Heterosis following long-term bidirectional selection for mating frequency in male Japanese quail

Reciprocal crosses (sire line shown first and dam line second) among high (H) and low (L) selected lines and the randombred control line (C), which was the base population for the selected lines, were made after 40 generations of bidirectional selection for mating frequency of male Japanese quail. Significant heterosis for the selected trait was found only in crosses between Lines C and L, being 62 and 92% for LC and CL, respectively. Heterosis for percentage of maters was present in all crosses, ranging from 8% for HC and CH to 46% for HL. Three (HC, LH, and CL) of the six crosses had significant heterosis for both 4- and 8-wk BW. Heterosis for 4- and 8-wk BW was also significant for the HL and CH crosses, respectively. For area of the cloacal gland, heterosis was significant in five crosses. Although crosses tended to exhibit higher relative aggressiveness than their respective midparent means, heterosis for this trait was not significant. Reciprocal effects, although not important for most traits, were present for BW in crosses between Lines C and L and Lines H and C. In general, long-term selection for mating frequency of males changed the genetic basis of selected and correlated traits with considerable nonadditive genetic effects observed for most traits in specific crosses.