Sitobion in the South Seas - microsatellite revelations.
Sitobion miscanthi and S. nr fragariae infest grasses in Australia and New Zealand. S. miscanthi probably arrived in Australia from Asia before European settlement. It is now represented in Australia by at least four chromosomal races (2n=17, 18, 20 and 21) demonstrated by microsatellite DNA analysis to be survivors of only two original lineages. One of these lineages is now represented by three similar genotypes (the 2n=18 group) which differ by very few mutational changes. The other three karyotypic races have diverged by mutation in Australia from a separate common ancestor, and there has also been some mutational divergence within races. S. nr fragariae has been common in Australia since the 1960s, and microsatellites indicate a single successful colonisation event. Both species also occur in New Zealand, with representatives which are either genetically quite similar, or identical, to their Australian counterparts. However, while genetic analysis indicates no sexual recombination in a large Australian sample, apparently recombined microsatellite genotypes in New Zealand suggest that sexual reproduction has occurred in recent ancestors of some of the New Zealand lineages. Evidence from nuclear and mitochondrial markers indicates genetic exchange between the two 'species' in New Zealand.