Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    The longevity of colonies of fungus-growing termites and the stability of the symbiosis
    Wisselink, Margo ; Aanen, Duur K. ; ’t Padje, Anouk van - \ 2020
    Insects 11 (2020)8. - ISSN 2075-4450 - p. 1 - 15.
    Cheaters - Horizontal transmission - Mutation - Mutualism - Termitomyces

    The agricultural mutualistic symbiosis between macrotermitine termites and Termitomyces fungi is obligate for both partners. The termites provide a protective growth environment for the fungus by cultivating it inside their colony and providing it with foraged plant material. The termites use the fungus for plant substrate degradation, and the production of asexual fruiting bodies for nourishment and re-inoculation of the fungus garden. The termite colony can reach an age of up to several decades, during which time it is believed that a single fungal monoculture is asexually propagated by the offspring of a single founding royal pair. The termite-fungus mutualism has a long evolutionary history dating back more than 30 million years. Both on the time-scale of a termite colony lifespan and that of the mutualistic symbiosis, questions arise about stability. We address the physical stability of the mound, the termite colony and the monoculture fungal garden during a colony’s lifetime. On the long-term evolutionary scale, we address the stability of the symbiosis, where horizontal transmission of the symbiotic fungus raises the question of how the mutualistic interaction between host and symbiont persists over generations.

    Asexual and sexual reproduction are two separate developmental pathways in a Termitomyces species
    Vreeburg, Sabine M.E. ; Ruijter, Norbert C.A. de; Zwaan, Bas J. ; Costa, Rafael R. da; Poulsen, Michael ; Aanen, Duur K. - \ 2020
    Biology Letters 16 (2020)8. - ISSN 1744-9561 - 1 p.
    fungus-growing termites - mushroom formation - mutualism - nodules - symbiosis - Termitomyces

    Although mutualistic symbioses per definition are beneficial for interacting species, conflict may arise if partners reproduce independently. We address how this reproductive conflict is regulated in the obligate mutualistic symbiosis between fungus-growing termites and Termitomyces fungi. Even though the termites and their fungal symbiont disperse independently to establish new colonies, dispersal is correlated in time. The fungal symbiont typically forms mushrooms a few weeks after the colony has produced dispersing alates. It is thought that this timing is due to a trade-off between alate and worker production; alate production reduces resources available for worker production. As workers consume the fungus, reduced numbers of workers will allow mushrooms to 'escape' from the host colony. Here, we test a specific version of this hypothesis: the typical asexual structures found in all species of Termitomyces-nodules-are immature stages of mushrooms that are normally harvested by the termites at a primordial stage. We refute this hypothesis by showing that nodules and mushroom primordia are macro- and microscopically different structures and by showing that in the absence of workers, primordia do, and nodules do not grow out into mushrooms. It remains to be tested whether termite control of primordia formation or of primordia outgrowth mitigates the reproductive conflict.

    High diversity and low host-specificity of Termitomyces symbionts cultivated by Microtermes spp. indicate frequent symbiont exchange
    Peppel, Lennart J.J. van de; Aanen, Duur K. - \ 2020
    Fungal Ecology 45 (2020). - ISSN 1754-5048
    Fungiculture - Fungus-growing termites - Host-specificity - Microtermes - Mutualism - Symbiosis - Termitomyces - Transmission mode

    Fungus-growing termites (subfamily Macrotermitinae) live in an obligate mutualistic symbiosis with species of the fungal genus Termitomyces (Basidiomycota). Although the species that build large mounds are the most conspicuous, termites of the genus Microtermes construct large underground networks of tunnels connecting many fungus gardens. They are also the only entire genus within the Macrotermitinae in which vertical transmission of the fungal symbiont has evolved. To study patterns of genetic diversity in species of the genus Microtermes and their Termitomyces symbionts, we sampled at three different locations in South Africa and sequenced COI for the termites and ITS for the fungi. We discovered high genetic diversity in both termites and fungal symbionts but very low interaction specificity. This implies that frequent horizontal exchange of fungal symbionts occurs between species, despite vertical transmission across generations. We also estimated colony size based on termite haplotype and fungal genotype combinations and found indications that colonies may extend over large areas.

