Scholarly Literature
This is an aggregation of scholarly literature from peer-reviewed journals, bioRxiv , medRxiv and arXiv preprint servers focused on natural and engineered selfish genetic elements and genetic biocontrol. New citations are added as they appear. This content is intended for anyone interested in the scholarly literature on gene drive and genetic biocontrol.
Concept and history of genetic control
6014Scott, M. J. and Benedict, M. Q., Genetic Control of Malaria and Dengue, 2:31-54. 2016-12-30 20:16:45.
Genetic control of insects is an established method, mainly for insects that are important crop and veterinary pests such as medflies and screwworm. Efforts to use the same technologies against insects of medical importance, especially mosquitoes, have had limited success. The successes against mosquitoes have been accomplished using forms of both conventional and modern methods, both of which are promising. In this chapter, we provide highlights of the development of genetic control of agricultural pests and describe how the development of methods against mosquitoes reflects those advances. While admiring successful genetic control programs is motivating, we suggest that much can also be learned from both past successful and failed efforts, as doing so will increase our ability to improve future activities.
National Academies hit the brakes on gene drive-modified organisms
5657Abbasi, J., JAMA-Journal of the American Medical Association, 316:482-483. 2016-12-17 18:11:25.
Despite their potential for fighting Zika, malaria, and other public health scourges, organisms that have been engineered to quickly spread genetic modifications through a population—and possibly an entire species—are not ready for release into the wild, a committee of interdisciplinary experts concluded in a recent report by the National Academies of Sciences, Engineering, and Medicine (http://bit.ly/1UHuqQk). So-called gene drive–modified organisms “require more research in laboratories and highly controlled field trials,” the committee said in a statement (http://bit.ly/1tkWCTO). Gene drives are systems of “biased inheritance” that enhance a genetic element’s ability to pass from parent organism to offspring through sexual reproduction. These selfish genetic elements could be genes or their fragments, all or parts of chromosomes, or noncoding DNA, the report stated.
Invertebrate Biosecurity Challenges in High-Productivity Grassland: The New Zealand Example
13738S. L. Goldson, B. I. P. Barratt and K. F. Armstrong, Frontiers in Plant Science, 7. 2016-11-15 19:35:24.
This review explores the unique challenges faced by pasture biosecurity and what may be done to confront existing difficulties. While there is no silver bullet, and limited opportunity pre and at for improving pasture biosecurity, advancement may include increased and informed vigilance by farmers, pheromone traps and resistant plants to slow invasion. Increasingly, there is also the potential for more use of improved population dispersal models and surveillance strategies including unmanned aerial vehicles, as well as emerging techniques to determine invasive pest genomes and their geographical origins.
Mitonuclear interactions, mtDNA-mediated thermal plasticity, and implications for the Trojan Female Technique for pest control
13745J. N. Wolff, D. M. Tompkins, N. J. Gemmell and D. K. Dowling, Scientific Reports, 6. 2016-07-21 19:45:17.
Here we test whether the male-sterilizing effects previously associated with the mt: Cyt-b mutation are consistent across three thermal and three nuclear genomic contexts. The effects of this mutation were indeed moderated by the nuclear background and thermal environment, but crucially the fertility of males carrying the mutation was invariably reduced relative to controls. This mutation thus constitutes a promising candidate for the further development of the TFT.
Prospects and challenges of CRISPR/Cas genome editing for the study and control of neglected vector-borne nematode diseases
6017M. Zamanian and E. C. Andersen, The FEBS Journal, 283:3204-3221. 2016-06-14 20:22:18.
Neglected tropical diseases caused by parasitic nematodes inflict an immense health and socioeconomic burden throughout much of the developing world. Current estimates indicate that more than two billion people are infected with nematodes, resulting in the loss of 14 million disability-adjusted life years per annum. Although these parasites cause significant mortality, they primarily cause chronic morbidity through a wide range of severe clinical ailments. Treatment options for nematode infections are restricted to a small number of anthelmintic drugs, and the rapid expansion of anthelmintic mass drug administration raises concerns of drug resistance. Preservation of existing drugs is necessary, as well as the development of new treatment options and methods of control. We focus this review on how the democratization of CRISPR/Cas9 genome editing technology can be enlisted to improve our understanding of the biology of nematode parasites and our ability to treat the infections they cause. We will first explore how this robust method of genome manipulation can be used to newly exploit the powerful model nematode Caenorhabditis elegans for parasitology research. We will then discuss potential avenues to develop CRISPR/Cas9 editing protocols in filarial nematodes. Lastly, we will propose potential ways in which CRISPR/Cas9 can be used to engineer gene drives that target the transmission of mosquito-borne filarial nematodes.
Lethal Gene Drive Selects Inbreeding
13627J. J. Bull, bioRxiv, 046847. 2016-06-03 13:55:41.
ere, population genetic models are used to consider the evolution of inbreeding (specifically selfing) as a possible response to a recessively lethal HEG with complete segregation distortion. Numerical analyses indicate a rich set of outcomes, but selfing often evolves in response to the HEG, with a corresponding partial restoration of mean fitness. Whether selfing does indeed evolve and its effect in restoring fitness depends heavily on the magnitude of inbreeding depression. Overall, these results point toward an underappreciated evolutionary response to block the harmful effects of a selfish gene.
Mating competitiveness of sterile genetic sexing strain males (GAMA) under laboratory and semi-field conditions: Steps towards the use of the Sterile Insect Technique to control the major malaria vector Anopheles arabiensis in South Africa
25911G. Munhenga, B. D. Brooke, J. R. L. Gilles, K. Slabbert, A. Kemp, L. C. Dandalo, O. R. Wood, L. N. Lobb, D. Govender, M. Renke and L. L. Koekemoer, Parasites and Vectors, 9:122. 2016-03-02 13:00:23.
Anopheles arabiensis Patton is primarily responsible for malaria transmission in South Africa after successful suppression of other major vector species using indoor spraying of residual insecticides. Control of An. arabiensis using current insecticide based approaches is proving difficult owing to the development of insecticide resistance, and variable feeding and resting behaviours. The use of the sterile insect technique as an area-wide integrated pest management system to supplement the control of An. arabiensis was proposed for South Africa and is currently under investigation. The success of this technique is dependent on the ability of laboratory-reared sterile males to compete with wild males for mates. As part of the research and development of the SIT technique for use against An. arabiensis in South Africa, radio-sensitivity and mating competitiveness of a local An. arabiensis sexing strain were assessed.
Engineering the wild: Gene drives and intergenerational equity
6948J. Kuzma and L. Rawls, Jurimetrics, 56:279-296. 2016-03-01 16:08:02.
New genetic engineering methods are allowing scientists to insert genes into organisms that have the potential to spread themselves throughout natural populations upon the release of individuals carrying those genes. Gene drive technology is being researched and developed for purposes of reducing or eliminating human, ecological or agricultural pest populations, or immunizing other desirable or endangered species against pests and disease. The ability of humans to alter populations within ecosystems through genetic engineering raises issues associated with biodiversity and conservation that, in turn, may affect the abilities of current and future generations to use and enjoy the benefits of the natural world. Yet, children and future generations are not typically given voice in legal, policy, or ethical debates. This article examines several of the intergenerational equity issues posed by gene drive technologies. A typology of gene drive purposes and their potential ecological impacts is developed, followed by an examination of how they may intersect with concerns about intergenerational equity. To our knowledge, this analysis is the first to explore human intervention through genetically engineering populations in the wild and the impacts on future generations
Cheating evolution: engineering gene drives to manipulate the fate of wild populations
4083Champer, JB, A.; Akbari, O. S., Nature Reviews Genetics, 17:146-159. 2016-01-21 00:00:00.
