Biology subjects

Biedermann, P. H. W.

Publications and source records attributed to Biedermann, P. H. W..

7 recordsLinked to original sources

bioRxiv2026

Sociality in weevils is shaped by sheltering and convergent gene losses

Eusociality, characterized by overlapping generations, cooperative brood care, and reproductive division of labour, has arisen independently across diverse, phylogenetically distant insect orders, including Hymenoptera (ants, bees, and wasps), Blattodea (termites), and Coleoptera (weevils). While multiple studies have investigated the molecular evolution of sociality from solitary ancestors in Hymenoptera and Blattodea, so far little is known about the evolutionary signatures of social evolution in Coleoptera. Weevils (Curculionidae) provide an ideal system for addressing this question, as they cover the full spectrum of social complexity from parental care, through several origins of facultative eusociality to the only obligately eusocial beetle, Austroplatypus incompertus. We generated genome assemblies for A. incompertus and two facultatively eusocial weevil species, Xylosandrus germanus and Xyleborinus saxesenii, which together with 18 publicly available weevil genomes span two independent evolutionary origins of sociality. Our analyses reveal a genome-wide relaxation of purifying selection with increasing social complexity, which is most pronounced in A. incompertus. We find a significant excess of convergent gene family contractions in lineages where sociality evolved, and no evidence of elevated positive selection. These findings indicate that the molecular mechanisms of social evolution in weevils are primarily characterised by relaxed selection and gene loss, rather than adaptive innovation and gene family expansions. These observations are consistent with sheltering and reduced effective population size playing an important role, a pattern not previously observed in other clades.

evolutionary biology↗

bioRxiv2025

Growth variation of an ambrosia fungus on different tree species indicates host specialization

Ambrosia beetles rely on mutualistic fungi as a food source for themselves and especially for their offspring, yet the influence of host tree species on fungal growth and specialization is not well understood. In this study, we investigated the growth performance of the ambrosia fungus Dryadomyces montetyi, the primary symbiont of the oak pinhole borer Platypus cylindrus, on semi-artificial media infused with extracts of four tree species: Quercus robur, Fagus sylvatica, Abies alba, and Pseudotsuga menziesii. Fungal growth was quantified over time using logistic growth models, and final biomass was assessed through dry weight measurements. The growth of D. montetyi differed significantly among the different host tree substrates. Growth on F. sylvatica was comparable to that on Q. robur; however, both conifer-derived media (A. alba and P. menziesii) exhibited significantly reduced surface expansion and biomass accumulation. Tissue density measurements further indicated that the mycelium grown on Q. robur was denser than that grown on conifer media, although overall density was highest on a nutrient-rich medium without tree extract. These results demonstrate that D. montetyi performs best on angiosperm hosts, particularly oak, which aligns with the known host preferences of P. cylindrus. Our findings suggest that fungal performance is not solely determined by the typical polyphagy of ambrosia beetles but also reflects the host-related specialization of the fungal symbiont. This specialization certainly determines the host selection of P. cylindrus and the evolution of the tripartite interactions between this beetle, D. montetyi, and oak trees.

microbiology↗

bioRxiv2025

Old growth attributes by chain saw: how between-patch heterogeneity changes the metacommunities of beetles in temperate forests

Metacommunity theory has expanded our understanding of how spatial dynamics and local interactions influence species communities. Different assembly archetypes, reflecting different roles of species differences, habitat differences, and dispersal have been described, but we lack empirical studies specifically in terrestrial habitats testing which archetype is most important. In a replicated design we experimentally enhanced structural between-patch heterogeneity in homogeneous production forests and developed a statistical framework controlling for sample incompleteness to detect different metacommunity processes. Meta-analyses on >100K individuals of >1.3K beetle species showed an increase of [~]60 species in heterogenized forests at {gamma}-level promoted by increasing -diversity consistent with the mass-effect and an increase of {beta}-diversity by [~]10% supporting species-sorting. Additionally, we tested {beta}-deviations from random assembly as a proxy of neutral processes. Findings indicate that enhancing structural heterogeneity can shift forests from patch-dynamics dominance towards mass-effect and species-sorting, offering a promising pathway to restore biodiversity in managed landscapes.

ecology↗

bioRxiv2023

Distribution of the invasive Anisandrus maiche (Coleoptera: Scolytinae) in Switzerland, first record in Europe of its ambrosia fungus Ambrosiella cleistominuta, and its new association with Xylosandrus crassiusculus

