Scholarly Literature

This is a database of scholarly literature that concentrates currently on natural and engineered selfish genetic elements (gene drives).  The latest are shown here.
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Ethical, legal and social aspects of the approach in Sudan

25823
B. B. El Sayed, C. A. Malcolm, A. Babiker, E. M. Malik, M. A. H. El Tayeb, N. S. Saeed, A. H. D. Nugud and B. G. J. Knols,  Malaria Journal,  8:S3. 2009-11-16 10:10:31.
The global malaria situation, especially in Africa, and the problems frequently encountered in chemical control of vectors such as insecticide resistance, emphasize the urgency of research, development and implementation of new vector control technologies that are applicable at regional and local levels. The successful application of the sterile insect technique (SIT) for the control of the New World screwworm Cochliomyia hominivorax and several species of fruit flies has given impetus to the use of this method for suppression or elimination of malaria vectors in some areas of Africa including Northern State of Sudan. The research and development phase of the Northern State feasibility study has been started. Sudanese stakeholders are working side-by-side with the International Atomic Energy Agency in the activities of this important phase. Several ethical, legal and social issues associated with this approach arose during this phase of the project. They need to be seriously considered and handled with care. In this paper, these issues are described, and the current and proposed activities to overcome potential hurdles to ensure success of the project are listed.

Field site selection: getting it right first time around

25817
C. A. Malcolm, B. El Sayed, A. Babiker, R. Girod, D. Fontenille, B. G. J. Knols, A. H. Nugud and M. Q. Benedict,  Malaria Journal,  8. 2009-11-16 09:57:52.
The selection of suitable field sites for integrated control of Anopheles mosquitoes using the sterile insect technique (SIT) requires consideration of the full gamut of factors facing most proposed control strategies, but four criteria identify an ideal site: 1) a single malaria vector, 2) an unstructured, relatively low density target population, 3) isolation of the target population and 4) actual or potential malaria incidence. Such a site can exist in a diverse range of situations or can be created. Two contrasting SIT field sites are examined here: the desert-flanked Dongola Reach of the Nile River in Northern State, Sudan, where malaria is endemic, and the island of La Reunion, where autochthonous malaria is rare but risk is persistent. The single malaria-transmitting vector at both sites is Anopheles arabiensis. In Sudan, the target area is a narrow 500 km corridor stretching from the rocky terrain at the Fourth Cataract - just above the new Merowe Dam, to the northernmost edge of the species range, close to Egypt. Vector distribution and temporal changes in density depend on the Nile level, ambient temperature and human activities. On La Reunion, the An. arabiensis population is coastal, limited and divided into three areas by altitude and exposure to the trade winds on the east coast. Mosquito vectors for other diseases are an issue at both sites, but of primary importance on La Reunion due to the recent chikungunya epidemic. The similarities and differences between these two sites in terms of suitability are discussed in the context of area-wide integrated vector management incorporating the SIT.

Genetic control of invasive plants species using selfish genetic elements

13612
K. A. Hodgins, L. Rieseberg and S. P. Otto,  Evolutionary Applications,  2:555-569. 2009-10-30 13:00:19.
Invasive plants cause substantial environmental damage and economic loss. Here, we explore the possibility that a selfish genetic element found in plants called cytoplasmic male sterility (CMS) could be exploited for weed control. We developed an analytical model and a spatial simulation to assess the use of CMS alleles to manage weed populations.

Spatial and temporal distribution of the malaria mosquito Anopheles arabiensis in northern Sudan: influence of environmental factors and implications for vector control

