Molecular evidence for the adaptive evolution in euryhaline bivalves.

Area of Science:

• Marine biology
• Evolutionary genomics
• Molecular adaptation

Background:

• Marine bivalves in intertidal zones face salinity stress from environmental changes.
• Euryhaline bivalves possess sophisticated physiological mechanisms for salinity tolerance.
• Existing research primarily focuses on physiological responses, with limited understanding of evolutionary adaptations.

Purpose of the Study:

• To investigate the adaptive evolutionary characteristics of euryhaline bivalves using comparative genomics.
• To identify genetic changes associated with salinity tolerance in euryhaline species compared to stenohaline species.

Main Methods:

• Comparative genomics analysis of 7 euryhaline and 5 stenohaline bivalve species.
• Identification of significantly expanded gene families and positively selected genes.
• Enrichment analysis of selected genes in KEGG pathways and GO terms.

Main Results:

• Identified 24 expanded gene families and 659 positively selected genes in euryhaline bivalves.
• Found co-expansion of solute carrier family 23 (SLC23) for ascorbic acid transport.
• Detected positive selection in antioxidant genes (GST, TXNRD) for reactive oxygen species (ROS) scavenging.
• Observed enrichment of selected genes in metabolism (ALDH, ADH, GLS) and transport (SLC22, CLCND, VDCC) pathways.
• Noted positive selection in MCT and PLA2, potentially aiding lactic acid and membrane lipid management.

Conclusions:

• Adaptive evolution in euryhaline bivalves involves significant changes in osmoregulation, ROS scavenging, energy metabolism, and membrane lipid regulation.
• Genomic insights reveal molecular mechanisms underlying the remarkable salinity adaptation in these species.
• This study provides a foundation for understanding the genetic basis of environmental tolerance in marine invertebrates.