Distribution and host range of zombie fungi along latitudinal gradients

Background

Entomopathogenic fungi (EF) of the Hypocreales order, particularly those in the genera Cordyceps and Ophiocordyceps, play crucial roles in ecological systems by killing infected arthropods. Fungi in these genera are well known for striking interactions with their hosts, which includes manipulation of host behavior resulting in effective spore dispersal after death of the host. EF exhibit diverse host associations and show notable variations in species richness and host interactions across regions. Both species diversity and host specificity seem to change along latitudinal gradients for different organismal groups, but global patterns remain poorly understood for EF.

To address these questions, our team constructed EntomoFun, version 1.0 (https://datadryad.org/stash/dataset/doi:10.5061/dryad.1zcrjdg17). This global database compiles literature on EPF occurrences and host interactions, currently comprising 1791 records. This database will serve as an important data source to investigate global patterns in EF diversity and host relationships, focusing on how these patterns change along latitudinal gradients.

Different groups of macroorganisms typically follow a latitudinal gradient; their diversity decreases with increasing latitude. This is referred to as the latitudinal diversity gradient (LDG) in ecological studies. In contrast, the diversity of fungi, which produce propagules that are microscopic in size, is often thought of as cosmopolitan—although rigorous data are lacking. A huge study based on environmental DNA from soil samples around the world did find support for the LDG hypothesis for the diversity of fungi, with the exception of some ecological groups (e.g., ectomycorrhizal fungi).

Problems

While EF, particularly Cordyceps and Ophiocordyceps, are known for their diversity and ecological roles, several knowledge gaps exist:

  • Latitudinal gradients in EPF diversity. The way in which EPF species richness changes along latitudinal gradients is poorly understood. The tropics are known for higher biodiversity in general, but it is unclear whether this holds true for EPF specifically. It has been suggested that the diversity of EPF is higher in tropical regions but empirical data are lacking.
  • Host specialization along latitudinal gradients. It is unknown whether EPF host specialization—i.e., how host specific are fungal species to particular insect hosts—varies across different latitudes.

Goals

The primary goal of this research is to unravel the complex relationships between EPF diversity and host specialization along latitudinal gradients, focusing on the genera Cordyceps and Ophiocordyceps. Specifically, the following research questions will be addressed:

  1. Examine latitudinal changes in EPF diversity. Is there a discernible increase in species richness in tropical areas compared to subtropical and temperate regions?
  2. Estimate EPF diversity by climate zone. Are certain species or genera more abundant or unique to specific climatic zones?
  3. Investigate host specialization along latitudinal gradients. Do EPF in tropical regions infect a broader range of insect hosts, or are they more specialized compared to those in temperate zones?

This thesis research will improve our understanding of global biodiversity patterns and the ecological drivers of species interactions between entomopathogenic fungi and their insect hosts. The results of this study will have implications for conservation strategies, particularly in biodiversity hotspots where these fungi and their hosts play key roles in ecosystem functioning. The student who will take on this project will become familiar with biogeography studies, fungal taxonomy and ecology, statistical analyses, hierarchical occurrence models, and databasing.

References

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De Wint FC, Nicholson S, Koid QQ, Zahra S, Chestney-Claasen G, Seelan JSS, Xie J, Xing S, Fayle TM, Haelewaters D. 2024. EntomoFun 1.0: A global database of entomopathogenic fungi and associations with their hosts. Dryad. https://doi.org/10.5061/dryad.1zcrjdg17

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