E. S. Krafsur

Population structure of the tsetse fly Glossina pallidipes estimated by allozyme, microsatellite and mitochondrial gene diversities.

Diversities at nuclear and mitochondrial loci were examined in eleven natural populations of Glossina pallidipes from east and southern Africa. Alleles in each class of loci are assumed to be selectively neutral. Allozyme gene diversities (heterozygosities) averaged over eight loci were 0.146 among seven Kenya populations and 0.201 among four southern African populations. Microsatellite diversity averaged over three loci was 0.250 in Kenya and only 0.218 in southern Africa. Mitochondrial diversities averaged 0.504 in Kenya and only 0.156 in southern Africa. Mitochondrial and microsatellite diversities in the populations were strongly correlated with each other, but uncorrelated with allozyme diversities. In contrast to the allozyme diversities, mitochondrial and microsatellite variation indicated a severe and prolonged reduction in population size in southern Africa. Genetic distances among populations increased with the geographical distances between them. Allozyme diversities in southern populations were conserved. Genetic differentiation at allozyme loci among populations was greatly damped when compared with the other markers. The foregoing can be explained if allozyme diversities were maintained by balancing selection. Three main points emerged: genetic data confirm the historical evidence that southern G. pallidipes populations experienced a severe and prolonged bottleneck; allozyme variation was conserved in the bottlenecked populations; and gene flow among populations is surprisingly restricted.

Genetic differentiation of some Glossina morsitans morsitans populations

To study the population structure of Glossina morsitans morsitans Westwood (Diptera: Glossinidae), polymerase chain reaction (PCR) and single‐strand conformational polymorphism (SSCP) methods were used to estimate mitochondrial DNA diversity at four loci in six natural populations from Zambia, Zimbabwe and Mozambique, and in two laboratory cultures. The Zambian and Zimbabwean samples were from a single fly belt. Four alleles were recorded at 12S and 16S1, and five alleles at 16S2 and COI. Nucleotide sequencing confirmed their singularities. Chi‐square contingency tests showed that allele frequencies differed significantly among populations. Mean allele diversities in populations averaged over loci varied from 0.14 to 0.61. Little loss in haplotype diversity was detected in the laboratory cultures thereby indicating little inbreeding. Wright’s fixation index FST in the natural populations was 0.088u2003±u20030.016, the correlation of haplotypes within populations relative to correlations in the total. A function of its inverse allows an estimate of the mean equivalent number of females exchanged per population per generation, 5.2. No correlation was detected between pairwise genetic distance measures and geographical distances. Drift explains the high degree of differentiation.

Genetic differentiation of Glossina morsitans centralis populations.

Variation at mitochondrial and microsatellite loci was used to study the breeding and dispersal structure of Glossina morsitans centralis, in six natural populations from Botswana, the Caprivi Strip (Namibia), Zambia, and in a laboratory culture derived from Singida, Tanzania. Only seven mitochondrial haplotypes were found. Mean diversity averaged over the six natural populations was 0.216 ± 0.085. The fixation index FST = 0.866 indicated a high degree of genetic differentiation among populations. Fifty‐three alleles were detected among six microsatellite loci and six natural populations. Mean microsatellite diversity was 0.702 ± 0.091. Depending on the estimating model used, fixation indices varied from 0.15 to 0.225 confirming that G. m. centralis populations are strongly subdivided. For all FST estimates, positive correlations were detected between pair‐wise genetic distance measures and geographical distances. The difference in fixation indices estimated from mitochondrial or nuclear loci was explained by the greater sensitivity of mitochondrial genomes to genetic drift. Population differentiation can be explained by genetic drift and the subsequent recovery of extant populations from small, discontinuous populations. These data confirm genetically the collapse and retreat of G. m. centralis populations caused by the rinderpest epizootic of the late 19th and early 20th centuries.

Population genetics of Glossina morsitans submorsitans (Diptera: Glossinidae)

Breeding structure of Glossina morsitans submorsitans Newstead was evaluated by using genetic markers in mitochondrial DNA where diversity was scored at two loci in five natural populations from The Gambia and two populations in Ethiopia (form ugandensis Vanderplank), countries separated by c. 5450 km. Twenty six haplotype combinations were found, of which 17 were shared among two or more populations. Nine haplotypes were found in The Gambia and 23 haplotypes in Ethiopia. There were 12 unique haplotypes. Only six haplotypes were shared between the two countries. Populations in The Gambia (he = 0.26 +/- 0.04) showed less than a third of the diversity of populations in Ethiopia (he = 0.84 +/- 0.03). This suggests recovery from an earlier reduction in population. In a nested analysis of molecular variance of haplotype frequencies, 65% of the variance was due to differences within populations, 34% to differences between populations grouped by country, and only 1% was due to differences among populations within countries. In terms of gene flow, the fixation index FST = 0.35, which leads to an estimate by Wrights island model of less than one reproducing migrant per generation exchanged between the eastern and western submorsitans populations. Neis genetic similarity measure showed a deep division between Gambian and Ethiopian populations.