    Data from: Disease-free monoculture farming by fungus-growing termites
    Otani, Saria ; Challinor, Victoria L. ; Kreuzenbeck, Nina B. ; Kildgaard, Sara ; Christensen, Søren Krath ; Larsen, Louise Lee Munk ; Aanen, Duur ; Rasmussen, Silas Anselm ; Beemelmanns, Christine ; Poulsen, Michael - \ 2019
    Dryad
    Termitomyces - Macrotermes - Odontotermes - symbiosis - Amplicon Sequencing - LCMS
    Fungus-growing termites engage in an obligate mutualistic relationship with Termitomyces fungi, which they maintain in monocultures on specialised fungus comb structures, without apparent problems with infectious diseases. While other fungi have been reported in the symbiosis, detailed comb fungal community analyses have been lacking. Here we use culture-dependent and -independent methods to characterise fungus comb mycobiotas from three fungus-growing termite species (two genera). Internal Transcribed Spacer (ITS) gene analyses using 454 pyrosequencing and Illumina MiSeq showed that non-Termitomyces fungi were essentially absent in fungus combs, and that Termitomyces fungal crops are maintained in monocultures as heterokaryons with two or three abundant ITS variants in a single fungal strain. To explore whether the essential absence of other fungi within fungus combs is potentially due to the production of antifungal metabolites by Termitomyces or comb bacteria, we performed in vitro assays and found that both Termitomyces and chemical extracts of fungus comb material can inhibit potential fungal antagonists. Chemical analyses of fungus comb material point to a highly complex metabolome, including compounds with the potential to play roles in mediating these contaminant-free farming conditions in the termite symbiosis.
    Germline Evolution: Sequestered Cells or Immortal Strands?
    Aanen, Duur K. - \ 2019
    Current Biology 29 (2019)16. - ISSN 0960-9822 - p. R799 - R801.

    Mutation accumulation in long-lived fairy-ring mushrooms is orders of magnitude lower than predicted based on per-cell division mutation rates in other organisms. A possible explanation is the maintenance of ‘immortal’ template-DNA in the active periphery of the fairy ring.

    Enrichment of G4DNA and a Large Inverted Repeat Coincide in the Mitochondrial Genomes of Termitomyces
    Nieuwenhuis, Mathijs ; Peppel, Lennart J.J. van de; Bakker, Freek T. ; Zwaan, Bas J. ; Aanen, Duur K. - \ 2019
    Genome Biology and Evolution 11 (2019)7. - ISSN 1759-6653 - p. 1857 - 1869.
    fungi - G-quadruplex - inverted repeat - Lyophyllaceae - mtDNA

    Mitochondria retain their own genome, a hallmark of their bacterial ancestry. Mitochondrial genomes (mtDNA) are highly diverse in size, shape, and structure, despite their conserved function across most eukaryotes. Exploring extreme cases of mtDNA architecture can yield important information on fundamental aspects of genome biology. We discovered that the mitochondrial genomes of a basidiomycete fungus (Termitomyces spp.) contain an inverted repeat (IR), a duplicated region half the size of the complete genome. In addition, we found an abundance of sequences capable of forming G-quadruplexes (G4DNA); structures that can disrupt the double helical formation of DNA. G4DNA is implicated in replication fork stalling, double-stranded breaks, altered gene expression, recombination, and other effects. To determine whether this occurrence of IR and G4DNA was correlated within the genus Termitomyces, we reconstructed the mitochondrial genomes of 11 additional species including representatives of several closely related genera. We show that the mtDNA of all sampled species of Termitomyces and its sister group, represented by the species Tephrocybe rancida and Blastosporella zonata, are characterized by a large IR and enrichment of G4DNA. To determine whether high mitochondrial G4DNA content is common in fungi, we conducted the first broad survey of G4DNA content in fungal mtDNA, revealing it to be a highly variable trait. The results of this study provide important direction for future research on the function and evolution of G4DNA and organellar IRs.

