Karin Rengefors

• PhD
• Professor (Full) at Lund University

The response of microbial communities to long-term environmental change is poorly understood. Here, we study bacterioplankton communities in a unique system of coastal Antarctic lakes that were exposed to progressive long-term environmental change, using 454 pyrosequencing of the 16S rDNA gene (V3-V4 regions). At the time of formation, most of the...

The field of genetic diversity in protists, particularly phytoplankton, is under expansion. However, little is known regarding variation in genetic diversity within populations over time. The aim of our study was to investigate intrapopulation genetic diversity and genetic differentiation in the freshwater bloom-forming microalga Gonyostomum semen...

A fundamental question in ecology is whether microorganisms follow the same patterns as multicellular organisms when it comes to population structure and levels of genetic diversity. Enormous population sizes, predominately asexual reproduction and presumably high dispersal because of small body size could have profound implications on their geneti...

Evolutionary changes in populations of microbes, such as microalgae, cannot be traced using conventional metabarcoding loci as they lack intraspecific resolution. Consequently, selection and competition processes among strains of the same species cannot be resolved without elaborate isolation, culturing, and genotyping efforts. Bamboozle, a new bio...

The study of microbial diversity over time and space is fundamental to the understanding of their ecology and evolution. The underlying processes driving these patterns are not fully resolved but can be studied using population genetic approaches. Here we investigated the population genetic structure of Gonyostomum semen, a bloom-forming phytoplank...

Protists make up the vast diversity of eukaryotic life and play a critical role in biogeochemical cycling and in food webs. Because of their small size, cryptic life cycles, and large population sizes, our understanding of speciation in these organisms is very limited. We performed population genomic analyses on 153 strains isolated from eight popu...

Phytoplankton have short generation times, flexible reproduction strategies, large population sizes and high standing genetic diversity, traits that should facilitate rapid evolution under directional selection. We quantified local adaptation of copper tolerance in a population of the diatom Skeletonema marinoi from a mining-exposed inlet in the Ba...

The evolution of multicellular life has played a pivotal role in shaping biological diversity. However, we know surprisingly little about the natural environmental conditions that favour the formation of multicellular groups. Here we experimentally examine how key environmental factors (predation, nitrogen and water turbulence) combine to influence...

Sequencing of reduced representation libraries enables genotyping of many individuals for population genomic studies. However, high amounts of DNA are required, and the method cannot be applied directly on single cells, preventing its use on most microbes. We developed and implemented the analysis of single amplified genomes (SAGs) followed by rest...

Phytoplankton have short generation times, flexible reproduction strategies, large population sizes, and high standing genetic diversity, traits that should facilitate rapid evolution under directional selection. We quantified local adaptation of copper tolerance in a population of the diatom Skeletonema marinoi from a mining exposed inlet in the B...

Evolutionary changes in populations of microbes, such as microalgae, cannot be traced using conventional metabarcoding loci as they lack intraspecific resolution. Consequently, selection and competition processes amongst strains of the same species cannot be resolved without elaborate isolation, culturing, and genotyping efforts. Bamboozle, a new b...

Resurrection studies can answer some fundamental questions in aquatic ecology and evolutionary biology. For phytoplankton resting stages, longevity of thousands to millions of years has recently been reported. However, contamination during sediment sampling could distort these estimates, and this risk has not been systematically evaluated. Here we...

Marine microorganisms have the potential to disperse widely with few obvious barriers to gene flow. However, among microalgae, several studies have demonstrated that species can be highly genetically structured with limited gene flow among populations, despite hydrographic connectivity. Ecological differentiation and local adaptation have been sugg...

Diel vertical migration (DVM) is the most common behavioral phenomenon in zooplankton, and numerous studies have evaluated DVM under strong seasonality at higher latitudes. Yet, our understanding of the environmental drivers of DVM at low latitudes, where seasonal variation is less pronounced, remains limited. Therefore, we here examined patterns o...

