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Uncoiling Host-Parasite Interrelationships: Bounded Snail-Host Flexibility Amid Conserved Trematode Morphology
Taylor M Fiedor1, Samuel N Messinides1, Kyle D Gustafson1,2,3
1Beck College of Sciences & Mathematics, Arkansas State University, Jonesboro, Arkansas, USA.
Molecular Ecology
|April 15, 2026
Summary
Parasite evolution shows distinct patterns: larval forms are evolutionarily stable, while host use remains flexible. This explains how specialized parasites can adapt to new hosts, revealing key rules for symbiotic relationships.
Area of Science:
- Evolutionary biology
- Parasitology
- Community ecology
Background:
- Host-parasite communities are shaped by evolutionary constraints and ecological opportunities.
- Digenetic trematodes provide a model system to study evolutionary conservatism and ecological flexibility.
- Understanding these dynamics has implications for community structure and host-parasite interactions.
Purpose of the Study:
- To investigate the evolutionary patterns of digenetic trematode morphotypes and host use.
- To uncover parasite diversity and identify keystone host taxa.
- To resolve the parasite paradox regarding specialization and host shifts.
Main Methods:
- Conducted surveys across 120 sites in three ecoregions, examining 14,623 snails for trematode infections.
- Sequenced 18S and 28S ribosomal RNA genes from 104 cercariae representing 12 morphotypes.
- Applied model-based analyses to assess phylogenetic signal in morphotypes and host use evolution.
Main Results:
- Identified 22 trematode families, with infections concentrated in a few keystone snail taxa.
- Cercaria morphotypes showed strong phylogenetic signal, indicating evolutionary stability.
- Host use evolved under stabilizing selection, demonstrating flexibility within adaptive limits.
- Observed 'evolutionary reunions' where related trematodes re-associated with ancestral snail hosts.
Conclusions:
- Cercaria morphotypes are evolutionarily conserved, while host use is ecologically flexible.
- Keystone host taxa play a crucial role in maintaining parasite diversity.
- Evolutionary reunions, driven by ecological fitting, help explain parasite specialization and host shifts.
- Findings provide a molecular framework for understanding symbiotic interrelationships and predicting disease emergence and biodiversity changes.
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