Intraspecific genetic variability in mitochondrial DNA of the screwworm fly (Cochliomyia hominivorax)

Abstract

Mitochondrial DNA variability has been analyzed in the primary screwworm fly (Cochliomyia hominivorax) using restriction endonuclease fragment patterns and restriction site mapping. A total of 30 different screwworm lines originating from Texas to Costa Rica and the Island of Jamaica was examined using 15 restriction endonucleases. Eleven of the restriction enzymes revealed polymorphism and yielded 16 mitochondrial genotypes or haplotypes. Two of the haplotypes were widely distributed, haplotype 1 being found scattered across southern Mexico and haplotype 2 along the west coast of Mexico. Haplotype 1 also appeared paired with several other haplotypes in mixed lines that were most likely the result of collecting an egg mass to which more than one female had contributed or to some form of contamination by haplotype 1 after introduction into the laboratory. These lines became fixed before single insects were examined and thus it is impossible to rule out heteroplasmy. The other 14 haplotypes were found in only a single locale and 12 of these were found in only one line. The average sequence diversity among 27 mainland lines was about 0.5%. The two Jamaican lines and one east coast mainland line differed from the others by greater than 2%. The pattern of geographical distribution, a small number of apparently recurring haplotypes and a substantial number (75%) of the haplotypes unique, bears similarities to patterns observed in other insects such as Drosophila. The high frequency of unique genotypes in southern Mexico suggests a population with a very reduced gene flow, which may have had a positive effect on the sterile male release control program.

Mitochondrial DNA variation in screwworm

“…The Hind III site in amplicon 2 showed a similar pattern . This site was present in all of our South American and Caribbean samples, but was absent in all of Roehrdanz's (1989) North American samples except two . The Dde l sites in amplicon 2 appear to be associated with the Hinc II sites and may follow the same pattern .…”

“…haplotypes outside of their proposed range . Roehrdanz (1989) found one such sample, STD32, from Quintana Roo, Mexico, which was more similar to the Jamaican haplotype than that of the other Mexican samples . We observed two samples, Bijagau 2 and Trinidad 3, which were more similar to geographically distant populations than their local counterparts.…”

“…Combining our data for the Caribbean. Central America and South America with those of Roehrdanz (1989) Table 5 . Site changes denoted by asterisks occur more than once in the tree.…”

“…Roehrdanz and coworkers (Roehrdanz & Johnson . 1988 ;Roehrdanz . 1989 ;Taylor et al, 1991) found screwworm mitochondrial DNA (mtDNA) to be highly variable .…”

“…1989 ;Taylor et al, 1991) found screwworm mitochondrial DNA (mtDNA) to be highly variable . Virtually every screwworm sample from southern Mexico had a unique mtDNA haplotype (Roehrdanz, 1989) . Less variation was observed in samples from northern Mexico and the United States .…”