DNA markers for estimation of inbreeding depression and heterosis in the guppy Poecilia reticulata

Molecular markers have significant potential for use in precise breeding programmes in aquaculture. This paper reviews the use of DNA markers to estimate inbreeding depression and heterosis in the guppy Poecilia reticulata. Full-sib matings revealed that inbreeding causes declines in survival and salinity tolerance, but not in undwarfism, growth and high water temperature tolerance, indicating the effects of inbreeding differ among fitness-related traits. Salinity tolerance was used to quantify the level of inbreeding depression and heterosis because the trait is strongly sensitive to inbreeding and shows a linear decrease with an increase in inbreeding coefficient. A positive correlation was observed between heterozygosity at microsatellite loci and salinity tolerance among 17 guppy populations. This indicates that heterozygosity estimated from microsatellites is a useful indicator for the estimation of inbreeding depression, suggesting that overall heterozygosity is important for fitness-related traits that show inbreeding depression. Use of DNA markers to estimate the amount of heterosis in various strain combinations was examined using diallele and reciprocal crosses among four domestic strains. The amount of heterosis differed among the strain combinations and correlated with Nei's genetic distance measured by microsatellites and also by dissimilarity using random amplified polymorphic DNA (RAPD) analysis. This indicates that microsatellite and RAPD markers are useful for estimating the amount of heterosis in various strain combinations, further suggesting that the amount of heterosis depends on the genetic differences between the strains. The present study showed that DNA markers are useful tools for estimating inbreeding depression and heterosis in guppy breeding.