Journal of Heredity Advance Access published online on February 17, 2006
Journal of Heredity, doi:10.1093/jhered/esj014
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1 From the CIBIO/UP, Centro de Investigação em Biodiversidade e Recursos Genéticos, Campus Agrário de Vairão, 4485-661 Vairão, Portugal; From the Departamento de Zoologia-Antropologia, Faculdade de Ciências, Universidade do Porto, Praça Gomes Teixeira, 4099-002 Porto, Portugal; From the Laboratoire de Génétique des Poissons, Institut National de la Recherche Agronomique, 78352 Jouy-en-Josas, France; From the Laboratory of Genomic Diversity--National Cancer Institute, Frederick, MD 21702-1201; From the REQUIMTE, Departamento de Química, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 687, 4169-007 Porto, Portugal
* To whom correspondence should be addressed. The Atlantic Iberian brown trout is at the southwestern limit of its distribution. At this ecological edge, which was once a glacial refugia, anadromy becomes less common as increased water temperatures restricted populations closer to the headwaters. We examined 847 individuals from 20 populations from throughout this region and assessed spatial genetic structure using 11 protein and four microsatellite loci. The higher levels of heterozygosity and allelic diversity north of the southernmost limit of anadromy (SLA), as well as an isolation-by-distance model of population structure, likely influenced by the anadromous forms, suggest that more stable demographic conditions existed over time in this region. Populations south of the SLA were highly differentiated given the restricted size of the area (protein FST = 0.16 in the north and 0.63 in the south of the SLA; microsatellite FST = 0.18 in the north and 0.70 in the south of the SLA). The low levels of heterozygosity and the pattern of southward allele depletion in resident populations is indicative of fragmentation, caused by stressful ecological conditions that reduced the anadromy (restricting gene flow) and the effective population sizes (higher genetic drift), which, in combination, dramatically decreased within-population genetic variation and increased among-population genetic variation. The higher gene diversity north of the SLA does not reflect ancestry but rather the signature of a population size expansion, as evidence suggest the persistence of older populations (with several private alleles) south of the SLA. These data support a scenario that demonstrates how contemporary events (critical ecological conditions) can moderate historical influences, suggesting that careful interpretation of the evolutionary history of glacial refugia is necessary, especially where populations persisted for a long time but not always with optimal ecological conditions. These peripheral populations are of high conservation value and should be preserved to help conserve the future potential of the species.
Received July 12, 2005
Accepted December 9, 2005
Article
Life on the Edge: The Long-Term Persistence and Contrasting Spatial Genetic Structure of Distinct Brown Trout Life Histories at Their Ecological Limits
Agostinho Antunes 1 *,
Rui Faria 2,
Warren E. Johnson 3,
René Guyomard 4,
and
Paulo Alexandrino 2
2 From the CIBIO/UP, Centro de Investigação em Biodiversidade e Recursos Genéticos, Campus Agrário de Vairão, 4485-661 Vairão, Portugal; From the Departamento de Zoologia-Antropologia, Faculdade de Ciências, Universidade do Porto, Praça Gomes Teixeira, 4099-002 Porto, Portugal
3 From the Laboratory of Genomic Diversity--National Cancer Institute, Frederick, MD 21702-1201
4 From the Laboratoire de Génétique des Poissons, Institut National de la Recherche Agronomique, 78352 Jouy-en-Josas, France
Agostinho Antunes, E-mail: aantunes{at}ncifcrf.gov; aantunes@fc.up.pt
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