Biology subjects

Kauserud, H.

Publications and source records attributed to Kauserud, H..

14 recordsLinked to original sources

bioRxiv2026

Arthropod succession from deadwood to soil: increasing diversity and transitions between major forest substrates

Deadwood is a common ephemeral resource in boreal forests, but arthropod succession across the full decay gradient and transition into soil remains poorly understood. We analyzed the successional trajectory of arthropods in deadwood to soil. Further, we investigated whether the succession pattern differed in previously clear-cut and near-natural forests in southeastern Norway. This was done by DNA metabarcoding analyses of arthropod communities in collected deadwood and soil samples. We detected 741 arthropod OTUs, with 565 OTUs in deadwood and 291 in organic soil layers, of which 115 were found in both deadwood and organic soil layers. Arthropod richness increased with deadwood decay stage and organic soil layers supported higher richness than all deadwood decay stages. Community composition of arthropods changed significantly along the decay gradient, with late-decay stages sharing more OTUs with organic soil layers than with earlier decay stages. This suggests a gradual transition between communities in highly decayed deadwood and organic soil layers. Forest type (previously clear-cut vs. near-natural forest) had limited effects on overall richness and community composition, although previously clear-cut and near-natural forests supported partially distinct species pools and differed in co-occurrence patterns in late decay and organic soil layers. Our results show that arthropod communities are strongly structured along the decay gradient from freshly dead wood to organic soil layers. This highlights the importance of retaining deadwood across different decay stages for maintaining arthropod diversity and community convergence between deadwood and soil in boreal forests.

ecology↗

bioRxiv2026

Phenotypic Variation Reveals Contrasting Ecological Strategies in Wood-Decay Fungal Ecotypes Across a Hybrid Zone

Fungi play central roles in terrestrial ecosystem functioning and are the major decomposers of dead wood in forest systems. Wood decay fungi are adapted to growth and decay under different environmental conditions, but we have limited insight into the intraspecific variability in fungal growth and decay. In Fennoscandia, there are two genetically and ecologically distinct ecotypes of the wood-decay fungus Meruliopsis taxicola: a northern Continental ecotype associated with Norway spruce (Picea abies) growing in moist old-growth forests, and a southern Coastal ecotype growing on Scots pine (Pinus sylvestris) in harsher habitats. The two ecotypes hybridize in a narrow contact zone running through Fennoscandia. Here, we investigate the level of adaptation the two ecotypes show in phenotypic traits, and how hybrid isolates perform as compared with the parental genotypes. We performed in vitro experiments to quantify mycelial growth rate under varying temperature and drought conditions, as well as decomposition of the two substrates, Scots pine and Norway spruce. Isolates of the Continental ecotype exhibited generally higher growth rates in all environments and caused higher mass loss of both substrates. This is consistent with a more competitive life history strategy in the Continental ecotype, whereas Coastal isolates showed adaptions indicative of greater stress tolerance. Hybrid isolates displayed largely intermediate growth responses relative to the parental ecotypes. Together, these results reveal clear phenotypic divergence between M. taxicola ecotypes consistent with contrasting life-history strategies.

evolutionary biology↗

bioRxiv2026

Long-term shift in community composition of deadwood fungi after clear-cutting

O_LIRising anthropogenic pressures in the 20th century have caused extensive habitat loss and fragmentation, threatening biodiversity across ecosystems worldwide. In the boreal forest of Fennoscandia, clear-cut forestry has been a major driver of these changes, resulting in a fragmented landscape of even-aged forest stands. Several studies in recent years have investigated the effect of habitat fragmentation and loss on fungal communities associated with deadwood, but these have mainly focused on visible sporocarps and mushrooms. The effects of forestry on the whole fungal community within deadwood have not been explored as extensively, and especially not in the context of long-term effects. C_LIO_LIWe investigated the effects of clear-cutting on deadwood-inhabiting fungi in boreal Picea abies forests in Norway using ITS2 metabarcoding of sawdust samples collected from 459 logs distributed across 24 paired near-natural and previously clear-cut plots harvested 50 to 90 years ago. C_LIO_LIWhile the overall fungal richness associated with deadwood was similar between the two management types, community composition differed markedly. Plot-scale fungal diversity was linked to deadwood heterogeneity, and composition of the common species was additionally affected by the living tree structure. Nearly all red-listed species were exclusively found in the near-natural forest plots. These findings demonstrate that clear-cut forestry shifts fungal community structure rather than reducing the total number of species and that rare and common species are structured by different environmental drivers but respond in similar ways to large scale disturbance. C_LIO_LISynthesis: Our results highlight the importance of maintaining structural complexity of deadwood in boreal forests for fungal conservation. We found a consistent relationship between deadwood volumes and heterogeneity, and community diversity and species richness. This relationship was consistent even for previously clear-cut forests, showing that retaining structural heterogeneity in managed ecosystems has a positive impact on species diversity. C_LI