25826
T. B. Ageep, J. Cox, M. M. Hassan, B. G. J. Knols, M. Q. Benedict, C. A. Malcolm, A. Babiker and B. B. El Sayed,  Malaria Journal,  8:14. 2009-06-09 10:20:40.
Background: Malaria is an important public health problem in northern Sudan, but little is known about the dynamics of its transmission. Given the characteristic low densities of Anopheles arabiensis and the difficult terrain in this area, future vector control strategies are likely to be based on area-wide integrated pest management (AW-IPM) that may include the sterile insect technique ( SIT). To support the planning and implementation of future AW-IPM activities, larval surveys were carried out to provide key data on spatial and seasonal dynamics of local vector populations. Methods: Monthly cross-sectional larval surveys were carried out between March 2005 and May 2007 in two localities (Dongola and Merowe) adjacent to the river Nile. A stratified random sampling strategy based on the use of Remote Sensing (RS), Geographical Information Systems (GIS) and the Global Positioning System (GPS) was used to select survey locations. Breeding sites were mapped using GPS and data on larval density and breeding site characteristics were recorded using handheld computers. Bivariate and multivariate logistic regression models were used to identify breeding site characteristics associated with increased risk of presence of larvae. Seasonal patterns in the proportion of breeding sites positive for larvae were compared visually to contemporaneous data on climate and river height. Results: Of a total of 3,349 aquatic habitats sampled, 321 (9.6%) contained An. arabiensis larvae. The frequency with which larvae were found varied markedly by habitat type. Although most positive sites were associated with temporary standing water around the margins of the main Nile channel, larvae were also found at brickworks and in areas of leaking pipes and canals-often far from the river. Close to the Nile channel, a distinct seasonal pattern in larval populations was evident and appeared to be linked to the rise and fall of the river level. These patterns were not evident in vector populations breeding in artificial water sources away from the river. Conclusion: The GIS-based survey strategy developed in this study provides key data on the population dynamics of An. arabiensis in Northern State. Quantitative estimates of the contributions of various habitat types and their proximity to settlements provide a basis for planning a strategy for reducing malaria risk by elimination of the vector population.

Testosterone has a long-term effect on primary sex ratio of first eggs in pigeons-in search of a mechanism

4223
Goerlich, VCD, C.; Schaafsma, S. M.; Groothuis, T. G. G.,  General and Comparative Endocrinology,  163:184-192. 2009-01-21 00:00:00.
Despite accumulating evidence that birds, in which females are the heterogametic sex, are able to manipulate primary offspring sex ratio, the underlying mechanism remains elusive. Steroid hormones. which govern female reproduction and are also accumulated by the developing follicle could potentially affect primary sex ratio by differential follicle development in relation to future sex and meiotic drive, or by sex specific influence on oocyte abortion or fertilization. So far, experimental results on the involvement of maternal testosterone (T) in offspring sex manipulation are ambiguous. To investigate the effect of T on primary sex ratio and elucidate underlying mechanisms, we elevated circulating T levels in female homing pigeons (Columba livia). During the course of the experiment females produced three clutches-before and during T implantation, and one year after implant removal. Intriguingly, first eggs, but not second eggs of T females were significantly male biased relative to sham-implanted controls. One year after cessation of the treatment the male bias was still present, indicating long-term effects on female reproductive physiology. T treatment did not affect maternal body condition, nor was body condition correlated with offspring sex ratio. Our data on timing of oviposition, lack of infertile eggs, and yolk weight indicate a possible role for sex specific follicle abortion, perhaps in combination with meiotic drive. However, despite T treatment elevating maternal plasma levels, egg yolk T concentrations did not differ between treatment groups and did not vary with embryo sex, suggesting that yolk T is not involved in meiotic drive. (C) 2009 Elsevier Inc. All rights reserved.

Molecular signature of epistatic selection: interrogating genetic interactions in the sex-ratio meiotic drive of Drosophila simulans

4222
Chevin, LMB, H.; Montchamp-Moreau, C.; Hospital, F.,  Genetics Research,  91:171-182. 2009-01-20 00:00:00.
Fine scale analyses Of signatures of selection allow assessing quantitative aspects of a Species' evolutionary genetic history, such as the strength of selection on genes. When several selected loci lie in the same genomic region, their epistatic interactions may also be investigated. Here. we Study how the neutral polymorphism pattern was shaped by two close recombining loci that cause 'sex-ratio' meiotic drive in Drosophila simulans, as an example of strong selection with potentially strong epistasis. We compare the polymorphism data observed in a natural population with the results of forward stochastic simulations under several contexts of epistasis between the candidate loci for the drive. We compute the likelihood of different possible scenarios. in order to determine which configuration is most consistent with the data. Our results highlight that fine scale analyses of well-chosen candidate genomic regions provide information-rich data that can be used to investigate the genotype-phenotype-fitness map. which can hardly be Studied in genome-wide analyses. We also emphasize that initial conditions and time of observation (here, time after the Interruption Of a partial selective sweep) are crucial parameters in the interpretation of real data, while these are often overlooked in theoretical studies.

