School of BioSciences - Research Publications

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    Characterizing the Aedes aegypti Population in a Vietnamese Village in Preparation for a Wolbachia-Based Mosquito Control Strategy to Eliminate Dengue
    Jeffery, JAL ; Yen, NT ; Nam, VS ; Nghia, LT ; Hoffmann, AA ; Kay, BH ; Ryan, PA ; Gubler, D (PUBLIC LIBRARY SCIENCE, 2009-11)
    BACKGROUND: A life-shortening strain of the obligate intracellular bacteria Wolbachia, called wMelPop, is seen as a promising new tool for the control of Aedes aegypti. However, developing a vector control strategy based on the release of mosquitoes transinfected with wMelPop requires detailed knowledge of the demographics of the target population. METHODOLOGY/PRINCIPAL FINDINGS: In Tri Nguyen village (611 households) on Hon Mieu Island in central Vietnam, we conducted nine quantitative entomologic surveys over 14 months to determine if Ae. aegypti populations were spatially and temporally homogenous, and to estimate population size. There was no obvious relationship between mosquito (larval, pupal or adult) abundance and temperature and rainfall, and no area of the village supported consistently high numbers of mosquitoes. In almost all surveys, key premises produced high numbers of Ae. aegypti. However, these premises were not consistent between surveys. For an intervention based on a single release of wMelPop-infected Ae. aegypti, release ratios of infected to uninfected adult mosquitoes of all age classes are estimated to be 1.8-6.7ratio1 for gravid females (and similarly aged males) or teneral adults, respectively. We calculated that adult female mosquito abundance in Tri Nguyen village could range from 1.1 to 43.3 individuals of all age classes per house. Thus, an intervention could require the release of 2-78 wMelPop-infected gravid females and similarly aged males per house, or 7-290 infected teneral female and male mosquitoes per house. CONCLUSIONS/SIGNIFICANCE: Given the variability we encountered, this study highlights the importance of multiple entomologic surveys when evaluating the spatial structure of a vector population or estimating population size. If a single release of wMelPop-infected Ae. aegypti were to occur when wild Ae. aegypti abundance was at its maximum, a preintervention control program would be necessary to ensure that there was no net increase in mosquito numbers. However, because of the short-term temporal heterogeneity, the inconsistent spatial structure and the impact of transient key premises that we observed, the feasibility of multiple releases of smaller numbers of mosquitoes also needs to be considered. In either case, fewer wMelPop-infected mosquitoes would then need to be released, which will likely be more acceptable to householders.
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    Towards an Integrated Framework for Assessing the Vulnerability of Species to Climate Change
    Williams, SE ; Shoo, LP ; Isaac, JL ; Hoffmann, AA ; Langham, G ; Moritz, C (PUBLIC LIBRARY SCIENCE, 2008-12)
    Climate change is a major threat to global biodiversity. A novel integrated framework to assess vulnerability and prioritize research and management action aims to improve our ability to respond to this emerging crisis.
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    From parasite to mutualist:: Rapid evolution of Wolbachia in natural populations of Drosophila
    Weeks, AR ; Turelli, M ; Harcombe, WR ; Reynolds, KT ; Hoffmann, AA ; Keller, L (PUBLIC LIBRARY SCIENCE, 2007-05)
    Wolbachia are maternally inherited bacteria that commonly spread through host populations by causing cytoplasmic incompatibility, often expressed as reduced egg hatch when uninfected females mate with infected males. Infected females are frequently less fecund as a consequence of Wolbachia infection. However, theory predicts that because of maternal transmission, these "parasites" will tend to evolve towards a more mutualistic association with their hosts. Drosophila simulans in California provided the classic case of a Wolbachia infection spreading in nature. Cytoplasmic incompatibility allowed the infection to spread through individual populations within a few years and from southern to northern California (more than 700 km) within a decade, despite reducing the fecundity of infected females by 15%-20% under laboratory conditions. Here we show that the Wolbachia in California D. simulans have changed over the last 20 y so that infected females now exhibit an average 10% fecundity advantage over uninfected females in the laboratory. Our data suggest smaller but qualitatively similar changes in relative fecundity in nature and demonstrate that fecundity-increasing Wolbachia variants are currently polymorphic in natural populations.