Fecundity and size in the housefly: investigations of some environmental sources and genetic correlates of variation

Abstract. Environmental sources and genetic correlates of variation in fecundity and size were studied in field and laboratory housefly populations in central Iowa, U.S.A. Electrophoresis of enzymatic proteins was used to monitor genotypes and heterozygosity. In the field, mean fecundity declined as adult densities increased. Fecundity varied greatly within breeding seasons. Fly body size varied spatially and temporally during summer and winter. Fecundity and size were positively correlated. Size was independent of genotypes at the six loci studied. No relationship was observed between heterozygosity and the magnitude or variability of body size.

Mitochondrial diversity evaluated by the single strand conformation polymorphism method in African and North American house flies (Musca domestica L.).

Single strand conformation polymorphisms (SSCPs) provide a convenient and inexpensive method of surveying mitochondrial genetic variation in large samples. We investigated how much variation should be incorporated into such surveys by scoring SSCP variation at eight mitochondrial loci in each of four sub‐Saharan African and four North American house fly (Diptera: Muscidae.) populations. Hierarchical analysis of diversity was performed on haplotype frequencies at each locus and on haplotype frequencies formed by combining haplotypes from two, three, four, five and eight loci. Composite haplotypes at two loci were as informative about population structure as those composed of a greater number of loci. Increasing the number of loci increased diversity estimates within, but not between, populations. Mean composite haplotype diversities (16S2 and COII) were 0.49 ± 0.09 among the African populations and 0.32 ± 0.08 among the North American populations. Only two of 16 haplotypes were shared between continents. Neis genetic differentiation statistic between populations in continents GPC was 0.30 ± 0.06 and mean genetic differentiation between continents GCT was 0.39 ± 0.06. We conclude that there has been little detectable gene flow between North America and sub‐Saharan Africa.

Climatological correlates of screwworm (Cochliomyia hominivorax) abundance in Texas, U.S.A.

ABSTRACT. The causes of screwworm (Cochliomyia hominivorax) outbreaks in North America are not well understood, but the literature suggests that climate was historically important. Screwworm case incidence in each of seven climatological divisions of Texas was examined for the years 1962‐83, the period when sterile‐male releases were made. Weak but statistically significant correlations were found between winter and summer cases and mean winter and summer rainfall and temperature when the independent variables were examined one at a time. Multiple regression of log case incidence on previous quarterly cases and current rainfall and temperatures showed a significant, negative effect of temperature on summer cases. Lagged screwworm cases accounted for most of the variation in quarterly cases. No climatic effects were detected in the other seasons. Rainfall was statistically unrelated to screwworm abundance in any season even in an arid region. The analysis does not support a climatic genesis of screwworm outbreaks or eradication. The sterile‐male method is a credible explanation for screwworm disappearance.

Analysis of gene flow in North American face fly (Musca autumnalis) populations

Abstract. Vertical polyacrylamide gel electrophoresis was used to resolve enzymes at ten putative loci in face flies Musca autumnalis De Geer, a colonizing, Palaearctic species established in North America for at least 210 generations. Flies were sampled in 1991 from six locations in Iowa, two in Maryland, two in Minnesota, two in Tennessee, three in New York, and three in Missouri. Nondirectional temporal variation in gene frequencies over a 4‐year interval was detected at farms in central Iowa. Heterogeneity in allele frequencies was detected among farms in Iowa, Maryland, New York and Minnesota but not in Tennessee and Missouri. There were no consistent departures from random mating. Partitioning variances in gene frequencies showed that 58% of the variation occurred in populations among states and 43% between populations within states. Mean reproducing immigrants per population per generation was estimated to be eighteen flies. No regional genetic differentiation was detected, and there were no barriers to gene flow within or among diverse populations in the six states. Earlier data bearing on gene flow among and between Nearctic and Palearctic face fly samples were analysed and significant differentiation was not detected.

Induction of dominant lethal mutations for control of the facefly, Musca autumnalis DeGeer

Abstract. 1 Application of the sterile insect technique (SIT) to the facefly, Musca autumnalis DeGeer, is considered. 2 Six‐day‐old pupae were exposed to ionizing irradiation at doses in the range 100–1600 rads, each treatment being replicated six times. 3 Eclosion was unaffected but fecundity and fertility was inversely proportional to the radiation dose. 4 1600 rads gave 97% dominant lethality of sperm in treated males and suppressed ovarian development in females. Irradiated flies did not recover fertility. 5 Irradiation of males and females did not affect insemination rates. 6 Sterile males showed a decline in longevity and reduced mating competitiveness. 7 Local eradication of M. autumnalis is considered to be feasible if sufficient diapausing sterile flies are stockpiled and released in early spring, followed by additional releases of non‐diapausing flies in late spring and early summer, with further releases of diapausing sterile flies in late summer and autumn.