Evolution of the Schlafen genes, a gene family associated with embryonic lethality, meiotic drive, immune processes and orthopoxvirus virulence

4221
Bustos, ON, S.; Ayers, G.; Casola, C.; Perez-Lamigueiro, M. A.; Chippindale, P. T.; Pritham, E. J.; de la Casa-Esperon, E.,  Gene,  447:11-Jan. 2009-01-19 00:00:00.
Genes of the Schlafen family, first discovered in mouse, are expressed in hematopoietic cells and are involved in immune processes. Previous results showed that they are candidate genes for two major phenomena: meiotic drive and embryonic lethality (DDK syndrome). However, these genes remain poorly understood, mostly due to the limitations imposed by their similarity, close location and the potential functional redundancy of the gene family members. Here we use genomic and phylogenetic studies to investigate the evolution and role of this family of genes. Our results show that the Schlafen family is widely distributed in mammals, where we recognize four major clades that experienced lineage-specific expansions or contractions in various orders, including primates and rodents. In addition, we identified members of the Schlafen family in Chondrichthyes and Amphibia, indicating an ancient origin of these genes. We find evidence that positive selection has acted on many Schlafen genes. Moreover, our analyses indicate that a member of the Schlafen family was horizontally transferred from murine rodents to orthopoxviruses, where it is hypothesized to play a role in allowing the virus to survive host immune defense mechanisms. The functional relevance of the viral Schlafen sequences is further underscored by our finding that they are evolving under purifying selection. This is of particular importance, since orthopoxviruses infect mammals and include variola, the causative agent of smallpox, and monkeypox, an emerging virus of great concern for human health. (C) 2009 Elsevier B.V. All rights reserved.

Deployment of innovative genetic vector control strategies: progress on regulatory and biosafety aspects, capacity building and development of best-practice guidance

4220
Beech, CV, S.S.; Quinlan, M.M.; Capurro, Margareth L.; Alphey, L.; Bayard, V.; Bouare, M.; McLeod, M.C.; Kittayapong, P.; Lavery, J.; Lim, L.H.; Marrelli, M.T.; Nagaraju, J.; Ombongi, K.; Othman, R.Y.; Pillai, V.; Ramsey, J.; Reuben, R.; Rose, R.I.; Tyagi, B.K.; Mumford, J.,  AsPac J. Mol. Biol. Biotechnol.,  17:75-85. 2009-01-18 00:00:00.
In the ongoing fight against vectors of human diseases, disease endemic countries (DECs) may soon benefit from innovative control strategies involving modified insect vectors. For instance, three promising methods (viz. RIDL® [Release of Insects with a Dominant Lethal], Wolbachia infection, and refractory mosquito technology) are being developed by researchers around the world to combat Aedes aegypti, the primary mosquito vector of viral fevers such as dengue (serotypes 1–4), chikungunya and yellow fever. Some of these techniques are already being extended to other vectors such as Aedes albopictus (the secondary vector of these diseases) and Anopheles mosquito species that transmit malaria. To enable DECs to take advantage of these promising methods, initiatives are underway that relate to biosafety, risk assessment and management, and ethical–social–cultural (ESC) aspects to consider prior to and during the possible deployment of these technologies as part of an integrated vector control programme. This is a brief overview of the objectives and timelines of some of the initiatives being championed by international institutions, including the United Nations Development Programme (UNDP), the World Health Organization (WHO) and the Grand Challenges in Global Health (GCGH) initiative co-sponsored by the Bill & Melinda Gates Foundation.

