Biology subjects

Spaak, P.

Publications and source records attributed to Spaak, P..

7 recordsLinked to original sources

bioRxiv2026

Rapid shallow-water saturation and deep-water expansion of an invasive freshwater ecosystem engineer in a deep European lake

Quagga mussels (Dreissena rostriformis bugensis) are ecosystem engineers that can alter nutrient cycling, benthic-pelagic coupling, and food-web structure in deep lakes. Although their invasion trajectories are well documented in the Laurentian Great Lakes in North America, depth-specific population dynamics remain poorly resolved in recently invaded European perialpine lakes. We analyzed five annual lake-wide surveys (2021-2025) from 54 stations spanning 2.4-253 m depth in Lake Constance to quantify changes in quagga mussel density, biomass, and shell-length distribution. Contrary to expectations of lake-wide exponential growth, shallow-water populations (< 20 m) showed no significant increase during the study period and appear to have reached carrying capacity before monitoring began. In contrast, densities increased monotonically at intermediate depths (40-125 m), indicating ongoing expansion into deeper strata. Mean shell length declined with depth, and size distributions in shallow waters shifted toward larger individuals, consistent with a transition from active recruitment to somatic growth of established mussels. Compared with the Laurentian Great Lakes, Lake Constance already has substantially higher shallow-water biomass, whereas deeper invasion trajectories are broadly similar. These results show that quagga mussel invasion in deep European lakes can combine rapid littoral saturation with slower profundal expansion, complicating direct transfer of predictions from the Great Lakes. Continued depth-stratified monitoring will be essential for anticipating future ecosystem effects in perialpine lakes.

ecology↗

bioRxiv2026

Host outnumbered: microbiomes and a fungal parasite interact to shape host genotype-dependent survival

Microbiomes are key determinants of host health, yet empirical evidence demonstrating their influence on host-parasite interactions is limited. We conducted a proof-of-principle experiment using the water flea Daphnia magna and its virulent yeast para-site Australozyma monospora (formerly Metschnikowia bicuspidata) to test if micro-biome composition alters infection outcomes. Axenic hosts were inoculated with a control microbiome (homogenates of laboratory-cultured Daphnia reared in natural freshwater) or a single bacterial strain (Rhizobium sp.), and exposed to the parasite. Host survival differed markedly between microbiome treatments and depended on parasite exposure. Prior to parasite exposure, hosts of one genotype exhibited high juvenile mortality when inoculated with the control microbiome (79%), compared to Rhizobium (19%) (the other genotype: 48% vs. 50%). Parasite exposure reduced survival, but the extent varied with microbiome composition: survival of hosts with a control microbiome (averaged across genotypes) declined from 66% to 0%; survival of those inoculated with Rhizobium sp. declined from 35% to 10%. In contrast, micro-biome composition did not influence parasite infectivity or net reproduction. Our results indicate that microbiome effects on host survival are genotype- and life-stage-dependent, differ between parasite-free and parasite-exposed conditions and may impact host-parasite dynamics primarily by influencing host viability rather than para-site performance.

ecology↗

bioRxiv2024

Terrestrial herbivory drives adaptive evolution in an aquatic community via indirect effects

Indirect ecological effects, which occur when the impact of one species on another is mediated by a third species or the shared environment, are ubiquitous in nature. Given the complexity of natural systems, indirect ecological effects were thought to be important in driving eco-evolutionary processes across community boundaries. However, we know remarkably little about such effects. Here we show that indirect effects of terrestrial insect (aphids) herbivory on macrophytes (duckweed) drives adaptive evolution of water fleas (Daphnia) in large outdoor aquatic mesocosms. Aphid herbivory reduced macrophyte growth and increased the abundance of phytoplankton, which in turn increased the abundance of Daphnia. Whole genome pool sequencing and phenotypic assays revealed an impact on the genetic compositions of the Daphnia populations and transplant experiments indicated that these evolutionary changes were adaptive. Furthermore, these changes in the aquatic community altered the interactions of the aphids and the macrophytes. These results demonstrate that indirect ecological effects can shape eco-evolutionary interactions between different communities.

evolutionary biology↗

bioRxiv2024

Zooplankton bacterial communities are influenced by infection status, environmental conditions and diet quantity across natural epidemics

