Inbreeding and inbreeding depression of female reproductive traits in two populations of Coho salmon selected using BLUP predictors of breeding values

Levels of inbreeding and inbreeding depression were studied in two populations of Coho salmon (Oncorhynchus kisutch) in Chile. The two populations, termed even year, and odd year were artificially selected by weight at harvest over four generations, using the best linear unbiased prediction (BLUP) of breeding values. Also, general linear models (GLM) were used to analyze the effects of inbreeding on reproductive traits of the females and on survival of the progeny. The selection resulted in 56-76% of the parents of the base population not contributing with descendents in the fourth generation. The inbreeding rate was greater in the even population (ΔF=2.45% per generation) than the odd population (ΔF=1.10% per generation) as a direct consequence of the smaller number of founder individuals in the former population (Ne=61 and 106, respectively). The level of inbreeding in the last generation was 9.5% (S.D.=2.7, range 5-19%) for year-class 2000 and 4.3% (S.D.=2.6, range 1-12%) for year-class 2001. Significant inbreeding depression was estimated for the gonadosomatic index (-5.3% per each 10% increase in inbreeding) in population year 2000, and for body length at spawning (-1.56%) in population year 2001. The inbreeding did not significantly reduce other traits such as weight body at spawning, weight of the gonad, number of green eggs, or relative fecundity. No significant inbreeding depression was observed in either population regarding the survival of eggs in the eyed stage. Given the deleterious effects of inbreeding on reproductive traits, salmon selection programs should employ methods which limit the rate of increase of this factor.