Longitudinal genetic analysis of growth-related traits in red swamp crayfish Procambarus clarkii (Girard)

The red swamp crayfish, Procambarus clarkii, is an economically important species especially in China. Their exoskeleton places serious constraints on growth and culture management. Their growth is achieved through intermittent molting/ecdysis. The longitudinal genetic dynamics for growth-related traits at different ecdysial points in P. clarkii has been unclear to date. In this study, conditional genetic analysis was carried out for growth-related traits (body weight, body length, chela length, and cephalothorax length) based upon a mixed genetic model with conditional additive, dominance, and genotype by environment effects in P. clarkii. A complete diallel cross was made among three geographic populations of P. clarkii for the genetic mating design. Results of the conditional genetic analysis showed that from 4(th) molt to 9(th) molt the conditional additive variations were increased significantly whereas the conditional non-additive genetic variations (dominance and genotype by environment interaction) were decreased significantly for these growth-related traits. This indicated that lots of new expression of additive effect genes for body weight, body length, chela length, and cephalothorax length occurred during ontogeny, and environment played a significant role in the expression of genes affecting these growth-related traits. Growth of the four traits was mainly affected by non-additive genetic effects in early developmental stage (prior to 4(th) molt). The cumulative conditional additive variation for the growth-related traits from 4(th) molt to 9(th) molt accounted for a large majority of the total conditional additive variations from 2(nd) molt to 9(th) molt, indicating that this period was very important for the growth of this species. Using the conditional analysis method, dynamics of growth-related traits during an important ontogenetic phase of red swamp crayfish was uncovered. Our results provide valuable insights into refining production of this species.