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Piet Spaak

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University College Dublin

University of Copenhagen

Utrecht University

Edwin A. Hernández-Delgado

Universidad de Puerto Rico Rio

Armando Marques-Guedes

UNL - New University of Lisbon

Gloria I. López

University of Haifa

Columbia University

Utah Geological Survey

Sahar F Mehanna

National Institute of Oceanography and Fisheries

Adam Mickiewicz University in Poznań

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Papers by Piet Spaak

Habitat fragmentation and genetic diversity. What we can learn by stuying alpine aquatic insects

An abundant future for quagga mussels in deep European lakes

bioRxiv (Cold Spring Harbor Laboratory), Jun 4, 2023

Quagga mussels have expanded their range across the northern hemisphere in recent decades owing t... more Quagga mussels have expanded their range across the northern hemisphere in recent decades owing to their dispersal abilities, prolific reproduction rates, and broad ecological tolerances. Their remarkable capacity to filter particulates from the water column has had profound effects on inland aquatic ecosystems. In the North American Great Lakes, quagga mussel populations have increased inexorably since the late 1980's, but it remains unclear whether quagga mussels will follow a similar trajectory in Europe where they have appeared more recently. Here we apply knowledge from a 33-year quagga population monitoring effort in the North American lakes to predict future quagga populations in deep European lakes, where quaggas are quickly becoming a conspicuous part of the underwater landscape. We predict that quagga mussel biomass in Lakes Biel, Constance, and Geneva may increase by a factor of 9-20 by 2045. Like in North America, this increase may be characterized by a shift to larger individuals and deeper depths as the population matures. If realized, this rapid expansion of quagga mussels would likely drive the largest aquatic ecosystem change in deep European lakes since the eutrophication period of the mid-20 th century. Introduction: The range of the quagga mussel (Dreissena rostriformis bugensis (Andrusov)) has rapidly expanded in the Northern Hemisphere since the 1980's due to human activities that provided previously unavailable means of spread (Karatayev and Burlakova 2022b, Matthews et al 2014, Bij de Vaate et al 2013). After arriving in a new location, their spread is amplified by the .

The stable isotopic composition of Daphnia ephippia reflects changes in delta C-13 and delta O-18 values of food and water

Biogeosciences, 2015

The stable isotopic composition of fossil resting eggs (ephippia) of Daphnia spp. is being used t... more The stable isotopic composition of fossil resting eggs (ephippia) of Daphnia spp. is being used to reconstruct past environmental conditions in lake ecosystems. However, the underlying assumption that the stable isotopic composition of the ephippia reflects the stable isotopic composition of the parent Daphnia, of their diet and of the environmental water have yet to be confirmed in a controlled experimental setting. We performed experiments with Daphnia pulicaria cultures, which included a control treatment conducted at 12 °C in filtered lake water and with a diet of fresh algae, and three treatments in which we manipulated the 2 stable carbon isotopic composition (δ 13 C value) of the algae, stable oxygen isotopic composition (δ 18 O value) of the water, and the water temperature, respectively. The stable nitrogen isotopic composition (δ 15 N value) of the algae was similar for all treatments. At 12 °C, differences in algal δ 13 C values and in δ 18 O values of water are reflected in those of Daphnia. The differences between ephippia and Daphnia stable isotope ratios were similar in the different treatments (δ 13 C: +0.2 ± 0.4 ‰ (standard deviation); δ 15 N:-1.6 ± 0.4 ‰; δ 18 O:-0.9 ± 0.4 ‰) indicating that changes in dietary δ 13 C values and in δ 18 O values of water are passed on to these fossilizing structures. A higher water temperature (20 °C) resulted in lower δ 13 C values in Daphnia and ephippia than in the other treatments with the same food source and in a minor change in the difference between δ 13 C values of ephippia and Daphnia (to-1.3 ± 0.3 ‰). This may have been due to microbial processes or increased algal respiration rates in the experimental containers, which may not affect Daphnia in natural environments. There was no significant difference in the offset between δ 18 O and δ 15 N values of ephippia and Daphnia between the 12 °C and 20 °C treatments, but the δ 18 O values of Daphnia and ephippia were on average 1.2 ‰ lower at 20 °C compared with 12 °C. We conclude that the stable isotopic composition of Daphnia ephippia provides information on that of the parent Daphnia and of the food and water they were exposed to, with small offsets between Daphnia and ephippia relative to variations in Daphnia stable isotopic composition reported from downcore studies. However, our experiments also indicate that temperature may have a minor influence on the δ 13 C, δ 15 N and δ 18 O values of Daphnia body tissue and ephippia. This aspect deserves attention in further controlled experiments.