Inland waters receive and process large amounts of colored organic matter from the terrestrial surroundings. These inputs dramatically affect the chemical, physical, and biological properties of water bodies, as well as their roles as global carbon sinks and sources. However, manipulative studies, especially at ecosystem scale, require large amount...

Genetic diversity is the basis for evolutionary adaptation and selection under changing environmental conditions. Phytoplankton populations are genotypically diverse, can become genetically differentiated within small spatiotemporal scales and many species form resting stages. Resting stage accumulations in sediments (seed banks) are expected to se...

Despite widespread metal pollution of coastal ecosystems, little is known of its effect on marine phytoplankton. We designed a co-cultivation experiment to test if toxic dose-response relationships can be used to predict the competitive outcome of two species under metal stress. Specifically, we took into account intraspecific strain variation and...

Microalgal range expansions are increasing in frequency and magnitude but generally remain unnoticed until mass development occurs. Gonyostomum semen is a freshwater raphidophyte that causes nuisance blooms in lakes and has recently expanded its distribution across Europe. G. semen was considered to mainly occur in humic lakes in the boreal region...

A study on the freshwater dinoflagellate (Dinophyceae) of Colombia was carried out based on samples from four swamps, nine reservoirs, a small insular lake, and additional specimens deposited in the phycological collection of Universidad de Antioquia, Colombia, and the collection of Universidad de La Plata, Argentina. For most species, detailed mor...

The bloom‐forming freshwater alga Gonyostomum semen is associated with acidic, mesotrophic brown water lakes in boreal regions. However, researchers have been unable to conclusively link G. semen abundance and bloom formation to typical brown water lake traits, i.e. high water color and DOC (dissolved organic carbon) concentrations. Iron is a main...

Predation is a well‐studied driver of ecological selection on prey traits, which frequently drives divergence in anti‐predator performance across environments that vary in predation risk. However, predation also alters prey mortality regimes, where low predation risk often results in higher prey densities and consequently higher intensities of intr...

Inland waters receive and process large amounts of colored organic matter from the terrestrial surroundings. These inputs dramatically affect the chemical, physical, and biological properties of water bodies, as well as their roles as global carbon sinks and sources. To understand the complex changes associated with allochthonous inputs, experiment...

Species invasion and range expansion are currently under much scrutiny due to increasing anthropogenic impact on the natural environment. This is also true for harmful algal blooms, which have been reported to have increased in frequency. However, this research is challenging due to the ephemeral nature, small size, and mostly low concentrations of...

While lake systems in temperate regions have been extensively studied, tropical and subtropical systems have received less attention. Here, we describe the water chemistry and biota of ten inland blue holes on Andros Island, The Bahamas, representative of the morphological, abiotic, and biotic variation among Androsian inland blue holes. The majori...

Strains of microalgae vary in traits between species and populations due to adaptation or stochastic processes. Traits of individual strains may also vary depending on the acclimatization state and external forces, such as abiotic stress. In this study we tested how metal tolerance differs among marine diatoms at three organizational levels: specie...

Phytoplankton are present in a large variety of aquatic environments, ranging from small freshwater ponds to the oceans. Typically, freshwater and marine species are not closely related, indicating an ancient divergence and that salinity poses a strong dispersal barrier. Here we reveal a common recent origin of two dinoflagellates that are well ada...

The fresh-water cyanobacterium Microcystis is known to form blooms world-wide, and is often responsible for the production of microcystins found in lake water. Microcystins are non-ribosomal peptides with toxic effects, e.g. on vertebrates, but their function remains largely unresolved. Moreover, not all strains produce microcystins, and many diffe...

Crustacean copepods in high-latitude lakes frequently alter their pigmentation facultatively to defend themselves against prevailing threats, such as solar ultraviolet radiation (UVR) and visually oriented predators. Strong seasonality in those environments promotes phenotypic plasticity. To date, no one has investigated whether low-latitude copepo...

