Population genetic structure of a planktonic diatom in the Gulf of naples : <i>Pseudo-nitzschia multistriata</i>

The planktonic diatom Pseudo-nitzschia multistriata appeared in plankton samples taken at the MareChiara station in the Gulf of Naples in 1995 and has appeared ever since in autumn, and since 2004 also in summer. This thesis focuses on population genetic structure of the species using the Internal Transcribed Spacers in the rDNA as well as seven polymorphic microsatellites.Cells isolated from plankton samples taken in 2008 and 2009 were grown into strains from which ITS-sequences and microsatellite fingerprints were gathered. Microsatellite screening uncovered two populations in sympatry in 2008, only one of which reappeared in 2009. The ITS sequences of the strains were of distinct types,called A-type, B-type and a mixed type (NB). The two populations also showed distinct ITS-type proportions, supporting their distinctness. Intra-population proportions of ITS-types among strains were similar in summer and autumn 2009,indicating stability over the growth season. But proportions differed between 2008 and 2009, suggesting substantial immigration the second year. These results suggest that, P. multistriata in the Mediterranean consists of a dynamic patchwork of populations.Microsatellite inheritance was studied over the vegetative and sexual parts of the biennial life cycle of P. multistriata. Substitutions were recorded in strains rescreened after several months of maintenance. Longer microsatellites changed more frequently than shorter ones and di-nucleotide ones more than tri-nucleotide ones.Strains interbred independently from population assignment. Comparisons of parental and offspring genotypes showed microsatellite inheritance patterns generally following Mendelian rules. Genetic identity of sister cells emerging from zygotes formed on the same parental gametangia indicate that one of the two nuclei resulting from the first meiotic division is eliminated. Each maternal gamete fuses with a paternal gamete, resulting in two zygotes, which, in this case, were genotypically identical. Thus, mutations boost allele diversity and biennial sexual reproduction boosts ITS-genotype variability and genotypic diversity

Mendelian Inheritance Pattern and High Mutation Rates of Microsatellite Alleles in the Diatom Pseudo-nitzchia multistriata

The diatom Pseudo-nitzschia multistriata exhibits a diplontic life cycle composed of an extensive phase of vegetative cell division and a brief phase of sexual reproduction. To explore genotypic stability, we genotyped seven polymorphic microsatellite loci in 26 monoclonal strains over 3–16 months in a culture maintenance regime. Moreover, to assess inheritance patterns of the microsatellite alleles, we genotyped 246 F1 strains resulting from four mating experiments between parental strains of know genotype. Results generally conformed expectations according to Mendelian inheritance patterns, but deviations were detected indicating mutations during sexual reproduction. A total of forty-two mutations were detected in the clonal cultures over time. Microsatellites with more core-repeats accumulated mutations faster. The mutation rate varied significantly across loci and strains. A binomial mass function and a computer simulation showed that the mutation rate was significantly higher during the first months of culture (μ≈3×10-3 per locus per cell division) and decreased to μ≈1×10-3 in the strains kept for 16 months. Our results suggest that genetic mutations acquired in both the vegetative phase and sexual reproduction add to the allelic diversity of microsatellites, and hence to the genotypic variation present in a natural population

Ice Nucleation Activity and Aeolian Dispersal Success in Airborne and Aquatic Microalgae

Microalgae are common members of the atmospheric microbial assemblages. Diverse airborne microorganisms are known to produce ice nucleation active (INA) compounds, which catalyze cloud and rain formation, and thus alter cloud properties and their own deposition patterns. While the role of INA bacteria and fungi in atmospheric processes receives considerable attention, the numerical abundance and the capacity for ice nucleation in atmospheric microalgae are understudied. We isolated 81 strains of airborne microalgae from snow samples and determined their taxonomy by sequencing their ITS markers, 18S rRNA genes or 23S rRNA genes. We studied ice nucleation activity of airborne isolates, using droplet freezing assays, and their ability to withstand freezing. For comparison, we investigated 32 strains of microalgae from a culture collection, which were isolated from polar and temperate aqueous habitats. We show that ∼17% of airborne isolates, which belonged to taxa Trebouxiphyceae, Chlorophyceae and Stramenopiles, were INA. A large fraction of INA strains (over 40%) had ice nucleation activity at temperatures ≥-6°C. We found that 50% of aquatic microalgae were INA, but the majority were active at temperatures &lt;-12°C. Most INA compounds produced by microalgae were proteinaceous and associated with the cells. While there were no deleterious effects of freezing on the viability of airborne microalgae, some of the aquatic strains were killed by freezing. In addition, the effect of desiccation was investigated for the aquatic strains and was found to constitute a limiting factor for their atmospheric dispersal. In conclusion, airborne microalgae possess adaptations to atmospheric dispersal, in contrast to microalgae isolated from aquatic habitats. We found that widespread taxa of both airborne and aquatic microalgae were INA at warm, sub-zero temperatures (&gt;-15°C) and may thus participate in cloud and precipitation formation

