Tracking the global dispersal of a cosmopolitan insect pest, the peach potato aphid.
BACKGROUND
Global commerce and human transportation are responsible for the range expansion of various insect pests such as the plant sucking aphids. High resolution DNA markers provide the opportunity to examine the genetic structure of aphid populations, identify aphid genotypes and infer their evolutionary history and routes of expansion which is of value in developing management strategies. One of the most widespread aphid species is the peach-potato aphid Myzus persicae, which is considered as a serious pest on various crops in many parts of the world. The present study examined the genetic variation of this aphid at a world scale and then related this to distribution patterns. In particular, 197 aphid parthenogenetic lineages from around the world were analysed with six microsatellite loci.


RESULTS
Bayesian clustering and admixture analysis split the aphid genotypes into three genetic clusters: European M. persicae persicae, New Zealand M. persicae persicae and Global M. persicae nicotianae. This partition was supported by FST and genetic distance analyses. The results showed two further points, a possible connection between genotypes found in the UK and New Zealand and globalization of nicotianae associated with colonisation of regions where tobacco is not cultivated. In addition, we report the presence of geographically widespread clones and for the first time the presence of a nicotianae genotype in the Old and New World. Lastly, heterozygote deficiency was detected in some sexual and asexual populations.


CONCLUSIONS
The study revealed important genetic variation among the aphid populations we examined and this was partitioned according to region and host-plant. Clonal selection and gene flow between sexual and asexual lineages are important factors shaping the genetic structure of the aphid populations. In addition, the results reflected the globalization of two subspecies of M. persicae with successful clones being spread at various scales throughout the world. A subspecies appears to result from direct selection on tobacco plants. This information highlights the ultimate ability of a polyphagous aphid species to generate and maintain ecologically successful gene combinations through clonal propagation and the role of human transportation and global commerce for expanding their range.
1Department of Biochemistry-Biotechnology, University of Thessaly, Ploutonos 26, 41221 Larissa, Greece. johnmargaritopoulos@gmail.com
John T
JT
Margaritopoulos
Louise
L
Kasprowicz
Gaynor L
GL
Malloch
Brian
B
Fenton
D000818:Animals; D001042:Aphids / Q000235:genetics* / Q000254:growth & development; D001499:Bayes Theorem; D016000:Cluster Analysis; D005787:Gene Frequency; D014644:Genetic Variation; D005828:Genetics, Population; D049750:Genome, Insect; D005838:Genotype; D005843:Geography; D015810:Linkage Disequilibrium; D018895:Microsatellite Repeats; D012100:Reproduction, Asexual / Q000235:genetics