ecology↗

bioRxiv2024

Yeasts prefer daycares and molds prefer private homes

Indoor fungi can cause negative health effects due to the production of toxins or volatiles that trigger the immune system of the occupants. To what degree indoor fungi (mycobiomes) differ between buildings with different usage is poorly known. Here, we compare the indoor mycobiomes in 123 childrens daycare centers and 214 private homes throughout Norway, as revealed by metabarcoding of DNA extracted from dust samples collected by community scientists. Although the fungal richness per se was similar in dust samples from daycares and homes, the fungal community composition differed. Yeast fungi, distributed mainly across the orders Saccharomycetales, Filobasidiales and Tremellales, were proportionally more abundant in the daycares, while filamentous fungi, including spore-producing molds such as Aspergillus, Penicillum and Cladosporium, were relatively more abundant in homes. Number of occupants, which is considerably higher in daycares, correlated significantly with the fungal community shift. We hypothesize that the density of occupants and their age distribution drive the systematic difference of yeasts and filamentous fungi in the two building types. ImportanceWorldwide, people spend most of their time indoors; in their homes, workplaces, schools and daycares. The indoor environment can thus largely influence our health. In this study, we revealed that number of occupants and possibly their age distribution are important explanatory variables for the fungal communities of the indoor environments in homes and daycares. Knowledge of these communities are important for further studies on how fungal diversity affect our health.

microbiology↗

bioRxiv2024

The Ribosomal Operon Database (ROD): A full-length rDNA operon database extracted from genome assemblies

Current rDNA reference sequence databases are tailored towards shorter DNA markers, such as parts of the 16/18S marker or the ITS region. However, due to advances in long-read DNA sequencing technologies, longer stretches of the rDNA operon are increasingly used in environmental sequencing studies to increase the phylogenetic resolution. There is, therefore, a growing need for longer rDNA reference sequences. Here, we present the Ribosomal Operon Database (ROD), which includes eukaryotic full-length rDNA operons fished from publicly available genome assemblies. Full-length operons were detected in 34.1% of the 34,701 examined eukaryotic genome assemblies from NCBI. In most cases (53.1%), more than one operon variant was detected, which can be due to intragenomic operon copy variability, allelic variation in non-haploid genomes, or technical errors from the sequencing and assembly process. The highest copy number found was 5,947 in Zea mays. In total, 453,697 unique operons were detected, with 69,480 operon variant clusters remaining after intragenomic clustering at 99% sequence identity. The operon length varied extensively across eukaryotes, ranging from 4,136 to 16,463 bp, which will lead to considerable PCR bias during amplification of the entire operon. Clustering the full-length operons revealed that the different parts (i.e., 18S, 28S, the hypervariable region V4 of 18S, and ITS) provide divergent taxonomic resolution, with 18S and the V4 region being the most conserved. The Ribosomal Operon Database (ROD) will be updated regularly to provide an increasing number of full-length rDNA operons to the scientific community.

genomics↗

bioRxiv2023

Reticulate evolution and rapid development of reproductive barriers upon secondary contact pose challenges for species delineation in a forest fungus

Reproductive barriers within morphospecies of the mushroom-forming fungi tend to be stronger between sympatric lineages, leading to speculation on whether they are being reinforced by selection against hybrids. In this study we use population genomic analyses together with in vitro crosses of a global sample of the wood decay fungus Trichaptum abietinum to investigate reproductive barriers within this morphotaxon and the processes that have shaped them. Our phylogeographic analyses show that the morphospecies is delimited into six major lineages, one in Asia, two in Europe, and three in North America. The two lineages present in Europe are interfertile and admixed, whereas our crosses show that the North American lineages are reproductively isolated. In Asia a more complex pattern appears, with partial intersterility between multiple sub-lineages that likely originated independently and more recently than the reproductive barriers in North America. We found pre-mating barriers in T. abietinum to be moderately correlated with genomic divergence, whereas fitness of the mated hybrids showed a strong positive correlation with increasing genomic divergence. Genome wide association analyses identified candidate genes with programmed cell death annotations, which are known to be involved in intersterility in distantly related fungi. Our demographic modelling and phylogenetic network analyses suggest that reproductive barriers in Trichaptum abietinum could have been reinforced upon secondary contact between lineages that diverged in allopatry during the Pleistocene glacial cycles. Our combination of experimental and genomic approaches demonstrate how T. abietinum is a tractable system for studying speciation mechanims.

