Homogeneity test of Hardy-Weinberg deviations in Brazilian littorinids: Evidence for selection?

Echinolittorina lineolata, Littoraria flava and L. angulifera (Gastropoda: Littorinidae) have a wide distribution along the Brazilian coast. The aim of this study was to evaluate the occurrence of Hardy-Weinberg disequilibrium in these species and to verify if there is a pattern in deviations. Isozyme analyses were done on 20 populations of E. lineolata, nine of L. flava and 10 of L. angulifera, collected along 4,000 km of the Brazilian coast. Sixteen polymorphic loci were analysed in E. lineolata, 15 in L. angulifera and 17 in L. flava. Most populations showed heterozygote deficiency in several loci. A homogeneity test among loci showed heterogeneous F-IS values in most populations. This result ruled out inbreeding and the Wahlund effect as the main causes of departure in these populations. In all littorinid species, at least one PGM locus had homogeneous F-IS values. This finding may suggest that this enzyme could have an important role in the fitness of these periwinkles.