Genetic variation and heterosis of the interspecific abalone hybrid of Haliotis rubra and H. laevigata

The interspecific abalone hybrid of Haliotis rubra x H. laevigata is an important commercial species for abalone aquaculture in Australia. A selective breeding program is in operation to genetically improve hybrid performance for total weight, meat yield, and appearance traits (epipodium pattern and foot colour). This study provides estimates of heterosis for these traits and genetic parameters for the two parental species and their hybrid populations, measured using 73,107 individuals collected over 14 generations. Measurements were made at 1.5 and 2.5 years for total weight, meat yield and appearance traits. Genetic variation was significant for all eval-uated traits and was predominantly due to additive genetic variation. The heritability (h2) estimates of total weight at 2.5 years for H. rubra and H. laevigata was 0.54 +/- 0.03 and 0.45 +/- 0.02, respectively, but higher in the hybrid population (0.57 +/- 0.01). For other traits the h2 estimates of hybrid populations were within the range of those for pure species. The range of h2 (with SE) at 2.5 years for meat yield, epipodium pattern and foot colour were 0.27 (0.06) to 0.78 (0.04), 0.35 (0.05) to 0.62 (0.03), and 0.18 (0.03) to 0.30 (0.02), respectively. Heterosis was present for all traits except foot colour. Effects were strongest for total weight, with a 67% gain over the mid parent value, and less for meat yield, epipodium pattern, and foot colour with gains of 6%, 9% and 6% over mid parent value, respectively. Genetic correlations between pure species performance and hybrid performance for total weight were 0.45 (0.17) for H. rubra and 0.75 (0.06) for H. laevigata and ranged from 0.27 to 0.85 for other traits. These correlations were a basis for decisions about the commercial breeding strategy. The strategy adopted is a form of reciprocal recurrent selection which uses a hybrid progeny test. Selection is based on estimation of additive hybrid effects and measurements are made on both hybrid and pure species which are treated as separate and correlated traits.