evolutionary biology↗

bioRxiv2022

Beetles provide directed dispersal of viable spores of a keystone wood decay fungus

Wood decay fungi are considered to be dispersed by wind, but dispersal by animals may also be important, and more so in managed forests where dead wood is scarce. We investigated whether beetles could disperse spores of the keystone species Fomitopsis pinicola. Beetles were collected on sporocarps and newly felled spruce logs, a favourable habitat for spore deposition. Viable spores (and successful germination) of F. pinicola were detected by dikaryotization of monokaryotic bait mycelium from beetle samples. Viable spores were on the exoskeleton and in the faeces of all beetles collected from sporulating sporocarps. On fresh spruce logs, nine beetle species transported viable spores, of which several bore into the bark. Our results demonstrate that beetles can provide directed dispersal of wood decay fungi. Potentially, it could contribute to a higher persistence of some species in fragmented forests where spore deposition by wind on dead wood is less likely.

ecology↗

bioRxiv2021

Invertebrate-induced priority effects and secondary metabolites control fungal community composition in dead wood

During decomposition of organic matter, microbial communities may follow different successional trajectories depending on the initial environment and colonizers. The timing and order of the assembly history can lead to divergent communities through priority effects. We explored how assembly history and resource quality affected fungal dead wood communities and decomposition, 1.5 and 4.5 years after tree felling. Additionally, we investigated the effect of invertebrate exclusion during the first two summers. For aspen (Populus tremula) logs, we measured initial resource quality of bark and wood, and surveyed the fungal communities by DNA metabarcoding at different time points during succession. We found that a gradient in fungal community composition was related to resource quality and discuss how this may reflect tolerance-dominance trade-offs in fungal life history strategies. As with previous studies, the initial amount of bark tannins was negatively correlated with wood decomposition rate over 4.5 years. The initial fungal community explained variation in community composition after 1.5, but not 4.5 years, of succession. Although the assembly history of initial colonizers may cause alternate trajectories in successional communities, our results indicate that the communities may easily converge with the arrival of secondary colonizers. We also identified a strong invertebrate-induced priority effect of fungal communities, even after 4.5 years of succession, thereby adding crucial knowledge to the importance of invertebrates in affecting fungal community development. By measuring and manipulating aspects of assembly history and resource quality that have rarely been studied, we expand our understanding of the complexity of fungal community dynamics.

ecology↗

bioRxiv2021

Fungal biodiversity in Arctic paleoecosystems assessed by metabarcoding of lake sedimentary ancient DNA

Fungi are crucial organisms in most ecosystems as they exert ecological key functions and are closely associated with land plants. Fungal community changes may therefore help reveal biodiversity changes in past ecosystems. Lake sediments contain DNA of organisms in the catchment area, which allows reconstructing past biodiversity by using metabarcoding of ancient sedimentary DNA. We developed a novel PCR primer combination for fungal metabarcoding targeting a short amplicon to account for length bias of amplification due to ancient DNA degradation. In-silico PCRs showed higher diversity using this primer combination than using previously established fungal metabarcoding primers. We analyzed existing data from sediment cores from four artic and one boreal lake in Siberia. These cores had been stored for 2-22 years and examined degradation effects of ancient DNA and storage time-related bias in fungal communities. Amplicon size differed between fungal divisions, however, we observed no significant effect of sample age on amplicon length and GC content, suggesting robust results. We also found no indication of post-coring fungal growth during storage distorting ancient fungal communities. Terrestrial soil fungi, including mycorrhizal fungi and saprotrophs, were predominant in all lakes, which supports the use of lake sedimentary ancient DNA for reconstructing terrestrial communities.

