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Exposure to pesticides may cause adaptation not only in agricultural pests and pathogens, but also in non-target organisms. Previous studies mainly searched for adaptations in non-target organisms in pesticide-polluted sites. However, organisms may propagate heritable pesticide effects, such as increased tolerance, to non-exposed populations through gene flow. We examined the pesticide tolerance—as one of the pre-assumptions of local adaptation—of the freshwater crustacean Gammarus spp. (at genus level reflecting the gammarid community). The pesticide tolerance was quantified in acute toxicity tests using the insecticide imidacloprid. Gammarids were sampled at pesticide-polluted agricultural sites (termed agriculture), least impacted upstream sites (termed refuge) and transitional sites (termed edge) in six small streams of south-west Germany. Furthermore, we examined the population genetic structure of Gammarus fossarum and the energy reserves (here lipid content) of G. fossarum as well as of Gammarus spp. at the three site types (i.e. agriculture, edge and refuge). We found significantly lower imidacloprid tolerance of Gammarus spp. from agricultural sites compared to edge and refuge sites, potentially due to higher environmental stress at agricultural sites, as indicated by a slightly lower lipid content per mg gammarid tissue. We found no differences in pesticide tolerance between edge and refuge populations, indicating no propagation of pesticide effects to edges. The genetic structure among G. fossarum populations showed significant differentiation between streams, but not within a stream across the site types. We suggest that high gene flow within each stream hindered population differentiation and resulted in similar (pre)adaptations to local stress levels between site types, although they exhibited different pesticide pollution. Further studies on target genes (e.g., conferring pesticide tolerance), population structure and fitness of different phenotypes i

Niche and neutral processes drive community assembly and metacommunity dynamics, but their relative importance might vary with the spatial scale. The contribution of niche processes is generally expected to increase with increasing spatial extent at a higher rate than that of neutral processes. However, the extent to what community composition is limited by dispersal (usually considered a neutral process) over increasing spatial scales might depend on the dispersal capacity of composing species. To investigate the mechanisms underlying the distribution and diversity of species known to have great powers of dispersal (hundreds of kilometres), we analysed the relative importance of niche processes and dispersal limitation in determining beta-diversity patterns of aquatic plants and cladocerans over regional (up to 300 km) and continental (up to 3300 km) scales. Both taxonomic groups were surveyed in five different European regions and presented extremely high levels of beta-diversity, both within and among regions. High beta-diversity was primarily explained by species replacement (turnover) rather than differences in species richness (i.e. nestedness). Abiotic and biotic variables were the main drivers of community composition. Within some regions, small-scale connectivity and the spatial configuration of sampled communities explained a significant, though smaller, fraction of compositional variation, particularly for aquatic plants. At continental scale (among regions), a significant fraction of compositional variation was explained by a combination of spatial effects (exclusive contribution of regions) and regionally-structured environmental variables. Our results suggest that, although dispersal limitation might affect species composition in some regions, aquatic plant and cladoceran communities are not generally limited by dispersal at the regional scale (up to 300 km). Species sorting mediated by environmental variation might explain the high species turnover of

Niche and neutral processes drive community assembly and metacommunity dynamics, but their relative importance might vary with the spatial scale. The contribution of niche processes is generally expected to increase with increasing spatial extent at a higher rate than that of neutral processes. However, the extent to what community composition is limited by dispersal (usually considered a neutral process) over increasing spatial scales might depend on the dispersal capacity of composing species. To investigate the mechanisms underlying the distribution and diversity of species known to have great powers of dispersal (hundreds of kilometres), we analysed the relative importance of niche processes and dispersal limitation in determining beta-diversity patterns of aquatic plants and cladocerans over regional (up to 300 km) and continental (up to 3300 km) scales. Both taxonomic groups were surveyed in five different European regions and presented extremely high levels of beta-diversity, both within and among regions. High beta-diversity was primarily explained by species replacement (turnover) rather than differences in species richness (i.e. nestedness). Abiotic and biotic variables were the main drivers of community composition. Within some regions, small-scale connectivity and the spatial configuration of sampled communities explained a significant, though smaller, fraction of compositional variation, particularly for aquatic plants. At continental scale (among regions), a significant fraction of compositional variation was explained by a combination of spatial effects (exclusive contribution of regions) and regionally-structured environmental variables. Our results suggest that, although dispersal limitation might affect species composition in some regions, aquatic plant and cladoceran communities are not generally limited by dispersal at the regional scale (up to 300 km). Species sorting mediated by environmental variation might explain the high species turnover of

Niche and neutral processes drive community assembly and metacommunity dynamics, but their relative importance might vary with the spatial scale. The contribution of niche processes is generally expected to increase with increasing spatial extent at a higher rate than that of neutral processes. However, the extent to what community composition is limited by dispersal (usually considered a neutral process) over increasing spatial scales might depend on the dispersal capacity of composing species. To investigate the mechanisms underlying the distribution and diversity of species known to have great powers of dispersal (hundreds of kilometres), we analysed the relative importance of niche processes and dispersal limitation in determining beta-diversity patterns of aquatic plants and cladocerans over regional (up to 300 km) and continental (up to 3300 km) scales. Both taxonomic groups were surveyed in five different European regions and presented extremely high levels of beta-diversity, both within and among regions. High beta-diversity was primarily explained by species replacement (turnover) rather than differences in species richness (i.e. nestedness). Abiotic and biotic variables were the main drivers of community composition. Within some regions, small-scale connectivity and the spatial configuration of sampled communities explained a significant, though smaller, fraction of compositional variation, particularly for aquatic plants. At continental scale (among regions), a significant fraction of compositional variation was explained by a combination of spatial effects (exclusive contribution of regions) and regionally-structured environmental variables. Our results suggest that, although dispersal limitation might affect species composition in some regions, aquatic plant and cladoceran communities are not generally limited by dispersal at the regional scale (up to 300 km). Species sorting mediated by environmental variation might explain the high species turnover of

