Spatial exclusion leads to "tug-of-war" ecological dynamics between competing species within microchannels

Area of Science:

• Microbial Ecology
• Evolutionary Biology
• Biophysics

Background:

• Microbial competition shapes community structure and diversity.
• Classical models like the Moran model study fixation and invasion dynamics.
• Cellular competition in confined spaces requires models incorporating spatial interactions.

Purpose of the Study:

• To extend the Moran model by incorporating mechanical interactions of cells in a 1D microchannel.
• To investigate how spatial exclusion affects species competition, fixation, and invasion.
• To understand the implications for maintaining species diversity in dense cellular ecosystems.

Main Methods:

• Developed a spatial exclusion model based on the Moran model for cells dividing in a 1D open microchannel.
• Characterized collective cell growth and expulsion dynamics.
• Analyzed fixation times, fixation/extinction probabilities, and invasion likelihood under spatial constraints.

Main Results:

• Spatial exclusion significantly accelerates mean fixation time, with logarithmic scaling to system size, unlike algebraic scaling in well-mixed models.
• Fixation/extinction probability becomes highly dependent on initial fractional abundance.
• Invasive species success is substantially reduced, and fitness differences have attenuated effects on fixation dynamics due to 'tug-of-war' and avalanche dynamics.

Conclusions:

• Spatial exclusion in microchannels fundamentally alters competition dynamics compared to well-mixed models.
• These findings explain altered fixation and invasion probabilities in spatially structured microbial communities.
• Results are testable in microfluidic devices and have implications for understanding diversity in biofilms and intestinal crypts.