Effect of inbreeding on salinity tolerance in the guppy ( Poecilia reticulata)

This experiment was designed to study the relationship between different levels of inbreeding and observed inbreeding depression for salinity tolerance, one of the most important tolerances to environmental conditions, in the guppy ( Poecilia reticulata). Two generations of full-sib mating and six generations of mating in the n=10 produced individuals with an expected level of inbreeding coefficient of 0.375 and 0.265, respectively. A significant decrease in the mean value of salinity tolerance, expressed by survival time in 35-ppt seawater, was observed in both the full-sib mated line and the closed line of n=10, indicating inbreeding depression for salinity tolerance. The mean and coefficient of variation (C.V.) of salinity tolerance decreased linearly with the increase in inbreeding coefficient with a rate of 9.1% and 10.1% per 10% increase in the inbreeding coefficient, respectively. Analyses among seven lines of the full-sib matings indicated that inbreeding caused the larger reduction of the means observed in the lines having higher salinity tolerance at the P generation and decreased both deviations of the means among the lines and C.V. within each line. The linear decrease in salinity tolerance with an increase in inbreeding coefficient suggests that inbreeding depression for salinity tolerance results from additive combination among the loci responsible for inbreeding depression.