1. The relative role of environmental and regional processes in determining patterns of biodiversity may vary across spatial scales. In inland aquatic communities, macrophytes and zooplankton have the potential to disperse over large spatial scales (hundreds of kilometres), but the role of environmental and regional processes in determining species richness (SR) at different spatial scales is poorly understood. 2. To assess the relative importance of environmental and regional processes acting on both regional (within-region) and continental (among-region) scales, we surveyed 139 waterbodies in five geographic regions (Spain, Italy, the Netherlands, Scotland and Norway) and in each region measured environmental variables, descriptors of connectivity and SR of two aquatic taxa, namely aquatic plants and cladocerans. 3. Analyses using boosted regression trees and generalised linear models, integrated with multiple imputation of missing data, indicated that both environmental and regional processes were related to local SR. 4. Total phosphorus was the main environmental correlate of SR, showing a unimodal relationship with both taxonomic groups. Conductivity and lake depth were also related to cladoceran SR, and Secchi depth was related to aquatic plant richness. 5. The SR of aquatic plants and cladocerans were significantly correlated, but this relationship was mainly indirect (i.e. determined by the effect of common environmental variables). 6. The limited role of connectivity and space (lack of spatial autocorrelation in model residuals) relative to environment suggests that dispersal limitation is not as important as the environment in explaining richness patterns for both groups within regions. However, region identity strongly influenced SR, which suggests an important effect of biogeographic factors (e.g. the level of endemicity; the number of unique species in each region) and/or dispersal limitation at the continental scale. 7. We conclude that environmental f

The relative role of environmental and regional processes in determining patterns of biodiversity may vary across spatial scales. In inland aquatic communities, macrophytes and zooplankton have the potential to disperse over large spatial scales (hundreds of kilometres), but the role of environmental and regional processes in determining species richness (SR) at different spatial scales is poorly understood. To assess the relative importance of environmental and regional processes acting on both regional (within-region) and continental (among-region) scales, we surveyed 139 waterbodies in five geographic regions (Spain, Italy, the Netherlands, Scotland and Norway) and in each region measured environmental variables, descriptors of connectivity and SR of two aquatic taxa, namely aquatic plants and cladocerans. Analyses using boosted regression trees and generalised linear models, integrated with multiple imputation of missing data, indicated that both environmental and regional processes were related to local SR. Total phosphorus was the main environmental correlate of SR, showing a unimodal relationship with both taxonomic groups. Conductivity and lake depth were also related to cladoceran SR, and Secchi depth was related to aquatic plant richness. The SR of aquatic plants and cladocerans were significantly correlated, but this relationship was mainly indirect (i.e. determined by the effect of common environmental variables). The limited role of connectivity and space (lack of spatial autocorrelation in model residuals) relative to environment suggests that dispersal limitation is not as important as the environment in explaining richness patterns for both groups within regions. However, region identity strongly influenced SR, which suggests an important effect of biogeographic factors (e.g. the level of endemicity; the number of unique species in each region) and/or dispersal limitation at the continental scale. We conclude that environmental factors and biogeograp

The relative role of environmental and regional processes in determining patterns of biodiversity may vary across spatial scales. In inland aquatic communities, macrophytes and zooplankton have the potential to disperse over large spatial scales (hundreds of kilometres), but the role of environmental and regional processes in determining species richness (SR) at different spatial scales is poorly understood. To assess the relative importance of environmental and regional processes acting on both regional (within-region) and continental (among-region) scales, we surveyed 139 waterbodies in five geographic regions (Spain, Italy, the Netherlands, Scotland and Norway) and in each region measured environmental variables, descriptors of connectivity and SR of two aquatic taxa, namely aquatic plants and cladocerans. Analyses using boosted regression trees and generalised linear models, integrated with multiple imputation of missing data, indicated that both environmental and regional processes were related to local SR. Total phosphorus was the main environmental correlate of SR, showing a unimodal relationship with both taxonomic groups. Conductivity and lake depth were also related to cladoceran SR, and Secchi depth was related to aquatic plant richness. The SR of aquatic plants and cladocerans were significantly correlated, but this relationship was mainly indirect (i.e. determined by the effect of common environmental variables). The limited role of connectivity and space (lack of spatial autocorrelation in model residuals) relative to environment suggests that dispersal limitation is not as important as the environment in explaining richness patterns for both groups within regions. However, region identity strongly influenced SR, which suggests an important effect of biogeographic factors (e.g. the level of endemicity; the number of unique species in each region) and/or dispersal limitation at the continental scale. We conclude that environmental factors and biogeograp

1. The relative role of environmental and regional processes in determining patterns of biodiversity may vary across spatial scales. In inland aquatic communities, macrophytes and zooplankton have the potential to disperse over large spatial scales (hundreds of kilometres), but the role of environmental and regional processes in determining species richness (SR) at different spatial scales is poorly understood. 2. To assess the relative importance of environmental and regional processes acting on both regional (within-region) and continental (among-region) scales, we surveyed 139 waterbodies in five geographic regions (Spain, Italy, the Netherlands, Scotland and Norway) and in each region measured environmental variables, descriptors of connectivity and SR of two aquatic taxa, namely aquatic plants and cladocerans. 3. Analyses using boosted regression trees and generalised linear models, integrated with multiple imputation of missing data, indicated that both environmental and regional processes were related to local SR. 4. Total phosphorus was the main environmental correlate of SR, showing a unimodal relationship with both taxonomic groups. Conductivity and lake depth were also related to cladoceran SR, and Secchi depth was related to aquatic plant richness. 5. The SR of aquatic plants and cladocerans were significantly correlated, but this relationship was mainly indirect (i.e. determined by the effect of common environmental variables). 6. The limited role of connectivity and space (lack of spatial autocorrelation in model residuals) relative to environment suggests that dispersal limitation is not as important as the environment in explaining richness patterns for both groups within regions. However, region identity strongly influenced SR, which suggests an important effect of biogeographic factors (e.g. the level of endemicity; the number of unique species in each region) and/or dispersal limitation at the continental scale. 7. We conclude that environmental f

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 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., 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 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.

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 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., 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 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.