Zooplankton-associated microbiomes play an important role for host health and contribute to ecosystem processes such as nutrient cycling. Yet, few studies have assessed how environmental gradients and biotic interactions, including parasitism and diet, may shape the microbiome composition of wild zooplankton. Here, we analysed the microbiomes of water fleas from the Daphnia longispina species complex using 16S rRNA gene sequencing and a long-term field dataset spanning six sampling events over 13 years. Sampling coincided with outbreaks of the virulent eukaryotic gut parasite Caullerya mesnili. Additionally, we explored how microbiome structure varied in relation to water parameters, phytoplankton density (i.e. Daphnia diet), and zooplankton density and community structure. Daphnia microbiomes displayed strong temporal variation, and comparatively small differences based on host infection status. Microbiome beta diversity correlated with phytoplankton density but not with its community composition, including green algae, protists and cyanobacteria. Environmental conditions, including temperature, dissolved oxygen and cyanobacterial abundance - previously found to drive Caullerya epidemics - were also associated with distinct microbiome structures. Importantly, microbiome beta diversity co-varied with infection prevalence, suggesting a link between microbiome shifts, epidemic size, and environmental conditions driving large epidemics. Dominant bacterial taxa correlated with Daphnia density, whereas the phylogenetic composition of rare taxa was associated with total zooplankton density. These findings demonstrate the dynamic nature of Daphnia microbiomes and suggest potential mechanisms by which they may mediate disease dynamics, particularly through associations with diet quantity, temperature, and host population density.

ecology↗

bioRxiv2022

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

AimBiological invasions are a major threat to biodiversity in both aquatic and terrestrial habitats. Insects represent an important group of species in freshwater and terrestrial habitats, and they constitute a large proportion of non-native species. However, while many non-native insects are known from terrestrial ecosystems, it remains unclear how they are represented in freshwater habitats. Comparisons of the richness of invaders relative to the richness of native species between freshwater and terrestrial habitats are scarce, which hinders syntheses of invasion processes. Here, we used data from three regions on different continents to determine whether non-native insects are under- or overrepresented in freshwater compared to terrestrial assemblages. LocationEurope, North America, New Zealand MethodsWe compiled a comprehensive inventory of the native and non-native insect species established in freshwater and terrestrial habitats of the three study regions. We then contrasted the richness of non-native and native species among freshwater and terrestrial insects for all insect orders in each region. Using binomial regression, we analysed the proportions of non-native species in freshwater and terrestrial habitats across the three regions. ResultsIn most insect orders living in freshwater, non-native species were under-represented, while they were over-represented in a number of terrestrial orders. This pattern occurred in purely aquatic orders as well as in orders with both freshwater and terrestrial species. Overall, the proportion of non-native species was significantly lower in freshwater than in terrestrial species. Main conclusionsDespite the numerical and ecological importance of insects among all non-native species, non-native insect species are surprisingly rare in freshwater habitats, and this pattern is consistent across the three investigated study regions. We briefly review hypotheses concerning species traits and invasion pathways that are most likely to explain these patterns. Our findings contribute to a growing appreciation of drivers and impacts of biological invasions.

ecology↗

bioRxiv2022

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

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 host-associated 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 host-microbiota-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.

ecology↗

bioRxiv2018

High dispersal levels and lake warming are emergent drivers of cyanobacterial community assembly over the Anthropocene

Disentangling the relative importance of deterministic and stochastic processes in shaping natural communities is central to ecology. Studies on community assembly over broad temporal and spatial scales in aquatic microorganisms are scarce. Here, we used 16S rDNA sequence data from lake sediments to test for community assembly patterns in cyanobacterial phylogenies across ten European peri-Alpine lakes and over a century of eutrophication and climate warming. We studied phylogenetic similarity in cyanobacterial assemblages over spatial and temporal distance, and environmental gradients, comparing detected patterns with theoretical expectations from deterministic and stochastic processes. We found limited evidence for deviation of lake communities from a random assembly model and no significant effects of geographic distance on phylogenetic similarity, suggesting no dispersal limitation and high levels of stochastic assembly. We did not detect a significant effect of phosphorus and nitrogen levels on deviation of community phylogenies from random. We found however a significant decay of phylogenetic similarity for non-random communities over a gradient of air temperature and water column stability. We show how phylogenetic data from sedimentary archives can improve our understanding of microbial community assembly processes, and support previous evidence that climate warming has been the strongest environmental driver of cyanobacterial community assembly over the Anthropocene.

ecology↗