Relationships between genetic variation measured by microsatellite DNA markers and a fitness-related trait in the guppy (Poecilia reticulata)

We explored two microsatellite-based variables, heterozygosity and a measure of genomic diversity based on the mean squared distance between microsatellite alleles within an individual (mean d(2)), in relation to inbreeding depression for a fitness-related trait using 925 individuals of 17 populations with various genetic backgrounds, three wild populations, three domestic populations and 11 domestic strains, in the guppy (Poecilia reticulata). Mean heterozygosity observed at four microsatellite loci differed among the populations and was higher in the wild populations than in the domestic strains. Salinity tolerance, measured by the survival time after transfer from fresh water to 35 ppt seawater, was used to examine the level of inbreeding depression because the trait decreases linearly with an increase in inbreeding coefficient and shows significant heterosis. Among the 17 populations, salinity tolerance differed significantly and was positively correlated with the mean heterozygosity. This suggests that overall heterozygosity affects expression of a fitness-related trait that shows inbreeding depression and heterosis. Within each population, individual salinity tolerance did not correlate with the individual level of multilocus heterozygosity or with mean d(2). These results indicate that although the effect of the individual loci linked to loci screened is too small to be detected by examining the individual level of inbreeding depression within a population, the mean heterozygosity of a set of microsatellite loci may be sensitive enough to be a useful indicator for inbreeding depression at the population level. (C) 2002 Elsevier Science B.V. All rights reserved.