduced levels of gene flow. We argue that founder events combined with rapid local adaptation may underlie the striking patterns of genetic differentiation for neutral markers in many aquatic organisms. Rapid population growth and local adaptation upon colonization of a new habitat result in the effective monopolization of resources, yielding a strong priority effect. Once a population is locally adapted, the presence of a large resting propagule bank provides a powerful buffer against newly invading genotypes, so enhancing priority effects. Under this Monopolization Hypothesis, high genetic differentiation among nearby populations largely reflects founder events. Phylogeographic data support a scenario of low effective dispersal among populations and persistent effects of historical colonization in cyclical parthenogens. A comparison of patterns of gene flow in taxa with different life cycles suggests an important role of local adaptation in reducing gene flow among populations. We argue that patterns of regional genetic differentiation may often reflect historical colonization of new habitats rather than contemporary gene flow.


BMC Evolutionary Biology | 2007

Cryptic animal species are homogeneously distributed among taxa and biogeographical regions.

Markus Pfenninger; Klaus Schwenk

Cryptic species are two or more distinct but morphologically similar species that were classified as a single species. During the past two decades we observed an exponential growth of publications on cryptic species. Recently published reviews have demonstrated cryptic species have profound consequences on many biological disciplines. It has been proposed that their distribution is non-random across taxa and biomes. We analysed a literature database for the taxonomic and biogeographical distribution of cryptic animal species reports. Results from regression analysis indicate that cryptic species are almost evenly distributed among major metazoan taxa and biogeographical regions when corrected for species richness and study intensity. This indicates that morphological stasis represents an evolutionary constant and that cryptic metazoan diversity does predictably affect estimates of earths animal diversity. Our findings have direct theoretical and practical consequences for a number of prevailing biological questions with regard to global biodiversity estimates, conservation efforts and global taxonomic initiatives.BackgroundCryptic species are two or more distinct but morphologically similar species that were classified as a single species. During the past two decades we observed an exponential growth of publications on cryptic species. Recently published reviews have demonstrated cryptic species have profound consequences on many biological disciplines. It has been proposed that their distribution is non-random across taxa and biomes.ResultsWe analysed a literature database for the taxonomic and biogeographical distribution of cryptic animal species reports. Results from regression analysis indicate that cryptic species are almost evenly distributed among major metazoan taxa and biogeographical regions when corrected for species richness and study intensity.ConclusionThis indicates that morphological stasis represents an evolutionary constant and that cryptic metazoan diversity does predictably affect estimates of earths animal diversity. Our findings have direct theoretical and practical consequences for a number of prevailing biological questions with regard to global biodiversity estimates, conservation efforts and global taxonomic initiatives.


Proceedings of the National Academy of Sciences of the United States of America | 2007

The power of species sorting: Local factors drive bacterial community composition over a wide range of spatial scales

Katleen Van der Gucht; Karl Cottenie; Koenraad Muylaert; Nele Vloemans; Sylvie Cousin; Steven Declerck; Erik Jeppesen; Jm Conde-Porcuna; Klaus Schwenk; Gabriel Zwart; H. Degans; Wim Vyverman; Luc De Meester

There is a vivid debate on the relative importance of local and regional factors in shaping microbial communities, and on whether microbial organisms show a biogeographic signature in their distribution. Taking a metacommunity approach, spatial factors can become important either through dispersal limitation (compare large spatial scales) or mass effects (in case of strongly connected systems). We here analyze two datasets on bacterial communities [characterized by community fingerprinting through denaturing gradient gel electrophoresis (DGGE)] in meso- to eutrophic shallow lakes to investigate the importance of spatial factors at three contrasting scales. Variation partitioning on datasets of both the bacterial communities of 11 shallow lakes that are part of a strongly interconnected and densely packed pond system <1 km apart, three groups of shallow lakes ≈100 km apart, as well as these three groups of shallow lakes combined that span a large part of a North-South gradient in Europe (>2,500 km) shows a strong impact of local environmental factors on bacterial community composition, with a marginal impact of spatial distance. Our results indicate that dispersal is not strongly limiting even at large spatial scales, and that mass effects do not have a strong impact on bacterial communities even in physically connected systems. We suggest that the fast population growth rates of bacteria facilitate efficient species sorting along environmental gradients in bacterial communities over a very broad range of dispersal rates.


