Common functional targets of adaptive micro- and macro-evolutionary divergence in killifish

Area of Science:

• * Evolutionary biology
• * Comparative physiology
• * Functional genomics

Background:

• * Environmental salinity is a major obstacle for aquatic organism dispersal.
• * Adaptation to varying salinity levels drives species diversification.
• * The functional basis of evolved salinity tolerance remains poorly understood.

Purpose of the Study:

• * To investigate the mechanistic basis of evolved osmotic plasticity in killifish.
• * To compare physiological and genomic responses to osmotic challenges between two killifish species.
• * To understand how within-species adaptation contributes to macro-evolutionary divergence.

Main Methods:

• * Comparative physiology experiments involving hypo-osmotic challenges.
• * Functional genomics, including genome-wide expression profiling.
• * Common-garden experiments comparing Fundulus majalis and Fundulus heteroclitus.

Main Results:

• * Fundulus heteroclitus exhibited faster gill epithelial remodeling under osmotic stress compared to Fundulus majalis.
• * Transcriptome analysis revealed conserved acclimation mechanisms (e.g., paracellular permeability) and species-specific responses (e.g., cell volume regulation).
• * Baseline gene expression divergence within species appeared neutral, but inter-species divergence deviated from neutral expectations.

Conclusions:

• * Evolved osmotic plasticity in killifish involves both conserved and species-specific genomic and physiological mechanisms.
• * Mechanisms underlying fine-tuning within species also contribute to macro-evolutionary diversification across osmotic environments.
• * Fundulus heteroclitus displays enhanced osmotic plasticity, particularly towards freshwater, compared to Fundulus majalis.