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Seasonal isolation and adaptation among chum salmon, Oncorhynchus keta (Walbaum), populations

University of British Columbia

To test the hypothesis that temporal isolation due to differences in season of breeding could result in genetic divergence among chum salmon populations, I compared the reproductive environments, phenotypes and genotypic performances of early and late season breeding stocks of chum salmon, Oncorhynchus keta. These were autumn (AB) and winter (WB) spawners from one Vancouver Island stream (Bush Creek) and another winter spawning stock (W) from a nearby stream (Walker Creek). All stocks had similar time of downstream migration of the fry. No differences were found among the W and AB stocks in age at maturity, length composition of spawners, egg size, vertebral count of adults and fry and time of fry migration. The WB stock differed from the other stocks in egg size and vertebral number of adults and fry. In 1981, WB spawners were larger than AB spawners. In 1982, WB spawners were younger than AB spawners. Analysis of ten external morphological features of the fry revealed that there was considerable overlap in body form of the stocks. To test the hypothesis that phenotypic similarities observed among seasonal ecotypes in the wild were due to genetic differences, sample populations were reared under controlled conditions in the laboratory. When reared at 6°C, under the autumn - winter - spring progression and the winter -spring progression, the early spawning population in Bush Creek took significantly more time to hatch and emerge than the spatially and temporally isolated population of Walker Creek, and the combined average of the late spawning populations. At 10°C the populations had similar incubation rates. Temperature regime, population and temperature regime by population interaction all had significant effects on vertebral number. AB progrency were morphologically distinct from WB and W. These results indicate that the early spawning population differs genetically from the late spawning populations. To test the hypothesis that selection on the speed of development from fertilization to hatch and emergence would reduce the additive genetic variation in these traits, individual families were reared from AB, WB and W. Heritabilities were found to be between 0.27 and 0.54. The high heritabilities suggest that some countervailing force is opposing selection on incubation rate. Analysis of diversity using biochemical genetics techniques suggest that genetic migration goes from the WB stock to the AB stock. Genetic distance measures and a Wagner-Tree analysis indicate that biochemically AB and WB are more closely related than W. It is postulated that the genetically determined program for incubation which results in synchronous downstream migration has survival value. Survival could be enhanced by predator satiation or synchrony with food resources in the estuary.

Text

2010-10-18

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http://hdl.handle.net/2429/29303

Zoology

University of British Columbia

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