Ecology | 2005

MULTI-GROUP BIODIVERSITY IN SHALLOW LAKES ALONG GRADIENTS OF PHOSPHORUS AND WATER PLANT COVER

Steven Declerck; Jochen Vandekerkhove; Liselotte Sander Johansson; Koenraad Muylaert; Jm Conde-Porcuna; K Van der Gucht; Carmen Pérez-Martínez; Torben L. Lauridsen; Klaus Schwenk; Gabriel Zwart; W Rommens; J. López-Ramos; Erik Jeppesen; Wim Vyverman; Luc Brendonck; L. De Meester

This study aimed at unraveling the structure underlying the taxon-richness matrix of shallow lakes. We assessed taxon richness of a large variety of food-web com- ponents at different trophic levels (bacteria, ciliates, phytoplankton, zooplankton, fish, macro-invertebrates, and water plants) in 98 shallow lakes from three European geographic regions: Denmark (DK), Belgium/The Netherlands (BNL), and southern Spain (SP). Lakes were selected along four mutually independent gradients of total phosphorus (TP), vege- tation cover (SUBMCOV), lake area (AREA), and connectedness (CONN). Principal-com- ponents analysis (PCA) indicated that taxon diversity at the ecosystem level is a multidi- mensional phenomenon. Different PCA axes showed associations with richness in different subsets of organism groups, and differences between eigenvalues were low. Redundancy analysis showed a unique significant contribution to total richness variation of SUBMCOV in all three regions, of TP in DK and SP, and of AREA in DK and BNL. In DK, several organism groups tended to show curvilinear responses to TP, but only one was significantly hump shaped. We postulate that the unimodal richness responses to TP that are frequently reported in the literature for many organism groups may be partly mediated by the unimodal response of macrophyte vegetation to lake productivity.


Philosophical Transactions of the Royal Society B | 2008

Introduction. Extent, processes and evolutionary impact of interspecific hybridization in animals

Klaus Schwenk; Nora Brede; Bruno Streit

Since the time of Charles Darwin, studies of interspecific hybridization have been a major focus for evolutionary biologists. Although this phenomenon has often been viewed as problematic in the fields of ecology, taxonomy and systematics, it has become a primary source of data for studies on speciation and adaptation. Effects from genetic/evolutionary processes, such as recombination and natural selection, usually develop over extended periods of time; however, they are accelerated in cases of hybridization. Interspecific hybrids exhibit novel genomes that are exposed to natural selection, thus providing a key to unravel the ultimate causes of adaptation and speciation. Here we provide firstly a historic perspective of hybridization research, secondly a novel attempt to assess the extent of hybridization among animals and thirdly an overview of the reviews and case studies presented in this theme issue.


Aquatic Ecology | 1998

Genetic markers, genealogies and biogeographic patterns in the cladocera

Klaus Schwenk; Anna Sand; Maarten Boersma; Michaela Brehm; Eva Mader; Doorle Offerhaus; Piet Spaak

Cladoceran crustaceans are an important component of zooplankton in a wide range of freshwater habitats. Although the ecological characteristics of several cladoceran species have been well studied, biogeographical studies have been hampered by problematic taxonomic affiliations. However, recently developed molecular techniques, provide a powerful tool to subject aquatic taxa to comparative analyses. Here we highlight recent molecular approaches in aquatic ecology by presenting a simple method of DNA preparation and PCR amplification of the mitochondrial DNA (16S rDNA) in species from nine different families within the cladocera. On a broad taxonomic scale, sequence analysis of this mtDNA fragment has been used to produce the first molecular based phylogeny of the cladocera. This analysis clustered the cladoceran families in a fashion similar to that suggested by previous systematic classifications. In a more detailed analysis of the family Daphniidae, nuclear randomly amplified polymorphic DNA (RAPD), mitochondrial restriction fragment length polymorphism (RFLP) and morphological analyses were combined to identify species and interspecific hybrids within the Daphnia galeata species complex across 50 lakes in 13 European countries and one lake in Africa. The study revealed interspecific hybridization and backcrossing between some taxa (D. cucullata and D. galeata) to be widespread, and species and hybrids to frequently occur in sympatry. Genetic, as well as morphological information, suggests the occurrence of D. hyalina outside the Holarctic.


Cellular and Molecular Life Sciences | 1995

Evolutionary and Ecological Consequences of Interspecific Hybridization in Cladocerans

Klaus Schwenk; Piet Spaak

The evolutionary process of interspecific hybridization in cladocerans is reviewed based on ecological and population genetic data. The evolutionary consequences of hybridization, biogeographic patterns and fitness comparisons are analyzed within the conceptual framework of theories on hybridization. Among species of theD. longispina complex no interpopulational transition zones (hybrid zones) have been detected, but rather patchy distributions of hybrids and parentals have been found. Hybrids occur across broad geographic ranges and can be more abundant than parental species. Due to asexual reproduction (ameiotic parthenogenesis), hybrid breakdown can be avoided, and hybrids can even (temporarily) combine advantageous traits of both parental species. Evolutionary consequences may arise from repeated backcrossing, which in some cases results in introgression and patterns of reticulate evolution.


