Ecological Genetics of Sex-Chromosome Traits in the Tiger Swallowtail Butterfly Hybrid Zone

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9981608 PorterThe tiger swallowtail butterfly species Papilio glaucus and P. canadensismeet in a narrow zone of hybridization across the eastern US. They differin ecologically important traits, including the control of winter diapauseand the mimicry (only by P. glaucus females) of a related, distastefulspecies. These traits are controlled by genes on the X- and Y-chromosomes.Theoretical advances in the biology of hybrid zones, such as this one,have allowed the measurement of the strength of natural selection acting onecologically important traits, as well as the rate that other genes canslip through to the opposite species. The authors will use this theory tomeasure the strength of natural selection acting on diapause, wingcoloration and other X- and Y-associated traits. They will do parallelfield experiments to measure selection on these traits. Finally, they willmeasure the ability of this selection to block the spread of other genesbetween these hybridizing species.Sex chromosomes play a central role in biology and have several propertiesunique from other chromosomes, but biologists have few data from natureabout how evolutionary forces affect sex-chromosome variation. The authorsof this study exploit key features of the biology of these butterflies tostudy the evolutionary pressures acting on sex chromosomes and the spreadof genes between related species.