Veliger density and environmental conditions control quagga mussel colonization rates in two perialpine lakes

Journal of Great Lakes Research, May 1, 2023

Environmentally independent selection for hybrids between divergent freshwater stickleback lineages in semi‐natural ponds

Journal of Evolutionary Biology, Jul 2, 2023

Hybridization following secondary contact of genetically divergent populations can influence the ... more Hybridization following secondary contact of genetically divergent populations can influence the range expansion of invasive species, though specific outcomes depend on the environmental dependence of hybrid fitness. Here, using two genetically and ecologically divergent threespine stickleback lineages that differ in their history of freshwater colonization, we estimate fitness variation of parental lineages and hybrids in semi‐natural freshwater ponds with contrasting histories of nutrient loading. In our experiment, we found that fish from the older freshwater lineage (Lake Geneva) and hybrids outperformed fish from the younger freshwater lineage (Lake Constance) in terms of both growth and survival, regardless of the environmental context of our ponds. Across all ponds, hybrids exhibited the highest survival. Although wild‐caught adult populations differed in their functional and defence morphology, it is unclear which of these traits underlie the fitness differences observed among juveniles in our experiment. Overall, our work suggests that when hybrid fitness is insensitive to environmental conditions, as observed here, introgression may promote population expansion into unoccupied habitats and accelerate invasion success.

Revisiting the phylogenetic position of Caullerya mesnili (Ichthyosporea), a common Daphnia parasite, based on 22 protein-coding genes

Molecular Phylogenetics and Evolution, Oct 1, 2020

Caullerya mesnili is a common and virulent parasite of the water flea, Daphnia. It was classified... more Caullerya mesnili is a common and virulent parasite of the water flea, Daphnia. It was classified within the Haplosporidia (Rhizaria) for over a century. However, a recent molecular phylogeny based on the 18S rRNA gene suggested it belonged to the Ichthyosporea, a class of protists closely related to animals within the Opisthokonta clade. The exact phylogenetic position of C. mesnili remained uncertain because it appeared in the 18S rRNA tree with a very long branch and separated from all other taxa, suggesting that its position could be artifactual. A better understanding of its phylogenetic position has been constrained by a lack of molecular markers and the difficulty of obtaining a suitable quantity and quality of DNA from in vitro cultures, as this intracellular parasite cannot be cultured without its host. We isolated and collected spores of C. mesnili and sequenced genomic libraries. Phylogenetic analyses of a newly generated multi-protein data set (22 proteins, 4,998 amino acids) and of sequences from the 18S rRNA gene both placed C. mesnili within the Ichthyophonida subclade of Ichthyosporea, as sister-taxon to Abeoforma whisleri and Pirum gemmata. Our study highlights the utility of metagenomic approaches for obtaining genomic information from intracellular parasites and for more accurate phylogenetic placement in evolutionary studies.

Starving with a full gut? Effect of suspended particles on the fitness of Daphnia hyalina

Hydrobiologia, Oct 23, 2007

Suspended particles are abiotic factors that can affect the abundance of cladocerans such as daph... more Suspended particles are abiotic factors that can affect the abundance of cladocerans such as daphnids. Ultra-oligotrophic Lake Brienz, situated in the front ranges of the Swiss Alps, is dominated by two major inflows that annually transport over 300,000 tons of suspended glacial material into the lake. A laboratory flow-through experiment was performed to test whether these suspended particles have an influence on the fitness of Daphnia hyalina from Lake Brienz, measured as body size, fecundity and juvenile growth rate, especially when they are simultaneously exposed to low food concentrations. Our results show that the concentration of suspended particles present in Lake Brienz does not reduce the fitness of daphnids, even at very low food concentration. In fact, a low concentration of suspended particles increased the fitness. Reduction of fitness could only be observed at a suspended particle concentration of over 25 mg l À1 , a level that has never been recorded in Lake Brienz.

