Realized genetic parameters from an antagonistic selection index in Tribolium castaneum

Abstract

Simultaneous selection of two highly correlated traits was practiced in Tribolium castaneum in a replicated experiment for six generations. Two lines were selected in each of three replicates: P+A− for an antagonistic selection index to increase pupal weight at 21 days and decrease adult weight at 31 days, and P−A+ for an antagonistic selection index to decrease pupal weight and increase adult weight. Genetic correlation between pupal and adult weights estimated in the base population was 0.95. Estimates of realized heritabilities and genetic correlation were obtained and compared with full-sib estimates. For the aggregate genotype, the P+A− line had a significant positive selection response, while the P−A+ line showed a significant negative response as would be expected. The response to divergent selection was asymmetrical, being less for the low pupal weight and high adult weight line than vice versa. Less asymmetry was found for the realized heritability, which agreed very well with the index heritability estimated in the base population. Both individual traits changed in the same direction, increasing for the P+A− line and decreasing for P−A+ line, even though a significant response was found only for pupal weight in the P+A− line. Therefore, the response to antagonistic selection for each individual trait seems to be heavily controlled by the strength of the genetic correlation between them. The realized genetic correlation between pupal weight and adult weight obtained from antagonistic selection index was in excellent agreement with full-sib estimates. Realized heritabilities for each trait were overestimated, especially for adult weight, even though there were essentially no differences between realized and estimated values.Key words: selection (artificial), antagonistic index, parameters (realized), Tribolium.