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United States Department of Agriculture

Agricultural Research Service

Research Project: IMPROVEMENT OF PEST RESISTANCE AND QUALITY TRAITS OF SOYBEAN

Location: Corn, Soybean and Wheat Quality Research Unit

Title: Maintaining genetic diversity and population panmixia through dispersal and not gene flow in a Holocyclic heteroecious aphid species

Authors
item Orantes, Lucia -
item Zhang, Wei -
item Mian, Rouf
item Michel, Andrew -

Submitted to: Heredity
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 20, 2012
Publication Date: May 2, 2012
Repository URL: http://handle.nal.usda.gov/10113/56268
Citation: Orantes, L.C., Zhang, W., Mian, R.M., Michel, A.P. 2012. Maintaining genetic diversity and population panmixia through dispersal and not gene flow in a Holocyclic heteroecious aphid species. Heredity. 109(2):127-134.

Interpretive Summary: The soybean aphid is the number one insect pest of soybean in USA. The life cycle of the aphid alternate between sexual and asexual reproduction on primary and secondary hosts, respectively. Most aphids are generalists, but the soybean aphid survives only on the primary host buckthorn (Rhamnus spp.) and the secondary host soybean (Glycine max). Due to this specialization and sparse primary host distribution, colonization events could be localized and involve founder effects, impacting genetic diversity, population structure and adaptation. We characterized changes in genetic diversity and structure across time among A. glycines populations. Populations were sampled from secondary hosts twice in the same geographic location: once after secondary colonization (early-season) and again immediately prior to primary host colonization (late-season). We specifically tested for evidence of founder effects and genetic isolation in early-season populations, and whether or not late-season dispersal restored genetic diversity and reduced fragmentation. A total of 24 Single Nucleotide Polymorphism and 6 microsatellites markers were used to generate and compare population genetic statistics including the number of genotypes and spatial autocorrelation. We found significantly lower levels of genetic diversity and higher levels of genetic isolation among early-season collections, indicating secondary host colonization occurred locally and involved founder effects. While genetic relatedness significantly decreased with geographic distance in early-season collections, no spatial structure was observed in late-season collections.

Technical Abstract: Heteroecious holocyclic aphids alternate between sexual and asexual reproduction on primary and secondary hosts, respectively. Most of these aphids are generalists, but the aphid specialist Aphis glycines survives only on the primary host buckthorn (Rhamnus spp.) and the secondary host soybean (Glycine max). Due to this specialization and sparse primary host distribution, colonization events could be localized and involve founder effects, impacting genetic diversity, population structure and adaptation. We characterized changes in genetic diversity and structure across time among A. glycines populations. Populations were sampled from secondary hosts twice in the same geographic location: once after secondary colonization (early-season), and again immediately prior to primary host colonization (late-season). We specifically tested for evidence of founder effects and genetic isolation in early-season populations, and whether or not late-season dispersal restored genetic diversity and reduced fragmentation. A total of 24 SNPs and 6 microsatellites were used to generate and compare population genetic statistics including the number of genotypes, FST, and spatial autocorrelation. We found significantly lower levels of genetic diversity and higher levels of genetic isolation among early-season collections, indicating secondary host colonization occurred locally and involved founder effects. Pairwise FST decreased from 0.046 to 0.017 in early and late collections, respectively, and while genetic relatedness significantly decreased with geographic distance in early-season collections, no spatial structure was observed in late-season collections. Thus, late-season dispersal counteracts the population genetic impacts of secondary host colonization through homogenization and increases genetic diversity prior to primary host colonization.

Last Modified: 4/20/2014
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