Rate Of Diversification In Crickets (Orthoptera: Ensifera) And A Possible Role Of F Supergroup Wolbachia In Bush Crickets

Abstract

Part I: Rates of speciation can tell us more than how many species have survived over a period of time. They indicate whether there are some characteristics of organisms or biogeography scenarios facilitate or hinder speciation. Many groups of ensiferan insects (e.g. Hawaiian sword-tailed, North American ground and field crickets) have been reported to have rapid speciation rates. To investigate whether the pattern of rapid speciation is common in crickets, we estimated overall diversification rates as a whole and within the clade. Ensifera as a whole does not appear to have particularly rapid diversification rates compared to other insect suborders. In addition, some ensiferan clades are unexpectedly species rich given divergence times. The cause of elevated species richness remains unknown. Part II: Wolbachia pipientis, an intracellular, alpha-proteobacterium, is commonly found in arthropods and filarial nematodes. Most infected insects are known to harbor strains of Wolbachia from supergroups A or B, whereas supergroups C and D occur only in filarial nematodes. Here, we present molecular evidence from two genes (ftsZ and 16SrDNA) that 2 Orthopterans (the bush cricket species Orocharis saltator and Hapithus agitator; Gryllidae: Eneopterinae) are infected with Wolbachia from the F supergroup. Additionally, a series of PCR tests revealed that these bush cricket specimens did not harbor nematodes, thus indicating that our positive results were not a by-product of nematodes being present in these cricket samples. Patterns of molecular variation suggest that: (1) strains of F supergroup Wolbachia exhibit less genetic variation than the nematode-specific C and D supergroups but more than the A and B supergroups found in arthropods and (2) that there is no evidence of recombination within F supergroup strains. The above data support that horizontal transfer of F supergroup Wolbachia has likely occurred recently between these diverse taxonomic groups. Moreover, the limited genetic variation and lack of recombination in the F supergroup suggest it has radiated relatively rapidly with either (1) little time for recombination to occur or (2) selection against recombination as occurs in the mutualistic C and D strains of Wolbachia both of which remain to be explored further.