A molecular phylogenetic study of two relict species of melanopline grasshoppers

Two species belonging to the large grasshopper genus Melanoplus, Melanoplus gaspesiensis and Melanoplus madeleineae, are thought to have survived in refugia in eastern Canada during the Wisconsin glaciation period and perhaps during earlier glacial episodes as well. It has been proposed that either Melanoplus borealis, which is widely distributed today, or its antecedent gave rise to the two relict species. Our research, based on standard phylogenetic analyses of mitochondrial sequences, examines this claim by establishing the positions of M. gaspesiensis and M. madeleineae within Melanoplus. There is a very close and strongly supported connection between M. madeleineae and M. borealis (d = 1.36%), whereas M. gaspesiensis is more distant from the latter (d = 2.08%) and appears closely aligned with two other species. Molecular clock estimates of the times of separation of M. madeleineae and M. gaspesiensis from M. borealis are 0.68 and 1.04 million years ago, respectively. Within-species diversities of 1.01 and 0.70% for M. madeleineae and M. gaspesiensis, respectively, are of comparable magnitudes to that of the continentally distributed Melanoplus sanguinipes (0.86%), clearly indicating that neither species endured bottleneck effects despite isolation.