In 2022, two independent insect surveys in canton Ticino (southern Switzerland) revealed the widespread occurrence of the invasive ambrosia beetle Anisandrus maiche from southern to central-upper Ticino. This species is native to east Asia and has previously been found as a non-native invasive species in the United States, Canada, western Russia, Ukraine and, in 2021, in northern Italy. Here, we present the results of several trapping studies using different trap types (bottle traps, funnel traps and Polytrap intercept traps) and attractants and a map of the distribution of the species. In total, 685 specimens of A. maiche, all female, were trapped, and the identity of selected individuals was confirmed by morphological and molecular identification based on three mitochondrial and nuclear markers (COI, 28S and CAD). Traps checked from early April to early September 2022 in intervals of two to four weeks showed that flights of A. maiche occurred mainly from June to mid-August. Isolation of fungal associates of A. maiche from beetles trapped alive revealed the presence of four fungal species, including the ambrosia fungus Ambrosiella cleistominuta, the known mutualists of A. maiche. The identity of A. cleistominuta was confirmed by comparing DNA sequences of its nuclear, internal transcribed spacer (ITS) gene with reference sequences in NCBI and BOLDSYSTEMS. This represents the first record of A. cleistominuta in Europe. Ambrosiella cleistominuta was also found in association with another non-native invasive ambrosia beetle, Xylosandrus crassiusculus, at a botanic garden in central Ticino. As ambrosia beetles usually show a high degree of fidelity with only one mutualistic fungus (in the case of X. crassiusculus normally Ambrosiella roeperi), this association is highly unusual and probably the result of lateral transfer among these non-native invasive species. Of the other fungal associates isolated from A. maiche in Ticino, Fusarium lateritium is of note as there is a possibility that A. maiche could act as a vector of this plant pathogen. We highlight several research needs that should be addressed to gain insight into the potential impact of these non-native species and to overcome problems with heteroplasmy in COI sequences in studies of invasion and population genetics of ambrosia beetles.

ecology↗

bioRxiv2022

Friend or Foe: Ambrosia Beetle response to volatiles of common threats in their fungus gardens

Fungus farming insects encounter multiple microbial threats in their cultivar gardens. They can affect both the nutritional cultivar and the insects health. In this study, we explored the potential of ambrosia beetles and their larvae to detect the presence of ubiquitous weed or entomopathogenic fungi. The ability to recognize a threat offers individuals a chance to react. Our study organism, the fruit-tree pinhole borer, Xyleborinus saxesenii, is associated with two mutualistic fungi, Dryadomyces sulphureus (Raffaelea sulphurea) and Raffaelea canadensis. Both symbionts were tested in combinations with two common fungus-garden weeds (Aspergillus sp. and Penicillium commune) and the entomopathogen Beauveria bassiana in two-choice experiments. Behavioural repellence was found in many, but not all combinations. Larvae and adult females showed an opposite reaction towards the entomopathogen, whereas for Aspergillus sp., neither provoked repellence nor attraction of larvae and adult females, if R. canadensis was used as lure. Our results validate a response of both larvae and adult ambrosia beetles towards other fungal volatiles. Their decision to confront a potential threat or preferably to avoid it could be subject to a more complex context.

animal behavior and cognition↗

bioRxiv2022

First experimental evidence for active farming in ambrosia beetles and strong heredity of garden microbiomes

Fungal cultivation is a defining feature for advanced agriculture in attine ants and fungus-farming termites. In a third supposedly fungus-farming group, wood-colonizing ambrosia beetles (Curculionidae: Scolytinae and Platypodinae), an experimental proof for the effectiveness of beetle activity for selective promotion of their food fungi over others is lacking and farming has only been assumed based on observations of social and hygienic behaviors. Here, we experimentally removed mothers and their offspring from young nests of the fruit-tree pinhole borer, Xyleborinus saxesenii (Scolytinae). By amplicon sequencing of bacterial and fungal communities of nests with and without beetles we could show that beetles are indeed able to actively shift symbiont communities. Although being consumed, the Raffaelea food fungi were more abundant when beetles were present while a weed fungus (Chaetomium sp.) as well as overall bacterial diversity were reduced in comparison to nests without beetles. Core symbiont communities were generally low diverse and there were strong signs for vertical transmission not only for the cultivars, but also for secondary symbionts. Our findings verify the existence of active farming, even though the exact mechanisms underlying the selective promotion and/or suppression of symbionts need further investigation.

ecology↗

bioRxiv2019

Cycloheximide-Producing Streptomyces Associated with Xyleborinus saxesenii and Xyleborus affinis Fungus-Farming Ambrosia Beetles

Symbiotic microbes help a myriad of insects acquire nutrients. Recent work suggests that insects also frequently associate with actinobacterial symbionts that produce molecules to help defend against parasites and predators. Here we explore a potential association between Actinobacteria and two species of fungus-farming ambrosia beetles, Xyleborinus saxesenii and Xyleborus affinis. We isolated and identified actinobacterial and fungal symbionts from laboratory reared nests, and characterized small molecules produced by the putative actinobacterial symbionts. One 16S rRNA phylotype of Streptomyces (XylebKG-1) was abundantly and consistently isolated from the nests and adults of X. saxesenii and X. affinis nests. In addition to Raffaelea sulphurea, the symbiont that X. saxesenii cultivates, we also repeatedly isolated a strain of Nectria sp. that is an antagonist of this mutualism. Inhibition bioassays between S. griseus XylebKG-1 and the fungal symbionts from X. saxesenii revealed strong inhibitory activity of the actinobacterium towards the fungal antagonist Nectria sp. but not the fungal mutualist R. sulphurea. Bioassay guided HPLC fractionation of S. griseus XylebKG-1 culture extracts, followed by NMR and mass spectrometry identified cycloheximide as the compound responsible for the observed growth inhibition. A biosynthetic gene cluster putatively encoding cycloheximide was also identified in S. griseus XylebKG-1. The consistent isolation of a single 16S phylotype of Streptomyces from two species of ambrosia beetles, and our finding that a representative isolate of this phylotype produces cycloheximide, which inhibits a parasite of the system but not the cultivated fungus, suggests that these actinobacteria may play defensive roles within these systems.

microbiology↗