Genetic features of salinity tolerance in wild and domestic guppies (Poecilia reticulata)

To elucidate the genetic features of salinity tolerance in wild and domestic guppies, Poecilia reticulata, the present study examined the salinity tolerance in four Wild populations and 13 domestic strains. Salinity tolerance was measured as survival time after transfer from fresh water to 35 ppt seawater. In the wild guppies, all four of the wild populations showed significantly higher salinity tolerance than the 13 domestic strains. After domestication of the wild guppies, their salinity tolerance significantly decreased with reductions in salinity tolerant individuals, suggesting inbreeding depression. In the domestic guppies, on the other hand, strain differences were observed during both 1993 and 1997. A significant positive correlation between those in 1993 and 1997 suggests that the genetic constitutions for salinity tolerance have stabilized in each strain as a consequence of long-term maintenance F₁ hybrids between the domestic strains showed significantly higher salinity tolerance with many salinity tolerant individuals which were not observed in their parental strains, thus indicating a hererotic effect. The salinity tolerance in the F₁ hybrids reached the same level as that in the wild populations. Salinity tolerance significantly decreased with reductions in the salinity tolerant individuals in the F₂. The results of the domestications and the cross experiments suggested that the significant difference in salinity tolerance between the wild and the domestic guppies was caused by heterosis and inbreeding depression.