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 components 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), vegetation cover (SUBMCOV), lake area (AREA), and connectedness (CONN). Principal-components analysis (PCA) indicated that taxon diversity at the ecosystem level is a multidimensional 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. [KEYWORDS: biodiversity ; conservation management for species richness ; phosphorus ; productivity ; richness ; richness–productivity relationships ; shallow lake ; shallow-lake species richness structure ; water plants], 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 components 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), vegetation cover (SUBMCOV), lake area (AREA), and connectedness (CONN). Principal-components analysis (PCA) indicated that taxon diversity at the ecosystem level is a multidimensional 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. [KEYWORDS: biodiversity ; conservation management for species richness ; phosphorus ; productivity ; richness ; richness–productivity relationships ; shallow lake ; shallow-lake species richness structure ; water plants]

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 components 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), vegetation cover (SUBMCOV), lake area (AREA), and connectedness (CONN). Principal-components analysis (PCA) indicated that taxon diversity at the ecosystem level is a multidimensional 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. [KEYWORDS: biodiversity ; conservation management for species richness ; phosphorus ; productivity ; richness ; richness–productivity relationships ; shallow lake ; shallow-lake species richness structure ; water plants], 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 components 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), vegetation cover (SUBMCOV), lake area (AREA), and connectedness (CONN). Principal-components analysis (PCA) indicated that taxon diversity at the ecosystem level is a multidimensional 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. [KEYWORDS: biodiversity ; conservation management for species richness ; phosphorus ; productivity ; richness ; richness–productivity relationships ; shallow lake ; shallow-lake species richness structure ; water plants]

Species of the genus Daphnia, in particular the subgenus Hyalodaphnia, represent a taxonomically problematic group due to their phenotypic plasticity, local races and the formation of interspecific hybrids and backcrosses. In this study, we present a genetic approach utilising nuclear DNA to unequivocally identify species and interspecific hybrids. Several nuclear loci (ITS1-ITS2, CA14 and GA13) were amplified by PCR and products were subjected to diagnostic restriction enzymes (restriction fragment length polymorphism; RFLP). The application of this approach to several populations across Europe revealed that the markers are highly consistent and reproducible. In addition, we illustrate with a number of examples how this approach contributed to unravel previously unrecognised taxa, increased the sensitivity of biodiversity studies or contributed to the analysis of resting egg banks. Advantages and disadvantages of this approach compared to existing techniques are discussed and several empirical studies and their results are summarised. [KEYWORDS: Daphnia ; RFLP ; interspecific hybrids], Species of the genus Daphnia, in particular the subgenus Hyalodaphnia, represent a taxonomically problematic group due to their phenotypic plasticity, local races and the formation of interspecific hybrids and backcrosses. In this study, we present a genetic approach utilising nuclear DNA to unequivocally identify species and interspecific hybrids. Several nuclear loci (ITS1-ITS2, CA14 and GA13) were amplified by PCR and products were subjected to diagnostic restriction enzymes (restriction fragment length polymorphism; RFLP). The application of this approach to several populations across Europe revealed that the markers are highly consistent and reproducible. In addition, we illustrate with a number of examples how this approach contributed to unravel previously unrecognised taxa, increased the sensitivity of biodiversity studies or contributed to the analysis of resting egg banks. Advantages and disadvantages of this approach compared to existing techniques are discussed and several empirical studies and their results are summarised. [KEYWORDS: Daphnia ; RFLP ; interspecific hybrids]

Species of the genus Daphnia, in particular the subgenus Hyalodaphnia, represent a taxonomically problematic group due to their phenotypic plasticity, local races and the formation of interspecific hybrids and backcrosses. In this study, we present a genetic approach utilising nuclear DNA to unequivocally identify species and interspecific hybrids. Several nuclear loci (ITS1-ITS2, CA14 and GA13) were amplified by PCR and products were subjected to diagnostic restriction enzymes (restriction fragment length polymorphism; RFLP). The application of this approach to several populations across Europe revealed that the markers are highly consistent and reproducible. In addition, we illustrate with a number of examples how this approach contributed to unravel previously unrecognised taxa, increased the sensitivity of biodiversity studies or contributed to the analysis of resting egg banks. Advantages and disadvantages of this approach compared to existing techniques are discussed and several empirical studies and their results are summarised. [KEYWORDS: Daphnia ; RFLP ; interspecific hybrids]

We studied genetic differentiation of two subarctic Daphnia species (subgenus Hyalodaphnia; Cladocera: Anomopoda) in relation to ecological and morphological diversification. Daphnia longispina and the recently discovered species Daphnia umbra are genetically differentiated based on mitochondrial 12S rDNA and internal transcribed spacer (ITS) regions. Genetic differentiation of 12S rDNA among the two sister taxa is in the range of differentiation among other Hyalodaphnia species (uncorrected genetic distance = 0.11). Despite frequent interspecific hybridization among Daphnia (Hyalodaphnia) species, we found no interspecific hybrids of D. umbra and D. longispina. D. umbra is for the first time recorded to occur in Northern Finland and Russia (Pechora Delta), and to cooccur in neighboring sympatry with Daphnia longispina across a subarctic region in northern Finland. Species are ecologically differentiated: D. umbra occurred at higher elevations, in larger and deeper water bodies than D. longispina. Species did not differ significantly in levels of ultraviolet-protective melanin pigmentation but varied with regard to environmental preferences, such as fish predation and levels of total dissolved organic carbon (DOC). These findings argue that ecological differentiation and divergent selection might have caused speciation or at least are responsible for the maintenance of reproductive isolation among subarctic Daphnia (Hyalodaphnia) species.