    Disease-free monoculture farming by fungus-growing termites
    Otani, Saria ; Challinor, Victoria L. ; Kreuzenbeck, Nina B. ; Kildgaard, Sara ; Krath Christensen, Søren ; Larsen, Louise Lee Munk ; Aanen, Duur K. ; Rasmussen, Silas Anselm ; Beemelmanns, Christine ; Poulsen, Michael - \ 2019
    Scientific Reports 9 (2019)1. - ISSN 2045-2322

    Fungus-growing termites engage in an obligate mutualistic relationship with Termitomyces fungi, which they maintain in monocultures on specialised fungus comb structures, without apparent problems with infectious diseases. While other fungi have been reported in the symbiosis, detailed comb fungal community analyses have been lacking. Here we use culture-dependent and -independent methods to characterise fungus comb mycobiotas from three fungus-growing termite species (two genera). Internal Transcribed Spacer (ITS) gene analyses using 454 pyrosequencing and Illumina MiSeq showed that non-Termitomyces fungi were essentially absent in fungus combs, and that Termitomyces fungal crops are maintained in monocultures as heterokaryons with two or three abundant ITS variants in a single fungal strain. To explore whether the essential absence of other fungi within fungus combs is potentially due to the production of antifungal metabolites by Termitomyces or comb bacteria, we performed in vitro assays and found that both Termitomyces and chemical extracts of fungus comb material can inhibit potential fungal antagonists. Chemical analyses of fungus comb material point to a highly complex metabolome, including compounds with the potential to play roles in mediating these contaminant-free farming conditions in the termite symbiosis.

    Mutation-rate plasticity and the germline of unicellular organisms
    Aanen, Duur K. ; Debets, Alfons J.M. - \ 2019
    Proceedings of the Royal Society. B: Biological Sciences 286 (2019)1902. - ISSN 0962-8452 - 7 p.
    asymmetrical cell division - density-associated mutation-rate plasticity - germline–soma distinction - immortal strand hypothesis - mutation rate - unicellular organisms

    The mutation rate is a fundamental factor in evolutionary genetics. Recently, mutation rates were found to be strongly reduced at high density in a wide range of unicellular organisms, prokaryotic and eukaryotic. Independently, cell division was found to become more asymmetrical at increasing density in diverse organisms; some 'mother' cells continue dividing, while their 'offspring' cells do not divide further. Here, we investigate how this increased asymmetry in cell division at high density can be reconciled with reduced mutation-rate estimates. We calculated the expected number of mutant cells due to replication errors under various modes of segregation of template-DNA strands and copy-DNA strands, both under symmetrical (exponential) and asymmetrical (linear) growth. We show that the observed reduction in the mutation rate at high density can be explained if mother cells preferentially retain the template-DNA strands, since new mutations are then confined to non-dividing daughter cells, thus reducing the spread of mutant cells. Any other inheritance mode results in an increase in the number of mutant cells at higher density. The proposed hypothesis that patterns of DNA-strand segregation are density-dependent fundamentally challenges our current understanding of mutation-rate estimates and extends the distinction between germline and soma to unicellular organisms.

    Reviewing the taxonomy of Podaxis : Opportunities for understanding extreme fungal lifestyles
    Conlon, Benjamin H. ; Aanen, Duur K. ; Beemelmanns, Christine ; Beer, Z.W. de; Fine Licht, Henrik H. De; Gunde-Cimerman, Nina ; Schiøtt, Morten ; Poulsen, Michael - \ 2019
    Fungal Biology 123 (2019)3. - ISSN 1878-6146 - p. 183 - 187.
    Basidiomycota - Drought - Extremophile - Low water activity - Termite

    There are few environments more hostile and species-poor than deserts and the mounds of Nasutitermitinae termites. However, despite the very different adaptations required to survive in such extreme and different environments, the fungal genus Podaxis is capable of surviving in both: where few other fungi are reported to grow. Despite their prominence in the landscape and their frequent documentation by early explorers, there has been relatively little research into the genus. Originally described by Linnaeus in 1771, in the early 20th Century, the then ∼25 species of Podaxis were almost entirely reduced into one species: Podaxis pistillaris. Since this reduction, several new species of Podaxis have been described but without consideration of older descriptions. This has resulted in 44 recognised species names in Index Fungorum but the vast majority of studies and fungarium specimens still refer to P. pistillaris. Studies of Podaxis' extremely different lifestyles is hampered by its effective reduction to a single-species genus. Here we examine the history of the taxonomy of Podaxis before focusing on its extreme lifestyles. From this, we consider how the muddled taxonomy of Podaxis may be resolved; opening up further avenues for future research into this enigmatic fungal genus.

