Intercontinental island hopping: Colonization and speciation of the grasshopper genus Phaulacridium (Orthoptera: Acrididae) in Australasia

Due to their distance from the pole and extent of surrounding oceans, southern hemisphere lands were not subjected to such severe climatic conditions in the Pleistocene as those in the northern hemisphere. Pleistocene climate cycling did however result in extensive shifts in habitat zones due to fluctuation of rainfall and temperature. Warm and wet conditions during interglacials supported southward extension of forests, whereas cooler and drier environments during glacial maxima increased the extent of dry grassland and scrub conditions. Such fluctuations are likely to have influenced the spatial distribution and evolution of the fauna of Australasia. Using data from four genes (two mitochondrial and two nuclear) the genetic structure of the trans-Tasman grasshopper genus Phaulacridium was used to infer phylogeographic patterns.The widespread New Zealand species Phaulacridium marginale shows a phylogeographic pattern typical of recent range expansion, with low genetic diversity within the species. In stark contrast, the other New Zealand species Phaulacridium otagoense is extremely localized in two small areas in southern New Zealand where it exhibits very high genetic diversity. The phylogeographic patterns in Australian Phaulacridium, however, show deeper divergence within the most widespread species, than between different species in the same area. Mismatched correlation between geographic scale and genetic diversity imply that populations’ genetics contain the signature of past species ranges.