Successive range expansion promotes diversity and accelerates evolution in spatially structured microbial populations

Area of Science:

• Ecology
• Evolutionary Biology
• Microbiology

Background:

• Range expansions are crucial ecological processes where populations spread into new territories.
• Genetic drift typically reduces genetic diversity during range expansions.
• The impact of successive range expansions on genetic diversity remains poorly understood, especially when secondary populations invade areas already occupied by primary populations.

Purpose of the Study:

• To investigate the effect of successive range expansion on local population diversity using a microbial model.
• To determine if secondary range expansions differ from primary expansions in their impact on genetic diversity.
• To explore the mechanisms driving diversity changes during successive range expansions.

Main Methods:

• Utilized an experimental microbial model system to simulate primary and successive range expansions.
• Observed the spatial structures formed by secondary expanding populations.
• Developed and employed a mathematical model to simulate dendritic structure formation.
• Introduced mutations into primary and secondary populations to track accumulation.

Main Results:

• Successive range expansion, unlike primary expansion, was found to promote local population diversity.
• Secondary populations formed fractal-like dendritic structures due to mechanical constraints from the primary population.
• These structures led to the fragmentation of the secondary population and increased intermixing with the primary population.
• Mutations were more likely to accumulate in the dendritic secondary populations.

Conclusions:

• Successive range expansion enhances local genetic diversity by promoting intermixing and facilitating mutation accumulation.
• The formation of dendritic structures is a key mechanism driving increased diversity in secondary expansions.
• These findings have significant implications for understanding microbial community ecology and evolution.
• The study highlights how spatial structures can influence evolutionary trajectories during range expansions.