    Can interaction specificity in the fungus-farming termite symbiosis be explained by nutritional requirements of the fungal crop?
    Costa, Rafael R. da; Vreeburg, Sabine M.E. ; Shik, Jonathan Z. ; Aanen, Duur K. ; Poulsen, Michael - \ 2019
    Fungal Ecology 38 (2019). - ISSN 1754-5048 - p. 54 - 61.
    Biomass - Carbohydrates - Geometric framework - Interaction specificity - Macrotermes - Nutrition - Odontotermes - Protein - Symbiosis - Termitomyces

    Fungus-growing termites are associated with genus-specific fungal symbionts, which they acquire via horizontal transmission. Selection of specific symbionts may be explained by the provisioning of specific, optimal cultivar growth substrates by termite farmers. We tested whether differences in in vitro performance of Termitomyces cultivars from nests of three termite species on various substrates are correlated with the interaction specificity of their hosts. We performed single-factor growth assays (varying carbon sources), and a two-factor geometric framework experiment (simultaneously varying carbohydrate and protein availability). Although we did not find qualitative differences between Termitomyces strains in carbon-source use, there were quantitative differences, which we analysed using principal component analysis. This showed that growth of Termitomyces on different carbon sources was correlated with termite host genus, rather than host species, while growth on different ratios and concentrations of protein and carbohydrate was correlated with termite host species. Our findings corroborate the interaction specificity between fungus-growing termites and Termitomyces cultivars and indicate that specificity between termite hosts and fungi is reflected both nutritionally and physiologically. However, it remains to be demonstrated whether those differences contribute to selection of specific fungal cultivars by termites at the onset of colony foundation.

