Variable host responses mediate host preference in marine flatworm-snail symbioses

Area of Science:

• Marine Biology
• Evolutionary Ecology
• Symbiosis Research

Background:

• Host preference in symbionts is driven by fitness trade-offs.
• Interspecific variations in host response traits can influence symbiont host preference evolution.

Purpose of the Study:

• To assess how symbiont host preference relates to host defenses and post-infestation performance.
• To investigate the association between the flatworm Paraprostatum echinolittorinae and its intertidal snail hosts.

Main Methods:

• Field characterization of worm infestation prevalence and intensity in five snail species.
• Laboratory experiments to test flatworm host choice and host behavioral rejection.
• Assessment of host growth and survival following infestation.

Main Results:

• Flatworms were significantly more prevalent in Tegula pellisserpentis, Nerita scabricosta, and N. funiculata compared to Planaxis planicostatus and Cerithium stercusmuscarum.
• Less preferred hosts exhibited behavioral rejection (mantle contractions, foot withdrawals), reducing infestation rates by 39%-67%.
• Flatworms preferred less defended hosts that supported higher densities without significant harm, suggesting a commensal relationship.

Conclusions:

• Host response traits, such as behavioral defenses, significantly modulate symbiont host choice.
• Variability in host responses is crucial for understanding the evolution of symbiont host preference.
• Future research should explicitly consider host response variability in host preference studies.