Evolutionary processes driving spatial patterns of intraspecific genetic diversity in river ecosystems

Area of Science:

• Ecology
• Evolutionary Biology
• Genetics

Background:

• Understanding the spatial distribution of genetic diversity is crucial in biological sciences.
• River ecosystems are predicted to show increasing neutral genetic diversity downstream, but this requires validation across taxa.
• The evolutionary processes driving this pattern remain unclear.

Purpose of the Study:

• To quantitatively synthesize and meta-analyze published data on the spatial distribution of genetic diversity in river ecosystems.
• To test the general assumption of downstream increases in intraspecific genetic diversity (DIGD) across diverse taxa.
• To identify the evolutionary processes that generate DIGD in riverine environments.

Main Methods:

• A meta-analysis of published studies on genetic diversity in river ecosystems.
• Simulations of genetic data in dendritic river systems to model evolutionary processes.
• Random forest models and approximate Bayesian computations to analyze empirical data and simulations.

Main Results:

• A downstream increase in intraspecific genetic diversity (DIGD) is a general, repeatable pattern across diverse taxa in river ecosystems.
• DIGD was more pronounced in species with waterborne dispersal compared to overland dispersal.
• Simulations identified downstream-biased dispersal, increased downstream habitat availability, and upstream colonization as potential drivers of DIGD.
• Empirical data suggest DIGD results from an interaction of these processes, not solely downstream-biased dispersal.

Conclusions:

• The downstream increase in genetic diversity (DIGD) is a widespread phenomenon in riverine systems, consistent across various species.
• Dispersal mode significantly influences the strength of DIGD, with waterborne dispersers exhibiting stronger patterns.
• Multiple interacting evolutionary processes, rather than a single factor like downstream-biased dispersal, are likely responsible for generating DIGD in rivers.