    Searching for Podaxis on the trails of early explorers in southern Africa
    Buys, M. ; Conlon, B. ; Fine Licht, Henrik H. De; Aanen, D.K. ; Poulsen, M. ; Beer, Z.W. de - \ 2018
    South African Journal of Botany 115 (2018). - ISSN 0254-6299 - p. 317 - 317.
    Podaxis pistillaris is the name often given to the torpedo-shaped mushrooms forming on termite mounds across southern Africa during the rainy season. Linnaeus described the species in 1871 based on a specimen from India. In 1881, he described a second species as Lycoperdon carcinomale from a South African specimen he received from Thunberg. In 1812, Burchell made a painting of the fungus during his exploration of southern Africa. In 1933, all 33 Podaxis species described by that time from Africa, Asia, Australia and the USA, were lumped as synonyms of P. pistillaris. Another 12 species were subsequently described, but most authors treated all these fungi as P. pistillaris. In a quest to resolve the taxonomy of the fungus, we studied Southern African specimens from various herbaria, and some specimens from the USA, Mexico, India, and Africa. We also visited the sites where Thunberg collected his specimen (Western Cape) and where Burchell made his painting (Northern Cape), but could not find fresh specimens. We distributed flyers to local communities in these areas and requested that they contact us should Podaxis be observed. Within six weeks we received specimens from a farm close to Burchell’s camp site, and more from the Northern and Eastern Cape. Ribosomal DNA sequences were successfully obtained from all the fresh and almost all herbarium specimens, including some older than 100 years. Phylogenetic analyses showed that the southern African specimens separate in at least five distinct species, some of which might represent novel taxa
    Asymmetrical template-DNA strand segregation can explain density-associated mutation-rate plasticity
    Aanen, D.K. ; Debets, A.J.M. - \ 2018
    BioRxiv - 9 p.
    The mutation rate is a fundamental factor in evolutionary genetics. Recently, mutation rates were found to be strongly reduced at high density in a wide range of unicellular organisms, prokaryotic and eukaryotic. Independently, cell division was found to become more asymmetrical at increasing density in diverse organisms; in yeast, some "mother" cells continue dividing, while their "offspring" cells do not divide further. Here, we investigate how this increased asymmetry in cell division at high density can be reconciled with reduced mutation-rate estimates. We calculated the expected number of mutant cells due to replication errors under various modes of segregation of template-DNA strands and copy-DNA strands, both under exponential and under linear growth. We show that the observed reduction in the mutation rate at high density can be explained if mother cells preferentially retain the template-DNA strands, since new mutations are then confined to non-dividing daughter cells thus reducing the spread of mutant cells. Any other inheritance mode results in an increase in the number of mutant cells at higher density. The proposed hypothesis that patterns of DNA-strand segregation are density dependent fundamentally challenges our current understanding of mutation-rate estimates and extends the distinction between germline and soma to unicellular organisms.
    Nuclear arms races: Experimental evolution for mating success in the mushroom-forming fungus Schizophyllum commune
    Nieuwenhuis, B.P.S. ; Aanen, D.K. - \ 2018
    PLoS ONE 13 (2018)12. - ISSN 1932-6203
    When many gametes compete to fertilize a limited number of compatible gametes, sexual selection will favour traits that increase competitive success during mating. In animals and plants, sperm and pollen competition have yielded many interesting adaptations for improved mating success. In fungi, similar processes have not been shown directly yet. We test the hypothesis that sexual selection can increase competitive fitness during mating, using experimental evolution in the mushroom-forming fungus Schizophyllum commune (Basidiomycota). Mating in mushroom fungi occurs by donation of nuclei to a mycelium. These fertilizing ‘male’ nuclei migrate through the receiving ‘female’ mycelium. In our setup, an evolving population of nuclei was serially mated with a non-evolving female mycelium for 20 sexual generations. From the twelve tested evolved lines, four had increased and one had decreased fitness relative to an unevolved competitor. Even though only two of those five remained significant after correcting for multiple comparisons, for all five lines we found a correlation between the efficiency with which the female mycelium is accessed and fitness, providing additional circumstantial evidence for fitness change in those five lines. In two lines, fitness change was also accompanied by increased spore production. The one line with net reduced competitive fitness had increased spore production, but reduced fertilisation efficiency. We did not find trade-offs between male reproductive success and other fitness components. We compare these findings with examples of sperm and pollen competition and show that many similarities between these systems and nuclear competition in mushrooms exist.
    The obligate alkalophilic soda-lake fungus Sodiomyces alkalinus has shifted to a protein diet
    Grum-Grzhimaylo, A. ; Falkoski, D.L. ; Heuvel, Joost van den; Valero Jimenez, C.A. ; Min, B. ; Choi, I.G. ; Lipzen, A. ; Daum, C.G. ; Aanen, D.K. ; Tsang, A. ; Henrissat, B. ; Bilanenko, E.N. ; Vries, R.P. de; Kan, J.A.L. van; Grigoriev, I.V. ; Debets, A.J.M. - \ 2018
    Molecular Ecology 27 (2018)23. - ISSN 0962-1083 - p. 4808 - 4819.
    Sodiomyces alkalinus is one of the very few alkalophilic fungi, adapted to grow optimally at high pH. It is widely distributed at the plant‐deprived edges of extremely alkaline lakes and locally abundant. We sequenced the genome of S. alkalinus and reconstructed evolution of catabolic enzymes, using a phylogenomic comparison. We found that the genome of S. alkalinus is larger, but its predicted proteome is smaller and heavily depleted of both plant‐degrading enzymes and proteinases, when compared to its closest plant‐pathogenic relatives. Interestingly, despite overall losses, S. alkalinus has retained many proteinases families and acquired bacterial cell wall‐degrading enzymes, some of them via horizontal gene transfer from bacteria. This fungus has very potent proteolytic activity at high pH values, but slowly induced low activity of cellulases and hemicellulases. Our experimental and in silico data suggest that plant biomass, a common food source for most fungi, is not a preferred substrate for S. alkalinus in its natural environment. We conclude that the fungus has abandoned the ancestral plant‐based diet and has become specialized in a more protein‐rich food, abundantly available in soda lakes in the form of prokaryotes and small crustaceans.
    The disposable male- the ultimate emancipation of females?
    Aanen, Duur K. - \ 2018
    BMC Biology 16 (2018)1. - ISSN 1741-7007 - 4 p.

