MITOCHONDRIAL-DNA VARIATION IN NORTH-AMERICAN MELANOPLINE GRASSHOPPERS

Restriction fragment analysis of mitochondrial DNA (mtDNA) was used to examine genetic variation within and among 11 species of grasshoppers in the subfamily Melanoplinae. Total DNA of 236 individuals was digested with 10 restriction enzymes and probed with three cloned EcoRI fragments representing the entire mitochondrial genome of Melanoplus sanguinipes. The average size of mtDNA for these species was about 16.1 kilobases. Average nucleotide diversities within species ranged from 0.00 to 0.31 per cent. Values are considered low and possibly reflect chronically small population sizes in pre-agricultural times as well as bottlenecks engendered by various glacial episodes. Species regarded as major pests appear to have larger diversities. For each species, common genotypes occur throughout the sampled region suggesting very little spatial differentiation although in a couple of melanoplines, one or two haplotypes are geographically restricted. Comparisons among species led to a hypothesis concerning their phylogenetic relationships. Not all affinities accorded with expectations based on morphological comparisons. The estimated time of divergence for the genus Melanoplus is at least 4 million years.