Species of the genus Daphnia, in particular the subgenus Hyalodaphnia, represent a taxonomically problematic group due to their phenotypic plasticity, local races and the formation of interspecific hybrids and backcrosses. In this study, we present a genetic approach utilising nuclear DNA to unequivocally identify species and interspecific hybrids. Several nuclear loci (ITS1-ITS2, CA14 and GA13) were amplified by PCR and products were subjected to diagnostic restriction enzymes (restriction fragment length polymorphism; RFLP). The application of this approach to several populations across Europe revealed that the markers are highly consistent and reproducible. In addition, we illustrate with a number of examples how this approach contributed to unravel previously unrecognised taxa, increased the sensitivity of biodiversity studies or contributed to the analysis of resting egg banks. Advantages and disadvantages of this approach compared to existing techniques are discussed and several empirical studies and their results are summarised. [KEYWORDS: Daphnia ; RFLP ; interspecific hybrids], Species of the genus Daphnia, in particular the subgenus Hyalodaphnia, represent a taxonomically problematic group due to their phenotypic plasticity, local races and the formation of interspecific hybrids and backcrosses. In this study, we present a genetic approach utilising nuclear DNA to unequivocally identify species and interspecific hybrids. Several nuclear loci (ITS1-ITS2, CA14 and GA13) were amplified by PCR and products were subjected to diagnostic restriction enzymes (restriction fragment length polymorphism; RFLP). The application of this approach to several populations across Europe revealed that the markers are highly consistent and reproducible. In addition, we illustrate with a number of examples how this approach contributed to unravel previously unrecognised taxa, increased the sensitivity of biodiversity studies or contributed to the analysis of resting egg banks. Advantages and disadvantages of this approach compared to existing techniques are discussed and several empirical studies and their results are summarised. [KEYWORDS: Daphnia ; RFLP ; interspecific hybrids]

Clonal diversity within plant populations is affected by factors that influence genet (clone) survival and seed recruitment, such as resource availability, disturbance, seed dispersal mechanism, propagule predation and the age of the population. Here we studied a population of Potamogeton pectinatus, a pseudo-annual aquatic macrophyte. Within populations reproduction appears to be mainly asexually through subterranean propagules (tubers), while recruitment via seeds is believed to be relatively unimportant. RAPD markers were used to analyse clonal diversity and genetic variation within the population. Ninety-seven genets were identified among 128 samples taken from eight plots. The proportion of distinguishable genets (0.76) and Simpson's diversity index (0.99) exhibited high levels of clonal diversity compared to other clonal plants. According to an analysis of molecular variance (amova) most genetic variation occurred between individuals within plots (93-97%) rather than between plots (8-3%). These results imply that sexual reproduction plays an unexpectedly important role within the population. Nevertheless, autocorrelation statistics revealed a spatial genetic structure resulting from clonal growth. In contrast to genetic variation, clonal diversity was affected by several ecological factors. Water depth and silt content had direct negative effects on clonal diversity. Tuber predation by Bewick's swans had an unexpected indirect negative effect on clonal diversity through reducing the tuber-bank biomass in spring, which on its turn was positively correlated to clonal diversity. The disturbance by swans, therefore, did not enhance seed recruitment and thus clonal diversity; on the contrary, heavily foraged areas are probably more prone to stochastic loss of genets leading to reduced clonal diversity., Clonal diversity within plant populations is affected by factors that influence genet (clone) survival and seed recruitment, such as resource availability, disturbance, seed dispersal mechanism, propagule predation and the age of the population. Here we studied a population of Potamogeton pectinatus, a pseudo-annual aquatic macrophyte. Within populations reproduction appears to be mainly asexually through subterranean propagules (tubers), while recruitment via seeds is believed to be relatively unimportant. RAPD markers were used to analyse clonal diversity and genetic variation within the population. Ninety-seven genets were identified among 128 samples taken from eight plots. The proportion of distinguishable genets (0.76) and Simpson's diversity index (0.99) exhibited high levels of clonal diversity compared to other clonal plants. According to an analysis of molecular variance (amova) most genetic variation occurred between individuals within plots (93-97%) rather than between plots (8-3%). These results imply that sexual reproduction plays an unexpectedly important role within the population. Nevertheless, autocorrelation statistics revealed a spatial genetic structure resulting from clonal growth. In contrast to genetic variation, clonal diversity was affected by several ecological factors. Water depth and silt content had direct negative effects on clonal diversity. Tuber predation by Bewick's swans had an unexpected indirect negative effect on clonal diversity through reducing the tuber-bank biomass in spring, which on its turn was positively correlated to clonal diversity. The disturbance by swans, therefore, did not enhance seed recruitment and thus clonal diversity; on the contrary, heavily foraged areas are probably more prone to stochastic loss of genets leading to reduced clonal diversity.

Clonal diversity within plant populations is affected by factors that influence genet (clone) survival and seed recruitment, such as resource availability, disturbance, seed dispersal mechanism, propagule predation and the age of the population. Here we studied a population of Potamogeton pectinatus, a pseudo-annual aquatic macrophyte. Within populations reproduction appears to be mainly asexually through subterranean propagules (tubers), while recruitment via seeds is believed to be relatively unimportant. RAPD markers were used to analyse clonal diversity and genetic variation within the population. Ninety-seven genets were identified among 128 samples taken from eight plots. The proportion of distinguishable genets (0.76) and Simpson's diversity index (0.99) exhibited high levels of clonal diversity compared to other clonal plants. According to an analysis of molecular variance (amova) most genetic variation occurred between individuals within plots (93-97%) rather than between plots (8-3%). These results imply that sexual reproduction plays an unexpectedly important role within the population. Nevertheless, autocorrelation statistics revealed a spatial genetic structure resulting from clonal growth. In contrast to genetic variation, clonal diversity was affected by several ecological factors. Water depth and silt content had direct negative effects on clonal diversity. Tuber predation by Bewick's swans had an unexpected indirect negative effect on clonal diversity through reducing the tuber-bank biomass in spring, which on its turn was positively correlated to clonal diversity. The disturbance by swans, therefore, did not enhance seed recruitment and thus clonal diversity; on the contrary, heavily foraged areas are probably more prone to stochastic loss of genets leading to reduced clonal diversity., Clonal diversity within plant populations is affected by factors that influence genet (clone) survival and seed recruitment, such as resource availability, disturbance, seed dispersal mechanism, propagule predation and the age of the population. Here we studied a population of Potamogeton pectinatus, a pseudo-annual aquatic macrophyte. Within populations reproduction appears to be mainly asexually through subterranean propagules (tubers), while recruitment via seeds is believed to be relatively unimportant. RAPD markers were used to analyse clonal diversity and genetic variation within the population. Ninety-seven genets were identified among 128 samples taken from eight plots. The proportion of distinguishable genets (0.76) and Simpson's diversity index (0.99) exhibited high levels of clonal diversity compared to other clonal plants. According to an analysis of molecular variance (amova) most genetic variation occurred between individuals within plots (93-97%) rather than between plots (8-3%). These results imply that sexual reproduction plays an unexpectedly important role within the population. Nevertheless, autocorrelation statistics revealed a spatial genetic structure resulting from clonal growth. In contrast to genetic variation, clonal diversity was affected by several ecological factors. Water depth and silt content had direct negative effects on clonal diversity. Tuber predation by Bewick's swans had an unexpected indirect negative effect on clonal diversity through reducing the tuber-bank biomass in spring, which on its turn was positively correlated to clonal diversity. The disturbance by swans, therefore, did not enhance seed recruitment and thus clonal diversity; on the contrary, heavily foraged areas are probably more prone to stochastic loss of genets leading to reduced clonal diversity.

