Species and Hybridization: Understanding the Exchange of Nuclear and Mitochondrial DNA in Song-Delimited Cicada Species Complexes

Two genera of cicadas were investigated to understand the complicated patterns of molecular phylogenetics and population genetics between closely related species. Male calling songs of cicadas are quickly evolving premating reproductive barriers that facilitate species formation and delimitation. The European cryptic species complex Cicadetta montana was used to test gene tree concordance of four genes and the ability of Maximum likelihood (GMYC) and Bayesian (BPP) molecular species delimitation methods to recognize song-delimited species. Both gene trees and molecular species delimitation methods were able to recognize many species, although they were unable to fully recover species in very closely related clades due to either recent rapid speciation or hybridization. In addition, polyphyletic East and West clades were found for C. brevipennis and C. cerdaniensis and none of the molecular species delimitation methods or gene trees identifying these two song-delimited species. Multiple molecular species delimitation methods should be used to guide species delimitation. The New Zealand genus Kikihia also contains a number of cryptic species distinguishable by male calling songs. Seven Kikihia species which come into contact at hybrid zones with at least one other species were investigated for genetic introgression. Mitochondrial DNA sequences and nuclear microsatellite markers from parental populations of each of the seven species and seven hybrid zones were used. Genetic introgression at hybrid zones with parental populations remaining distinct was the most common pattern found regardless of male song structure or genetic distance. One instance of mitochondrial introgression from one species into another was observed, however, no nuclear introgression was observed outside the hybrid zone between these species. The most distinct pattern of introgression was the subject of a more in-depth analysis including song analysis and ecological distribution modeling between the South Island west coast sister species K. “northwestlandica” and K. “southwestlandica”. These species show admixture within the hybrid zone and widespread nuclear introgression outside the hybrid zone, however, mitochondrial haplotypes are found only in the appropriate song-delimited species. Hybridization and introgression occur at every contact zone investigated here and results indicate that these species are in a stable state of exchanging genes while remaining distinct at loci important to species recognition.