    Sexual reproduction is costly compared to asexual reproduction, in particular because males generally contribute little to offspring. Research published today in BMC Biology shows that some populations of a termite species have disposed of males altogether. However, this need not necessarily be seen as a victory for the females, since males in most termite societies are active colony members that contribute their fair share to colony tasks.

    Phylogeny of Paecilomyces, the causal agent of pistachio and some other trees dieback disease in Iran
    Heidarian, Reza ; Fotouhifar, Khalil Berdi ; Debets, Alfons J.M. ; Aanen, Duur K. - \ 2018
    PLoS ONE 13 (2018)7. - ISSN 1932-6203

    One of the most important fungal agents of pistachio dieback disease belongs to the ascomycete genus Paecilomyces that has been identified as P. variotii. In 2012–2014, 700 plant samples from pistachio trees and 27 other plant species with dieback symptoms were collected from 10 provinces of Iran. Of the 567 pistachio samples, 277 Paecilomyces strains were obtained and from the 133 samples of other plants (except pistachio and including Pistacia mutica, Punica granatum, Prunus amygdalus, Caesalpinia gilliesii, Nerium oleander, Tamarix aphylla, Tamarix hispida and Haloxylon sp.), 23 fungal isolates were recovered and five isolates were obtained from the air of infected pistachio orchards. Based on morphology, all 305 isolates were identified as P. variotii. Physiological studies revealed that 299 isolates belong to P. formosus. Three isolates were assigned to P. variotii, while three isolates could not be assigned to any of the known species. Of the 305 isolates, 62 were selected for phylogenetic analysis based on DNA variation (ITS, β-tubulin and calmodulin). This analysis showed that all of our isolates form a clade with P. formosus. P. formosus consists of the three former species P. formosa, P. lecythidis and P. maximus. This study shows that our isolates form a strongly supported clade with strains of P. lecythidis. So, the causal agent of dieback disease of pistachio and other examined trees is P. formosus which is closely related to the former species P. lecythidis and has some differences with the former species P. formosa and P. maximus. Based on phylogenetic studies P. formosus thus seems to be a species complex that could be divided into three separate species.