ecology↗

bioRxiv2021

The indoor mycobiome of daycare centers is affected by occupancy and climate

Many children spend considerable time in daycare centers and may here be influenced by indoor microorganisms, including fungi. In this study, we investigate the indoor mycobiome of 125 daycare centers distributed along strong environmental gradients throughout Norway. Dust samples were collected from doorframes outside and inside buildings using a citizen science sampling approach. Fungal communities in the dust samples were analyzed using DNA metabarcoding of the ITS2 region. We observed a marked difference between the outdoor and indoor mycobiomes. The indoor mycobiome included considerably more yeasts and molds compared to the outdoor samples, with Saccharomyces, Mucor, Malassezia and Penicillium among the most dominant fungal genera. Changes in the indoor fungal richness and composition correlated to numerous variables related to both outdoor and indoor conditions; there was a clear geographic structure in the indoor mycobiome composition that mirrored the outdoor climate, ranging from humid areas in western Norway to drier and colder areas in eastern Norway. Moreover, the number of children in the daycare centers, as well as various building features, influenced the indoor mycobiome composition. We conclude that the indoor mycobiome in Norwegian daycare centers is structured by multiple factors and is dominated by yeasts and molds. This study exemplifies how citizen science sampling enables DNA-based analyses of a high number of samples covering wide geographic areas. ImportanceWith an alarming increase in chronic diseases like childhood asthma and allergies, there is an increased focus on the exposure of young children to indoor biological and chemical air pollutants. Our study of 125 daycares throughout Norway demonstrates that the indoor mycobiome not only reflects co-occurring outdoor fungi but includes a high abundance of yeast and mold fungi with an affinity for indoor environments. A multitude of factors influence the indoor mycobiome in daycares, including building type, inhabitants, as well as the outdoor environment. Many of the detected yeasts and molds are likely associated with the human body, where some have been coupled to allergies and respiratory problems. Our results call for further studies investigating the potential impact of the identified daycare-associated mycobiomes on children health.

microbiology↗

bioRxiv2021

DNA metabarcoding reveals host-specific communities of arthropods residing in fungal fruit bodies

Biological communities within living organisms are structured by their hosts traits. How host traits affect biodiversity and community composition is poorly explored for some associations, such as arthropods within fungal fruit bodies. Using DNA metabarcoding, we revealed the arthropod communities in living fruit bodies of eleven wood-decay fungi from boreal forests and investigated how they were affected by different fungal traits. Arthropod diversity was higher in fruit bodies with a larger surface area-to-volume ratio, suggesting that colonisation is crucial to maintain arthropod populations. Diversity was not higher in long-lived fruit bodies, most likely because these fungi invest in physical or chemical defences against arthropods. Arthropod community composition was structured by all measured host traits, namely fruit body size, thickness, surface area, morphology and toughness. Notably, we identified a community gradient where soft and short-lived fruit bodies harboured more true flies, while tougher and long-lived fruit bodies had more oribatid mites and beetles, which might reflect different development times of the arthropods. Ultimately, close to 75% of the arthropods were specific to one or two fungal hosts. Besides revealing surprisingly diverse and host-specific arthropod communities within fungal fruit bodies, our study provided insight on how host traits structure communities.

ecology↗

bioRxiv2021

Long-term balancing selection in highly dynamic mating loci generates trans-species polymorphisms in fungi