Assessment of transmission distortion on chromosome 6p in healthy individuals using tagSNPs

4231
Santos, PSCH, J.; Schlattmann, P.; Konig, I. R.; Ziegler, A.; Uchanska-Ziegler, B.,  European Journal of Human Genetics,  17:1182-1189. 2009-01-09 00:00:00.
The best-documented example for transmission distortion (TD) to normal offspring are the t haplotypes on mouse chromosome 17. In healthy humans, TD has been described for whole chromosomes and for particular loci, but multiple comparisons have presented a statistical obstacle in wide-ranging analyses. Here we provide six high-resolution TD maps of the short arm of human chromosome 6 (Hsa6p), based on single-nucleotide polymorphism (SNP) data from 60 trio families belonging to two ethnicities that are available through the International HapMap Project. We tested all approximately 70 000 previously genotyped SNPs within Hsa6p by the transmission disequilibrium test. TagSNP selection followed by permutation testing was performed to adjust for multiple testing. A statistically significant evidence for TD was observed among male parents of European ancestry, due to strong and wide-ranging skewed segregation in a 730 kb long region containing the transcription factor-encoding genes SUPT3H and RUNX2, as well as the microRNA locus MIRN586. We also observed that this chromosomal segment coincides with pronounced linkage disequilibrium (LD), suggesting a relationship between TD and LD. The fact that TD may be taking place in samples not selected for a genetic disease implies that linkage studies must be assessed with particular caution in chromosomal segments with evidence of TD. European Journal of Human Genetics (2009) 17, 1182-1189; doi:10.1038/ejhg.2009.16; published online 4 March 2009

Multi-Locus Assortment (MLA) for transgene dispersal and elimination in mosquito populations

4230
Rasgon, JL,  PLOS One,  4:e5833. 2009-01-08 00:00:00.
: Replacement of wild-type mosquito populations with genetically modified versions is being explored as a potential strategy to control vector-borne diseases. Due to lower expected relative fitness of transgenic individuals, transgenes must be driven into populations for these scenarios to be successful. Several gene drive mechanisms exist in a theoretical sense but none are currently workable in mosquitoes. Even if strategies were workable, it would be very difficult to recall released transgenes in the event of unforeseen consequences. What is needed is a way to test transgenes in the field for feasibility, efficacy and safety prior to releasing an active drive mechanism. Methodology/Principal Findings: We outline a method, termed Multi-locus assortment (MLA), to spread transgenes into vector populations by the release of genetically-modified mosquitoes carrying multiple stable transgene inserts. Simulations indicate that [1] insects do not have to carry transgenes at more than 4 loci, [2] transgenes can be maintained at high levels by sequential small releases, the frequency of which depends on the construct fitness cost, and [3] in the case of unforeseen negative non-target effects, transgenes can be eliminated from the population by halting transgenic releases and/or mass releases of wild-type insects. We also discuss potential methods to create MLA mosquito strains in the laboratory. Conclusions/Significance: While not as efficient as active drive mechanisms, MLA has other advantages: [1] MLA strains can be constructed for some mosquito species with currently-available technology, [2] MLA will allow the ecological components of transgenic mosquito releases to be tested before actual gene drive mechanisms are ready to be deployed, [3] since MLA is not self-propagating, the risk of an accidental premature release into nature is minimized, and [4] in the case that active gene drive mechanisms prove impossible to develop, the MLA approach can be used as a back-up transgene dispersal mechanism for disease control efforts in some systems.

Large-scale selective sweep among Segregation Distorter chromosomes in African populations Drosophila melanogaster

4229
Presgraves, DCG, P. R.; Cherukuri, A.; Lyttle, T. W.,  PLOS Genetics,  5:e1000463. 2009-01-07 00:00:00.
Segregation Distorter (SD) is a selfish, coadapted gene complex on chromosome 2 of Drosophila melanogaster that strongly distorts Mendelian transmission; heterozygous SD/SD(+) males sire almost exclusively SD-bearing progeny. Fifty years of genetic, molecular, and theory work have made SD one of the best-characterized meiotic drive systems, but surprisingly the details of its evolutionary origins and population dynamics remain unclear. Earlier analyses suggested that the SD system arose recently in the Mediterranean basin and then spread to a low, stable equilibrium frequency (1-5%) in most natural populations worldwide. In this report, we show, first, that SD chromosomes occur in populations in sub-Saharan Africa, the ancestral range of D. melanogaster, at a similarly low frequency (similar to 2%), providing evidence for the robustness of its equilibrium frequency but raising doubts about the Mediterranean-origins hypothesis. Second, our genetic analyses reveal two kinds of SD chromosomes in Africa: inversion-free SD chromosomes with little or no transmission advantage; and an African-endemic inversion-bearing SD chromosome, SD-Mal, with a perfect transmission advantage. Third, our population genetic analyses show that SD-Mal chromosomes swept across the African continent very recently, causing linkage disequilibrium and an absence of variability over 39% of the length of the second chromosome. Thus, despite a seemingly stable equilibrium frequency, SD chromosomes continue to evolve, to compete with one another, or evade suppressors in the genome.

