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

Abstract

The present study examines the relationships between heterozygosity and a fitness-related trait that shows heterosis in six wild populations and 14 domestic strains of the guppy ( Poecilia reticulata). Mean heterozygosity, estimated from five polymorphic and 23 monomorphic allozyme loci, and salinity tolerance, measured as the mean survival time after transfer from fresh water to 35 ppt seawater, were greater in the wild populations than in the domestic strains. The result suggested that inbreeding has decreased both the mean heterozygosity and the salinity tolerance in the domestic strains. Although the individual level of multilocus heterozygosity and allozyme genotype did not correlate with the individual salinity tolerance within each population, a positive correlation ( P<0.01) was observed between the mean heterozygosity 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 the individual loci screened is too small to be detected by examining a limited number of one-locus genotypes. However, the mean heterozygosity of a set of loci may be sensitive enough to be a useful indicator for inbreeding depression of the fitness-related trait in a population.