Engineered gene drives - the process of stimulating the biased inheritance of specific genes - have the potential to enable the spread of desirable genes throughout wild populations or to suppress harmful species, and may be particularly useful for the control of vector-borne diseases such as malaria. Although several types of selfish genetic elements exist in nature, few have been successfully engineered in the laboratory thus far. With the discovery of RNA-guided CRISPR-Cas9 (clustered regularly interspaced short palindromic repeats-CRISPR-associated 9) nucleases, which can be utilized to create, streamline and improve synthetic gene drives, this is rapidly changing. Here, we discuss the different types of engineered gene drives and their potential applications, as well as current policies regarding the safety and regulation of gene drives for the manipulation of wild populations.
No evidence for female discrimination against male house mice carrying a selfish genetic element
4103Sutter, AL, A. K., Current Zoology, 62:675-685. 2016-01-21 00:00:00.
Meiotic drivers distort transmission to the next generation in their favor, with detrimental effects on the fitness of their homologues and the rest of the genome. Male carriers of meiotic drivers commonly inflict costs on their mates through genetic incompatibility, reduced fecundity, or biased brood sex ratios. Given these costs, evidence for female discrimination against male carriers is surprisingly rare. One of few examples is the t haplotype in house mice, a meiotic driver that shows strong transmission distortion in males and is typically homozygote lethal. As a consequence, mating between 2 t heterozygous (+/t) mice leads to high embryo mortality. Previous experiments showing that +/t females avoid this incompatibility cost by preferring +/+versus +/t males have inferred preference based on olfactory cues or brief social interactions. Evidence from mating contexts in laboratory settings and semi-natural populations has been inconclusive. Here, we investigated female choice from a large number of no-choice mating trials. We found no evidence for discrimination against +/t males based on mating, remating, and copulatory behavior. Further, we found no evidence for avoidance of incompatibility through selective interactions between gametes. The likelihood of mating showed significant effects of female weight and genotype, suggesting that our test paradigm enabled females to exhibit mate choice. We discuss the strengths and limitations of our approach. By explicitly considering selection at both the individual and gene level, we argue why precopulatory female discrimination by +/t females may be less evolutionarily stable than discrimination by all females based on postcopulatory mechanisms.
Genome editing: intellectual property and product development in plant biotechnology
4102Schinkel, HS, S., Plant Cell Reports, 35:1487-1491. 2016-01-20 00:00:00.
Genome editing is a revolutionary technology in molecular biology. While scientists are fascinated with the unlimited possibilities provided by directed and controlled changes in DNA in eukaryotes and have eagerly adopted such tools for their own experiments, an understanding of the intellectual property (IP) implications involved in bringing genome editing-derived products to market is often lacking. Due to the ingenuity of genome editing, the time between new product conception and its actual existence can be relatively short; therefore knowledge about IP of the various genome editing methods is relevant. This point must be regarded in a national framework as patents are instituted nationally. Therefore, when designing scientific work that could lead to a product, it is worthwhile to consider the different methods used for genome editing not only for their scientific merits but also for their compatibility with a speedy and reliable launch into the desired market.
Marcus Rhoades on preferential segregation in maize
4082Birchler, JA, Genetics, 203:1489-1490. 2016-01-20 00:00:00.
Rhoades was studying a variant form of chromosome 10 with a conspicuous abnormality; it carried extensive heterochromatin at the tip of the long arm. This variant had been found by Albert Longley in indigenous maize varieties from the southwestern United States and provided to Rhoades for the pedestrian task of determining the recombination frequency between the anthocyanin pigment gene, R, and the end of the chromosome. The abnormal chromosome 10 originally carried the recessive, r, allele (colorless kernels) and was crossed to other lines carrying the dominant R (red kernels). Much to the surprise of Rhoades, when these heterozygotes were testcrossed with the recessive, there was a strong skew from a 1:1 ratio. Rather than the roughly even mix of colorless and red kernels that he expected, around two-thirds were colorless. This excess of r alleles was caused by linkage to the variant chromosome; in the few progeny that transferred the dominant R allele to the abnormal chromosome 10, subsequent testcrosses demonstrated that it was now the dominant allele that was preferentially inherited.
Gene drive through a landscape: Reaction-diffusion models of population suppression and elimination by a sex ratio distorter
4081Beaghton, AB, P. J.; Burt, A., Theoretical Population Biology, 108:51-69. 2016-01-19 00:00:00.
Some genes or gene complexes are transmitted from parents to offsprihg at a greater-than-Mendelian rate, and can spread and persist in populations even if they cause some harm to the individuals carrying them. Such genes may be useful for controlling populations or species that are harmful. Driving-Y chromosomes may be particularly potent in this regard, as they produce a male-biased sex ratio that, if sufficiently extreme, can lead to population elimination. To better understand the potential of such genes to spread over a landscape, we have developed a series of reaction-diffusion models of a driving-Y chromosome in 1-D and radially-symmetric 2-D unbounded domains. The wild-type system at carrying capacity is found to be unstable to the introduction of driving-Y males for all models investigated. Numerical solutions exhibit travelling wave pulses and fronts, and analytical and semi-analytical solutions for the asymptotic wave speed under bounded initial conditions are derived. The driving-Y male invades the wild-type equilibrium state at the front of the wave and completely replaces the wild-type males, leaving behind, at the tail of the wave, a reduced- or zero-population state of females and driving-Y males only. In our simplest model of a population with one life stage and density-dependent mortality, wave speed depends on the strength of drive and the diffusion rate of Y-drive males, and is independent of the population dynamic consequences (suppression or elimination). Incorporating an immobile juvenile stage of fixed duration into the model reduces wave speed approximately in proportion to the relative time spent as a juvenile. If females mate just once in their life, storing sperm for subsequent reproduction, then wave speed depends on the movement of mated females as well as Y-drive males, and may be faster or slower than in the multiple-mating model, depending on the relative duration of juvenile and adult life stages. Numerical solutions are shown for parameter values that may in part be representative for Anopheles gambiae, the primary vector of malaria in sub-Saharan Africa. (C) 2015 The Authors. Published by Elsevier Inc.
Random and non-random mating populations: Evolutionary dynamics in meiotic drive
4101Sarkar, B, Mathematical Biosciences, 271:29-41. 2016-01-19 00:00:00.
Game theoretic tools are utilized to analyze a one-locus continuous selection model of sex-specific meiotic drive by considering nonequivalence of the viabilities of reciprocal heterozygotes that might be noticed at an imprinted locus. The model draws attention to the role of viability selections of different types to examine the stable nature of polymorphic equilibrium. A bridge between population genetics and evolutionary game theory has been built up by applying the concept of the Fundamental Theorem of Natural Selection. In addition to pointing out the influences of male and female segregation ratios on selection, configuration structure reveals some noted results, e.g., Hardy-Weinberg frequencies hold in replicator dynamics, occurrence of faster evolution at the maximized variance fitness, existence of mixed Evolutionarily Stable Strategy (ESS) in asymmetric games, the tending evolution to follow not only a 1:1 sex ratio but also a 1:1 different alleles ratio at particular gene locus. Through construction of replicator dynamics in the group selection framework, our selection model introduces a redefining bases of game theory to incorporate non-random mating where a mating parameter associated with population structure is dependent on the social structure. Also, the model exposes the fact that the number of polymorphic equilibria will depend on the algebraic expression of population structure. (C) 2015 Elsevier Inc. All rights reserved.