Have Human Impacts Changed Alpine Zooplankton Diversity over the past 100 Years?

Arctic, Antarctic, and Alpine Research, Nov 1, 2001

Anthropogenic stress and fish introduction generally are thought to have elimi • nated vulnerable... more Anthropogenic stress and fish introduction generally are thought to have elimi • nated vulnerable and sensitive zooplankton species from many alpine lakes, ere .. ating impoverished communities. To investigate this hypothesis we resamplecl. lakes studied in the early 20th century and compared past and present zooplanktor 1 composition and taxa richness. We also studied how human induced changes may influence genetic diversity of present-day populations of the widespread cladoc• eran, Daphnia. Resampling did not show a drastic overall change in planktonic crustacean composition. Taxa richness significantly decreased with increasing laki. altitude, but no other environmental factor correlated with richness. Large zoo• plankton tax.a were found in lakes both with and without fish. Therefore we conclude that the presence of fish can be excluded as the general factor explaininll the occurrence or absence of large zooplankton in alpine lakes. Levels of chlo• rophyll a and POC best distinguished lakes with Daphnia from lakes withoul Daphnia. In 8 out of 12 lakes sexual Daphnia were more abundant than asexual individuals. Clonal diversity ranged from 0.01 to 1.3 but was not related to the proportion of sexual individuals. The ability to create resting stages may be ari essential factor for the maintenance of genetic diversity and the long-term persistence of Daphnia and other zooplankton taxa. water samples; Regula Illi for identifying the rotifers; and Bet• tina Wagner, Christine Dambone, and Barbara Keller for laboratory assistance. Sabine Giessler and Klaus Schwenk assisted with Daphnia identification. Jan Fott and Andrew Bohonac provided useful comments on an earlier version of this manuscript.

Evolutionary and ecological consequences of interspecific hybridization in cladocerans

Experientia, May 1, 1995

The evolutionary process of interspecific hybridization in cladocerans is reviewed based on ecolo... more 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 the D. 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.

Author response for "Environmentally independent selection for hybrids between divergent freshwater stickleback lineages in semi‐natural ponds

Überdüngung verändert die Daphniengemeinschaft

EGRAS (ecological grassland simulator) opnieuw geprogrammeerd en bewerkt voor de PC

Dit rapport is het vijfde in een serie doctoraatverslagen, waarin de ontwikkeling van het begrazi... more Dit rapport is het vijfde in een serie doctoraatverslagen, waarin de ontwikkeling van het begrazingsmodel "EGRAS" (Ecological GRAssland Simulator) beschreven is. Dit model simuleert de groei van de vegetatie onder invloed van begrazing door pinken op de Schildhoek en Pampusplaat in het Lauwersmeergebied. Friso en van Esch (1983) ontwikkelden een wiskundig model bestaande uit de submodellen: Groei, Consumptie, Sterfte, Vergaan en Vestiging. Loonen en Moesker (1985) breidden dit model verder uit en maakten het "computeroperabel" d.m.v. een Pascal programma dat op de Groningse "CYBER" draaide. Hutjes (1987) verzamelde gegevens over decompositie en verwerkte die met de gegevens van do Leeuw in een nieuw sub-model voor de stikstofkringloop. Tevens verscheen in 1987 een artikel van Fresco et al. Zij beschreven het model met nieuwe, Engelse namen voor de variabelen en gebruikten het model om de invloed van grotere begrazingsdruk op de vegetatie te onderzoeken. Het voorgaande laat zien dat er al veel over het model "EGRAS" geschreven is. Het hoofddoel van dit onderzoek was het opnieuw programmeren van het model "EGRAS" voor de PC. Leidraad hierbij was het artikel van Fresco et al. (1987) . De door hen geintroduceerde naamgeving van parameters en variabelen is gevolgd. Voor de precieze invulling van procedures is, waar nodig, teruggevallen op het verslag en de listing van het programma van Loonen en Moesker (1985). Voor de modellering van de stikstofkringloop is gebruik gemaakt van het programma van Ronald Hutjes (1987). De Leeuw en Hutjes hebben het decompositieproces in het proefgebied uitvoerig beschreven en gemodelleerd. Ze hebben echter niet de mineralisatie van stikstof onderzocht. Hiervoor was door Loonen en Moesker een constante genaamd “omzetting" in het model ingebouwd. Hutjes verbeterde de modellering van de mineralisatie door de formule van Kemmers en Jansen (1985) in te bouwen. Hierdoor werd de maximale mineralisatiesnelheid vermenigvuldigd met reductie factoren voor temperatuur en vochttoestand. Over de waarde van de maximale mineralisatiesnelheid waren in het gebied geen metingen gedaan.In een zeer beperkt mineralisatie-onderzoek heb ik onderzocht of de K-waarden voor de verschillende vegetatietypen, zoals die door de Leeuw en Hutjes beschreven zijn, verschillen. Deze resultaten zijn verwerkt in de unit Soil.

