Inbreeding depression and heterosis in various quantitative traits of the guppy, Poecilia reticulata

The present study examines the effects of inbreeding and crossing on various quantitative traits in the guppy, Poecilia reticulata. Effects of inbreeding and crossing were examined in six quantitative traits; body length at birth, survival at day 120, undwarf rate at day 120, body length at day 120, salinity tolerance and high temperature tolerance. Full-sib matings revealed that the amount of inbreeding depression varied from - 1.0% to 24.6% among the traits and a significant decrease in survival at day 120 and salinity tolerance was observed. This result indicates that inbreeding reduces the performance for some of the quantitative traits but not all. On the other hand, crosses between genetically different strains showed that the amount of heterosis varied from - 1.3% to 42.2% among the six quantitative traits and a significant increase in survival at day 120 and salinity tolerance was observed. The relationship between the amount of inbreeding depression and heterosis supports the theory that the phenomenon of heterosis is the reverse of inbreeding depression, indicating that the traits which have decreased by inbreeding can be recovered by means of crossing. (C) 2003 Elsevier Science B.V. All rights reserved.