Sexual antagonism and meiotic drive cause stable linkage disequilibrium and favour reduced recombination on the X chromosome
4100Rydzewski, WTC, S. A.; Lievano, G.; Lynch, V. D.; Patten, M. M., Journal of Evolutionary Biology, 29:1247-1256. 2016-01-18 00:00:00.
Sexual antagonism and meiotic drive are sex-specific evolutionary forces with the potential to shape genomic architecture. Previous theory has found that pairing two sexually antagonistic loci or combining sexual antagonism with meiotic drive at linked autosomal loci augments genetic variation, produces stable linkage disequilibrium (LD) and favours reduced recombination. However, the influence of these two forces has not been examined on the X chromosome, which is thought to be enriched for sexual antagonism and meiotic drive. We investigate the evolution of the X chromosome under both sexual antagonism and meiotic drive with two models: in one, both loci experience sexual antagonism; in the other, we pair a meiotic drive locus with a sexually antagonistic locus. We find that LD arises between the two loci in both models, even when the two loci freely recombine in females and that driving haplotypes will be enriched for male-beneficial alleles, further skewing sex ratios in these populations. We introduce a new measure of LD, D-z('), which accounts for population allele frequencies and is appropriate for instances where these are sex specific. Both models demonstrate that natural selection favours modifiers that reduce the recombination rate. These results inform observed patterns of congealment found on driving X chromosomes and have implications for patterns of natural variation and the evolution of recombination rates on the X chromosome.
Target Malaria has a killer in its sights: Eliminating the world’s deadliest disease has been a priority for decades, and, thanks to innovative gene-drive technology, Target Malaria is getting closer to achieving that goal
4080Banks, J, IEEE Pulse, 7:30-33. 2016-01-18 00:00:00.
The mosquito is the deadliest animal in the world (Figure 1). It is the main carrier of parasites that cause malaria, which is a bigger killer than any other disease in history; in fact, some blame malaria for the deaths of half the humans who have ever lived. Today, malaria continues to have a devastating effect on the health of millions of people.
Genetic engineering to eradicate invasive mice on islands: modeling the efficiency and ecological impacts
4079Backus, GAG, K., Ecosphere, 7:e01589. 2016-01-17 00:00:00.
Invasive rodents are usually eradicated from islands through the application of chemical toxicants that can harm surrounding ecosystems. A recently proposed alternative involves engineering a house mouse (Mus musculus) to carry a genetic construct that would cause a majority of its offspring to be male, many of which would be sterile. Releasing these genetically engineered mice to interbreed with an invasive population would reduce the number of fertile female mice until no more remain. We constructed a mathematical model to analyze the population dynamics of eradication with this genetically engineered mouse and determined its eradication efficiency through model analysis and simulations. Because genetically engineered mice would likely have a fitness disadvantage compared to wild mice, we found that they would need to be repeatedly released into the population to ensure complete eradication. However, if genetically engineered mice have a substantial survival advantage, we determined that the genetic construct could theoretically spread and eradicate a population after a single pulsed release onto the target island or after an engineered mouse escapes to a non-target location. Also, while the species specificity of genetic engineering avoids some of the non-target impacts of traditional eradication methods, ecological impacts could manifest indirectly. We compared several metrics to estimate potential transient impacts on the ecosystem and found that there is a trade-off between the speed of an eradication and the intensity of increased disruptive ecological interactions. Together, our results can inform safe and efficient ecological practices for eradication with developing genetic engineering technology.
Intragenomic conflict produces sex ratio dynamics that favor maternal sex ratio distorters
4099Rood, ESF, S., Ecology and Evolution, 6:8085-8093. 2016-01-17 00:00:00.
Maternal sex ratio distorters (MSDs) are selfish elements that enhance their transmission by biasing their host's sex allocation in favor of females. While previous models have predicted that the female-biased populations resulting from sex ratio distortion can benefit from enhanced productivity, these models neglect Fisherian selection for nuclear suppressors, an unrealistic assumption in most systems. We used individual-based computer simulation modeling to explore the intragenomic conflict between sex ratio distorters and their suppressors and explored the impacts of these dynamics on population-level competition between species characterized by MSDs and those lacking them. The conflict between distorters and suppressors was capable of producing large cyclical fluctuations in the population sex ratio and reproductive rate. Despite fitness costs associated with the distorters and suppressors, MSD populations often exhibited enhanced productivity and outcompeted non-MSD populations in single and multiple-population competition simulations. Notably, the conflict itself is beneficial to the success of populations, as sex ratio oscillations limit the competitive deficits associated with prolonged periods of male rarity. Although intragenomic conflict has been historically viewed as deleterious to populations, our results suggest that distorter-suppressor conflict can provide population-level advantages, potentially helping to explain the persistence of sex ratio distorters in a range of taxa.
A meiotic drive element in the maize pathogen Fusarium verticillioides is located within a 102 kb region of chromosome V
4098Pyle, JP, T.; Merrill, B.; Nsokoshi, C.; McCall, M.; Proctor, R. H.; Brown, D. W.; Hammond, T. M., G3-Genes Genomes Genetics, 6:2543-2552. 2016-01-16 00:00:00.
Fusarium verticillioides is an agriculturally important fungus because of its association with maize and its propensity to contaminate grain with toxic compounds. Some isolates of the fungus harbor a meiotic drive element known as Spore killer (Sk(K)) that causes nearly all surviving meiotic progeny from an Sk(K) x Spore killer-susceptible (Sk(S)) cross to inherit the Sk(K) allele. Sk(K) has been mapped to chromosome V but the genetic element responsible for meiotic drive has yet to be identified. In this study, we used cleaved amplified polymorphic sequence markers to genotype individual progeny from an Sk(K) x Sk(S) mapping population. We also sequenced the genomes of three progeny from the mapping population to determine their single nucleotide polymorphisms. These techniques allowed us to refine the location of Sk(K) to a contiguous 102 kb interval of chromosome V, herein referred to as the Sk region. Relative to Sk(S) genotypes, Sk(K) genotypes have one extra gene within this region for a total of 42 genes. The additional gene in Sk(K) genotypes, herein named SKC1 for Spore Killer Candidate 1, is the most highly expressed gene from the Sk region during early stages of sexual development. The Sk region also has three hyper-variable regions, the longest of which includes SKC1. The possibility that SKC1, or another gene from the Sk region, is an essential component of meiotic drive and spore killing is discussed.
Selfish genetic elements and the gene’s-eye view of evolution
4078Ågren, JA, Current Zoology, 62:659-665. 2016-01-16 00:00:00.
During the last few decades, we have seen an explosion in the influx of details about the biology of selfish genetic elements. Ever since the early days of the field, the gene’s-eye view of Richard Dawkins, George Williams, and others, has been instrumental to make sense of new empirical observations and to the generation of new hypotheses. However, the close association between selfish genetic elements and the gene’s-eye view has not been without critics and several other conceptual frameworks have been suggested. In particular, proponents of multilevel selection models have used selfish genetic elements to criticize the gene’s-eye view. In this paper, I first trace the intertwined histories of the study of selfish genetic elements and the gene’s-eye view and then discuss how their association holds up when compared with other proposed frameworks. Next, using examples from transposable elements and the major transitions, I argue that different models highlight separate aspects of the evolution of selfish genetic elements and that the productive way forward is to maintain a plurality of perspectives. Finally, I discuss how the empirical study of selfish genetic elements has implications for other conceptual issues associated with the gene’s-eye view, such as agential thinking, adaptationism, and the role of fitness maximizing models in evolution.
