Rapid speciation and karyotype evolution in Orthoptera

Abstract

To test the hypothesis that high speciation rate in groups is coupled with high rate of karyotype evolution but also that younger groups having a higher rate of karyotypic diversity, I estimated rates of speciation and rates of karyotype evolution in 1,177 species belonging to 26 families in the insect order Orthoptera. Rates of karyotype evolution were estimated using the diploid number and the number of chromosome arms (fundamental number) from published karyotypes of Orthoptera. Rates of speciation were quantified considering the number of species examined karyotypically in each family, the most recent common ancestor of each family and the information about extinction rate. The rate of speciation was strongly correlated with rate of karyotype evolution and the average rates of speciation was nearly ~177 times higher than the background rate estimated for Orthoptera based on acoustic communication using phylogenomic data, as well as 8.4 and 35.6 times higher than the estimated speciation rate in vertebrates and bivalve mollusks respectively, indicating that Orthoptera has evolved very fast at chromosomal level. The findings supported the hypothesis of a high speciation rate in lineages with high rate of chromosomal evolution but there were not evidences that younger groups tended to have higher rate of karyotypic diversity. Furthermore, rates of karyotype evolution most closely fitted the punctuational evolutionary model indicating the existence of long periods of stasis of karyotype change with most karyotype change occurring quickly over short evolutionary times. I discussed genetic drift, divergent selection and meiotic drive as potential biological mechanisms to explain karyotype evolution allowing or impeding for the fixation of chromosomal rearrangements and in turn speciation in orthopterans lineages.