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Asexual Reproduction and Growth Rate: Independent and Plastic Life History Traits in Neurospora crassa

Summary

This research investigated how two important life traits in fungi – growth rate and spore production – relate to each other in the fungus Neurospora crassa. Contrary to traditional expectations, the study found that these traits can vary independently rather than trading off against each other. This means fungi can potentially optimize both traits simultaneously in different environments. Impacts on everyday life: • Helps predict how fungi might adapt to new environments, which is important for controlling fungal diseases • Improves understanding of how fungi grow and reproduce in different conditions, relevant for industrial fermentation and food production • Demonstrates why we need to measure multiple characteristics when studying fungal fitness, rather than relying on single measurements • Provides insights that could help develop better antifungal treatments • Advances our understanding of how organisms balance different life functions, with broader implications for evolution and adaptation

Background

Life history theory predicts trade-offs between traits influencing fitness, as resources allocated to one function are unavailable to another. Growth and reproduction are iconic performance traits in life history evolution theory, with trade-offs reported in various organisms. In filamentous fungi like Neurospora crassa, growth occurs through hyphal extension while asexual spores are produced on specialized structures. Understanding relationships between growth and reproduction is important for fungal evolution, ecology and predicting environmental change impacts.

Objective

This study aimed to examine the relationship between asexual reproduction and growth rate in Neurospora crassa, where shared genetic and physiological factors and a source-sink energetic relationship between growth and reproduction may constrain the evolution of these traits. The researchers tested growth-reproduction relationships by independently selecting for either mycelial growth rate or asexual spore production in a heterogeneous lab-derived population.

Results

The study found that growth and reproduction are highly plastic in N. crassa and do not trade off either among wild strains or after laboratory selection in two environments. There was no predictable growth-reproduction relationship in the environments tested, indicating an effective absence of genetic constraint between these traits. Selection experiments successfully increased both target traits – spore production increased 40% and growth rate increased 33% relative to the ancestral population. Importantly, increases in one trait did not consistently result in decreases in the other trait.

Conclusion

Growth rate and asexual reproduction appear to be largely independent traits in N. crassa that may not respond predictably to environmental change. The study suggests that reliance on a single trait as a proxy for fitness in fungal studies may be inadvisable. The findings highlight the challenges in seeking meaningful yet tractable proxies of fitness for fungal studies, as high plasticity and lack of predictable correlation between traits can lead to erroneous inferences about biological fitness.
  • Published in:The ISME Journal,
  • Study Type:Experimental Evolution Study,
  • Source: 10.1038/s41396-018-0294-7
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