The complex evolution of chloroplasts in microalgae has resulted in highly diverse pigment profiles. Freshwater raphidophytes, for example, display a very different pigment composition than marine raphidophytes. To investigate potential differences in the evolutionary origin of chloroplasts in these two groups of raphidophytes, the plastid genomes...

Most microalgal species are geographically widespread, but little is known about how they are dispersed. One potential mechanism for long‐distance dispersal is through birds, which may transport cells internally (endozoochory) and deposit them during, or in‐between, their migratory stopovers. We hypothesize that dinoflagellates, in particular resti...

Whether or not communities of microbial eukaryotes are structured in the same way as bacteria is a general and poorly explored question in ecology. Here, we investigated this question in a set of planktonic lake microbiotas in Eastern Antarctica that represent a natural community ecology experiment. Most of the analysed lakes emerged from the sea d...

Recently radiated dinoflagellates Apocalathium aciculiferum (collected in Lake Erken, Sweden), A. malmogiense (Baltic Sea) and Apocalathium aff. malmogiense (Highway Lake, Antarctica) represent a lineage with an unresolved phylogeny. We determined their phylogenetic relationships using phylotranscriptomics based on 792 amino acid sequences. Our res...

Whether or not communities of microbial eukaryotes are structured in the same way as prokaryotes is a basic and poorly explored question in ecology. Here we investigated this question in a set of planktonic lake microbiotas in Eastern Antarctica that represent a natural community ecology experiment. Most of the analysed lakes emerged from the sea d...

Eukaryotic phytoplankton exhibit an enormous species richness, displaying a range of phylogenetic, morphological and physiological diversity. Yet, until recently, very little was known about the diversity, genetic variation and evolutionary processes within species and populations. An approach to explore this diversity and to understand evolution o...

A number of marine and freshwater harmful algal bloom (HAB) species have colonized new areas and expanded their habitat range in recent years. Nevertheless it is notoriously difficult to establish when colonization first occurred, what the dispersal routes are, and to separate recent invasion from increases in existent but small populations. The fr...

Marine planktonic microalgae have potentially global dispersal, yet reduced gene flow has been confirmed repeatedly for several species. Over larger distances (>200 km) geographic isolation and restricted oceanographic connectivity have been recognized as instrumental in driving population divergence. Here we investigated whether similar patterns,...

In temperate systems, phytoplankton spring blooms deplete inorganic nutrients and are major sources of organic matter for the microbial loop. In response to phytoplankton exudates and environmental factors, heterotrophic microbial communities are highly dynamic and change their abundance and composition both on spatial and temporal scales. Yet, mos...

Aim To test if a phytoplankton bloom is panmictic, or whether geographical and environmental factors cause spatial and temporal genetic structure. Location Baltic Sea. Method During four cruises, we isolated clonal strains of the diatom Skeletonema marinoi from 9 to 10 stations along a 1132 km transect and analysed the genetic structure using eig...

Colonization of new habitats through dispersal of phytoplankton cysts might be limited, if resident populations outcompete invaders during germination. We reciprocally transferred Gonyostomum semen (Raphidophyceae) cysts from three lakes into native and foreign waters originating from the respective habitats. Germination rate and germling growth we...

Gonyostmum semen is a freshwater raphidophyte that has increased in occurrence and abundance in several countries in northern Europe since the 1980s. More recently, the species has expanded rapidly also in north-eastern Europe, and it is frequently referred to as invasive. To better understand the species history, we have explored the phylogeograph...

Figure S1. Bayesian phylogenetic tree of the large subunit of the ribosomal DNA (LSU).

Many recent studies have found genetically differentiated populations in microorganisms despite potentially high dispersal. We designed a study to specifically examine the importance of physical dispersal barriers, i.e. geographic distance and lack of hydrological connectivity, in restricting gene flow and enhancing divergence in limnic microorgani...

