Within-Host "Infraecology": Asymmetric Interactions Between Two Co-infecting Eye Parasites

Area of Science:

• Ecology
• Parasitology
• Evolutionary Biology

Background:

• Parasites within a host compete for resources, similar to ecological competition in macroenvironments.
• Within-host habitats can be spatially heterogeneous, leading to unequal resource availability for different parasite species.
• Asymmetric resource access, such as in vertebrate eyes, can create competitive hierarchies among parasites.

Purpose of the Study:

• To experimentally investigate parasitic interactions in asymmetric within-host environments.
• To compare the infection success and growth of lens-dwelling and vitreous-dwelling parasites in the presence and absence of each other.
• To determine if resource competition between parasites is asymmetric based on their spatial niche.

Main Methods:

• Experimental infection of fish with two parasite species: Diplostomum pseudospathaceum (lens) and Tylodelphys clavata (vitreous).
• Comparison of infection success and parasite growth in single infections versus co-infections.
• Analysis of asymmetric interactions based on parasite location relative to nutrient sources.

Main Results:

• Parasite species exhibited antagonistic interactions, decreasing each other's infection success.
• Parasite growth was affected asymmetrically: D. pseudospathaceum (lens) inhibited T. clavata (vitreous) growth.
• T. clavata did not affect the growth of D. pseudospathaceum, supporting the hypothesis of asymmetric competition.

Conclusions:

• Within-host spatial heterogeneity and parasite interactions significantly influence infection success and community structure.
• Asymmetric resource competition, driven by niche differentiation, is a key factor in structuring parasite communities.
• Infraecological dynamics, or within-host interactions, are crucial for understanding parasite infection dynamics and host virulence.