Control of mosquito-borne infectious diseases: Sex and gene drive
Adelman, ZNT, Z. J., Trends in Parasitology, 32:219-229. 2016-01-15 00:00:00.Sterile male releases have successfully reduced local populations of the dengue vector, Aedes aegypti, but challenges remain in scale and in separating sexes before release. The recent discovery of the first mosquito male determining factor (M factor) will facilitate our understanding of the genetic programs that initiate sexual development in mosquitoes. Manipulation of the M factor and possible intermediary factors may result in female-to-male conversion or female killing, enabling efficient sex separation and effective reduction of target mosquito populations. Given recent breakthroughs in the development of CRISPR-Cas9 reagents as a source of gene drive, more advanced technologies at driving maleness, the ultimate disease refractory phenotype, become possible and may represent efficient and self-limiting methods to control mosquito populations.
Driven to extinction? The ethics of eradicating mosquitoes with gene-drive technologies
4097Pugh, J, Journal of Medical Ethics, 42:578-581. 2016-01-15 00:00:00.
Mosquito-borne diseases represent a significant global disease burden, and recent outbreaks of such diseases have led to calls to reduce mosquito populations. Furthermore, advances in gene-drive' technology have raised the prospect of eradicating certain species of mosquito via genetic modification. This technology has attracted a great deal of media attention, and the idea of using gene-drive technology to eradicate mosquitoes has been met with criticism in the public domain. In this paper, I shall dispel two moral objections that have been raised in the public domain against the use of gene-drive technologies to eradicate mosquitoes. The first objection invokes the concept of the sanctity of life' in order to claim that we should not drive an animal to extinction. In response, I follow Peter Singer in raising doubts about general appeals to the sanctity of life, and argue that neither individual mosquitoes nor mosquitoes species considered holistically are appropriately described as bearing a significant degree of moral status. The second objection claims that seeking to eradicate mosquitoes amounts to displaying unacceptable degrees of hubris. Although I argue that this objection also fails, I conclude by claiming that it raises the important point that we need to acquire more empirical data about, inter alia, the likely effects of mosquito eradication on the ecosystem, and the likelihood of gene-drive technology successfully eradicating the intended mosquito species, in order to adequately inform our moral analysis of gene-drive technologies in this context.
Occasional recombination of a selfish X-chromosome may permit its persistence at high frequencies in the wild
4096Pieper, KED, K. A., Journal of Evolutionary Biology, 29:2229-2241. 2016-01-14 00:00:00.
The sex-ratio X-chromosome (SR) is a selfish chromosome that promotes its own transmission to the next generation by destroying Y-bearing sperm in the testes of carrier males. In some natural populations of the fly Drosophila neotestacea, up to 30% of the X-chromosomes are SR chromosomes. To investigate the molecular evolutionary history and consequences of SR, we sequenced SR and standard (ST) males at 11 X-linked loci that span the ST X-chromosome and at seven arbitrarily chosen autosomal loci from a sample of D. neotestacea males from throughout the species range. We found that the evolutionary relationship between ST and SR varies among individual markers, but genetic differentiation between SR and ST is chromosome-wide and likely due to large chromosomal inversions that suppress recombination. However, SR does not consist of a single multilocus haplotype: we find evidence for gene flow between ST and SR at every locus assayed. Furthermore, we do not find long-distance linkage disequilibrium within SR chromosomes, suggesting that recombination occurs in females homozygous for SR. Finally, polymorphism on SR is reduced compared to that on ST, and loci displaying signatures of selection on ST do not show similar patterns on SR. Thus, even if selection is less effective on SR, our results suggest that gene flow with ST and recombination between SR chromosomes may prevent the accumulation of deleterious mutations and allow its long-term persistence at relatively high frequencies.
Gene silencing and gene drive in dengue vector control
4095Paulraj, MGI, S.; Reegan, A. D., Indian Journal of Natural Products and Resources, 7:193-200. 2016-01-13 00:00:00.
Vector-borne diseases are the most feared diseases throughout the world. Mosquitoes are the prime human disease vectors as they are responsible for nearly one million human deaths every year. So they are declared as the most dangerous insects to mankind. Aedes aegypti and Ae. albopictus are the most significant mosquito species, because of their role in transmitting dengue virus. These blood feeding ectoparasites of man and other vertebrates have developed excellent adaptations to survive and multiply in and around human habitations. Chemical-based mosquito control method does not give good results due to rapid development of pesticide resistance in mosquitoes. The past four decades have witnessed the development of several alternate mosquito control methods. Genetic control technologies have been recently developed as efficient and ecofriendly methods. Inundate release of genetically modified mosquitoes with lethal or pathogen-resistant genes for population reduction is a recent technology in mosquito control programme. Recent developments in molecular and genome editing technologies have made it easy to produce thousands of transgenic mosquitoes for field release. The present review highlights various scientific reports and research findings on gene silencing and gene drive techniques in dengue mosquito control.
Comparative analysis of regions with distorted segregation in three diploid populations of potato
4094Manrique-Carpintero, NCC, J. J.; Veilleux, R. E.; Buell, C. R.; Douches, D. S., G3-Genes Genomes Genetics, 6:2617-2628. 2016-01-12 00:00:00.
Genes associated with gametic and zygotic selection could underlie segregation distortion, observed as alterations of expected Mendelian genotypic frequencies in mapping populations. We studied highly dense genetic maps based on single nucleotide polymorphisms to elucidate the genetic nature of distorted segregation in potato. Three intra-and interspecific diploid segregating populations were used. DRH and D84 are crosses between the sequenced doubled monoploid DM 1-3 516 R44 Solanum tuberosum Group Phureja and either RH89-039-16 S. tuberosum or 84SD22, a S. tuberosum x S. chacoense hybrid. MSX902 is an interspecific cross between 84SD22 and Ber83 S. berthaultii x 2 x species mosaic. At the 0.05 significance level, 21%, 57%, and 51% of the total markers mapped in DRH, D84, and MSX902 exhibited distorted segregation, respectively. Segregation distortion regions for DRH were located on chromosomes 9 and 12; for D84 on chromosomes 2, 3, 4, 6, 7, and 8; and on chromosomes 1, 2, 7, 9, and 12 for MSX902. In general, each population had unique segregation distortion regions and directions of distortion. Interspecific crosses showed greater levels of distorted segregation and lower recombination rates as determined from the male parents. The different genomic regions where the segregation distortion regions occurred in the three populations likely reflect unique genetic combinations producing distorted segregation.
The evolutionary consequences of selfish genetic elements
Lindholm, AKP, T. A. R., Current Zoology, 62:655-658. 2016-01-11 00:00:00.The traditional view of the genome was once that it is broadly cooperative, with all genes working together amicably to improve the success of the individual as a whole. Benefits to the individual, after all, benefit all the component genes, as fair Mendelian inheritance ensures that all the genes and alleles a parent carries are equally likely to be inherited by an offspring. However, more detailed studies of inheritance have shown that this rosy view of cooperation within the genome is untrue. Instead, many genes act selfishly, manipulating gametogenesis to bias transmission in their favor (Burt and Trivers 2006). This increases their representation in offspring at a cost to the fitness of the individual and the cooperative genes.
The Ecology and Evolutionary Dynamics of Meiotic Drive
4092Lindholm, AKD, K. A.; Firman, R. C.; Fishman, L.; Forstmeier, W.; Holman, L.; Johannesson, H.; Knief, U.; Kokko, H.; Larracuente, A. M.; Manser, A.; Montchamp-Moreau, C.; Petrosyan, V. G.; Pomiankowski, A.; Presgraves, D. C.; Safronova, L. D.; Sutter, A.; Unckless, R. L.; Verspoor, R. L.; Wedell, N.; Wilkinson, G. S.; Price, T. A. R., Trends in Ecology & Evolution, 31:315-326. 2016-01-10 00:00:00.