Hybridization is a common phenomenon in Daphnia (Cladocera; Anomopoda); interspecific hybrids have been found between several species and hybrids are found in many European lakes. Although much information on the morphology, ecology and genetics of hybrids is available, little is known about the level of reproductive isolation among species or about the relative fitness of hybrids and parental species. In order to facilitate studies on differentiation and speciation processes and comparative experimental studies on hybrids and recombinant genotypes, we present the first successful laboratory crossing experiments of two different Daphnia species, D. galeata and D. cucullata. Males and sexual females from two D. galeata and two D. cucullata clones were reciprocally crossed, juveniles hatched from resting eggs and reared until maturity. Hatching and juvenile survival rates of hybrids were relatively low (12.1% and 24%, respectively). D. galeata and D. cucullata clones vary in their level of successful interspecific matings and in the number of subsequent offspring. In general, hybrid crosses between D. cucullata females and D. galeata males were more successful than reciprocal crosses. [KEYWORDS: interspecific hybridization; Daphnia; laboratory hybrids; Hyalodaphnia; reproductive isolation; ephippia Hybrid species complex; life-history variation; resting eggs; lake-daphnia; cladocera; population; crustacea; evolution; pulex; mitochondrial], Hybridization is a common phenomenon in Daphnia (Cladocera; Anomopoda); interspecific hybrids have been found between several species and hybrids are found in many European lakes. Although much information on the morphology, ecology and genetics of hybrids is available, little is known about the level of reproductive isolation among species or about the relative fitness of hybrids and parental species. In order to facilitate studies on differentiation and speciation processes and comparative experimental studies on hybrids and recombinant genotypes, we present the first successful laboratory crossing experiments of two different Daphnia species, D. galeata and D. cucullata. Males and sexual females from two D. galeata and two D. cucullata clones were reciprocally crossed, juveniles hatched from resting eggs and reared until maturity. Hatching and juvenile survival rates of hybrids were relatively low (12.1% and 24%, respectively). D. galeata and D. cucullata clones vary in their level of successful interspecific matings and in the number of subsequent offspring. In general, hybrid crosses between D. cucullata females and D. galeata males were more successful than reciprocal crosses. [KEYWORDS: interspecific hybridization; Daphnia; laboratory hybrids; Hyalodaphnia; reproductive isolation; ephippia Hybrid species complex; life-history variation; resting eggs; lake-daphnia; cladocera; population; crustacea; evolution; pulex; mitochondrial]

Hybridization is a common phenomenon in Daphnia (Cladocera; Anomopoda); interspecific hybrids have been found between several species and hybrids are found in many European lakes. Although much information on the morphology, ecology and genetics of hybrids is available, little is known about the level of reproductive isolation among species or about the relative fitness of hybrids and parental species. In order to facilitate studies on differentiation and speciation processes and comparative experimental studies on hybrids and recombinant genotypes, we present the first successful laboratory crossing experiments of two different Daphnia species, D. galeata and D. cucullata. Males and sexual females from two D. galeata and two D. cucullata clones were reciprocally crossed, juveniles hatched from resting eggs and reared until maturity. Hatching and juvenile survival rates of hybrids were relatively low (12.1% and 24%, respectively). D. galeata and D. cucullata clones vary in their level of successful interspecific matings and in the number of subsequent offspring. In general, hybrid crosses between D. cucullata females and D. galeata males were more successful than reciprocal crosses. [KEYWORDS: interspecific hybridization; Daphnia; laboratory hybrids; Hyalodaphnia; reproductive isolation; ephippia Hybrid species complex; life-history variation; resting eggs; lake-daphnia; cladocera; population; crustacea; evolution; pulex; mitochondrial], Hybridization is a common phenomenon in Daphnia (Cladocera; Anomopoda); interspecific hybrids have been found between several species and hybrids are found in many European lakes. Although much information on the morphology, ecology and genetics of hybrids is available, little is known about the level of reproductive isolation among species or about the relative fitness of hybrids and parental species. In order to facilitate studies on differentiation and speciation processes and comparative experimental studies on hybrids and recombinant genotypes, we present the first successful laboratory crossing experiments of two different Daphnia species, D. galeata and D. cucullata. Males and sexual females from two D. galeata and two D. cucullata clones were reciprocally crossed, juveniles hatched from resting eggs and reared until maturity. Hatching and juvenile survival rates of hybrids were relatively low (12.1% and 24%, respectively). D. galeata and D. cucullata clones vary in their level of successful interspecific matings and in the number of subsequent offspring. In general, hybrid crosses between D. cucullata females and D. galeata males were more successful than reciprocal crosses. [KEYWORDS: interspecific hybridization; Daphnia; laboratory hybrids; Hyalodaphnia; reproductive isolation; ephippia Hybrid species complex; life-history variation; resting eggs; lake-daphnia; cladocera; population; crustacea; evolution; pulex; mitochondrial]

