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Highly potent host external immunity acts as a strong selective force enhancing rapid parasite virulence evolution
Charlotte Rafaluk1,2,3, Wentao Yang1, Andreas Mitschke1,3
1Evolutionary Ecology and Genetics, Zoological Institute, Christian-Albrechts-Universität zu Kiel, Am Botanischen Garten 1-9, Kiel, 24118, Germany.
Environmental Microbiology
|March 28, 2017
Summary
Parasites like Beauveria bassiana evolved increased virulence against Tribolium castaneum by overcoming external immunity. This adaptation was primarily due to enhanced resistance to host defenses, not increased toxin production.
Area of Science:
- Evolutionary biology
- Host-parasite interactions
- Insect pathology
Background:
- Virulence evolution is driven by host-parasite coevolutionary dynamics.
- Pathogens face challenges from host external immune systems, which use antimicrobial compounds.
- Beauveria bassiana (entomopathogenic fungus) and Tribolium castaneum (red flour beetle) provide a model for studying these interactions.
Purpose of the Study:
- To investigate the impact of external immunity on parasite virulence evolution.
- To determine the mechanisms by which Beauveria bassiana adapts to host defenses.
- To assess the role of oxidative stress resistance in overcoming external immunity.
Main Methods:
- An experimental evolution approach was used, involving coevolution between Beauveria bassiana and Tribolium castaneum.
- Parasite virulence was measured as host mortality.
- Transcriptomic analysis of evolved Beauveria bassiana was performed.
Main Results:
- A significant increase in virulence (host mortality) was observed in Beauveria bassiana after seven transfers.
- The virulence increase resulted from evolved resistance to the host's external immune system.
- Transcriptomic data indicated the upregulation of oxidative stress resistance genes in evolved strains.
Conclusions:
- External immunity is a potent selective pressure driving virulence evolution in parasites.
- Beauveria bassiana overcame host defenses primarily through enhanced oxidative stress resistance.
- Adaptation to external immunity, rather than increased pathogenicity factors, explains the observed virulence increase.
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