Meiotic drivers are genetic variants that selfishly manipulate the production of gametes to increase their own rate of transmission, often to the detriment of the rest of the genome and the individual that carries them. This genomic conflict potentially occurs whenever a diploid organism produces a haploid stage, and can have profound evolutionary impacts on gametogenesis, fertility, individual behaviour, mating system, population survival, and reproductive isolation. Multiple research teams are developing artificial drive systems for pest control, utilising the transmission advantage of drive to alter or exterminate target species. Here, we review current knowledge of how natural drive systems function, how drivers spread through natural populations, and the factors that limit their invasion.
Stability of underdominant genetic polymorphisms in population networks
4091Laruson, AJR, F. A., Journal of Theoretical Biology, 390:156-163. 2016-01-09 00:00:00.
Heterozygote disadvantage is potentially a potent driver of population genetic divergence. Also referred to as underdominance, this phenomena describes a situation where a genetic heterozygote has a lower overall fitness than either homozygote. Attention so far has mostly been given to underdominance within a single population and the maintenance of genetic differences between two populations exchanging migrants. Here we explore the dynamics of an underdominant system in a network of multiple discrete, yet interconnected, populations. Stability of genetic differences in response to increases in migration in various topological networks is assessed. The network topology can have a dominant and occasionally non-intuitive influence on the genetic stability of the system. (C) 2015 Elsevier Ltd. All rights reserved.
Pollen killer gene S35 function requires interaction with an activator that maps close to S24, another pollen killer gene in rice
4090Kubo, TY, A.; Kurata, N., G3-Genes Genomes Genetics, 6:1459-1468. 2016-01-08 00:00:00.
Pollen killer genes disable noncarrier pollens, and are responsible for male sterility and segregation distortion in hybrid populations of distantly related plant species. The genetic networks and the molecular mechanisms underlying the pollen killer system remain largely unknown. Two pollen killer genes, S24 and S35, have been found in an intersubspecific cross of Oryza sativa ssp. indica and japonica. The effect of S24 is counteracted by an unlinked locus EFS. Additionally, S35 has been proposed to interact with S24 to induce pollen sterility. These genetic interactions are suggestive of a single S24-centric genetic pathway (EFS-S24-S35) for the pollen killer system. To examine this hypothetical genetic pathway, the S35 and the S24 regions were further characterized and genetically dissected in this study. Our results indicated that S35 causes pollen sterility independently of both the EFS and S24 genes, but is dependent on a novel gene close to the S24 locus, named incentive for killing pollen (INK). We confirmed the phenotypic effect of the INK gene separately from the S24 gene, and identified the INK locus within an interval of less than 0.6 Mb on rice chromosome 5. This study characterized the genetic effect of the two independent genetic pathways of INK-S35 and EFS-S24 in indica-japonica hybrid progeny. Our results provide clear evidence that hybrid male sterility in rice is caused by several pollen killer networks with multiple factors positively and negatively regulating pollen killer genes.
Mechanisms of sex determination and transmission ratio distortion in Aedes aegypti
4089Hoang, KPT, T. M.; Ho, T. X.; Le, V. S., Parasites & Vectors, 9:49. 2016-01-07 00:00:00.
: More effective mosquito control strategies are urgently required due to the increasing prevalence of insecticide resistance. The sterile insect technique (SIT) and the release of insects carrying a dominant lethal allele (RIDL) are two proposed methods for environmentally-friendly, species-targeted population control. These methods may be more suitable for developing countries if producers reduce the cost of rearing insects. The cost of control programs could be reduced by producing all-male mosquito populations to circumvent the isolation of females before release without reducing male mating competitiveness caused by transgenes. Results: An RNAi construct targeting the RNA recognition motif of the Aedes aegypti transformer-2 (tra-2) gene does not trigger female-to-male sex conversion as commonly observed among dipterous insects. Instead, homozygous insects show greater mortality among m-chromosome-bearing sperm and mm zygotes, yielding up to 100 % males in the subsequent generations. The performance of transgenic males was not significantly different to wild-type males in narrow-cage competitive mating experiments. Conclusion: Our data provide preliminary evidence that the knockdown of Ae. aegypti tra-2 gene expression causes segregation distortion acting at the level of gametic function, which is reinforced by sex-specific zygotic lethality. This finding could promote the development of new synthetic sex distorter systems for the production of genetic sexing mosquito strains.
Rapid evolution of a Y-chromosome heterochromatin protein underlies sex chromosome meiotic drive
4088Helleu, QG, P. R.; Dubruille, R.; Ogereau, D.; Prud'homme, B.; Loppin, B.; Montchamp-Moreau, C., Proceedings of the National Academy of Sciences of the United States of America, 113:4110-4115. 2016-01-06 00:00:00.
Sex chromosome meiotic drive, the non-Mendelian transmission of sex chromosomes, is the expression of an intragenomic conflict that can have extreme evolutionary consequences. However, the molecular bases of such conflicts remain poorly understood. Here, we show that a young and rapidly evolving X-linked heterochromatin protein 1 (HP1) gene, HP1D2, plays a key role in the classical Paris sex-ratio (SR) meiotic drive occurring in Drosophila simulans. Driver HP1D2 alleles prevent the segregation of the Y chromatids during meiosis II, causing female-biased sex ratio in progeny. HP1D2 accumulates on the heterochromatic Y chromosome in male germ cells, strongly suggesting that it controls the segregation of sister chromatids through heterochromatin modification. We show that Paris SR drive is a consequence of dysfunctional HP1D2 alleles that fail to prepare the Y chromosome for meiosis, thus providing evidence that the rapid evolution of genes controlling the heterochromatin structure can be a significant source of intragenomic conflicts.
A CRISPR-Cas9 gene drive system-targeting female reproduction in the malaria mosquito vector Anopheles gambiae
4087Hammond, AG, R.; Kyrou, K.; Simoni, A.; Siniscalchi, C.; Katsanos, D.; Gribble, M.; Baker, D.; Marois, E.; Russell, S.; Burt, A.; Windbichler, N.; Crisanti, A.; Nolan, T., Nature Biotechnology, 34:78-83. 2016-01-05 00:00:00.
Gene drive systems that enable super-Mendelian inheritance of a transgene have the potential to modify insect populations over a timeframe of a few years. We describe CRISPR-Cas9 endonuclease constructs that function as gene drive systems in Anopheles gambiae, the main vector for malaria. We identified three genes (AGAP005958, AGAP011377 and AGAP007280) that confer a recessive female-sterility phenotype upon disruption, and inserted into each locus CRISPR-Cas9 gene drive constructs designed to target and edit each gene. For each targeted locus we observed a strong gene drive at the molecular level, with transmission rates to progeny of 91.4 to 99.6%. Population modeling and cage experiments indicate that a CRISPR-Cas9 construct targeting one of these loci, AGAP007280, meets the minimum requirement for a gene drive targeting female reproduction in an insect population. These findings could expedite the development of gene drives to suppress mosquito populations to levels that do not support malaria transmission.
Cas9-triggered chain ablation of cas9 as a gene drive brake
4106Wu, BL, L. Q.; Gao, X. J. J., Nature Biotechnology, 34:137-138. 2016-01-04 00:00:00.
