Evolution of stickleback spines through independent cis-regulatory changes at HOXDB

Understanding the genetic mechanisms leading to new traits is a fundamental goal of evolutionary biology. We show that HOXDB regulatory changes have been used repeatedly in different stickleback fish species to alter the length and number of bony dorsal spines. In Gasterosteus aculeatus, a variant HOXDB allele is genetically linked to shortening an existing spine and adding a spine. In Apeltes quadracus, a variant allele is associated with lengthening an existing spine and adding a spine. The alleles alter the same conserved non-coding HOXDB enhancer by diverse molecular mechanisms, including SNPs, deletions, and transposable element insertions. The independent cis-acting regulatory changes are linked to anterior expansion or contraction of HOXDB expression. Our findings support the long-standing hypothesis that natural Hox gene variation underlies key morphological patterning changes in wild populations and illustrate how different mutational mechanisms affecting the same region may produce opposite gene expression changes with similar phenotypic outcomes. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=154 SRC="FIGDIR/small/472698v1_ufig1.gif" ALT="Figure 1"> View larger version (32K): org.highwire.dtl.DTLVardef@8e6675org.highwire.dtl.DTLVardef@e89e13org.highwire.dtl.DTLVardef@1e1f1dcorg.highwire.dtl.DTLVardef@cdb6f8_HPS_FORMAT_FIGEXP M_FIG C_FIG