Submitted to: BMC Research Notes
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/26/2013
Publication Date: 7/2/2013
Citation: Dickey, A., Hall, P.M., Shatters, Jr., R.G., McKenzie, C.L. 2013. Evolution and homoplasy at the Bem6 microsatellite locus in three sweetpotato whitefly (Bemisia tabaci) cryptic species. BioMed Central Research Notes. 6:249. Available: http://www.biomedcentral.com/1756-0500/6/249. Interpretive Summary: The evolution of microsatellite genetic markers is often complex. Sometimes individuals have the same size microsatellite DNA fragment and are mistakenly determined to share a recent common ancestor. Sequencing these DNA fragments reveals some of these cases of mistaken identity. In species that cannot be distinguished based on anatomical features, this is a particular problem. In the case of sweet potato whitefly Bemisia tabaci, a damaging pest of a variety of crops, three different species which can not be distinguished visually showed evidence of hybridizing or being more closely related because they have the same size Bem6 microsatellite fragments. But once the fragments were DNA sequenced, no evidence of fragment sharing or hybridization remained. Sequencing the fragments also provided clues about how this section of DNA evolves; by adding or deleting one seven-nucleotide piece at a time from a part of the fragment where these seven-nucleotide pieces are repeated. Four distinct seven-nucleotide repeat pieces were found in the microsatellite fragments among the three species.
Technical Abstract: The evolution of individual microsatellite loci is often complex and homoplasy is common but often goes undetected. Sequencing alleles at a microsatellite locus can provide a more complete picture of the common evolutionary mechanisms occurring at that locus and can reveal cases of homoplasy. Within species homoplasy can lead to an underestimate of differentiation among populations and among species homoplasy can produce a misleading interpretation regarding shared alleles and hybridization. This is especially problematic with cryptic species. By sequencing alleles from three cryptic species of Bemisia tabaci, designated MEAM1, MED, and NW, the evolution of the Bem6 (CA8)imp microsatellite locus is inferred as one of primarily stepwise mutation occurring at four distinct heptaucleotide tandem repeats. In two of the species this pattern yields a compound tandem repeat. Homoplasy was detected both among species and within species. In the absence of sequencing, size homoplasious alleles would lead to an overestimate of alleles shared and hybridization among cryptic species. The implications for the nomenclature of heptanucleotide tandem repeats and for the evolution of compound microsatellites are discussed.