GENETIC-DIFFERENCES BETWEEN 2 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 s urvival 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 cla ssified as stressful because of high temperatures and low food availab ility, were significantly lower than in Bahia Magdalena, a food-rich e nvironment with lower temperatures. The populations were differentiate d during the last month of grow out in both environments, but only for shell width when grown in Bahia Magdalena, whereas when grown in Bahi a 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 signi ficance of this same interaction was caused by a greater environmental sensitivity of the Magdalena population when reared in Concepcion. Fo r survival, both the Magdalena population and the cross between Magdal ena and Concepcion, demonstrated a high sensitivity to this environmen t, with significantly lower survivals than the Concepcion population. Though there was heterosis for growth, indicating some degree of domin ance on the genetic scale, and the heterosis at Concepcion was signifi cantly larger than that seen at Magdalena, no 'useful heterosis' was s een for any trait in either environment, because the cross was never s uperior to the best growing population. There was no heterosis for sur vival in either environment. The cause of the increased heterosis for growth at Concepcion is discussed in the context of heterozygote super iority in stressful environments vs, the inadequacy of the additive an d dominance quantitative model under which the estimation of heterosis stands, when an interaction between genotypes and environments is det ected as significant. The results indicated the Concepcion population is adapted to grow and survive in the stressful environmental conditio ns characterizing Bahia Concepcion, whereas these adaptations were not present for the Magdalena population. (C) 1998 Elsevier Science B.V. All rights reserved.