    Social Immunity : The Disposable Individual
    Aanen, Duur K. - \ 2018
    Current Biology 28 (2018)7. - ISSN 0960-9822 - p. R322 - R324.
    Workers in an ant colony can kill fungus-infected brood, thereby protecting the rest of the colony from fungal infection. This form of social immunity is analogous to the immune system of multicellular organisms where immune cells kill infected cells. Workers in an ant colony can kill fungus-infected brood, thereby protecting the rest of the colony from fungal infection. This form of social immunity is analogous to the immune system of multicellular organisms where immune cells kill infected cells.
    Enzyme activities at different stages of plant biomass decomposition in three species of fungusgrowing termites
    Costa, Rafael R. da; Hu, Haofu ; Pilgaard, Bo ; Sabine, Sabine M. ; Schückel, Julia ; Pedersen, Kristine S.K. ; Kračun, Stjepan K. ; Busk, Peter K. ; Harholt, Jesper ; Sapountzis, Panagiotis ; Lange, Lene ; Aanen, Duur K. ; Poulsen, Michael - \ 2018
    Applied and Environmental Microbiology 84 (2018)5. - ISSN 0099-2240
    AZCL - Chromogenic substrates - HPLC - Macrotermes - Odontotermes - Peptide pattern recognition - Plant substrate - RNA-seq - Symbiosis - Termitomyces
    Fungus-growing termites rely on mutualistic fungi of the genus Termitomyces and gut microbes for plant biomass degradation. Due to a certain degree of symbiont complementarity, this tripartite symbiosis has evolved as a complex bioreactor, enabling decomposition of nearly any plant polymer, likely contributing to the success of the termites as one of the main plant decomposers in the Old World. In this study, we evaluated which plant polymers are decomposed and which enzymes are active during the decomposition process in two major genera of fungus-growing termites. We found a diversity of active enzymes at different stages of decomposition and a consistent decrease in plant components during the decomposition process. Furthermore, our findings are consistent with the hypothesis that termites transport enzymes from the older mature parts of the fungus comb through young worker guts to freshly inoculated plant substrate. However, preliminary fungal RNA sequencing (RNA-seq) analyses suggest that this likely transport is supplemented with enzymes produced in situ. Our findings support that the maintenance of an external fungus comb, inoculated with an optimal mixture of plant material, fungal spores, and enzymes, is likely the key to the extraordinarily efficient plant decomposition in fungus-growing termites.
    Low intraspecific genetic diversity indicates asexuality and vertical transmission in the fungal cultivars of ambrosia beetles
    Peppel, L.J.J. van de; Aanen, D.K. ; Biedermann, P.H.W. - \ 2018
    Fungal Ecology 32 (2018). - ISSN 1754-5048 - p. 57 - 64.
    Ambrosia fungus - Ambrosiella - Anisandrus - Asexuality - Clonal fungiculture - Genetic diversity - Symbiosis - Vertical transmission - Xylosandrus
    Ambrosia beetles farm ascomycetous fungi in tunnels within wood. These ambrosia fungi are regarded asexual, although population genetic proof is missing. Here we explored the intraspecific genetic diversity of Ambrosiella grosmanniae and Ambrosiella hartigii (Ascomycota: Microascales), the mutualists of the beetles Xylosandrus germanus and Anisandrus dispar. By sequencing five markers (ITS, LSU, TEF1α RPB2, β-tubulin) from several fungal strains, we show that X. germanus cultivates the same two clones of A. grosmanniae in the USA and in Europe, whereas A. dispar is associated with a single A. hartigii clone across Europe. This low genetic diversity is consistent with predominantly asexual vertical transmission of Ambrosiella cultivars between beetle generations. This clonal agriculture is a remarkable case of convergence with fungus-farming ants, given that both groups have a completely different ecology and evolutionary history.
    Symbiogenesis : Beyond the endosymbiosis theory?
    Aanen, Duur K. ; Eggleton, Paul - \ 2017
    Journal of Theoretical Biology 434 (2017). - ISSN 0022-5193 - p. 99 - 103.
    Cockroaches - Endosymbiosis theory - Eusociality - Flagellates - Gut symbionts - Insects - Termites

    Symbiogenesis, literally ‘becoming by living together’, refers to the crucial role of symbiosis in major evolutionary innovations. The term usually is reserved for the major transition to eukaryotes and to photosynthesising eukaryotic algae and plants by endosymbiosis. However, in some eukaryote lineages endosymbionts have been lost secondarily, showing that symbiosis can trigger a major evolutionary innovation, even if symbionts were lost secondarily. This leads to the intriguing possibility that symbiosis has played a role in other major evolutionary innovations as well, even if not all extant representatives of such groups still have the symbiotic association. We evaluate this hypothesis for two innovations in termites (Termitoidae, also known informally as “Isoptera”): i) the role of flagellate gut protist symbionts in the transition to eusociality from cockroach-like ancestors, and ii) the role of non-gut associated symbionts in the transition to ‘higher’ termites, characterized by the absence of flagellate gut protists. In both cases we identify a crucial role for symbionts, even though in both cases, subsequently, symbionts were lost again in some lineages. We also briefly discuss additional possible examples of symbiogenesis. We conclude that symbiogenesis is more broadly applicable than just for the endosymbiotic origin of eukaryotes and photosynthetic eukaryotes, and may be a useful concept to acknowledge the important role of symbiosis for evolutionary innovation. However, we do not accept Lynn Margulis's view that symbiogenesis will lead to a paradigm shift from neoDarwinism, as the role of symbiosis in evolutionary change can be integrated with existing theory perfectly.

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