We designed and synthesized a transgene system that we named Cas9-triggered chain ablation (CATCHA). The CATCHA transgene encodes a guide RNA (gRNA) that is expressed ubiquitously from a U6:2 promoter. The gRNA targets a site within the DNA sequence of cas9. The guide RNA is flanked by homology arms (of 1,042 bp and 1,003 bp) that match the cas9 sequences next to the gRNA-specified cleavage site (Fig. 1a). In the presence of both CATCHA and cas9, Cas9 proteins will be guided to cleave the cas9 genomic locus from which Cas9 proteins are expressed. Upon repair of the cleaved cas9 by homology-directed repair (HDR), the cas9 locus will be converted to CATCHA. Such conversion in heterozygous offspring favors amplification of CATCHA in the cas9- carrying population
Putting the brakes on CRISPR-Cas9 gene drive systems
4086Graham, DM, Lab Animal, 45:47-47. 2016-01-04 00:00:00.
The sudden emergence and worldwide adoption of CRISPR gene-editing technology confronts humanity with unprecedented opportunities and choices. CRISPR's transformative impact on our future understanding of biology, along with its potential to unleash control over the most fundamental of biological processes, is predictable by already achieved applications. Although its origin, composition, and function were revealed only recently, close to 3000 CRISPR-based publications have appeared including insightful and diversely focused reviews referenced here. Adding further to scientific and public awareness, a recent symposium addressed the ethical implications of interfacing CRISPR technology and human biology. However, the magnitude of CRISPR's rapidly emerging power mandates its broadest assessment. Only with the participation of a diverse and informed community can the most effective and humanity-positive CRISPR applications be defined. This brief review is aimed at those with little previous exposure to the CRISPR revolution. The molecules that constitute CRISPR's core components and their functional organization are described along with how the mechanism has been harnessed to edit genome structure and modulate gene function. Additionally, a glimpse into CRISPR's potential to unleash genetic changes with far-reaching consequences is presented.
The ability to gain matings, not sperm competition, reduces the success of males carrying a selfish genetic element in a fly
4105Verspoor, RLH, G. D. D.; Price, T. A. R., Animal Behaviour, 115:207-215. 2016-01-03 00:00:00.
Females are expected to avoid low-quality males fathering their offspring. X chromosome meiotic drive (XCMD) makes males very low-quality mates. XCMDs are X chromosomes that, in males, cause the failure of all Y chromosome sperm, so all functional sperm carry the driving X and produce daughters. This transmission advantage can allow the XCMD to spread through populations. However, XCMD males typically have low fertility, are very poor at sperm competition, only produce daughters, and bear low fitness alleles associated with XCMD. This imposes significant costs on females that mate with these males. Recently, several studies have shown that females can reduce the risk of their offspring inheriting XCMDs by mating with multiple males (polyandry), as XCMD males typically lose out to normal males in sperm competition. Hence it has been suggested that increased polyandry may be likely to evolve whenever a costly XCMD is common in a population, and that polyandry may be a key factor in preventing XCMDs spreading through populations. We tested this by examining the fruit fly Drosophila subobscura, in which females are known to mate only once in European populations where XCMDs are absent. However, in North African populations an XCMD, referred to as 'SRs', occurs. If the association between XCMDs and polyandry is true, then these North African populations should have evolved polyandry. However, we found no evidence of polyandry in North African D. subobscura populations. Instead, we found some evidence that males that carry SRs are slightly less successful at gaining matings in noncompetitive situations. These results show that polyandry does not necessarily evolve in response to the presence of harmful X chromosome drive. With both sperm competition and female choice both being unlikely to substantially reduce the success of XCMD in D. subobscura, the factors that prevent SRs spreading through these populations remain mysterious. (C) 2016 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.
The dawn of active genetics
4085Gantz, VMB, E., Bioessays, 38:50-63. 2016-01-03 00:00:00.
On December 18, 2014, a yellow female fly quietly emerged from her pupal case. What made her unique was that she had only one parent carrying a mutant allele of this classic recessive locus. Then, one generation later, after mating with a wild-type male, all her offspring displayed the same recessive yellow phenotype. Further analysis of other such yellow females revealed that the construct causing the mutation was converting the opposing chromosome with 95% efficiency. These simple results, seen also in mosquitoes and yeast, open the door to a new era of genetics wherein the laws of traditional Mendelian inheritance can be bypassed for a broad variety of purposes. Here, we consider the implications of this fundamentally new form of active genetics, its applications for gene drives, reversal and amplification strategies, its potential for contributing to cell and gene therapy strategies, and ethical/biosafety considerations associated with such active genetic elements.
Meiotic drive changes sperm precedence patterns in house mice: potential for male alternative mating tactics?
4104Sutter, AL, A. K., BMC Evolutionary Biology, 16:15. 2016-01-02 00:00:00.
Background: With female multiple mating (polyandry), male-male competition extends to after copulation (sperm competition). Males respond to this selective pressure through physiological, morphological and behavioural adaptations. Sperm competitiveness is commonly decreased in heterozygote carriers of male meiotic drivers, selfish genetic elements that manipulate the production of gametes in males. This might give carriers an evolutionary incentive to reduce the risk of sperm competition. Here, we explore this possibility in house mice. Natural populations frequently harbour a well-characterised male driver (t haplotype), which is transmitted to 90 % of heterozygous (+/t) males' offspring. Previous research demonstrated strong detrimental effects on sperm competitiveness, and suggested that +/t males are particularly disadvantaged against wild type males when first-to-mate. Low paternity success in the first-to-mate role is expected to favour male adaptations that decrease the risk of sperm competition by preventing female remating. Genotype-specific paternity patterns (sperm precedence) could lead to genetically determined alternative reproductive tactics that can spread through gene level selection. Here, we seek confirmation that +/t males are generally disadvantaged when first-to-mate and address whether males of different genotypes differ in reproductive tactics (copulatory and morphological) to maximise individual or driver fitness. Finally, we attempt to explain the mechanistic basis for alternative sperm precedence patterns in this species. Results: We confirmed that +/t males are weak sperm competitors when first to mate. When two +/t males competed, the second-to-mate was more successful, which contrasts with first male sperm precedence when wild type males competed. However, we found no differences between male genotypes in reproductive behaviour or morphology that were consistent with alternative reproductive tactics. Sperm of +/+ and +/t males differed with respect to in vitro sperm features. Premature hypermotility in +/t males' sperm can potentially explain why +/t males are very weak sperm competitors when first-to-mate. Conclusions: Our results demonstrate that meiotic drivers can have strong effects on sperm precedence patterns, and may provide a heritable basis for alternative reproductive tactics motivated by reduced sperm competitiveness. We discuss how experimental and evolutionary constraints may help explain why male genotypes did not show the predicted differences.
R2d2 drives selfish sweeps in the house mouse
4084Didion, JPM, A. P.; Yadgary, L.; Bell, T. A.; McMullan, R. C.; de Solorzano, L. O.; Britton-Davidian, J.; Bult, C. J.; Campbell, K. J.; Castiglia, R.; Ching, Y. H.; Chunco, A. J.; Crowley, J. J.; Chesler, E. J.; Forster, D. W.; French, J. E.; Gabriel, S. I.; Gatti, D. M.; Garland, T.; Giagia-Athanasopoulou, E. B.; Gimenez, M. D.; Grize, S. A.; Gunduz, I.; Holmes, A.; Hauffe, H. C.; Herman, J. S.; Holt, J. M.; Hua, K. J.; Jolley, W. J.; Lindholm, A. K.; Lopez-Fuster, M. J.; Mitsainas, G.; Mathias, M. D.; McMillan, L.; Ramalhinho, M. D. M.; Rehermann, B.; Rosshart, S. P.; Searle, J. B.; Shiao, M. S.; Solano, E.; Svenson, K. L.; Thomas-Laemont, P.; Threadgill, D. W.; Ventura, J.; Weinstock, G. M.; Pomp, D.; Churchill, G. A.; de Villena, F. P. M., Molecular Biology and Evolution, 33:1381-1395. 2016-01-02 00:00:00.
