LENGTH POLYMORPHISMS IN AN INTRON OF AMINOPEPTIDASE N PROVIDE A USEFUL NUCLEAR DNA MARKER FOR LITTORINA SPECIES (CAENOGASTROPODA)

Abstract

Studies of population genetic structure and hybridization among ecotypes of Littorina require both mitochondrial and nuclear markers, yet relatively few nuclear markers have been described. We used universal PCR primers for aminopeptidase N that were originally developed for the Pacific oyster, to amplify the gene in Littorina subrotundata. Three different sized PCR products (320 bp, 460 bp and 720 bp) were obtained and identified as three different proteins containing the zinc-binding motif HEXXHXW, characteristic of aminopeptidase N. We chose the locus with the longest intron, APN54, and designed primers in the flanking exon sequence that were specific for locus APN54 for Littorina species. The Littorina-specific primers successfully amplified only the APN54 locus in all seven species of Littorina tested and showed considerable between- and within-species polymorphism in intron sequence and length. We present data from two populations of two different species, L. subrotundata and L. sitkana, that show our new nuclear marker has two or three common alleles per locus and is therefore an especially efficient population marker for small sample sizes.