Genetic differences between two populations of catarina scallop (Argopecten ventricosus) for adaptations for growth and survival in a stressful environment

Genetic differences between populations and heterosis for growth and survival were evaluated for catarina scallop in two native environments. Significant differences in growth and survival between environments were seen. Growth and survival in Bahia Concepcion, an environment classified as stressful because of high temperatures and low food availability, were significantly lower than in Bahia Magdalena, a food-rich environment with lower temperatures. The populations were differentiated during the last month of grow out in both environments, but only for shell width when grown in Bahia Magdalena, whereas when grown in Bahia Concepcion genetic differences between the populations were seen for all growth traits and survival. For shell width, the best population in each environment was the one native to that bay, which resulted in the significance of the interaction between genotypes and environments for this trait. However, for the other three growth traits, the significance of this same interaction was caused by a greater environmental sensitivity of the Magdalena population when reared in Concepcion. For survival, both the Magdalena population and the cross between Magdalena and Concepcion, demonstrated a high sensitivity to this environment, with significantly lower survivals than the Concepcion population. Though there was heterosis for growth, indicating some degree of dominance on the genetic scale, and the heterosis at Concepcion was significantly larger than that seen at Magdalena, no 'useful heterosis' was seen for any trait in either environment, because the cross was never superior to the best growing population. There was no heterosis for survival in either environment. The cause of the increased heterosis for growth at Concepcion is discussed in the context of heterozygote superiority in stressful environments vs, the inadequacy of the additive and dominance quantitative model under which the estimation of heterosis stands, when an interaction between genotypes and environments is detected as significant. The results indicated the Concepcion population is adapted to grow and survive in the stressful environmental conditions characterizing Bahia Concepcion, whereas these adaptations were not present for the Magdalena population. (C) 1998 Elsevier Science B.V. All rights reserved.