PERSPECTIVE The ecological forecast horizon, and examples of its uses and determinants

Test of in situ (underwater) automated imaging, as provided by the Scripps Plankton Camera, for monitoring and analysis of lake phytoplankton

Test of in situ (underwater) automated imaging, as provided by the Scripps Plankton Camera, for m... more

Eco-Evolutionary Dynamics in Freshwater Systems

Elsevier eBooks, 2022

There is an increasing recognition that evolutionary dynamics may occur at timescales that are su... more There is an increasing recognition that evolutionary dynamics may occur at timescales that are sufficiently rapid to impact ecological responses to environmental change and influence ecological dynamics. In the development of the emerging paradigm of eco-evolutionary dynamics, studies of freshwater organisms have been very important. Here we highlight a number of key observations and achievements, and point to remaining challenges.

Ecology and genetics of interspecific hybridization in Daphnia

Birkhäuser Basel eBooks, 1997

A central question in evolutionary biology concerns the ecological and genetic processes by which... more A central question in evolutionary biology concerns the ecological and genetic processes by which species hybridize. We analyze the evolutionary consequences of hybridization, biogeographic patterns and fitness comparisons in the crustacean Daphnia (Branchiopoda) within the conceptual framework of theories on interspecific hybridization. In contrast to most cases of hybridization among animals, Daphnia species and hybrids do not form interpopulational transition

Infection by a eukaryotic gut parasite in wild <i>Daphnia</i> sp. associates with a distinct bacterial community

bioRxiv (Cold Spring Harbor Laboratory), Feb 26, 2022

Host-associated bacterial communities can play an important role in host fitness and resistance t... more Host-associated bacterial communities can play an important role in host fitness and resistance to diseases. Yet, few studies have investigated tripartite interaction between a host, parasite and hostassociated bacterial communities in natural settings. Here, we use 16S amplicon sequencing to compare gut-and body-bacterial communities of wild water fleas belonging to the Daphnia longispina complex, between uninfected hosts and those infected with the common and virulent eukaryotic gut parasite Caullerya mesnili (Family: Ichthyosporea). We report community-level changes in host-associated bacteria with the presence of the parasite infection; namely decreased alpha diversity and increased beta diversity at the site of infection, i.e. host gut (but not host body). We also report decreased abundance of bacterial taxa proposed elsewhere to be beneficial for the host, and an appearance of taxa specifically associated with infected hosts. Our study highlights the hostmicrobiota-infection link in a natural system and raises questions about the role of host-associated microbiota in natural disease epidemics as well as the functional roles of bacteria specifically associated with infected hosts.

