Biology subjects

Berger, S. A.

Publications and source records attributed to Berger, S. A..

5 recordsLinked to original sources

bioRxiv2026

Lake ecosystem responses to runoff variability across time and space

Inland waters in the Northern Hemisphere are experiencing increased annual runoff due to higher overall precipitation as well as intensified short-term events such as heavy rainfall, floods and storms. These events affect the total loading and variability of inputs of allochthonous, coloured dissolved organic matter (cDOM) and inorganic nutrients into lakes. Previous studies have shown that increased total cDOM and inorganic nutrient loads affect phytoplankton biomass and metabolic rates, but it is unknown how the effects of different cDOM and nutrient pulse scenarios are modified by spatial and seasonal differences in lake characteristics. Here, we conducted a coordinated, standardized mesocosm experiment across three lakes with different ambient cDOM and nutrient concentrations. In two of these lakes, the experiment was implemented in two seasons. The same total amounts of cDOM, nitrate and phosphate were added to all mesocosms, but in pulses that differed in intensity and frequency. We found that pulse intensity and frequency affected chlorophyll a and phycocyanin concentrations and metabolic rates, i.e. gross primary production and respiration, differently. Specifically, more pronounced effects were found in response to the extreme pulse scenario compared to those with more frequent, smaller pulse additions. Furthermore, the effects were mainly temporary and varied more among lakes than between seasons. The clearest differences between the extreme and more gradual runoff scenarios were found in the lake with the lowest background cDOM and nitrate concentrations, likely because lower light limitation and possibly stronger initial N-limitation caused a faster response to the nutrient addition. Our results highlight that both antecedent lake conditions and characteristics of runoff events can affect phytoplankton biomass and metabolic rates and that comparative experimental approaches are needed to reveal the complexity of the responses.

ecology↗

bioRxiv2025

Analysis of microalgae autofluorescence using full-spectrum cytometry to discriminate and monitor microalgae and bacteria

AbstractThe autofluorescence of algal pigments allows for non-invasive, high-throughput characterization of microalgae at a single-cell resolution. We applied full-spectrum cytometry, imaging flow cytometry, and cell sorting to analyze the spectral and morphological diversity among major microalgal groups and 102 Chlorophyta strains. The distinct spectral signatures from chlorophylls, carotenoids, and phycobiliproteins enabled us to achieve taxonomic resolution with clear separation of phycobiliprotein-containing taxa. Furthermore, principal component analysis of Volvocales revealed three spectral clusters supported by corresponding differences in cell size and shape. Additionally, in Gonium cultures, we observed that spectral signatures in the yellow-green region were altered by bacterial presence, suggesting that interactions between algal host and bacteria affect pigment-related fluorescence. Spectral heterogeneity observed within monocultures was linked to pigment accumulation, cell size, and morphological variability. These findings establish full-spectrum cytometry as a powerful method for profiling pigment composition, physiology, and structural diversity in microalgae, with broad applications in microbial ecology, environmental monitoring, and biotechnology.

microbiology↗

bioRxiv2023

Synergistic effects of predation and parasitism on competition between edible and inedible phytoplankton

Fungi can affect aquatic ecosystems through syntrophic and parasitic interactions with other organisms and organic matter. In pelagic systems, fungal parasites on phytoplankton can control trophic interactions and food-web dynamics, e.g., zooplankton grazing on fungal parasite zoospores creates an alternative energy pathway (termed "mycoloop") from otherwise inedible phytoplankton species. We aim to investigate how the mycoloop influences community dynamics in aquatic food-webs combining experimental and modelling approaches. We assembled an experimental system consisting of an inedible (host) phytoplankton species and its parasitic chytrid, an edible (non-host) phytoplankton species, and a zooplankton grazer. Chytrids parasitizing increased edible phytoplankton abundance, while zooplankton grazing decreased edible phytoplankton abundance. In the presence of zooplankton and chytrids, competition effects between edible and inedible phytoplankton species depended on nutrient levels. At high nutrient levels, competition was balanced by an indirect positive chytrid effect and negative zooplankton grazing effects on edible phytoplankton. In contrast, at low nutrient levels, we found chytrid had a negative impact on edible phytoplankton synergistically with zooplankton. Mathematical investigations suggest that the synergistic effect can be caused by the mycoloop. This indicates that the mycoloop substantially affects predator-prey interactions and phytoplankton competition with yet unknown ecological consequences.

ecology↗

bioRxiv2022

The influence of movement-related costs when searching to act and acting to search

Real world search behaviour often involves limb movements, either during search or following search. Here we investigated whether movement-related costs influence search behaviour in two kinds of search tasks. In our visual search tasks, participants made saccades to find a target object among distractors and then moved a cursor, controlled by the handle of a robotic manipulandum, to the target. In our manual search tasks, participants moved the cursor to perform the search, placing it onto objects to reveal their identity as either a target or a distractor. Across experiments, we manipulated either the effort or time costs associated with movement such that these costs varied across the search space. We varied effort by applying different resistive forces to the handle and we varied time costs by altering the speed of the cursor. Our analysis of cursor and eye movements during manual and visual search, respectively, showed that effort influenced manual search but did not influence visual search. In contrast, time costs influenced both visual and manual search. Our results demonstrate that, in addition to perceptual and cognitive factors, movement-related costs can also influence search behaviour. Public Significance StatementMany of the tasks we perform on a daily basis involve searching for targets. Numerous studies have investigated perceptual and cognitive factors that influence decisions about where to search. However, few studies have examined how search is influenced by movement-related costs associated with manual search (e.g., opening drawers to find a corkscrew) or acting on an object once it has been located (e.g., reaching for a particular bottle of wine once it has been spied in a rack). We show that movement effort and time costs associated with manual search, and time costs associated with moving after visual search, can influence decision-making about where to search over time.

neuroscience↗

bioRxiv2022

From microbes to mammals: pond biodiversity homogenization across different land-use types in an agricultural landscape

Local biodiversity patterns are expected to strongly reflect variation in topography, land use, dispersal boundaries, nutrient supplies, contaminant spread, management practices and other anthropogenic influences. In contrast, studies focusing on specific taxa revealed a biodiversity homogenization effect in areas subjected to long-term intensive industrial agriculture. We investigated whether land use affects biodiversity and metacommunity structure in 67 kettle holes (KH) representing small aquatic islands embedded in the patchwork matrix of a largely agricultural landscape comprising grassland, forest, and arable fields. These KH, similar to millions of standing water bodies of glacial origin, spread across northern Europe, Asia, and North America, are physico-chemically diverse, differ in the degree of coupling with their surroundings. We assessed biodiversity patterns of eukaryotes, Bacteria and Archaea in relation to environmental features of the KH, using deep-amplicon-sequencing of eDNA. First, we asked whether deep sequencing of eDNA provides a representative picture of KH biodiversity across the three domains of life. Second, we investigated if and to what extent KH biodiversity is influenced by the surrounding land-use. Our data shows that deep eDNA amplicon sequencing is useful for in-depth assessments of cross-domain biodiversity comprising both micro- and macro-organisms, but, has limitations with respect to single-taxa conservation studies. Using this broad method, we show that sediment eDNA, integrating several years to decades, depicts the history of agricultural land-use intensification. The latter, coupled with landscape wide nutrient enrichment (including by atmospheric deposition), groundwater connectivity between KH and organismal movement in the tight network of ponds, resulted in a biodiversity homogenization in the KH water, levelling off todays detectable differences in KH biodiversity between land-use types.

ecology↗