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    The analysis of quantitative variation in natural populations with isofemale strains
    HOFFMANN, AA ; PARSONS, PA (BioMed Central, 1988-03-01)
    Isofemale strains are having an increasing role in the analysis of variability of ecological and behavioural traits in natural populations. This paper therefore considers the association between heritability and phenotypic variation within and between isofemale strains. Heritability from an isofemale strain analysis approximates narrow heritability over a wide range of dominance values, particularly when genes contributing to variation in a trait are at intermediate frequencies. Meaningful heritability estimates require that isofemale strains are maintained at a population size greater than 50 and tested within 5 generations after establishment. Values of heritabilities for morphological traits in Drosophila melanogaster were similar to those estimated from a conventional sib analysis. Published data on isofemale strains can therefore be put into a theoretical framework. The contribution of isofemale strain analyses to the debate about the number of loci affection variation in quantitative traits is briefly discussed.
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    Population-genetics of the metabolically related Adh, Gpdh and Tpi polymorphisms in Drosophila melanogaster: II. Temporal and spatial variation in and orchard population
    NIELSEN, KM ; HOFFMANN, AA ; MCKECHNIE, SW (BioMed Central, 1985-01-01)
    Seasonal and spatial variation in gene frequencies at 3 diallelic loci : alcohol dehydrogenase (Adh), glycerophosphate dehydrogenase (Gpdh) and triosephosphate isomerase (Tpi), have been studied in an orchard population of D. melanogaster. Gene frequency at the Tpi locus varied seasonally and was associated positively with total monthly rainfall measured both immediately prior to and concurrent with the month of collection. Temporal herteogeneity, not associated with the environmental parameters, was present at the Adh locus. Gpdh-F frequency was negatively associated with mean monthly maximum temperature measured prior to the time of collection. Within the orchard site, spatial heterogeneity in gene frequency at the Tpi locus was observed within collections. a deficiency of Gpdh heterozygotes was observed in individual trap samples and among collections with traps pooled. Overall, this variation is interpreted as being due to sampling from a population of partially isolated subgroups, founded by few individuals, and dependent upon transient pockets of fruit resources.
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    Bidirectional selection for olfactory response to acetaldehyde and ethanol in Drosophila melanogaster
    HOFFMANN, AA (BioMed Central, 1983-01-01)
    Drosophila melanogaster adults were successfully selected for increased and decreased olfactory response to different concentrations of acetaldehyde and ethanol, using a choice type olfactometer. The response to selection was not concentration specific. Lines were also tested with n-propanol, n-butanol, acetic acid, propionic acid, benzaldehyde, methyl acetate, ethyl acetate and 3-hydroxybutan-2-one. The behavior of the lines was similar for most of these chemicals, indicating an odorant specific response to selection. However, ethanol selected lines differed in their response to n-propanol and possibly n-butanol, suggesting a role for the alcohol group in determining the specificity of genetic variation in olfactory response. Utilization of acetic acid, ethanol and acetaldehyde as resources by the selected lines was tested using adult longevity. The only significant result was that lines selected for increased attraction to ethanol ulitised 9 p. 100 and 12 p. 100 ethanol more than lines selected for decreased attraction. Gene frequencies were monitored at 3 enzyme loci – alcohol dehydrogenase, triose phosphate isomerase, α-glycerophosphate dehydrogenase – associated with the metabolism of ethanol and acetaldehyde. There were no changes associated with the metabolism of ethanol and acetaldehyde. There were no changes associated with the response to selection, and the ADH-F allele increased in both selected and unselected lines.