Effects of antropogenic pollution on host parasite interactions

Fewer non‐native insects in freshwater than in terrestrial habitats across continents

Diversity and Distributions, Sep 9, 2022

This is an open access article under the terms of the Creative Commons Attribution License, which... more

The distribution and spread of quagga mussels in perialpine lakes north of the Alps

Aquatic Invasions, 2022

Habitat fragmentation and genetic diversity. What we can learn by stuying alpine aquatic insects

An abundant future for quagga mussels in deep European lakes

bioRxiv (Cold Spring Harbor Laboratory), Jun 4, 2023

Quagga mussels have expanded their range across the northern hemisphere in recent decades owing t... more Quagga mussels have expanded their range across the northern hemisphere in recent decades owing to their dispersal abilities, prolific reproduction rates, and broad ecological tolerances. Their remarkable capacity to filter particulates from the water column has had profound effects on inland aquatic ecosystems. In the North American Great Lakes, quagga mussel populations have increased inexorably since the late 1980's, but it remains unclear whether quagga mussels will follow a similar trajectory in Europe where they have appeared more recently. Here we apply knowledge from a 33-year quagga population monitoring effort in the North American lakes to predict future quagga populations in deep European lakes, where quaggas are quickly becoming a conspicuous part of the underwater landscape. We predict that quagga mussel biomass in Lakes Biel, Constance, and Geneva may increase by a factor of 9-20 by 2045. Like in North America, this increase may be characterized by a shift to larger individuals and deeper depths as the population matures. If realized, this rapid expansion of quagga mussels would likely drive the largest aquatic ecosystem change in deep European lakes since the eutrophication period of the mid-20 th century. Introduction: The range of the quagga mussel (Dreissena rostriformis bugensis (Andrusov)) has rapidly expanded in the Northern Hemisphere since the 1980's due to human activities that provided previously unavailable means of spread (Karatayev and Burlakova 2022b, Matthews et al 2014, Bij de Vaate et al 2013). After arriving in a new location, their spread is amplified by the .

The stable isotopic composition of Daphnia ephippia reflects changes in delta C-13 and delta O-18 values of food and water

Biogeosciences, 2015

The stable isotopic composition of fossil resting eggs (ephippia) of Daphnia spp. is being used t... more The stable isotopic composition of fossil resting eggs (ephippia) of Daphnia spp. is being used to reconstruct past environmental conditions in lake ecosystems. However, the underlying assumption that the stable isotopic composition of the ephippia reflects the stable isotopic composition of the parent Daphnia, of their diet and of the environmental water have yet to be confirmed in a controlled experimental setting. We performed experiments with Daphnia pulicaria cultures, which included a control treatment conducted at 12 °C in filtered lake water and with a diet of fresh algae, and three treatments in which we manipulated the 2 stable carbon isotopic composition (δ 13 C value) of the algae, stable oxygen isotopic composition (δ 18 O value) of the water, and the water temperature, respectively. The stable nitrogen isotopic composition (δ 15 N value) of the algae was similar for all treatments. At 12 °C, differences in algal δ 13 C values and in δ 18 O values of water are reflected in those of Daphnia. The differences between ephippia and Daphnia stable isotope ratios were similar in the different treatments (δ 13 C: +0.2 ± 0.4 ‰ (standard deviation); δ 15 N:-1.6 ± 0.4 ‰; δ 18 O:-0.9 ± 0.4 ‰) indicating that changes in dietary δ 13 C values and in δ 18 O values of water are passed on to these fossilizing structures. A higher water temperature (20 °C) resulted in lower δ 13 C values in Daphnia and ephippia than in the other treatments with the same food source and in a minor change in the difference between δ 13 C values of ephippia and Daphnia (to-1.3 ± 0.3 ‰). This may have been due to microbial processes or increased algal respiration rates in the experimental containers, which may not affect Daphnia in natural environments. There was no significant difference in the offset between δ 18 O and δ 15 N values of ephippia and Daphnia between the 12 °C and 20 °C treatments, but the δ 18 O values of Daphnia and ephippia were on average 1.2 ‰ lower at 20 °C compared with 12 °C. We conclude that the stable isotopic composition of Daphnia ephippia provides information on that of the parent Daphnia and of the food and water they were exposed to, with small offsets between Daphnia and ephippia relative to variations in Daphnia stable isotopic composition reported from downcore studies. However, our experiments also indicate that temperature may have a minor influence on the δ 13 C, δ 15 N and δ 18 O values of Daphnia body tissue and ephippia. This aspect deserves attention in further controlled experiments.

