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United States Department of Agriculture

Agricultural Research Service

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Research Project: Molecular Markers for Determining Population Differences in Screwworms Originating from Different Geographic Areas

Location: Screwworm Research

2010 Annual Report


1a.Objectives (from AD-416)
Develop molecular genetic techniques for identifying the geographic origin of screwworm samples. The successful exclusion of screwworms from eradicated, as well as from historically non-endemic, areas relies on the accurate and timely identification of suspicious samples and would be greatly enhanced with identification of the origin of outbreaks. In previous research by the collaborator from UN-L, molecular genetic techniques including random amplified polymorphic DNA (RAPD) and amplified fragment length polymorphisms (AFLP) have shown usefulness in identifying ambiguous samples and promise for determining their geographic origin: these techniques need further optimization and standardization. Additionally, genetic variability identified from the molecular data may then be analyzed in a Geographical Information System (GIS) for landscape distribution of genetic variation. If geographic barriers are shown to inhibit movements of screwworms, as inferred by genetic differences, then these barriers would be useful to establishing new eradication programs. Full success of this project will provide primers to identify the species and the geographic area of origin for all life stages of screwworms, providing a valuable new tool for eradication and exclusion personnel responding to suspected outbreaks.


1b.Approach (from AD-416)
Standard Protocols, developed in the Genetics Laboratory of the Department of Entomology at UN-L, for RAPD and AFLP have shown potential for both species identification and determination of geographic origin. They will be used to further explore and catalog genetic variability of screwworm samples collected from different geographic regions (more than 5 areas) of South America; more than two sub-samples, separated by several weeks, will be collected. We will use Landsat TM imagery of the study sites to select areas of favorable screwworm habitat: this will streamline the field collections for each of the areas. Banding patterns for each technique will be evaluated for uniqueness of 'DNA fingerprints'. Band(s), from either or both techniques, that are unique (for identifying the geographic origin of screwworms) and consistently produced on gels will be excised from the gel, sequenced, and primers developed and tested for unique amplification from screwworm samples from different geographic origins. Resultant analyses of molecular data, particularly distance matrices and dendrograms that summarize genetic variability, will be used in GIS analysis for visualizing spatial population structures for the remaining areas of native screwworm populations. We will analyze differences in DNA 'fingerprints', and possibly limited sequence differences, of geographically different populations of screwworm. All spatial and geographical analysis will be performed using ESRI ARCGIS 8. Kridging, a spatial modeling technique, will be used on these structures to identify geographic areas of high genetic variability.


3.Progress Report

A Ph.D. student has conducted clinical analysis, using the technique called random amplified polymorphic DNA - polymerase chain reaction (RAPD-PCR), of unknown samples of screwworm larvae sent from the outbreak in Panama (May 2009). These analyses took much of the student's time. Progress was made toward sequencing DNA bands from RAPD-PCR for use in developing a marker unique towards screwworms, an important first step in rapid, positive identification of new cases of screwworms. The student is now awaiting samples from South America and other regions where screwworm is endemic so to begin genetic analysis and compare DNA "fingerprints". This work will help determine spatial distribution of genetic subtypes of screwworm flies across their current range. The ADODR monitored the progress of this project by communicating weekly by telephone and email with cooperator, as well as through face-to-face meetings with the cooperator at least 3 times per year.


Last Modified: 7/28/2014
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