A selective sweep is the result of strong positive selection driving newly occurring or standing genetic variants to fixation, and can dramatically alter the pattern and distribution of allelic diversity in a population. Population-level sequencing data have enabled discoveries of selective sweeps associated with genes involved in recent adaptations in many species. In contrast, much debate but little evidence addresses whether "selfish" genes are capable of fixation-thereby leaving signatures identical to classical selective sweeps-despite being neutral or deleterious to organismal fitness. We previously described R2d2, a large copy-number variant that causes nonrandom segregation of mouse Chromosome 2 in females due to meiotic drive. Here we show population-genetic data consistent with a selfish sweep driven by alleles of R2d2 with high copy number (R2d2(HC)) in natural populations. We replicate this finding inmultiple closed breeding populations from six outbred backgrounds segregating for R2d2 alleles. We find that R2d2(HC) rapidly increases in frequency, and in most cases becomes fixed in significantly fewer generations than can be explained by genetic drift. R2d2(HC) is also associated with significantly reduced litter sizes in heterozygous mothers, making it a true selfish allele. Our data provide direct evidence of populations actively undergoing selfish sweeps, and demonstrate that meiotic drive can rapidly alter the genomic landscape in favor of mutations with neutral or even negative effects on overall Darwinian fitness. Further study will reveal the incidence of selfish sweeps, and will elucidate the relative contributions of selfish genes, adaptation and genetic drift to evolution.
Production of a YY Male Brook Trout Broodstock for Potential Eradication of Undesired Brook Trout Populations
11516D. J. Schill, J. A. Heindel, M. R. Campbell, K. A. Meyer and E. Mamer, North American Journal of Aquaculture, 78:72-83. 2015-12-31 15:35:45.
Brook Trout Salvelinus fontinalis introduced outside of their native range often negatively impact native aquatic fauna or provide marginal fisheries and are frequently targeted for manual or piscicide removal in lakes and streams. Unfortunately, complete eradication of exotic Brook Trout populations via these methods is rarely achieved; new approaches are needed. A potential alternative is a Trojan Y Chromosome (TYC) program in which hatchery-produced genetically YY male fish would be regularly released into an undesired population over time, skewing the population towards 100% males, theoretically resulting in wild population extirpation. We developed two genetic sex markers for Brook Trout and employed juvenile sex reversal methods commonly used in commercial aquaculture to develop a YY broodstock that can produce offspring for possible future use as biological control agents. Our search for genetic sex markers proved successful, with genotypic sex determination for two assays matching the observed phenotype for 90 out of 90 individuals. In the first phase of the program, estradiol-infused feed readily feminized genetic XY males into neofemales (FXY fish) at a high rate (99.6%; n = 224). Survival of progeny from such egg-laying FXY fish averaged 88% to eye-up and 91% from eye-up to ponding, values similar to untreated Brook Trout reared at the same facility. In the second program phase, we cultured both sperm-and egg-producing supermales (YY fish), a vital step towards development of TYC technology on a large aquaculture scale. Results showed that, in the hatchery, estradiol treatment does not reduce Brook Trout growth. This study demonstrates that hatchery production of a YY Brook Trout broodstock is feasible, modest in cost (less than US$10,000), and can be completed in 4 years. Although several hurdles remain before a full-scale stocking program could occur, we believe that future work on the TYC strategy for Brook Trout is warranted.
Stochastic models for the Trojan Y-Chromosome eradication strategy of an invasive species
11514X. Y. Wang, J. R. Walton and R. D. Parshad, Journal of Biological Dynamics, 10:179-199. 2015-12-16 15:32:37.
The Trojan Y-Chromosome (TYC) strategy, an autocidal genetic bio-control method, has been proposed to eliminate invasive alien species. In this work, we develop a Markov jump process model for this strategy, and we verify that there is a positive probability for wild-type females going extinct within a finite time. Moreover, when sex-reversed Trojan females are introduced at a constant population size, we formulate a stochastic differential equation (SDE) model as an approximation to the proposed Markov jump process model. Using the SDE model, we investigate the probability distribution and expectation of the extinction time of wild-type females by solving Kolmogorov equations associated with these statistics. The results indicate how the probability distribution and expectation of the extinction time are shaped by the initial conditions and the model parameters.
The effect of malaria control on Plasmodium falciparum in Africa between 2000 and 2015
12672S. Bhatt, D. J. Weiss, E. Cameron, D. Bisanzio, B. Mappin, U. Dalrymple, K. E. Battle, C. L. Moyes, A. Henry, P. A. Eckhoff, E. A. Wenger, O. Briët, M. A. Penny, T. A. Smith, A. Bennett, J. Yukich, T. P. Eisele, J. T. Griffin, C. A. Fergus, M. Lynch, F. L, Nature, 526:207-211. 2015-09-16 17:16:47.
Since the year 2000, a concerted campaign against malaria has led to unprecedented levels of intervention coverage across sub-Saharan Africa. Understanding the effect of this control effort is vital to inform future control planning. H
The Trojan Female Technique for pest control: a candidate mitochondrial mutation confers low male fertility across diverse nuclear backgrounds in Drosophila melanogaster
13733D. K. Dowling, D. M. Tompkins and N. J. Gemmell, Evolutionary Applications, 8:8710880. 2015-07-15 19:28:56.
The Trojan Female Technique (TFT) was recently proposed as a prospective approach to biological pest control. However, applicability of the TFT relies on mitochondrial mutations whose male-sterilizing effects are general across nuclear genomic contexts. We test this assumption, expressing the candidate TFT-mutation bearing haplotype alongside a range of nuclear backgrounds and comparing its fertility in males, relative to that of control haplotypes
Back to the future: the sterile insect technique against mosquito disease vectors
25916R. S. Lees, J. R. L. Gilles, J. Hendrichs, M. J. B. Vreysen and K. Bourtzis, Current Opinion in Insect Science, 10:156-162. 2015-06-03 13:09:41.
With the global burden of mosquito-borne diseases increasing, and some conventional vector control tools losing effectiveness, the sterile insect technique (SIT) is a potential new tool in the arsenal. Equipment and protocols have been developed and validated for efficient mass-rearing, irradiation and release of Aedines and Anophelines that could be useful for several control approaches. Assessment of male quality is becoming more sophisticated, and several groups are well advanced in pilot site selection and population surveillance. It will not be long before SIT feasibility has been evaluated in various settings. Until perfect sexing mechanisms exist, combination of Wolbachia-induced phenotypes, such as cytoplasmic incompatibility and pathogen interference, and irradiation may prove to be the safest solution for population suppression.
Ecological and evolutionary applications for environmental sex reversal of fish
11518A. McNair, P. M. Lokman, G. P. Closs and S. Nakagawa, Quarterly Review of Biology, 90:23-44. 2015-03-01 15:38:29.
Environmental sex reversal (ESR), which results in a mismatch between genotypic and phenotypic sex, is well documented in numerous fish species and may be induced by chemical exposure. Historically, research involving piscine ESR has been carried out with a view to improving profitability in aquaculture or to elucidate the processes governing sex determination and sexual differentiation. However, recent studies in evolution and ecology suggest research on ESR now has much wider applications and ramifications. We begin with an overview of ESR in fish and a brief review of the traditional applications thereof We then discuss ESR and its potential demographic consequences in wild populations. Theory even suggests sex-reversed fish may be purposefully released to manipulate population dynamics. We suggest new research directions that may prove fruitful in understanding how ESR at the individual level translates to population-level processes. In the latter portion of the review we focus on evolutionary applications of ESR Sex-reversal studies from the aquaculture literature provide insight in to the evolvability of determinants of sexual phenotype. Additionally, induced sex reversal can provide information about the evolution of sex chromosomes and sex-linked traits. Recently, naturally occurring ESR has been implicated as a mechanism contributing to the evolution of sex chromosomes.
