Inbreeding and its consequences for genetic variation and early life history in chinook salmon

Abstract

As a necessary background for my experimental studies, I reviewed inbreeding and its consequences and the relationship between genetic variability and fitness in salmonid fishes. Inbreeding directly reduces individual heterozygosity and can reduce genetic variation within populations through the loss of genotypes. Although inbreeding occurs naturally, much of the evidence for inbreeding stems from direct or indirect results of human activity. The potential consequences of inbreeding highlight the importance of maintaining genetic diversity in salmonid populations. A relationship between genetic variability and fitness varies both among and within species. The genetic bases of inbreeding depression and the relationship between genetic variability and fitness are complex, and quantification of the genetic effects of inbreeding over the entire life cycle remains challenging.My experimental studies examined the effects of inbreeding in chinook salmon bred and reared under controlled cultured conditions. Using progeny of unrelated, half-sib and full-sib mating designs, data were collected on genotypic and allelic variation and survival rates for two different broods. Data on a measurement of developmental stability, fluctuating asymmetry (FA), were collected for one brood. The average heterozygosity at 10 DNA microsatellite loci per family decreased significantly with inbreeding in both broods and changes were in accordance with theoretical expectations. No different viability between homozygotes and heterozygotes by the stage of sampling was detected. The average number of alleles at all loci per family also decreased with inbreeding although the decreases were significant for only one brood. Survivals to eyeing, hatch and alevin were higher in offspring from unrelated matings than from both half-sib and full-sib matings although the differences were significant between only unrelated and half-sib matings in one brood. No linear relation between depression in survival rate and levels of inbreeding was detected. Consistent increases with inbreeding in FA were detected for three out of eight meristic characters. These changes were, however, not significant. Although low power due to limited number of families within each mating group appeared to contribute to the failure to detect an effect of inbreeding on FA, the trends suggest that developmental instability is likely to increase under inbreeding. These initial studies provide a foundation for insights into the effects of further inbreeding through subsequent inbred generations of these lineages.