Experimental Immigration Mediates Ecological Selection and Drift in Monarch Microbiome Assembly

Area of Science:

• Ecology
• Microbiology
• Evolutionary Biology

Background:

• Host-microbiome research often overlooks multiscale processes, focusing instead on host selection.
• This narrow focus struggles to explain the significant variation in microbial communities observed among individuals.

Purpose of the Study:

• To investigate how immigration from the regional species pool affects the balance between niche selection and drift in structuring gut bacterial communities.
• To test the hypothesis that immigration influences microbial community variation across ontogeny and among individuals.

Main Methods:

• Integrated multi-scale ecological theory with experimental manipulation of bacterial colonization in monarch butterfly caterpillars.
• Manipulated immigration levels to observe effects on gut bacterial community composition.

Main Results:

• Increased immigration led to greater dominance of specific bacteria and increased convergence of gut microbial composition throughout the caterpillar's life stage.
• Limited immigration resulted in more stochastic colonization, leading to higher, unpredictable variability in bacterial composition among individuals.

Conclusions:

• Immigration acts as a critical mediator between host selection and ecological drift in host-microbiome symbioses.
• Ecological processes operating at scales beyond the individual host are essential for understanding and structuring host-microbiome interactions.