Balancing selection, an evolutionary force that retains genetic diversity, has been detected in multiple genes and organisms, such as the sexual mating loci in fungi. However, to quantify the strength of balancing selection and define the mating-related genes require a large number of specimens. In tetrapolar basidiomycete fungi, sexual type is determined by two unlinked loci, MATA and MATB. Genes in both loci defines mating type identity, control successful mating and completion of the life cycle. These loci are usually highly diverse. Previous studies have speculated, based on culture crosses, that species of the non-model genus Trichaptum (Hymenochaetales, Basidiomycota) possess a tetrapolar mating system, with multiple alleles. Here, we sequenced a hundred and eighty specimens of three Trichaptum species. We characterized the chromosomal location of MATA and MATB, the molecular structure of MAT regions and their allelic richness. Our sequencing effort was sufficient to molecularly characterize multiple MAT alleles segregating before the speciation event of Trichaptum species. Our analyses suggested that long-term balancing selection has generated trans-species polymorphisms. Mating sequences were classified in different allelic classes based on an amino acid identity (AAI) threshold supported by phylogenetics. The inferred allelic information mirrored the outcome of in vitro crosses, thus allowing us to support the degree of allelic divergence needed for successful mating. Even with the high amount of divergence, key amino acids in functional domains are conserved. The observed allelic classes could potentially generate 14,560 different mating types. We conclude that the genetic diversity of mating in Trichaptum loci is due to long-term balancing selection, with limited recombination and duplication activity. Our large number of sequenced specimens highlighted the importance of sequencing multiple individuals from different species to detect the mating-related genes, the mechanisms generating diversity and the evolutionary forces maintaining them. Author summaryFungi have complex mating systems, and basidiomycete fungi can encode thousands of mating types. Individuals with the same mating type cannot mate. This sexual system has evolved to facilitate sexual mating, increasing the chances to recombine into advantageous allelic combination and prune deleterious alleles. We explored the genomes of hundred and eighty specimens, combined with experimental mating studies of selected specimens, from a non-model organism (Trichaptum). We characterized the genomic regions controlling sex. The mating ability of the specimens confirmed the role of the mating alleles observed in the genomic data. The detailed analyses of many specimens allowed us to observe gene duplication and rearrangements within the mating loci, increasing the diversity within these loci. We supported previous suggestions of balancing selection in this region, an evolutionary force that maintains genomic diversity. These results supports that our fungal specimens are prone to outcross, which might facilitate the adaptation to new conditions.

genomics↗

bioRxiv2021

Mycena species can be opportunist-generalist plant root invaders

Recently, several saprotrophic genera have been found to invade/interact with plant roots in laboratory growth experiments, and this coincides with reports of abundant saprotrophic fungal sequences in plant roots. However, it is uncertain if this reflects field phenomena, and if reports on coincidentally amplified saprotrophs are simply coincidental. We investigated root invasion by presumed saprotrophic fungi by focusing on the large genus Mycena in 1) a systematic analysis of the occurrence of saprotrophic fungi in new and previously published ITS1/ITS2 datasets generated from roots of 10 mycorrhizal plant species, and 2) we analysed natural abundances of 13C/15N stable isotope signatures of fungal/plant communities from five comparable field locations to examine the trophic status of Mycena species. Mycena was the only saprotrophic genus consistently found in 9 of 10 plant host roots, with high within-host variation in Mycena sequence proportions (0-80%) recovered. Mycena carpophores displayed isotopic signatures consistent with published 13C/15N profiles of both saprotrophic or mutualistic lifestyles, with considerable intraspecific variation, resembling the patterns seen in growth experiments. These results indicate that multiple Mycena species opportunistically invade the roots of a range of plant species, possibly forming a spectrum of interactions. This potentially challenges our general understanding of fungal ecology. Originality significance statementThis is the first study to apply a dual approach of systematic metabarcoding of plant roots and stable isotope signatures on dried field material to the large and common saprotrophic fungal genus Mycena. This is significant as it shows that members of this genus, normally not expected to be found inside plant roots at all, are in fact associated eith multiple plant hosts. The study furthermore shows that species in this genus may occupy different ecological roles in the field besides being saprotrophic. That a large and common fungal genus known to be a quantitatively important litter decayer can be an opportunistic root invader and interact with host plants is of interest to all mycologists and ecologists working on plant-fungus/microb symbiosis.

ecology↗

bioRxiv2017

Yeasts Dominate Soil Fungal Communities In Three Lowland Neotropical Rainforests

Forest soils typically harbour a vast diversity of fungi, but are usually dominated by filamentous (hyphae-forming) taxa. Compared to temperate and boreal forests, though, we have limited knowledge about the fungal diversity in tropical rainforest soils. Here we show, by environmental metabarcoding of soil samples collected in three Neotropical rainforests, that Yeasts dominate the fungal communities in terms of the number of sequencing reads and OTUs. These unicellular forms are commonly found in aquatic environments, and their hyperdiversity may be the result of frequent inundation combined with numerous aquatic microenvironments in these rainforests. Other fungi that are frequent in aquatic environments, such as the abundant Chytridiomycotina, were also detected. While there was low similarity in OTU composition within and between the three rainforests, the fungal communities in Central America were more similar to each other than the communities in South America, reflecting a general biogeographic pattern also seen in animals, plants, and protists.\n\nContactdunthorn@rhrk.uni-kl.de

microbiology↗