Drive and sperm: The evolution and genetics of male meiotic drive

4228
Presgraves, D,  Sperm Biology: an Evolutionary Perspective,  12:471-506. 2009-01-06 00:00:00.
Some selfish genetic elements in eukaryotic genomes have been harnessed to perform essential functions for their hosts, whereas others have gained transmission advantages at the expense of their hosts. Meiotic drive elements are particularly dramatic examples of the latter. Meiotic drive is the unequal—and thus non-Mendelian—transmission of alternative alleles or chromosomes from heterozygotes. Most drive elements achieve greater than Mendelian transmission from their carriers by excluding, impairing or killing competing alternative gametes. The best-characterized drive elements are the Segregation Distorter (SD) complex in the fruitfly Drosophila melanogaster and the t-haplotype in the Mus house mouse species. Despite being found in very distantly related species, both meiotic drive systems share genetic and chromosomal features that appear to characterize meiotic drive systems in general. For these, and all systems characterized to date, drive involves an interaction between at least two loci in which a trans-acting drive allele at one locus impairs transmission of sensitive alleles at a cis-acting target locus. In effect, the drive allele produces a toxin that incapacitates sperm bearing sensitive forms of the target. Drive chromosomes bear a driver and a drive-insensitive target, whereas non-drive chromosomes lack the driver and typically carry a drivesensitive target. This chapter reviews the genetics, molecular basis, and evolutionary history of several well-characterized drive systems, and considers the impact of drive on spermatogenesis and sperm competition, including potential evolutionary responses of organisms to drive.

The effect of gene drive on containment of transgenic mosquitoes

4227
Marshall, JM,  Journal of Theoretical Biology,  258:250-265. 2009-01-05 00:00:00.
Mosquito-borne diseases such as malaria and dengue fever continue to be a major health problem through Much of the world. Several new potential approaches to disease control utilize gene drive to spread anti-pathogen genes into the mosquito Population. Prior to a release, these projects will require trials in outdoor cages from which transgenic mosquitoes may escape, albeit in small numbers. Most genes introduced in small numbers are very likely to be lost from the environment; however, gene drive mechanisms enhance the invasiveness of introduced genes. Consequently, introduced transgenes may be more likely to persist than ordinary genes following an accidental release. Here, we develop stochastic models to analyze the loss probabilities for several gene drive mechanisms, including homing endonuclease genes, transposable elements, Medea elements, the intracellular bacterium Wolbachia, engineered underdominance genes, and meiotic drive. We find that Medea and Wolbachia present the best compromise between invasiveness and containment for the six gene drive systems Currently being considered for the control of mosquito-borne disease. Published by Elsevier Ltd.

Major evolutionary transitions in centromere complexity

4226
Malik, HSH, S.,  Cell,  138:1067-1082. 2009-01-04 00:00:00.
Centromeres are chromosomal elements that are both necessary and sufficient for chromosome segregation. However, the puzzlingly broad range in centromere complexity, from simple "point" centromeres to multi-megabase arrays of DNA satellites, has defied explanation. We posit that ancestral centromeres were epigenetically defined and that point centromeres, such as those of budding yeast, have derived from the partitioning elements of selfish plasmids. We further propose that the larger centromere sizes in plants and animals and the rapid evolution of their centromeric proteins is the result of an intense battle for evolutionary dominance due to the asymmetric retention of only one product of female meiosis.

