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RESEARCH PRODUCT

Geographic distribution and seasonal variation of mitochondrial DNA haplotypes in the aphidRhopalosiphum padi(Hemiptera: Aphididae)

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AbstractThis study examines the spatial and seasonal patterning of mitochondrial DNA diversity in French populations of the bird cherry-oat aphid,Rhopalosiphum padi(Linnaeus), on both its primary and secondary hosts. Our results confirm the presence of two major mitochondrial lineages that are generally associated with the breeding system variation (cyclic and obligate parthenogenesis) shown by this species. The strength of this relationship varies regionally, being most evident in the south and west. Cyclically parthenogenetic populations show no significant regional or seasonal genetic divergence reflecting high levels of gene flow, possibly promoted by their obligate host-alternation. However, obligately parthenogenetic populations show a north-south cline in the distribution of the dominant haplotypes. This pattern might result from a selective advantage of some obligately parthenogenetic lineages under cold temperature regime. Alternatively, this cline might be established by a gradient in the intensity of nuclear gene flow between cyclically and obligately parthenogenetic populations mediated by androcyclic males. The discrimination between these possible explanations will require extending analysis to include hypervariable nuclear markers.