Claudia Buser Moser

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Buser Moser

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Claudia

ORCID

0000-0002-9761-584X

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Publications 1 - 5 of 5

Building on 150 Years of Knowledge: The Freshwater Isopod Asellus aquaticus as an Integrative Eco-Evolutionary Model System
Lafuente, Elvira; Lürig, Moritz D.; Rövekamp, Moritz; et al. (2021)
Frontiers in Ecology and Evolution
Interactions between organisms and their environments are central to how biological diversity arises and how natural populations and ecosystems respond to environmental change. These interactions involve processes by which phenotypes are affected by or respond to external conditions (e.g., via phenotypic plasticity or natural selection) as well as processes by which organisms reciprocally interact with the environment (e.g., via eco-evolutionary feedbacks). Organism-environment interactions can be highly dynamic and operate on different hierarchical levels, from genes and phenotypes to populations, communities, and ecosystems. Therefore, the study of organism-environment interactions requires integrative approaches and model systems that are suitable for studies across different hierarchical levels. Here, we introduce the freshwater isopod Asellus aquaticus, a keystone species and an emerging invertebrate model system, as a prime candidate to address fundamental questions in ecology and evolution, and the interfaces therein. We review relevant fields of research that have used A. aquaticus and draft a set of specific scientific questions that can be answered using this species. Specifically, we propose that studies on A. aquaticus can help understanding (i) the influence of host-microbiome interactions on organismal and ecosystem function, (ii) the relevance of biotic interactions in ecosystem processes, and (iii) how ecological conditions and evolutionary forces facilitate phenotypic diversification.
Evidence for toxin-encoding coinfections driving intransitive dynamics between allelopathic phenotypes in natural yeast populations
Travers-Cook, Tommy J.; Gonzalez-Gonzalez, Emmy; Jokela, Jukka; et al. (2026)
Journal of Evolutionary Biology
Competitive intransitivity, or non-hierarchical competitive interactions, such as those exemplified by the rock-paper-scissors game where no single competitor wins outright, has been proposed as a key mechanism for maintaining biodiversity; however, empirical evidence supporting the importance of intransitivity remains limited. Natural populations of Saccharomyces cerevisiae often include strains harboring totivirus-satellite coinfections that encode a lethal toxic glycoprotein capable of eliminating competing yeast strains. Killer strains are sparsely distributed in natural populations, despite their assumed competitive advantage. Yeast isolates occasionally exhibit toxin resistance, but it remains untested whether they can outcompete and replace killer strains. Similarly, the persistence of toxin-susceptible yeast is not well understood-particularly whether they can invade resistant populations in the absence of killers, thereby completing an intransitive loop. In a multi-year collection of yeast isolates from vineyards across New Zealand, we observed a near-complete disappearance of a previously common killer yeast genotype of S. cerevisiae over consecutive years. Using space-time-shift competition assays, we demonstrate that strains sympatric to this killer genotype were universally toxin-resistant, unlike the allopatric strains that were frequently eliminated in competition assays. Furthermore, the extinction of the focal killer genotype appears to have enabled the emergence of toxin-susceptible competitors in sites formerly occupied by the killer genotype. Our findings suggest that the competitive advantage of toxin production is evident in natural populations but appears to be eroded when resistance evolves in competitors of the focal killer genotype. We suggest that such killer-resistant-susceptible polymorphisms are being maintained by evolutionary dynamics akin to rock-paper-scissors-like intransitivity, driven by the invasion of susceptible strains after costly resistance has driven killer strains to extinction in natural populations, all being driven by toxin-encoding coinfections.
Totivirus-satellite coinfection prevalence and host genotype associations in wild Saccharomyces cerevisiae
Travers-Cook, Tommy J.; Knight, Sarah J.; Lee, Soon; et al. (2025)
FEMS Microbiology Ecology