Priority effects occur when a species or genotype with earlier arrival has an advantage such that its relative abundance in the community or population is increased compared with later-arriving species. Few studies have dealt with this concept in the context of within-species competition. Skeletonema marinoi is a marine diatom that shows a high deg...

Recent studies show that both marine and limnic microalgal species often consist of several genetically distinct populations. This is also valid for the nuisance freshwater algae Gonyostomum semen, which originates from acidic, brown water swamp lakes, but can nowadays also be found in clearer lakes with close to neutral pH. We hypothesized that th...

Processes of rapid radiation among unicellular eukaryotes are much less studied than among multicellular organisms. We have investigated a lineage of cold-water microeukaryotes (protists) that appear to have diverged recently. This lineage stands in stark contrast to known examples of phylogenetically closely related protists, in which genetic diff...

Colonization of new habitats through dispersal of phytoplankton cysts might be limited, if resident populations outcompete invaders during germination. We reciprocally transferred Gonyostomum semen (Raphidophyceae) cysts from three lakes into native and foreign waters originating from the respective habitats. Germination rate and germling growth we...

Aquatic habitats are usually structured by light attenuation with depth resulting in different microalgal communities, each one adapted to a certain light regime by their specific pigment composition. Several taxa contain pigments restricted to one phylogenetic group, making them useful as marker pigments in phytoplankton community studies. The nui...

Here we investigated whether there is evidence of local adaptation in strains of an ancestrallymarine dinoflagellate to the lacustrine environment they now inhabit(optimal genotypes) and/orif they have evolved phenotypic plasticity (a range of phenotypes). Eleven strains of Polarella glacialis were isolated and cultured from three different environ...

Current sampling of genomic sequence data from eukaryotes is relatively poor, biased, and inadequate to address important questions about their biology, evolution, and ecology; this Community Page describes a resource of 700 transcriptomes from marine microbial eukaryotes to help understand their role in the world's oceans.

Biological invasions often cause major perturbations in the environment and are well studied among macroorganisms. Less is known about invasion by free-living microbes. Gonyostomum semen (Raphidophyceae) is a freshwater phytoplankton species that has increased in abundance in Northern Europe since the 1980's and has expanded its habitat range. In t...

Sterols are a class of membrane-reinforcing, ringed lipids which have a long history of examination in algae as a means of deriving chemotaxonomic relationships and as potential lipidic biomarkers. The Raphidophyceae represent a class of harmful, bloom-forming, marine and freshwater algae. To date, there have been four published examinations of the...

Resting stages (e.g. cysts) play an important role in the life history and ecology of phytoplankton, e.g. the survival, reproduction, genetic recombination, and dispersal of many species. Marine dinoflagellates cysts have been intensively studied by both geologists and biologists, but freshwater cysts have received less attention. There are approxi...

Gonyostomum semen (Ehrenb) Diesing is a bloom-forming and noxious phytoplankton species, that usually occurs in brown-water lakes and which is often referred to as an invasive species. The aim of our study was to analyze changes over time in the occurrence and distribution of blooms, and to find possible drivers of this change. We also performed sp...

The nuisance alga Gonyostomum semen (Raphidophyceae) has expanded in the Nordic countries during the last decades and can dominate lake phytoplankton communities almost completely. A possible explanation to its dominance could be limited grazing by zooplankton. We investigated the potential grazing pressure on G. semen using an experimental approac...

This chapter explains that allelopathy is a complex process involved in the interaction of primary producers with other photosynthetic target organisms. It examines laboratory studies that allow the bioassay-directed fractionation of active compounds. Some of these studies say that environmental factors and the community composition can strongly af...

We tested the effect of the cyanobacterium Gloeotrichia echinulata on a diverse array of phytoplankton. We found that Gloeotrichia increased the growth rates of five of seven phytoplankton species up to 620% in comparison with a medium-only control after 96 h.

