Colonisation, Gene Frequencies and Enzyme Activity at GPI Locus of Balanus amphitrite (Cirripedia: Thoracica) in the Lagoon of Venice

Abstract

From May 1997 to April 1998 we have studied the colonisation dynamics of 88 experimental panels, monitoring the allele and genotypic frequencies at GPI locus and GPI activity, of Balanus amphitrite in 3 sites from the lagoon of Venice. Two sampling stations are characterised by severe chemical (the Industrial Channel) and thermal pollution (the outflow of the cooling system of the Fusiria electric power plant). A third station is located in the southern part of the lagoon (Chioggia) where chemical pollution is relatively low and thermal pollution absent. The mean number of successfully colonising animals is significantly different among sites and 80% of total collected individuals is from the power plant oufflow. Very low variability at GPI locus is observed in all sites and on all dates; the frequency of the most common allele is higher than 90%. Most animals (91%) are homozygotes and significant deficiency of heterozygotes, with respect to the H-W equilibrium, is described in populations from the power plant outflow and from Chioggia after 160 and 310 days from panel immersion, respectively. The GPI activity is higher in homozygotes than in heterozygotes and is significantly different among stations. The low genetic variability at GPI locus cannot be linked to chemical and thermal pollution. Differences in enzymatic activity between genotypes and among sites indicate high fitness and plasticity of the homozygote organisms.