The relationship between allozyme heterozygosity and salinity tolerance inwild and domestic populations of the guppy (Poecilia reticulata)

The present study examines the relationships between heterozygosity and a f itness-related trait that shows heterosis in six wild populations and 14 do mestic strains of the guppy (Poecilia reticulata). Mean heterozygosity, est imated from five polymorphic and 23 monomorphic allozyme loci, and salinity tolerance, measured as the mean survival time after transfer from fresh wa ter to 35 ppt seawater, were greater in the wild populations than in the do mestic strains. The result suggested that inbreeding has decreased both the mean heterozygosity and the salinity tolerance in the domestic strains. Al though the individual level of multilocus heterozygosity and allozyme genot ype did not correlate with the individual salinity tolerance within each po pulation, a positive correlation (P < 0.01) was observed between the mean h eterozygosity and the salinity tolerance among the wild populations and the domestic strains. These results suggest that overall heterozygosity may be important in determining a fitness-related trait, but that the effect of t he individual loci screened is too small to be detected by examining a limi ted number of one-locus genotypes. However, the mean heterozygosity of a se t of loci may be sensitive enough to be a useful indicator for inbreeding d epression of the fitness-related trait in a population. (C) 2000 Elsevier S cience B.V. All rights reserved.