Footprints of natural selection at the mannose-6-phosphate isomerase locus in barnacles

• The mannose-6-phosphate isomerase (Mpi) locus in Semibalanus balanoides has been studied as a candidate gene for balancing selection for more than two decades. Previous work has shown that Mpi allozyme genotypes (fast and slow) have different fre-quencies across Atlantic intertidal zones due to selection on post-settlement survival (i.e., allele zonation). We present the complete gene sequence of the Mpi locus and quantify nucleotide polymor-phism in S. balanoides, as well as divergence to its sister taxon Semibalanus cariosus. We show that the slow allozyme contains a derived charge-altering amino acid polymorphism, and both allo-zyme classes correspond to two haplogroups with multiple internal haplotypes. The locus shows several footprints of balancing selec-tion around the fast/slow site: an enrichment of positive Tajima's D for nonsynonymous mutations, an excess of polymorphism, and a spike in the levels of silent polymorphism relative to silent diver-gence, as well as a site frequency spectrum enriched for midfre-quency mutations. We observe other departures from neutrality across the locus in both coding and noncoding regions. These in-clude a nonsynonymous trans-species polymorphism and a recent mutation under selection within the fast haplogroup. The latter suggests ongoing allelic replacement of functionally relevant amino acid variants. Moreover, predicted models of Mpi protein structure provide insight into the functional significance of the putatively selected amino acid polymorphisms. While footprints of selection are widespread across the range of S. balanoides, our data show that intertidal zonation patterns are variable across both spatial and temporal scales. These data provide further evidence for heteroge-neous selection on Mpi.

Subject headings

NATURVETENSKAP  -- Biologi -- Genetik (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Genetics (hsv//eng)

NATURVETENSKAP  -- Biologi -- Ekologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Ecology (hsv//eng)

Keyword

population genetics

ecological genomics

balancing selection

barnacles

Semibalanus balanoides

northern acorn barnacle

balancing selection

semibalanus-balanoides

drosophila-melanogaster

physiological stress

genetic-structure

local

adaptation

spatial scale

polymorphism

mpi

Science & Technology - Other Topics

Publication and Content Type

ref (subject category)

art (subject category)