Molecular Ecology | 1996

RAPD identification of microsatellites in Daphnia.

Andrea Ender; Klaus Schwenk; Thomas Städler; Bruno Streit; Bernd Schierwater

Simple sequence repeats (SSRs, or microsatellites) have been constantly gaining importance as single‐locus DNA markers in population genetics and behavioural ecology. We tested a PCR‐based strategy for finding microsatellite loci in anonymous genomes, which avoids genomic library construction and screening, and the need for larger amounts of DNA. In the first step, parts of a genome are randomly amplified with arbitrary 10mer primers using RAPD fingerprinting. Labelled SSR‐oligonucleotides serve as probes to detect complementary sequences in RAPD products by means of Southern analyses. Subsequently, positive RAPD fragments of suitable size are cloned and sequenced. Using GA and GT probes, we applied this approach to waterfleas (Daphnia) and revealed 37 hybridization signals in 20 RAPD profiles. Thirteen positive RAPD fragments from three Daphnia species and two hybrid ‘species’ were cloned and sequenced. In all cases simple sequence repeats were detected. We characterized seven perfect repeat loci, which were found to be polymorphic within and between species.


Zoologica Scripta | 2008

A taxonomic reappraisal of the European Daphnia longispina complex (Crustacea, Cladocera, Anomopoda)

Adam Petrusek; Anders Hobæk; Jens Petter Nilssen; Morten Skage; Martin Černý; Nora Brede; Klaus Schwenk

The Daphnia longispina complex contains some of the most common water flea species in the northern hemisphere, and has been a model organism for many ecological and evolutionary studies. Nevertheless, the systematics and nomenclature of this group, in particular its Palaearctic members, have been in flux for the past 150 years; this hinders the correct interpretation of scientific results and promotes the erroneous use of species names. We revise the systematics of this species complex based on mitochondrial sequence variation (12S rDNA and COI) of representative populations across Europe, with a special focus on samples from type localities of the respective taxa. Combining genetic evidence and morphological assignments of analysed individuals, we propose a comprehensive revision of the European members of the D. longispina complex. We show that D. hyalina and D. rosea morphotypes have evolved several times independently, and we find no evidence to maintain these morphotypes as distinct biological species. Alpine individuals described as D. zschokkei are conspecific with the above‐mentioned lineage. We suggest that this morphologically and ecologically plastic but genetically uniform hyalina–rosea–zschokkei clade should be identified as D. longispina (O. F. Müller, 1776). The valid name of Fennoscandian individuals labelled D. longispina sensu stricto in the recent literature is D. lacustris G. O. Sars, 1862. Additionally, we discovered another divergent lineage of this group, likely an undescribed species, in southern Norway. Our results present a solution for several prevailing taxonomic problems in the genus Daphnia, and have broad implications for interpretation of biogeographical patterns, and ecological and evolutionary studies.


Proceedings of the National Academy of Sciences of the United States of America | 2009

The impact of human-made ecological changes on the genetic architecture of Daphnia species

Nora Brede; Christoph Sandrock; Dietmar Straile; Piet Spaak; Thomas Jankowski; Bruno Streit; Klaus Schwenk

The overenrichment (eutrophication) of aquatic ecosystems with nutrients leading to algal blooms and anoxic conditions has been a persistent and widespread environmental problem. Although there are many studies on the ecological impact of elevated phosphorus (P) levels (e.g., decrease in biodiversity and water quality), little is known about the evolutionary consequences for animal species. We reconstructed the genetic architecture of a Daphnia species complex in 2 European lakes using diapausing eggs that were isolated from sediment layers covering the past 100 years. Changes in total P were clearly associated with a shift in species composition and the population structure of evolutionary lineages. Although environmental conditions were largely re-established after peak eutrophication during the 1970s and 1980s, original species composition and the genetic architecture of species were not restored but evolved along new evolutionary trajectories. Our data demonstrate that anthropogenically induced temporal alterations of habitats are associated with long-lasting changes in communities and species via interspecific hybridization and introgression.

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Bruno Streit

Goethe University Frankfurt

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Adam Petrusek

Charles University in Prague

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Anne Thielsch

Goethe University Frankfurt

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Luc De Meester

Katholieke Universiteit Leuven

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Carsten Nowak

American Museum of Natural History

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Christian Vogt

Goethe University Frankfurt

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Nora Brede

Goethe University Frankfurt

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Markus Pfenninger

Goethe University Frankfurt

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Matthias Oetken

Goethe University Frankfurt

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