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Multiple ice-age refugia in Pacific cod, Gadus macrocephalus.

Michael F Canino1, Ingrid B Spies, Kathryn M Cunningham

  • 1NOAA Fisheries, Alaska Fisheries Science Center, 7600 Sand Point Way NE, Seattle, WA 98115, USASchool of Aquatic and Fishery Sciences, University of Washington, Seattle, WA 98105, USADepartment of Biological Sciences, University of Alaska Anchorage, 3211 Providence Drive, Anchorage, AK 99508, USAAlaska Department of Fish and Game, 333 Raspberry Road, Anchorage, AK 99518, USA.

Molecular Ecology
|September 8, 2010
PubMed
Summary

Pleistocene ice ages shaped Pacific cod (Gadus macrocephalus) populations. Genetic data reveal distinct northwestern and northeastern Pacific groups, likely isolated during glaciations, now in secondary contact.

Keywords:
Gadus macrocephalusPacific codPleistoceneglacial refugiapostglacial colonizationvicariance

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Area of Science:

  • Marine Biology
  • Population Genetics
  • Evolutionary Biology

Background:

  • Pleistocene ice ages significantly impacted marine species' historical abundances.
  • Pacific cod (Gadus macrocephalus) populations in the North Pacific are of ecological and economic importance.
  • Understanding population structure is crucial for effective fisheries management and conservation.

Purpose of the Study:

  • To investigate the genetic variation and population structure of Pacific cod across the North Pacific.
  • To determine the influence of past glaciations on the current genetic makeup of Gadus macrocephalus.
  • To identify distinct genetic lineages and their historical connectivity.

Main Methods:

  • Analysis of genetic variation using 11 microsatellite loci and mitochondrial DNA (mtDNA).
  • Sampling across twelve locations from the Sea of Japan to Washington State.
  • Statistical analyses including genetic differentiation (FST), correlation with geographical distance, and Bayesian skyline plots.

Main Results:

  • High levels of both microsatellite (mean H = 0.868) and mtDNA haplotype (mean h = 0.958) diversity were observed.
  • Significant genetic differentiation correlated with geographical distance for both marker types.
  • A strong genetic discontinuity was found between northwestern and northeastern Pacific populations, suggesting past isolation.
  • Distinct partitions were identified within the Sea of Japan, Okhotsk Sea, and between coastal and Georgia Basin populations in the northeast Pacific.
  • Evidence for population expansions predating the last glacial maximum was detected.

Conclusions:

  • Past glaciations created significant genetic discontinuities in Pacific cod populations, with evidence of at least two major glacial refugia.
  • Current genetic structure reflects secondary contact between previously isolated groups following postglacial expansions.
  • Distinct glacial histories in the northwest and northeast Pacific likely facilitated separate population expansions and colonization routes.
  • The findings provide critical insights into the long-term evolutionary history and resilience of Pacific cod populations.