Microevolution, low clonal diversity and genetic affinities of parthenogenetic Sitobion aphids in New Zealand

In sharp contrast to their southeast Asian and European counterparts, Sitob ion miscanthi and S. near fragariae aphids in Australia exhibit a complete absence of sexual reproduction. This demands an explanation within the cont ext of the evolution and maintenance of sex and parthenogenesis. Accordingl y, we executed a genetic analysis of the two species in neighbouring New Ze aland. Microsatellites and single-stranded conformation polymorphism/sequen ce analysis of the nuclear gene elongation factor Icl were used to identify aphid clones and confirm species identification, respectively. Karyotypic variation was also investigated. The New Zealand fauna showed few (nonrecom bining) genotypes and appears to have received migrants from both Australia and Asia. Other genotypes have apparently arisen in situ in New Zealand, e xhibiting stepwise mutation of microsatellite alleles and also karyotypic c hange. Thus, these data represent rare evidence of evolution within wild-li ving parthenogenetic lineages. Karyotypic changes appear to occur at a rate even greater than that of microsatellite evolution. Strong geographical pa rtitioning of genotypes/karyotypes was found, with certain ones predominati ng over large areas. These data suggest that clonal selection could be impo rtant in the distribution and patterning of genetic variation. We present a model to explain the genetic patterns, with particular reference to the ab sence of sexual reproduction in Sitobion aphids in New Zealand and Australi a.