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Evidence for toxin-encoding coinfections driving intransitive dynamics between allelopathic phenotypes in natural
Tommy J Travers-Cook1,2,3, Emmy Gonzalez-Gonzalez2,3, Jukka Jokela2,3
1Department of Zoology, University of British Columbia, Vancouver, Canada.
Journal of Evolutionary Biology
|December 17, 2025
Summary
Competitive intransitivity, like rock-paper-scissors, maintains biodiversity. In yeast populations, killer strains declined as resistant strains evolved, allowing susceptible strains to re-emerge, demonstrating this ecological dynamic.
Area of Science:
- Ecology
- Evolutionary Biology
- Microbiology
Background:
- Competitive intransitivity, where no single competitor dominates, is theorized to maintain biodiversity.
- Empirical evidence for intransitivity's role in natural populations is scarce.
- Yeast populations (Saccharomyces cerevisiae) exhibit killer-susceptible-resistant dynamics driven by toxin-encoding coinfections.
Purpose of the Study:
- To investigate the empirical evidence for competitive intransitivity in natural yeast populations.
- To understand the dynamics of killer, resistant, and susceptible yeast strains.
- To explore the role of toxin production and resistance in maintaining yeast biodiversity.
Main Methods:
- Multi-year collection of yeast isolates from New Zealand vineyards.
- Space-time-shift competition assays to evaluate yeast strain interactions.
- Analysis of killer yeast genotype dynamics and the emergence of resistant and susceptible strains.
Main Results:
- A common killer yeast genotype significantly declined over several years.
- Sympatric yeast strains were predominantly resistant to the killer toxin, unlike allopatric strains.
- Killer yeast extinction facilitated the re-emergence of toxin-susceptible yeast strains.
Conclusions:
- The competitive advantage of yeast killer toxins is diminished by evolved resistance.
- Killer-resistant-susceptible polymorphisms are maintained by rock-paper-scissors-like evolutionary dynamics.
- Yeast populations demonstrate intransitive interactions, contributing to biodiversity maintenance.
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