Saccharomyces cerevisiae is occasionally infected by dsRNA totiviruses and their toxin-encoding dsRNA satellite nucleic acids. The autonomous totivirus and its satellite can coexist but with an asymmetric dependence of the satellite on the totivirus for replication and maintenance inside the host cell. Satellites provide their yeast hosts with inhibitory toxins and the necessary self-immunity; loss of the satellite equates to loss of toxin immunity. Because these viral elements lack known extracellular stages, and sex is suspected to be rare, they are assumed to be transmitted vertically, implying that infection states should correlate with host genotypes. However, totivirus-satellite coinfections are rarely examined in natural populations, leaving their associations with host genotypes poorly understood. We screened a multiyear, vineyard-associated population of S. cerevisiae isolates from New Zealand to examine the stability of host-virus associations over time, both within and across genotypes. Over half of the wild isolates harbored infections (55%), but less than half of these (37% of infected) had toxin-encoding satellites. Genotypes that persisted across years typically maintained consistent infection states. However, we also observed stepwise transitions from coinfection through infection to an infection-free state, as well as acquisition of totiviruses and satellites. Genotypes clustered strongly by infection state, and population heterozygosity was significantly lower than expected, supporting vertical transmission while suggesting that outcrossing is not responsible for the acquisition of higher infection states. Despite occasional intragenotypic transitions, genotype clustering by infection state remained intact, suggesting that such transitions are transient and that host genotypes may have optimal infection states with regard to totiviruses and their satellites.
Parasite infection and the movement of the aquatic snail Potamopyrgus antipodarum along a depth cline
Feijen, Frida; Buser Moser, Claudia; Klappert, Kirsten; et al. (2023)
Ecology and Evolution
Parasite species that use two or more host species during their life cycle depend on successful transmission between these species. These successive host species may have different habitat requirements. For example, one host species may be aquatic while the other is terrestrial. To overcome this complicating factor in transmission, a wide diversity of parasite species have adaptations that alter the habitat preference in one host species to facilitate transmission to the next host species. Two common trematode parasites in New Zealand, Atriophallophorus winterbourni and Notocotylus spp., both have a life cycle with two host species. The aquatic snail Potamopyrgus antipodarum is the intermediate host, from which the parasites require transmission to dabbling ducks or other waterfowl. Of these parasites, A. winterbourni is most frequently found in snails from the shallow-water margin. This may indicate parasite-induced movement of infected snails into the foraging habitat of dabbling ducks. To test whether the parasites manipulate the snails to move into shallow water, we stretched tubular mesh cages across depth-specific ecological habitat zones in a lake. Both infected and healthy snails were released into the cages. After 11 days, significantly higher infection frequencies of A. winterbourni were retrieved from the shallowest end of the cages, while Notocotylus spp. frequencies did not vary with depth. The hypothesis that A. winterbourni induces its snail host to move into the shallow-water habitat cannot be rejected based on the experimental results. Although further research is needed to address alternative explanations, the depth preference of infected snails may be due to a parasite adaptation that facilitates trophic transmission of parasites to dabbling ducks.
The evolutionary ecology of fungal killer phenotypes
Travers Cook, Thomas J.; Jokela, Jukka; Buser Moser, Claudia (2023)
Proceedings of the Royal Society B: Biological Sciences
Ecological interactions influence evolutionary dynamics by selecting upon fitness variation within species. Antagonistic interactions often promote genetic and species diversity, despite the inherently suppressive effect they can have on the species experiencing them. A central aim of evolutionary ecology is to understand how diversity is maintained in systems experiencing antagonism. In this review, we address how certain single-celled and dimorphic fungi have evolved allelopathic killer phenotypes that engage in antagonistic interactions. We discuss the evolutionary pathways to the production of lethal toxins, the functions of killer phenotypes and the consequences of competition for toxin producers, their competitors and toxin-encoding endosymbionts. Killer phenotypes are powerful models because many appear to have evolved independently, enabling across-phylogeny comparisons of the origins, functions and consequences of allelopathic antagonism. Killer phenotypes can eliminate host competitors and influence evolutionary dynamics, yet the evolutionary ecology of killer phenotypes remains largely unknown. We discuss what is known and what remains to be ascertained about killer phenotype ecology and evolution, while bringing their model system properties to the reader's attention.

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Claudia Buser Moser

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