S10-1.2 Saturday, Jan. 7 Population genomics of the acorn barnacle: tests of balancing selection at Mpi and diversifying selection across the genome RAND, DM; FLIGHT, PA*; Brown University; Brown University David_Rand@brown.edu
The acorn barnacle, Semibalanus balanoides, has been a model system in marine ecology for decades owing to its distinctive zonation in the intertidal, high dispersal and recruitment dynamics. These features make it an excellent model for studies of selection in the wild given its sessile habit and the range of microenvironments that span the intertidal. The glycolytic allozyme locus Mpi has figured prominently in the population genetics of the acorn barnacle as a gene responding to balancing selection in alternative environments. Here we report the DNA sequence of Mpi and identify the amino acid charge change site that is the putative target of selection. Sequence variation around this site is consistent with historical balancing selection as indicated by an excess of intermediate frequency polymorphisms. To provide a more rigorous null model for patterns of variation in the barnacle genome, whole genome sequence data were collected using the Illumina platform applied to pooled samples of 20 individuals from each of three sites (Rhode Island USA, Maine USA and Southwold UK). The allele frequencies at over 300,000 high quality SNPs were quantified in these three populations and coalescent simulations were used to estimate the site frequency spectrum of variation across the genome. These data allow us to verify that the excess high frequency polymorphism at Mpi is a significant departure from the genomic average. Moreover, comparison of the three populations revealed many loci that show elevated population differentiation (Fst) providing interesting new candidates for the action of diversifying selection between these geographic localities. The utility of this pooled population genomic sequencing in non-model organisms will be discussed in light of approaches to identify the targets of natural selection in the wild.