Skeeter Buster: A stochastic, spatially explicit modeling tool for studying Aedes aegypti population replacement and population suppression strategies

4225
Magori, KL, M.; Puente, M. E.; Focks, D. A.; Scott, T. W.; Lloyd, A. L.; Gould, F.,  PLOS Neglected Tropical Diseases,  3:e508. 2009-01-03 00:00:00.
Dengue is the most important mosquito-borne viral disease affecting humans. The only prevention measure currently available is the control of its vectors, primarily Aedes aegypti. Recent advances in genetic engineering have opened the possibility for a new range of control strategies based on genetically modified mosquitoes. Assessing the potential efficacy of genetic (and conventional) strategies requires the availability of modeling tools that accurately describe the dynamics and genetics of Ae. aegypti populations. Methodology/Principal findingsWe describe in this paper a new modeling tool of Ae. aegypti population dynamics and genetics named Skeeter Buster. This model operates at the scale of individual water-filled containers for immature stages and individual properties (houses) for adults. The biology of cohorts of mosquitoes is modeled based on the algorithms used in the non-spatial Container Inhabiting Mosquitoes Simulation Model (CIMSiM). Additional features incorporated into Skeeter Buster include stochasticity, spatial structure and detailed population genetics. We observe that the stochastic modeling of individual containers in Skeeter Buster is associated with a strongly reduced temporal variation in stage-specific population densities. We show that heterogeneity in container composition of individual properties has a major impact on spatial heterogeneity in population density between properties. We detail how adult dispersal reduces this spatial heterogeneity. Finally, we present the predicted genetic structure of the population by calculating F(ST) values and isolation by distance patterns, and examine the effects of adult dispersal and container movement between properties. Conclusions/SignificanceWe demonstrate that the incorporated stochasticity and level of spatial detail have major impacts on the simulated population dynamics, which could potentially impact predictions in terms of control measures. The capacity to describe population genetics confers the ability to model the outcome of genetic control methods. Skeeter Buster is therefore an important tool to model Ae. aegypti populations and the outcome of vector control measures.

Gene-drive in age-structured insect populations

4224
Huang, YXL, A. L.; Legros, M.; Gould, F.,  Evolutionary Applications,  2:143-159. 2009-01-02 00:00:00.
To date, models of gene-drive mechanisms proposed for replacing wild-type mosquitoes with transgenic strains that cannot transmit diseases have assumed no age or mating structure. We developed a more detailed model to analyze the effects of age and mating-related factors on the number of engineered insects that must be introduced into a wild population to achieve successful gene-drive based on the Medea and engineered underdominance mechanisms. We found that models without age-structure and mating details can substantially overestimate or underestimate the numbers of engineered insects that must be introduced. In general, introduction thresholds are lowest when young adults are introduced. When both males and females are introduced, assortative mating by age has little impact on the introduction threshold unless the introduced females have diminished reproductive ability because of their age. However, when only males are introduced, assortative mating by age is generally predicted to increase introduction thresholds. In most cases, introduction thresholds are much higher for male-only introductions than for both-sex introductions, but when mating is nearly random and the introduced insects are adults with Medea constructs, male-only introductions can have somewhat lower thresholds than both-sex introductions. Results from this model suggest specific parameters that should be measured in field experiments.

Genes in conflict: The biology of selfish genetic elements

Burt, A. and R. Trivers,  Genes in conflict: the biology of selfish genetic elements,  2008-12-30 20:03:34.
In evolution, most genes survive and spread within populations because they increase the ability of their hosts (or their close relatives) to survive and reproduce. But some genes spread in spite of being harmful to the host organism—by distorting their own transmission to the next generation, or by changing how the host behaves toward relatives. As a consequence, different genes in a single organism can have diametrically opposed interests and adaptations. Covering all species from yeast to humans, Genes in Conflict is the first book to tell the story of selfish genetic elements, those continually appearing stretches of DNA that act narrowly to advance their own replication at the expense of the larger organism. As Austin Burt and Robert Trivers show, these selfish genes are a universal feature of life with pervasive effects, including numerous counter-adaptations. Their spread has created a whole world of socio-genetic interactions within individuals, usually completely hidden from sight. Genes in Conflict introduces the subject of selfish genetic elements in all its aspects, from molecular and genetic to behavioral and evolutionary. Burt and Trivers give us access for the first time to a crucial area of research—now developing at an explosive rate—that is cohering as a unitary whole, with its own logic and interconnected questions, a subject certain to be of enduring importance to our understanding of genetics and evolution.