Veliger density and environmental conditions control quagga mussel colonization rates in two perialpine lakes

Journal of Great Lakes Research, May 1, 2023

Environmentally independent selection for hybrids between divergent freshwater stickleback lineages in semi‐natural ponds

Journal of Evolutionary Biology, Jul 2, 2023

Hybridization following secondary contact of genetically divergent populations can influence the ... more Hybridization following secondary contact of genetically divergent populations can influence the range expansion of invasive species, though specific outcomes depend on the environmental dependence of hybrid fitness. Here, using two genetically and ecologically divergent threespine stickleback lineages that differ in their history of freshwater colonization, we estimate fitness variation of parental lineages and hybrids in semi‐natural freshwater ponds with contrasting histories of nutrient loading. In our experiment, we found that fish from the older freshwater lineage (Lake Geneva) and hybrids outperformed fish from the younger freshwater lineage (Lake Constance) in terms of both growth and survival, regardless of the environmental context of our ponds. Across all ponds, hybrids exhibited the highest survival. Although wild‐caught adult populations differed in their functional and defence morphology, it is unclear which of these traits underlie the fitness differences observed among juveniles in our experiment. Overall, our work suggests that when hybrid fitness is insensitive to environmental conditions, as observed here, introgression may promote population expansion into unoccupied habitats and accelerate invasion success.

Revisiting the phylogenetic position of Caullerya mesnili (Ichthyosporea), a common Daphnia parasite, based on 22 protein-coding genes

Molecular Phylogenetics and Evolution, Oct 1, 2020

Caullerya mesnili is a common and virulent parasite of the water flea, Daphnia. It was classified... more Caullerya mesnili is a common and virulent parasite of the water flea, Daphnia. It was classified within the Haplosporidia (Rhizaria) for over a century. However, a recent molecular phylogeny based on the 18S rRNA gene suggested it belonged to the Ichthyosporea, a class of protists closely related to animals within the Opisthokonta clade. The exact phylogenetic position of C. mesnili remained uncertain because it appeared in the 18S rRNA tree with a very long branch and separated from all other taxa, suggesting that its position could be artifactual. A better understanding of its phylogenetic position has been constrained by a lack of molecular markers and the difficulty of obtaining a suitable quantity and quality of DNA from in vitro cultures, as this intracellular parasite cannot be cultured without its host. We isolated and collected spores of C. mesnili and sequenced genomic libraries. Phylogenetic analyses of a newly generated multi-protein data set (22 proteins, 4,998 amino acids) and of sequences from the 18S rRNA gene both placed C. mesnili within the Ichthyophonida subclade of Ichthyosporea, as sister-taxon to Abeoforma whisleri and Pirum gemmata. Our study highlights the utility of metagenomic approaches for obtaining genomic information from intracellular parasites and for more accurate phylogenetic placement in evolutionary studies.

Starving with a full gut? Effect of suspended particles on the fitness of Daphnia hyalina

Hydrobiologia, Oct 23, 2007

Suspended particles are abiotic factors that can affect the abundance of cladocerans such as daph... more Suspended particles are abiotic factors that can affect the abundance of cladocerans such as daphnids. Ultra-oligotrophic Lake Brienz, situated in the front ranges of the Swiss Alps, is dominated by two major inflows that annually transport over 300,000 tons of suspended glacial material into the lake. A laboratory flow-through experiment was performed to test whether these suspended particles have an influence on the fitness of Daphnia hyalina from Lake Brienz, measured as body size, fecundity and juvenile growth rate, especially when they are simultaneously exposed to low food concentrations. Our results show that the concentration of suspended particles present in Lake Brienz does not reduce the fitness of daphnids, even at very low food concentration. In fact, a low concentration of suspended particles increased the fitness. Reduction of fitness could only be observed at a suspended particle concentration of over 25 mg l À1 , a level that has never been recorded in Lake Brienz.