We examined phylogenetic relationships among Daphnia using mitochondrial DNA (mtDNA) sequences from the small subunit ribosomal RNA (12S), cytochrome c oxidase subunit I and nuclear DNA sequences from the first and second internal transcribed spacer representing 1612 base positions. Phylogenecic analyses using several species of the three main Daphnia subgenera, Ctenodaphnia, Hyalodaphnia and Daphnia, revealed that the Hyalodaphnia are a monophyletic sister group of the Daphnia. Most Hyalodaphnia species occur on one continent, whereas only three are found in North America and Europe. Endemicity of species is associated with variation in thermal tolerance and habitat differentiation. Although many species of the Hyalonaphnia are known to hybridize in nature, mtDNA divergence is relatively high (ca. 9%) compared to other hybridizing arthropods (ca. 3%). Reproductive isolation in Daphnia seems to evolve significantly slower than genetic isolation. We related these findings to what is known about the ecology and genetics of Daphnia in order to better understand the evolutionary diversification of lineages. The relationship of these data to phylogenetic patterns is discussed in the context of speciation processes in Daphnia. [KEYWORDS: interspecific hybridization; Daphnia; phylogeny; speciation; reproductive isolation Mitochondrial-dna; interspecific hybridization; genetic differentiation; secondary structure; complex crustacea; daphnia; evolution; sequence; biogeography; substitution], We examined phylogenetic relationships among Daphnia using mitochondrial DNA (mtDNA) sequences from the small subunit ribosomal RNA (12S), cytochrome c oxidase subunit I and nuclear DNA sequences from the first and second internal transcribed spacer representing 1612 base positions. Phylogenecic analyses using several species of the three main Daphnia subgenera, Ctenodaphnia, Hyalodaphnia and Daphnia, revealed that the Hyalodaphnia are a monophyletic sister group of the Daphnia. Most Hyalodaphnia species occur on one continent, whereas only three are found in North America and Europe. Endemicity of species is associated with variation in thermal tolerance and habitat differentiation. Although many species of the Hyalonaphnia are known to hybridize in nature, mtDNA divergence is relatively high (ca. 9%) compared to other hybridizing arthropods (ca. 3%). Reproductive isolation in Daphnia seems to evolve significantly slower than genetic isolation. We related these findings to what is known about the ecology and genetics of Daphnia in order to better understand the evolutionary diversification of lineages. The relationship of these data to phylogenetic patterns is discussed in the context of speciation processes in Daphnia. [KEYWORDS: interspecific hybridization; Daphnia; phylogeny; speciation; reproductive isolation Mitochondrial-dna; interspecific hybridization; genetic differentiation; secondary structure; complex crustacea; daphnia; evolution; sequence; biogeography; substitution]

We examined phylogenetic relationships among Daphnia using mitochondrial DNA (mtDNA) sequences from the small subunit ribosomal RNA (12S), cytochrome c oxidase subunit I and nuclear DNA sequences from the first and second internal transcribed spacer representing 1612 base positions. Phylogenecic analyses using several species of the three main Daphnia subgenera, Ctenodaphnia, Hyalodaphnia and Daphnia, revealed that the Hyalodaphnia are a monophyletic sister group of the Daphnia. Most Hyalodaphnia species occur on one continent, whereas only three are found in North America and Europe. Endemicity of species is associated with variation in thermal tolerance and habitat differentiation. Although many species of the Hyalonaphnia are known to hybridize in nature, mtDNA divergence is relatively high (ca. 9%) compared to other hybridizing arthropods (ca. 3%). Reproductive isolation in Daphnia seems to evolve significantly slower than genetic isolation. We related these findings to what is known about the ecology and genetics of Daphnia in order to better understand the evolutionary diversification of lineages. The relationship of these data to phylogenetic patterns is discussed in the context of speciation processes in Daphnia. [KEYWORDS: interspecific hybridization; Daphnia; phylogeny; speciation; reproductive isolation Mitochondrial-dna; interspecific hybridization; genetic differentiation; secondary structure; complex crustacea; daphnia; evolution; sequence; biogeography; substitution], We examined phylogenetic relationships among Daphnia using mitochondrial DNA (mtDNA) sequences from the small subunit ribosomal RNA (12S), cytochrome c oxidase subunit I and nuclear DNA sequences from the first and second internal transcribed spacer representing 1612 base positions. Phylogenecic analyses using several species of the three main Daphnia subgenera, Ctenodaphnia, Hyalodaphnia and Daphnia, revealed that the Hyalodaphnia are a monophyletic sister group of the Daphnia. Most Hyalodaphnia species occur on one continent, whereas only three are found in North America and Europe. Endemicity of species is associated with variation in thermal tolerance and habitat differentiation. Although many species of the Hyalonaphnia are known to hybridize in nature, mtDNA divergence is relatively high (ca. 9%) compared to other hybridizing arthropods (ca. 3%). Reproductive isolation in Daphnia seems to evolve significantly slower than genetic isolation. We related these findings to what is known about the ecology and genetics of Daphnia in order to better understand the evolutionary diversification of lineages. The relationship of these data to phylogenetic patterns is discussed in the context of speciation processes in Daphnia. [KEYWORDS: interspecific hybridization; Daphnia; phylogeny; speciation; reproductive isolation Mitochondrial-dna; interspecific hybridization; genetic differentiation; secondary structure; complex crustacea; daphnia; evolution; sequence; biogeography; substitution]

