Balancing selection maintains intraspecific diversity in a deep-sea fish

Area of Science:

• Evolutionary Biology
• Population Genetics
• Marine Biology

Background:

• Genetic variation can be lost, fixed, or maintained by balancing selection.
• Balancing selection is understood theoretically but less so at the molecular level.
• Deep-sea fish (Coryphaenoides rupestris) inhabit diverse depth zones.

Purpose of the Study:

• Investigate evolutionary processes affecting non-synonymous variants in Coryphaenoides rupestris.
• Determine if genetic drift, directional selection, or balancing selection shapes allele frequencies.
• Understand the molecular basis of adaptation to different depths.

Main Methods:

• Candidate SNP genotyping at eight functionally relevant loci.
• Analysis of allele frequencies across depth gradients (~200m to ~2000m).
• Examination of allele frequency changes across five age categories and at specific depths.

Main Results:

• One allele predominates in deeper water at each locus.
• Minor allele frequencies significantly change with age across shallower depths.
• Deep-water alleles decline with age below a threshold depth, indicating segregation.

Conclusions:

• Data suggest segregation to shallow and deep habitats.
• Balancing selection is the most supported mechanism for maintaining ecotype diversity.
• Evidence supports long-term balancing selection at these loci.