SHAPIRO, M.D.; MARKS, M.E.; PEICHEL, C.L.; SCHLUTER, D.; KINGSLEY, D.M.; Stanford University, CA; Stanford University, CA; Hutchinson Cancer Research Center, Seattle, WA; University of British Columbia, Vancouver; Stanford University, CA: Genetic basis of pelvic reduction in sticklebacks

Reduction and loss of the appendicular skeleton occur frequently in the evolution of vertebrates, yet we know very little about the genetic mechanisms that generate these modifications. Stickleback fish (Family Gasterosteidae) show intraspecific and intergeneric diversity in pelvic skeletal morphology � including the complete loss of pelvic structures � and thus offer unique opportunities to dissect the genetic mechanisms of adaptive skeletal traits. We have examined the genetic architecture of pelvic reduction in a large cross between Japanese marine and Paxton Lake benthic freshwater populations of threespine stickleback (Gasterosteus aculeatus). We measured quantitative pelvic phenotypes in F2 progeny, including sizes of skeletal elements, and asymmetry between left and right sides. Genome-wide linkage mapping identified a single major chromosome region that controlled a significant amount of the variance in virtually every pelvic phenotype analyzed, and a number of smaller quantitative trait loci that contributed to some traits but not to others. To test the possibility that the same genetic mechanism(s) underlie pelvic reduction in different genera of fish, we also carried out intergeneric complementation tests using fish from threespine and ninespine (Pungitius pungitius) stickleback populations that both show pelvic reduction. The �Stichlingsbastarden� progeny of this cross failed to develop complete pelvic structures, suggesting a common genetic basis for pelvic reduction in both genera. These combined approaches will facilitate molecular studies of the genetic and developmental mechanisms that control evolutionary changes in skeletal morphology during adaptive radiations in vertebrates.