Gene drive turns mosquitoes into malaria fighters
4123Pennisi, E, Science, 350:1014-1014. 2015-01-21 00:00:00.
The war against malaria has a new ally: a controversial technology for spreading genes throughout a population of animals. In the laboratory, researchers have harnessed a so-called gene drive to efficiently endow mosquitoes with genes that make them immune to the malaria parasite—and unable to spread it. On its own, gene drive won't get rid of malaria, but if successfully applied in the wild the method could help wipe out the disease, at least in some corners of the world. The approach “can bring us to zero [cases],” says Nora Besansky, a geneticist at the University of Notre Dame in South Bend, Indiana, who specializes in malaria-carrying mosquitoes
Female house mice avoid fertilization by t haplotype incompatible males in a mate choice experiment
4122Manser, AK, B.; Lindholm, A. K., Journal of Evolutionary Biology, 28:54-64. 2015-01-20 00:00:00.
The t haplotype in house mice is a well-known selfish genetic element with detrimental, nonadditive fitness consequences to its carriers: recessive lethal mutations cause t/t homozygotes to perish in utero. Given the severe genetic incompatibility imposed by the t haplotype, we predict females to avoid fertilization by t haplotype incompatible males. Indeed, some of the strongest evidence for compatibility mate choice is related to the t haplotype in house mice. However, all previous evidence for compatibility mate choice in this system is based on olfactory preference. It is so far unknown how general these preferences are and whether they are relevant in an actual mating context. Here, we assess female compatibility mate choice related to t haplotypes in a setting that - for the first time - allowed females to directly interact and mate with males. This approach enabled us to analyse female behaviour during the testing period, and the resulting paternity success and fitness consequences of a given choice. We show that genetic incompatibilities arising from the t haplotype had severe indirect fitness consequences and t females avoided fertilization by t incompatible males. The results are inconclusive whether this avoidance of t fertilization by t females was caused by pre- or post-copulatory processes.
Can systematic reviews inform GMO risk assessment and risk management?
4121Kohl, CF, G.; Sweet, J.; Spok, A.; Haddaway, N.R.; Wilhelm, R.; Unger, S.; Schiemann, J., Frontiers in Bioengineering and Biotechnology, 3:113. 2015-01-19 00:00:00.
Systematic reviews represent powerful tools to identify, collect, synthesize, and evaluate primary research data on specific research questions in a highly standardized and reproducible manner. They enable the defensible synthesis of outcomes by increasing precision and minimizing bias whilst ensuring transparency of the methods used. This makes them especially valuable to inform evidence-based risk analysis and decision making in various topics and research disciplines. Although seen as a “gold standard” for synthesizing primary research data, systematic reviews are not without limitations as they are often cost, labor and time intensive and the utility of synthesis outcomes depends upon the availability of sufficient and robust primary research data. In this paper, we (1) consider the added value systematic reviews could provide when synthesizing primary research data on genetically modified organisms (GMO) and (2) critically assess the adequacy and feasibility of systematic review for collating and analyzing data on potential impacts of GMOs in order to better inform specific steps within GMO risk assessment and risk management. The regulatory framework of the EU is used as an example, although the issues we discuss are likely to be more widely applicable.
A prezygotic transmission distorter acting equally in female and male zebra finches Taeniopygia guttata
4120Knief, US, H.; Ellegren, H.; Kempenaers, B.; Forstmeier, W., Molecular Ecology, 24:3846-3859. 2015-01-18 00:00:00.
The two parental alleles at a specific locus are usually inherited with equal probability to the offspring. However, at least three processes can lead to an apparent departure from fair segregation: early viability selection, biased gene conversion and various kinds of segregation distortion. Here, we conduct a genome-wide scan for transmission distortion in a captive population of zebra finches (Taeniopygia guttata) using 1302 single-nucleotide polymorphisms (SNPs) followed by confirmatory analyses on independent samples from the same population. In the initial genome-wide scan, we found significant distortion at three linked loci on chromosome Tgu2 and we were able to replicate this finding in each of two follow-up data sets [overall transmission ratio=0.567 (95% CI=0.536-0.600), based on 1101 informative meioses]. Although the driving allele was preferentially transmitted by both heterozygous females [ratio=0.560 (95% CI=0.519-0.603)] and heterozygous males [ratio=0.575 (95% CI=0.531-0.623)], we could rule out postzygotic viability selection and biased gene conversion as possible mechanisms. Early postzygotic viability selection is unlikely, because it would result in eggs with no visible embryo and hence no opportunity for genotyping, and we confirmed that both females and males heterozygous for the driving allele did not produce a larger proportion of such eggs than homozygous birds. Biased gene conversion is expected to be rather localized, while we could trace transmission distortion in haplotypes of several megabases in a recombination desert. Thus, we here report the rare case of a prezygotically active transmission distorter operating equally effectively in female and male meioses.
Double trouble: combined action of meiotic drive and Wolbachia feminization in Eurema butterflies
4119Kern, PC, J. M.; Kageyama, D.; Riegler, M., Biology Letters, 11:20150095. 2015-01-17 00:00:00.
Arthropod sex ratios can be manipulated by a diverse range of selfish genetic elements, including maternally inherited Wolbachia bacteria. Feminization by Wolbachia is rare but has been described for Eurema mandarina butterflies. In this species, some phenotypic and functional females, thought to be ZZ genetic males, are infected with a feminizing Wolbachia strain, wFem. Meanwhile, heterogametic WZ females are not infected with wFem. Here, we establish a quantitative PCR assay allowing reliable sexing in three Eurema species. Against expectation, all E. mandarina females, including wFem females, had only one Z chromosome that was paternally inherited. Observation of somatic interphase nuclei confirmed that W chromatin was absent in wFem females, but present in females without wFem. We conclude that the sex bias in wFem lines is due to meiotic drive (MD) that excludes the maternal Z and thus prevents formation of ZZ males. Furthermore, wFem lines may have lost the W chromosome or harbour a dysfunctional version, yet rely on wFem for female development; removal of wFem results in all-male offspring. This is the first study that demonstrates an interaction between MD and Wolbachia feminization, and it highlights endosymbionts as potentially confounding factors in MD of sex chromosomes.
Coevolutionary dynamics of polyandry and sex-linked meiotic drive
4118Holman, LP, T. A. R.; Wedell, N.; Kokko, H., Evolution, 69:709-720. 2015-01-16 00:00:00.
Segregation distorters located on sex chromosomes are predicted to sweep to fixation and cause extinction via a shortage of one sex, but in nature they are often found at low, stable frequencies. One potential resolution to this longstanding puzzle involves female multiple mating (polyandry). Because many meiotic drivers severely reduce the sperm competitive ability of their male carriers, females are predicted to evolve more frequent polyandry and thereby promote sperm competition when a meiotic driver invades. Consequently, the driving chromosome's relative fitness should decline, halting or reversing its spread. We used formal modeling to show that this initially appealing hypothesis cannot resolve the puzzle alone: other selective pressures (e.g., low fitness of drive homozygotes) are required to establish a stable meiotic drive polymorphism. However, polyandry and meiotic drive can strongly affect one another's frequency, and polyandrous populations may be resistant to the invasion of rare drive mutants.