Despite many ecological and evolutionary studies, the history of several species complexes within the freshwater crustacean genus Daphnia (Branchiopoda, Anomopoda) is poorly understood. In particular, the Daphnia longispina group, comprising several large-lake species, is characterized by pronounced phenotypic plasticity, many hybridizing species arid backcrossing. We studied clonal assemblages from lakes and ponds comprising daphnids from several species complexes. In order to reveal patterns of reticulate evolution and introgression among species, we analysed three data sets and compared nuclear, mtDNA and morphological divergence using animals from 158 newly established clonal cultures. By examining 15 nuclear and II mitochondrial (12S/16S rDNA) genetic characters (allozymes/restriction enzymes), and 48 morphological traits, we found high clonal diversity and discontinuities in genotypic and morphological space which allowed us to group clones by cytonuclear differentiation into seven units (outgroup D. pulex). In contrast to six groups emerging from nuclear divergence (related to three traditional species, D. cucullata D. galeata, D. hyalina and three pairwise intermediate hybrids), a seventh group of clones was clearly resolved by morphological divergence: distinct mtDNA haplotypes within one nuclear defined cluster, 'D. hyalina', resembled traditional D; hyalina and D. rosea phenotypes, respectively. In other nuclear defined clusters, association between mtDNA haplotype and morphology was low, despite hybridization being bidirectional (reciprocal crosses). Morphological divergence was greatest between young sister species which are separated on the lake/pond level, suggesting a significant role for divergent selection during speciation along with habitat shifts. Phylogenetic analyses were restricted to four cytonuclear groups of crones related to species. mtDNA and nuclear phylogenies were consistent in low genetic divergence and monophyly of D. hyalina and D., Despite many ecological and evolutionary studies, the history of several species complexes within the freshwater crustacean genus Daphnia (Branchiopoda, Anomopoda) is poorly understood. In particular, the Daphnia longispina group, comprising several large-lake species, is characterized by pronounced phenotypic plasticity, many hybridizing species arid backcrossing. We studied clonal assemblages from lakes and ponds comprising daphnids from several species complexes. In order to reveal patterns of reticulate evolution and introgression among species, we analysed three data sets and compared nuclear, mtDNA and morphological divergence using animals from 158 newly established clonal cultures. By examining 15 nuclear and II mitochondrial (12S/16S rDNA) genetic characters (allozymes/restriction enzymes), and 48 morphological traits, we found high clonal diversity and discontinuities in genotypic and morphological space which allowed us to group clones by cytonuclear differentiation into seven units (outgroup D. pulex). In contrast to six groups emerging from nuclear divergence (related to three traditional species, D. cucullata D. galeata, D. hyalina and three pairwise intermediate hybrids), a seventh group of clones was clearly resolved by morphological divergence: distinct mtDNA haplotypes within one nuclear defined cluster, 'D. hyalina', resembled traditional D; hyalina and D. rosea phenotypes, respectively. In other nuclear defined clusters, association between mtDNA haplotype and morphology was low, despite hybridization being bidirectional (reciprocal crosses). Morphological divergence was greatest between young sister species which are separated on the lake/pond level, suggesting a significant role for divergent selection during speciation along with habitat shifts. Phylogenetic analyses were restricted to four cytonuclear groups of crones related to species. mtDNA and nuclear phylogenies were consistent in low genetic divergence and monophyly of D. hyalina and D.

The coexistence of Daphnia cucullata x galeata hybrids with the parental species D. galeata and D. cucullata was investigated by measuring areas and mesh sizes of filtering structures of these herbivorous zooplankton taxa cultivated at low and high food concentrations. The clearance rates and somatic growth rates were also determined. When reared at low food concentration, all taxa had larger filtering areas. Larger filtering areas also resulted in higher clearance rates. Differences between taxa in both filtering area and clearance rate were caused mainly by interspecific size differences. Hybrids had the largest absolute mesh sizes, and the parental species had smaller mesh sizes. Hybrids also showed heterosis in somatic growth rate at high food concentration. The observed taxon-specific differences in mesh size and somatic growth rate contribute to resource partitioning between the taxa and thus to their successful coexistence in lakes. [KEYWORDS: Daphnia; hybrids; feeding; plasticity; developmental instability Life-history variation; phenotypic plasticity; interspecific hybridization; developmental stability; mesh-sizes; heterozygosity; populations; adaptation; consequences; variability], The coexistence of Daphnia cucullata x galeata hybrids with the parental species D. galeata and D. cucullata was investigated by measuring areas and mesh sizes of filtering structures of these herbivorous zooplankton taxa cultivated at low and high food concentrations. The clearance rates and somatic growth rates were also determined. When reared at low food concentration, all taxa had larger filtering areas. Larger filtering areas also resulted in higher clearance rates. Differences between taxa in both filtering area and clearance rate were caused mainly by interspecific size differences. Hybrids had the largest absolute mesh sizes, and the parental species had smaller mesh sizes. Hybrids also showed heterosis in somatic growth rate at high food concentration. The observed taxon-specific differences in mesh size and somatic growth rate contribute to resource partitioning between the taxa and thus to their successful coexistence in lakes. [KEYWORDS: Daphnia; hybrids; feeding; plasticity; developmental instability Life-history variation; phenotypic plasticity; interspecific hybridization; developmental stability; mesh-sizes; heterozygosity; populations; adaptation; consequences; variability]

Despite many ecological and evolutionary studies, the history of several species complexes within the freshwater crustacean genus Daphnia (Branchiopoda, Anomopoda) is poorly understood. In particular, the Daphnia longispina group, comprising several large-lake species, is characterized by pronounced phenotypic plasticity, many hybridizing species arid backcrossing. We studied clonal assemblages from lakes and ponds comprising daphnids from several species complexes. In order to reveal patterns of reticulate evolution and introgression among species, we analysed three data sets and compared nuclear, mtDNA and morphological divergence using animals from 158 newly established clonal cultures. By examining 15 nuclear and II mitochondrial (12S/16S rDNA) genetic characters (allozymes/restriction enzymes), and 48 morphological traits, we found high clonal diversity and discontinuities in genotypic and morphological space which allowed us to group clones by cytonuclear differentiation into seven units (outgroup D. pulex). In contrast to six groups emerging from nuclear divergence (related to three traditional species, D. cucullata D. galeata, D. hyalina and three pairwise intermediate hybrids), a seventh group of clones was clearly resolved by morphological divergence: distinct mtDNA haplotypes within one nuclear defined cluster, 'D. hyalina', resembled traditional D; hyalina and D. rosea phenotypes, respectively. In other nuclear defined clusters, association between mtDNA haplotype and morphology was low, despite hybridization being bidirectional (reciprocal crosses). Morphological divergence was greatest between young sister species which are separated on the lake/pond level, suggesting a significant role for divergent selection during speciation along with habitat shifts. Phylogenetic analyses were restricted to four cytonuclear groups of crones related to species. mtDNA and nuclear phylogenies were consistent in low genetic divergence and monophyly of D. hyalina and D., Despite many ecological and evolutionary studies, the history of several species complexes within the freshwater crustacean genus Daphnia (Branchiopoda, Anomopoda) is poorly understood. In particular, the Daphnia longispina group, comprising several large-lake species, is characterized by pronounced phenotypic plasticity, many hybridizing species arid backcrossing. We studied clonal assemblages from lakes and ponds comprising daphnids from several species complexes. In order to reveal patterns of reticulate evolution and introgression among species, we analysed three data sets and compared nuclear, mtDNA and morphological divergence using animals from 158 newly established clonal cultures. By examining 15 nuclear and II mitochondrial (12S/16S rDNA) genetic characters (allozymes/restriction enzymes), and 48 morphological traits, we found high clonal diversity and discontinuities in genotypic and morphological space which allowed us to group clones by cytonuclear differentiation into seven units (outgroup D. pulex). In contrast to six groups emerging from nuclear divergence (related to three traditional species, D. cucullata D. galeata, D. hyalina and three pairwise intermediate hybrids), a seventh group of clones was clearly resolved by morphological divergence: distinct mtDNA haplotypes within one nuclear defined cluster, 'D. hyalina', resembled traditional D; hyalina and D. rosea phenotypes, respectively. In other nuclear defined clusters, association between mtDNA haplotype and morphology was low, despite hybridization being bidirectional (reciprocal crosses). Morphological divergence was greatest between young sister species which are separated on the lake/pond level, suggesting a significant role for divergent selection during speciation along with habitat shifts. Phylogenetic analyses were restricted to four cytonuclear groups of crones related to species. mtDNA and nuclear phylogenies were consistent in low genetic divergence and monophyly of D. hyalina and D.