Dispersal in a changing world: opportunities, insights and challenges

Abstract It has been long recognised that dispersal is an important life-history trait that plays a key role in the demography and evolution of populations and species. This then suggests that dispersal play a central role in the response of populations and species to ever-increasing global change, including climate change, habitat loss and fragmentation, and biological invasions. During a symposium held at Lund University (Sweden), the causes and consequences of dispersal were discussed, and here we provide an overview of the talks. As the discussions often gravitated towards the role and our understanding of dispersal in a changing world and given the urgent challenges posed by it, we place this overview in the context of global change. We draw and discuss four conclusions: (i) methodological advances provide opportunities for improved future studies, (ii) dispersal distances can be much greater than previously thought (examples in plants and vertebrates), but also much more restricted (examples in micro-organisms), (iii) dispersal is more dynamic than we often care to admit (e.g. due to individual variation, effects of parasites, variation in life history, developmental and evolutionary responses, community impacts), (iv) using results of dispersal research for detailed prediction of outcomes under global change is currently mostly out of reach – nevertheless, that should not stop us from showing the many negative consequences of global change, and how dispersal is often a limiting factor in adapting to this.This work has been supported by a Linnaeus grant to the Centre for Animal Movement Research (CAnMove) from the Swedish Research Council (349-2007-8690) and Lund University.Peer Reviewe

Applying landscape genetics to the microbial world

Landscape genetics, which explicitly quantifies landscape effects on gene flow and adaptation, has largely focused on macroorganisms, with little attention given to microor- ganisms. This is despite overwhelming evidence that microorganisms exhibit spatial genetic structuring in rela- tion to environmental variables. The increasing accessi- bility of genomic data has opened up the opportunity for landscape genetics to embrace the world of microorgan- isms, which may be thought of as ‘the invisible regula- tors’ of the macroecological world. Recent developments in bioinformatics and increased data accessibility have accelerated our ability to identify microbial taxa and characterize their genetic diversity. However, the influ- ence of the landscape matrix and dynamic environmental factors on microorganism genetic dispersal and adapta- tion has been little explored. Also, because many microorganisms coinhabit or codisperse with macroorgan- isms, landscape genomic approaches may improve insights into how micro- and macroorganisms recipro- cally interact to create spatial genetic structure. Conduct- ing landscape genetic analyses on microorganisms requires that we accommodate shifts in spatial and tem- poral scales, presenting new conceptual and methodologi- cal challenges not yet explored in ‘macro’-landscape genetics. We argue that there is much value to be gained for microbial ecologists from embracing landscape genetic approaches. We provide a case for integrating landscape genetic methods into microecological studies and discuss specific considerations associated with the novel challenges this brings. We anticipate that microor- ganism landscape genetic studies will provide new insights into both micro- and macroecological processes and expand our knowledge of species’ distributions, adaptive mechanisms and species’ interactions in chang- ing environments

Population genetic structure of a planktonic diatom in the Gulf of naples : Pseudo-nitzschia multistriata

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Description of Limnomonas gen. nov., L. gaiensis sp. nov. and L. spitsbergensis sp. nov. (Chlamydomonadales, Chlorophyta)

Two novel Chlamydomonas-like species, belonging to the Moewusii clade, have been de-scribed. The first species inhabits eutrophic and neutral to basic pH waters in Sweden and England. It is easily recognizable under a light microscope due to its morphology (a small green prolate spheroidal shape with a large and truncated papilla at its anterior end, two equal flagella, a single lateral eyespot, a basal nucleus, and a well-defined pyrenoid) and to its peculiar whole-body pen-dulum movement while resting on surfaces or attached to floating particles. The species occurs as free-living individuals and is able to gather temporarily into groups of individual cells. No particular binding structures or palmelloid cells were observed in cultures. The second species, previously assigned to Chlamydomonas cf. proboscigera, was collected from persistent snow in Svalbard, Norway. Its morphology is revised herein. Using SSU rDNA sequence analyses, these two species formed a well-supported clade. Moreover, ITS-2 secondary structure analyses confirmed sexual incompatibility between these biological species. Considering these results, a new genus Limnomonas and its type species L. gaiensis and L. spitsbergensis are proposed

Population connectivity, dispersal, and swimming behavior in Daphnia

The water flea Daphnia has the capacity to respond rapidly to environmental stressors, to disperse over large geographical scales, and to preserve its genetic material by forming egg banks in the sediment. Spatial and temporal distributions of D. magna have been extensively studied over the last decades using behavioral or genetic tools, although the correlation between the two has rarely been the focus. In the present study, we therefore investigated the population genetic structure and behavioral response to a lethal threat, ultraviolet radiation (UVR), among individuals from two different water bodies. Our results show two genetic populations with moderate gene flow, highly correlated with geographical location and with inheritable traits through generations. However, despite the strong genetic differences between populations, we show homogeneous refuge demand between populations when exposed to the lethal threat solar UVR

Ice nucleation activity and aeolian dispersal success in airborne and aquatic microalgae

Microalgae are common members of the atmospheric microbial assemblages. Diverse airborne microorganisms are known to produce ice nucleation active (INA) compounds, which catalyze cloud and rain formation, and thus alter cloud properties and their own deposition patterns. While the role of INA bacteria and fungi in atmospheric processes receives considerable attention, the numerical abundance and the capacity for ice nucleation in atmospheric microalgae are understudied. We isolated 81 strains of airborne microalgae from snow samples and determined their taxonomy by sequencing their ITS markers, 18S rRNA genes or 23S rRNA genes. We studied ice nucleation activity of airborne isolates, using droplet freezing assays, and their ability to withstand freezing. For comparison, we investigated 32 strains of microalgae from a culture collection, which were isolated from polar and temperate aqueous habitats. We show that ∼17% of airborne isolates, which belonged to taxa Trebouxiphyceae, Chlorophyceae and Stramenopiles, were INA. A large fraction of INA strains (over 40%) had ice nucleation activity at temperatures ≥-6°C. We found that 50% of aquatic microalgae were INA, but the majority were active at temperatures -15°C) and may thus participate in cloud and precipitation formation