Riverscape genetics identifies replicated ecological divergence across an Amazonian ecotone

Area of Science:

• Evolutionary biology
• Speciation research
• Amazonian biodiversity

Background:

• Ecological speciation, the evolution of reproductive isolation driven by divergent selection on ecological traits, is a key but controversial topic, especially in tropical regions.
• Understanding speciation mechanisms is crucial for biodiversity conservation in heterogeneous environments.

Purpose of the Study:

• To investigate ecologically based speciation in the Amazonian electric fish, Steatogenys elegans, across an aquatic ecotone.
• To assess the relative roles of geography and divergent natural selection in driving biodiversity in this region.
• To explore the potential for replicated speciation events driven by environmental heterogeneity.

Main Methods:

• Phylogenetics, genome scans, and population genetics were employed.
• A novel individual-based evolutionary landscape genetics approach incorporating selection was utilized.
• The study focused on sympatric lineages of Steatogenys elegans inhabiting rivers with distinct hydrochemical properties.

Main Results:

• Two closely related, sympatric lineages of Steatogenys elegans exhibiting divergence were identified.
• Divergent selection across an Amazonian aquatic ecotone, characterized by differing water properties, appears to drive replicated ecological speciation.
• A link between selection across an ecological gradient and reproductive isolation was established, with assortative mating by water color proposed as a mechanism.

Conclusions:

• Ecologically driven speciation is a significant factor in tropical biodiversity, emphasizing the importance of environmental heterogeneity.
• The study highlights the utility of spatially explicit evolutionary landscape genetics frameworks for understanding natural selection's spatial dependence.
• Assortative mating based on water color is proposed as a key driver of divergence and reproductive isolation in this system.