Have Human Impacts Changed Alpine Zooplankton Diversity over the past 100 Years?

Arctic, Antarctic, and Alpine Research, Nov 1, 2001

Anthropogenic stress and fish introduction generally are thought to have elimi • nated vulnerable... more Anthropogenic stress and fish introduction generally are thought to have elimi • nated vulnerable and sensitive zooplankton species from many alpine lakes, ere .. ating impoverished communities. To investigate this hypothesis we resamplecl. lakes studied in the early 20th century and compared past and present zooplanktor 1 composition and taxa richness. We also studied how human induced changes may influence genetic diversity of present-day populations of the widespread cladoc• eran, Daphnia. Resampling did not show a drastic overall change in planktonic crustacean composition. Taxa richness significantly decreased with increasing laki. altitude, but no other environmental factor correlated with richness. Large zoo• plankton tax.a were found in lakes both with and without fish. Therefore we conclude that the presence of fish can be excluded as the general factor explaininll the occurrence or absence of large zooplankton in alpine lakes. Levels of chlo• rophyll a and POC best distinguished lakes with Daphnia from lakes withoul Daphnia. In 8 out of 12 lakes sexual Daphnia were more abundant than asexual individuals. Clonal diversity ranged from 0.01 to 1.3 but was not related to the proportion of sexual individuals. The ability to create resting stages may be ari essential factor for the maintenance of genetic diversity and the long-term persistence of Daphnia and other zooplankton taxa. water samples; Regula Illi for identifying the rotifers; and Bet• tina Wagner, Christine Dambone, and Barbara Keller for laboratory assistance. Sabine Giessler and Klaus Schwenk assisted with Daphnia identification. Jan Fott and Andrew Bohonac provided useful comments on an earlier version of this manuscript.

Evolutionary and ecological consequences of interspecific hybridization in cladocerans

Experientia, May 1, 1995

The evolutionary process of interspecific hybridization in cladocerans is reviewed based on ecolo... more 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 the D. 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.

Author response for "Environmentally independent selection for hybrids between divergent freshwater stickleback lineages in semi‐natural ponds

Überdüngung verändert die Daphniengemeinschaft

EGRAS (ecological grassland simulator) opnieuw geprogrammeerd en bewerkt voor de PC

Dit rapport is het vijfde in een serie doctoraatverslagen, waarin de ontwikkeling van het begrazi... more Dit rapport is het vijfde in een serie doctoraatverslagen, waarin de ontwikkeling van het begrazingsmodel "EGRAS" (Ecological GRAssland Simulator) beschreven is. Dit model simuleert de groei van de vegetatie onder invloed van begrazing door pinken op de Schildhoek en Pampusplaat in het Lauwersmeergebied. Friso en van Esch (1983) ontwikkelden een wiskundig model bestaande uit de submodellen: Groei, Consumptie, Sterfte, Vergaan en Vestiging. Loonen en Moesker (1985) breidden dit model verder uit en maakten het "computeroperabel" d.m.v. een Pascal programma dat op de Groningse "CYBER" draaide. Hutjes (1987) verzamelde gegevens over decompositie en verwerkte die met de gegevens van do Leeuw in een nieuw sub-model voor de stikstofkringloop. Tevens verscheen in 1987 een artikel van Fresco et al. Zij beschreven het model met nieuwe, Engelse namen voor de variabelen en gebruikten het model om de invloed van grotere begrazingsdruk op de vegetatie te onderzoeken. Het voorgaande laat zien dat er al veel over het model "EGRAS" geschreven is. Het hoofddoel van dit onderzoek was het opnieuw programmeren van het model "EGRAS" voor de PC. Leidraad hierbij was het artikel van Fresco et al. (1987) . De door hen geintroduceerde naamgeving van parameters en variabelen is gevolgd. Voor de precieze invulling van procedures is, waar nodig, teruggevallen op het verslag en de listing van het programma van Loonen en Moesker (1985). Voor de modellering van de stikstofkringloop is gebruik gemaakt van het programma van Ronald Hutjes (1987). De Leeuw en Hutjes hebben het decompositieproces in het proefgebied uitvoerig beschreven en gemodelleerd. Ze hebben echter niet de mineralisatie van stikstof onderzocht. Hiervoor was door Loonen en Moesker een constante genaamd “omzetting" in het model ingebouwd. Hutjes verbeterde de modellering van de mineralisatie door de formule van Kemmers en Jansen (1985) in te bouwen. Hierdoor werd de maximale mineralisatiesnelheid vermenigvuldigd met reductie factoren voor temperatuur en vochttoestand. Over de waarde van de maximale mineralisatiesnelheid waren in het gebied geen metingen gedaan.In een zeer beperkt mineralisatie-onderzoek heb ik onderzocht of de K-waarden voor de verschillende vegetatietypen, zoals die door de Leeuw en Hutjes beschreven zijn, verschillen. Deze resultaten zijn verwerkt in de unit Soil.

