Effects of pollution on heterozygosity in the barnacle Balanus amphitrite Darwin (Cirripedia: Thoracica)

The effects of thermal and chemical pollution on gene and genotype frequencies and on multilocus structure were studied in 3 populations of the barnacle Balanus amphitrite Darwin from the lagoon of Venice, Italy. One of these populations (A) was subjected to high chemical pollution; the second (B) was constantly exposed to temperatures about 10-degrees-C higher than the rest of the lagoon since it was settled in front of an electric power plant outflow; and the third (C) was sampled in an unpolluted area of the lagoon as a control. Juvenile and adult age classes of each of the 3 samples were studied by electrophoretic analysis of the polymorphic loci Mpi, Pgi and Pgm. Significant differences were found between Population A adults and both B and C adults for the majority of the genetic comparisons. B and C adult populations did not differ significantly. Statistical comparisons among the 3 juvenile populations showed a high genetic homogeneity. Comparisons between the 2 age classes within each of the 3 populations exhibited significant differences only between adults and juveniles of Population A at the level of gene and genotype frequencies. Moreover, in Population A a significantly higher survival of the multi-homozygote class was observed. No differences were detected between adults and juveniles of B and C samples. These results suggest the action, in Population A, of some selective factor during the post-settlement period. Thermal pollution does not seem to play any important selective role. The hypothesis is advanced that selection is operated by heavy metals.