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

Summary

This research demonstrates that ambrosia fungi, which are cultivated by beetles as food sources, grow better on certain types of trees. The fungus studied, Dryadomyces montetyi, grows faster and denser on hardwood trees like oak and beech compared to conifer trees like fir and Douglas-fir. This suggests that the fungal symbiont has evolved preferences for the same tree types that its beetle partner prefers, indicating a specialized relationship shaped by millions of years of evolution.

Background

Ambrosia beetles maintain obligate mutualistic associations with fungal symbionts that serve as nutritional sources for larvae and adults. While the beetle Platypus cylindrus shows preference for deciduous host trees, the role of host tree species in shaping fungal symbiont performance remains poorly understood.

Objective

This study investigated whether the ambrosia fungus Dryadomyces montetyi exhibits host specialization by measuring its growth performance on semi-artificial media infused with extracts from four tree species: Quercus robur, Fagus sylvatica, Abies alba, and Pseudotsuga menziesii.

Results

Dryadomyces montetyi showed significantly faster growth on deciduous tree-derived media (Q. robur and F. sylvatica) compared to conifer-derived media (A. alba and P. menziesii). Growth on Q. robur produced the largest colony area and highest mycelial density, while nutrient-rich laboratory medium SYEMA showed the fastest growth but this represents an artificial optimum.

Conclusion

The fungal symbiont demonstrates host specialization favoring deciduous trees, reflecting the known preference of P. cylindrus for broadleaf hosts. This host-related specialization of the fungal symbiont likely determines host tree selection by the beetle, influencing the evolution of tripartite beetle-fungus-tree interactions.
  • Published in:Frontiers in Insect Science,
  • Study Type:Experimental Study,
  • Source: PMID: 41476573, DOI: 10.3389/finsc.2025.1696497
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