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EVIDENCE FOR SYMPATRIC GENETIC DIVERGENCE OF ANADROMOUS AND NONANADROMOUS MORPHS OF SOCKEYE SALMON (ONCORHYNCHUS

Chris C Wood¹, Chris J Foote¹

¹Department of Fisheries and Oceans, Biological Sciences Branch, Pacific Biological Station, Nanaimo, British Columbia, V9R 5K6, Canada.

Evolution; International Journal of Organic Evolution

|June 1, 2017

Summary

Pacific salmon (Oncorhynchus nerka) morphs, sockeye and kokanee, exhibit significant differences in traits and reproductive isolation despite spawning together. This divergence likely occurred in sympatry, with limited gene flow between populations.

Keywords:

Anadromy Oncorhynchus nerka assortative mating divergent selection isolating mechanisms kokanee sockeye speciation sympatric populations

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Area of Science:

Evolutionary biology
Ichthyology
Population genetics

Background:

Pacific salmon (Oncorhynchus nerka) exhibit distinct anadromous (sockeye) and nonanadromous (kokanee) morphs.
These morphs coexist and spawn in sympatry in Takla Lake tributaries, British Columbia.

Purpose of the Study:

To investigate the reproductive isolation and divergence mechanisms between sympatric sockeye and kokanee morphs.
To quantify gene flow between these morphs and among different kokanee and sockeye populations.

Main Methods:

Comparative analysis of morphological, genetic (allozyme frequencies), and reproductive traits.
Common-rearing experiments to assess growth and maturity schedules.
Estimation of gene flow (m) using population genetic data.

Main Results:

Significant differences observed in morphology, gill raker number, allozyme frequencies, and reproductive traits between sockeye and kokanee.
Distinct growth rates and maturity schedules were noted in pure and hybrid morphs when reared together.
Low average gene flow (0.1-0.8%) was estimated between sockeye and kokanee morphs.

Conclusions:

Sockeye and kokanee represent reproductively isolated populations, confirming divergence in sympatry.
Potential reproductive isolating mechanisms warrant further investigation.
Limited gene flow suggests strong divergence despite sympatric spawning.