The coexistence of Daphnia cucullata x galeata hybrids with the parental species D. galeata and D. cucullata was investigated by measuring areas and mesh sizes of filtering structures of these herbivorous zooplankton taxa cultivated at low and high food concentrations. The clearance rates and somatic growth rates were also determined. When reared at low food concentration, all taxa had larger filtering areas. Larger filtering areas also resulted in higher clearance rates. Differences between taxa in both filtering area and clearance rate were caused mainly by interspecific size differences. Hybrids had the largest absolute mesh sizes, and the parental species had smaller mesh sizes. Hybrids also showed heterosis in somatic growth rate at high food concentration. The observed taxon-specific differences in mesh size and somatic growth rate contribute to resource partitioning between the taxa and thus to their successful coexistence in lakes. [KEYWORDS: Daphnia; hybrids; feeding; plasticity; developmental instability Life-history variation; phenotypic plasticity; interspecific hybridization; developmental stability; mesh-sizes; heterozygosity; populations; adaptation; consequences; variability], The coexistence of Daphnia cucullata x galeata hybrids with the parental species D. galeata and D. cucullata was investigated by measuring areas and mesh sizes of filtering structures of these herbivorous zooplankton taxa cultivated at low and high food concentrations. The clearance rates and somatic growth rates were also determined. When reared at low food concentration, all taxa had larger filtering areas. Larger filtering areas also resulted in higher clearance rates. Differences between taxa in both filtering area and clearance rate were caused mainly by interspecific size differences. Hybrids had the largest absolute mesh sizes, and the parental species had smaller mesh sizes. Hybrids also showed heterosis in somatic growth rate at high food concentration. The observed taxon-specific differences in mesh size and somatic growth rate contribute to resource partitioning between the taxa and thus to their successful coexistence in lakes. [KEYWORDS: Daphnia; hybrids; feeding; plasticity; developmental instability Life-history variation; phenotypic plasticity; interspecific hybridization; developmental stability; mesh-sizes; heterozygosity; populations; adaptation; consequences; variability]

Genetic variation within a worldwide collection of Potamogeton pectinatus L. was investigated by analyzing randomly amplified polymorphisms of nuclear DNA anti restriction fragment length polymorphisms of chloroplast DNA. Of the 51 plants investigated, 50 exhibited unique multi-locus nuclear genotypes. Analysis of chloroplast DNA revealed four unique haplotypes, as well as distinct cytonuclear genotypes in populations from geographically isolated regions (e.g., Donana, Spain and Pechora Delta, Russia). Based on the distributional pattern of P. pectinatus, previous studies have assumed that dispersal between populations is frequent and genotypes are distributed according to the island model of genetic structure. In contrast, we found that genetic distances and geographic distances were significantly correlated, indicating that the observed population structure can better be explained by stepping stone or isolation by distance models. Although no distinction of historic factors, such as founder effects, and current processes, such as environmental conditions, can be derived from this data set, we found indications for the impact of migrating water-fowl on plant distributional patterns. [KEYWORDS: genetic variation; aquatic macrophyte; RAPD; chloroplast DNA; dispersal Amplified polymorphic dna; genetic-relationships; plant- populations; isozyme evidence; patterns; markers; rapd; variability; divergence; filiformis], Genetic variation within a worldwide collection of Potamogeton pectinatus L. was investigated by analyzing randomly amplified polymorphisms of nuclear DNA anti restriction fragment length polymorphisms of chloroplast DNA. Of the 51 plants investigated, 50 exhibited unique multi-locus nuclear genotypes. Analysis of chloroplast DNA revealed four unique haplotypes, as well as distinct cytonuclear genotypes in populations from geographically isolated regions (e.g., Donana, Spain and Pechora Delta, Russia). Based on the distributional pattern of P. pectinatus, previous studies have assumed that dispersal between populations is frequent and genotypes are distributed according to the island model of genetic structure. In contrast, we found that genetic distances and geographic distances were significantly correlated, indicating that the observed population structure can better be explained by stepping stone or isolation by distance models. Although no distinction of historic factors, such as founder effects, and current processes, such as environmental conditions, can be derived from this data set, we found indications for the impact of migrating water-fowl on plant distributional patterns. [KEYWORDS: genetic variation; aquatic macrophyte; RAPD; chloroplast DNA; dispersal Amplified polymorphic dna; genetic-relationships; plant- populations; isozyme evidence; patterns; markers; rapd; variability; divergence; filiformis]

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. [KEYWORDS: microcrustaceans, Daphnia, evolution, interspecific hybridization, molecular systematics, aquatic ecology], 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. [KEYWORDS: microcrustaceans, Daphnia, evolution, interspecific hybridization, molecular systematics, aquatic ecology]