PERSPECTIVE The ecological forecast horizon, and examples of its uses and determinants

Test of in situ (underwater) automated imaging, as provided by the Scripps Plankton Camera, for monitoring and analysis of lake phytoplankton

Test of in situ (underwater) automated imaging, as provided by the Scripps Plankton Camera, for m... more

Eco-Evolutionary Dynamics in Freshwater Systems

Elsevier eBooks, 2022

There is an increasing recognition that evolutionary dynamics may occur at timescales that are su... more There is an increasing recognition that evolutionary dynamics may occur at timescales that are sufficiently rapid to impact ecological responses to environmental change and influence ecological dynamics. In the development of the emerging paradigm of eco-evolutionary dynamics, studies of freshwater organisms have been very important. Here we highlight a number of key observations and achievements, and point to remaining challenges.

Ecology and genetics of interspecific hybridization in Daphnia

Birkhäuser Basel eBooks, 1997

A central question in evolutionary biology concerns the ecological and genetic processes by which... more A central question in evolutionary biology concerns the ecological and genetic processes by which species hybridize. We analyze the evolutionary consequences of hybridization, biogeographic patterns and fitness comparisons in the crustacean Daphnia (Branchiopoda) within the conceptual framework of theories on interspecific hybridization. In contrast to most cases of hybridization among animals, Daphnia species and hybrids do not form interpopulational transition

Infection by a eukaryotic gut parasite in wild <i>Daphnia</i> sp. associates with a distinct bacterial community

bioRxiv (Cold Spring Harbor Laboratory), Feb 26, 2022

Host-associated bacterial communities can play an important role in host fitness and resistance t... more Host-associated bacterial communities can play an important role in host fitness and resistance to diseases. Yet, few studies have investigated tripartite interaction between a host, parasite and hostassociated bacterial communities in natural settings. Here, we use 16S amplicon sequencing to compare gut-and body-bacterial communities of wild water fleas belonging to the Daphnia longispina complex, between uninfected hosts and those infected with the common and virulent eukaryotic gut parasite Caullerya mesnili (Family: Ichthyosporea). We report community-level changes in host-associated bacteria with the presence of the parasite infection; namely decreased alpha diversity and increased beta diversity at the site of infection, i.e. host gut (but not host body). We also report decreased abundance of bacterial taxa proposed elsewhere to be beneficial for the host, and an appearance of taxa specifically associated with infected hosts. Our study highlights the hostmicrobiota-infection link in a natural system and raises questions about the role of host-associated microbiota in natural disease epidemics as well as the functional roles of bacteria specifically associated with infected hosts.

Effects of antropogenic pollution on host parasite interactions

Fewer non‐native insects in freshwater than in terrestrial habitats across continents

Diversity and Distributions, Sep 9, 2022

This is an open access article under the terms of the Creative Commons Attribution License, which... more

The distribution and spread of quagga mussels in perialpine lakes north of the Alps

Aquatic Invasions, 2022