Life Cycle in Periodical Cicadas

-Several lines of evidence suggest that the 13-year life cycle is genetically dominant over the 17-year life cycle in periodical cicadas. They are: (1) 13-year dominance best predicts the decline of 17 -year Brood X, and concomitant increase in Brood XIX in the midwest, following a hypothesized 1868 hybridization with 13-year Brood XIX through assimilation of heterozygotes into Brood XIX; (2) the pattern of 4-year off-schedule emergences of recessive segregates in Illinois following the proposed 1868 hybridization is consistent with a 13-year dominance model, but is inconsistent with a 17 -year dominance model; and (3) migration of a strongly selected and dominant 13-year allele best explains the synchronization and proximity of contrasting genotypes within the ranges of Broods XIX and XXIII in the mid west.