This study examined the sterol compositions of 102 dinoflagellates using clustering and cluster validation techniques, as a means of determining the relatedness of the organisms. In addition, dinoflagellate sterol-based relationships were compared statistically to 18S rDNA-based phylogenetic relationships using the Mantel test. Our results indicate...

The chain-forming dinoflagellate Gymnodinium catenatum Graham is responsible for outbreaks of paralytic shellfish poisoning (PSP), a human health threat in coastal waters. Sexuality in this species is of great importance in its bloom dynamics, and has been shown to be very complex but lacks an explanation. For this reason, we tested if unreported h...

Biosurfactants have been suggested as a method to control harmful algal blooms (HABs), but warrant further and more in-depth investigation. Here we have investigated the algicidal effect of a biosurfactant produced by the bacterium Pseudomonas aeruginosa on five diverse marine and freshwater HAB species that have not been tested previously. These i...

Until recently, the evolutionary relationships between marine and freshwater microbes were unclear, but the use of molecular phylogenies is beginning to shed light on this subject. An increasing amount of studies are showing that marine and freshwater microbes (including viruses) are usually not closely related, often grouping into distinct marine...

The relationships among cellular nutrient status, environmental conditions (temperature and nutrient availability), and cyst production were studied in batch cultures of three cold-water dinoflagellates (Scrippsiella hangoei, Gymnodinium corollarium, and Woloszynskia halophila) isolated from the Baltic Sea. We tested the effect of increasing temper...

Little is known about the extent of the genetic diversity and its structuring patterns in protist species living in lakes. Here, we have investigated the genetic diversity patterns within five dinoflagellate species (Peridinium aciculiferum, Peridinium cinctum, Peridiniopsis borgei, Polarella glacialis, Scrippsiella aff. hangoei) that are present i...

Here, we have identified a protist (dinoflagellate) lineage that has diversified recently in evolutionary terms. The species members of this lineage inhabit cold-water marine and lacustrine habitats, which are distributed along a broad range of salinities (0-32) and geographic distances (0-18 000 km). Moreover, the species present different degrees...

The saline lakes of the Vestfold Hills in Antarctica offer a remarkable natural laboratory where the adaptation of planktonic protists to a range of evolving physiochemical conditions can be investigated. This study illustrates how an ancestral marine community has undergone radical simplification leaving a small number of well-adapted species. Our...

The nuisance alga Gonyostomum semen (Raphidophyceae) is known to form dense blooms in many freshwater bodies, and has increased its distribution and abundance. However, information on the mechanisms behind bloom formation and maintenance is scarce. Field observations indicate that G. semen may be favored in humic lakes, In the present study, we per...

This study examined the sterol compositions of 102 dinoflagellates (including several previously unexamined species) using clustering techniques as a means of determining the relatedness of the organisms. In addition, dinoflagellate sterol-based relationships were compared statistically to dinoflagellate 18S rDNA-based phylogeny relationships using...

We have constructed extensive 18S-28S rDNA dinoflagellate phylogenies (>200 sequences for each marker) using Maximum Likelihood and Bayesian Inference to study the evolutionary relationships among marine and freshwater species (43 new sequences). Our results indicated that (a) marine and freshwater species are usually not closely related, (b) sever...

The dinoflagellate Peridinium aciculiferum forms blooms underneath the ice in temperate lakes and has previously been shown to have an allelopathic effect on a natural competitor as well as being haemolytic. Hence, we investigated whether P. aciculiferum is allelopathic towards a wide range of different freshwater phytoplankton species. We also tes...

The agents driving the divergence and speciation of free-living microbial populations are still largely unknown. We investigated the dinoflagellate morphospecies Scrippsiella hangoei and Peridinium aciculiferum, which abound in the Baltic Sea and in northern temperate lakes, respectively. Electron microscopy analyses showed significant interspecifi...