Towards a sterile insect technique field release of Anopheles arabiensis mosquitoes in Sudan: Irradiation, transportation, and field cage experimentation

25755
M. E. H. Helinski, M. M. Hassan, W. M. El-Motasim, C. A. Malcolm, B. G. J. Knols and B. El-Sayed,  Malaria Journal,  7:10. 2008-04-25 10:09:22.
Background: The work described in this article forms part of a study to suppress a population of the malaria vector Anopheles arabiensis in Northern State, Sudan, with the Sterile Insect Technique. No data have previously been collected on the irradiation and transportation of anopheline mosquitoes in Africa, and the first series of attempts to do this in Sudan are reported here. In addition, experiments in a large field cage under near-natural conditions are described. Methods: Mosquitoes were irradiated in Khartoum and transported as adults by air to the field site earmarked for future releases (400 km from the laboratory). The field cage was prepared for experiments by creating resting sites with favourable conditions. The mating and survival of (irradiated) laboratory males and field-collected males was studied in the field cage, and two small-scale competition experiments were performed. Results: Minor problems were experienced with the irradiation of insects, mostly associated with the absence of a rearing facility in close proximity to the irradiation source. The small-scale transportation of adult mosquitoes to the release site resulted in minimal mortality (< 6%). Experiments in the field cage showed that mating occurred in high frequencies (i.e. an average of 60% insemination of females after one or two nights of mating), and laboratory reared males (i.e. sixty generations) were able to inseminate wild females at rates comparable to wild males. Based on wing length data, there was no size preference of males for mates. Survival of mosquitoes from the cage, based on recapture after mating, was satisfactory and approximately 60% of the insects were recaptured after one night. Only limited information on male competitiveness was obtained due to problems associated with individual egg laying of small numbers of wild females. Conclusion: It is concluded that although conditions are challenging, there are no major obstacles associated with the small-scale irradiation and transportation of insects in the current setting. The field cage is suitable for experiments and studies to test the competitiveness of irradiated males can be pursued. The scaling up of procedures to accommodate much larger numbers of insects needed for a release is the next challenge and recommendations to further implementation of this genetic control strategy are presented.

The Impact of Dissociation on Transposon-Mediated Disease Control Strategies

23831
J. M. Marshall,  Genetics,  178:1673-1682. 2008-03-01 23:54:22.
Vector-borne diseases such as malaria and dengue fever continue to be a major health concern through much of the world. The emergence of chloroquine-resistant strains of malaria and insecticide-resistant mosquitoes emphasize the need for novel methods of disease control. Recently, there has been much interest in the use of transposable elements to drive resistance genes into vector populations as a means of disease control. One concern that must be addressed before a release is performed is the potential loss of linkage between a transposable element and a resistance gene. Transposable elements such as P and hobo have been shown to produce internal deletion derivatives at a significant rate, and there is concern that a similar process could lead to loss of the resistance gene from the drive system following a transgenic release. Additionally, transposable elements such as Himar1 have been shown to transpose significantly more frequently when free of exogenous DNA. Here, we show that any transposon-mediated gene drive strategy must have an exceptionally low rate of dissociation if it is to be effective. Additionally, the resistance gene must confer a large selective advantage to the vector to surmount the effects of a moderate dissociation rate and transpositional handicap.

Sex ratio distorter reduces sperm competitive ability in an insect

4243
Price, TARB, A. J.; Avent, T. D.; Snook, R. R.; Hurst, G. D. D.; Wedell, N.,  Evolution,  62:1644-1652. 2008-01-21 00:00:00.
Selfish genetic elements (SGEs) are ubiquitous in animals and often associated with low male fertility due to reduced sperm number in male carriers. In the fruit fly Drosophila pseudoobscura, the meiotic driving X chromosome "sex ratio" kills Y-bearing sperm in carrier males (SR males), resulting in female only broods. We competed SR males against the ejaculates of noncarrying standard males (ST males), and quantified the number of sperm transferred by SR and ST males to females. We show that SR males are very poor sperm competitors, which is partly related to transfer of fewer sperm during mating. However, sperm numbers alone cannot explain the observed paternity reduction, indicating SR males' sperm may be of reduced quality, possibly due to damage during the killing of the noncarrying Y-sperm. The reduction in sperm competitive ability due to SR is large enough to potentially stabilize the spread of sex ratio drive through populations. The poor sperm competitive ability of SR males coupled with their low fitness as mates could favor increased remating by females to reduce paternity by SR males. Given the generally poor performance of SGE-carrying males in sperm competition, this may generate strong selective pressure favoring polyandry in many species.

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