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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Defects in nuclear transport enhance segregation distortion

4242
McElroy, JMM, R. A.; McLean, J. R.,  Fly,  2:280-290. 2008-01-20 00:00:00.
The equal segregation of chromosomes into gametes is a central tenet of Mendelian genetics. It is this process that is responsible for generating predictable outcomes of crosses, as well as subjecting all chromosomes to the natural selective pressures that exert themselves on a population. Meiotic drive systems violate the principle, and result in a distortion of normal Mendelian ratios. Examples of such meiotic drive systems exist in many organisms, including insects, mammals and plants (reviewed in Lyttle).1 The most clearly understood of these is the Segregation Distorter (SD) system in Drosophila melanogaster. SD was first observed because males carrying one SD chromosome and one normal (SD+) chromosome failed to transmit the normal chromosome to their offspring, causing transmission ratios of near 100% of the SD chromosome.2 T

Transmission ratio distortion in Arabidopsis lyrata: effects of population divergence and the S-locus

4241
Leppala, JB, J. S.; Schierup, M. H.; Savolainen, O.,  Heredity,  100:71-78. 2008-01-19 00:00:00.
We investigated transmission ratio distortion within an Icelandic population of Arabidopsis lyrata using 16 molecular markers unlinked to the S-locus. Transmission ratio distortion was found more often than expected by chance at the gametic level, but not at the genotypic or zygotic level. The gametic effect may be due to meiotic drive or selection acting postmeiotically. At the gametic level, 10.9% of the tests were significant, which is substantially lower than earlier observed in an interpopulation cross (allowing for differences in power)-suggesting that the high level of transmission ratio distortion in the interpopulation cross is due to population divergence. It is also substantially lower than previously observed in intrapopulation crosses at the self-incompatibility locus, suggesting inherent fitness differences of the self-incompatibility alleles. We discuss the possible role of deleterious alleles accumulating at loci under balancing selection. Zygotic effects play a larger role in the interpopulation cross than in the intrapopulation crosses suggesting that Dobzhansky-Muller incompatibilities may be accumulating between the widely diverged populations.

The evolution of sex-independent transmission ratio distortion involving multiple allelic interactions at a single locus in rice

4240
Koide, YI, M.; Sawamura, N.; Nishimoto, D.; Matsubara, K.; Onishi, K.; Kanazawa, A.; Sano, Y.,  Genetics,  180:409-420. 2008-01-18 00:00:00.
Transmission ratio distortion (TRD) is frequently observed in inter-and intraspecific hybrids of plants, leading to a violation of Mendelian inheritance. Sex-independent TRD (siTRD) was detected in a hybrid between Asian cultivated rice and its wild ancestor. Here we examined how siTRD is controlled by the S-6 locus via a mechanism in which the S-6 allele acts as a gamete eliminator, and both the male and female gametes possessing the opposite allele (S-6(a)) are aborted only in heterozygotes (S-6/S-6(a)). Fine mapping revealed that the S-6 locus is located neaar the centromere of chromosome 6. Tescross experiments using near-isogenic lines (NILs) carrying either the S-6 or S-6(a) alleles revealed that Asian rice strains frequently harbor an additional allele (S-6(n)) the presence of which, in heterozygotic states (S-6/S-6(n) and S-6(a)/S-6(n)), does not result in siTRD. A prominent reduction in the nucleotide diversity of S-6 or S-6(a) carries relative to that of S-6(n) carries was detected in the chromosomal region. These results suggest that the two incompatible alleles (S-6/S-6(a)) arose independently from S-6(n) and established genetically discontinuous relationships between limited constituents of the Asian rice population.

X chromosome drive

4239
Jaenike, J,  Current Biology,  18:R508-R511. 2008-01-17 00:00:00.
In the past 10 years, the world record for the men's 100 meter dash has declined from 9.79 to 9.74 seconds, the detection of such small differences being made possible by sophisticated electronic timing devices. If someone were to run the 100 meters in 9.73999 seconds in the 2008 Olympics, would the timers be sensitive enough to show him to be the world's fastest human? Natural selection could, as differences in fitness of that magnitude (10?6) can be detected in species with large effective population sizes. In this way, natural selection can bring about the evolution of exquisitely well-adapted creatures.; Getting back to the race, imagine that one of the runners somehow manages to get a 50-meter head start. With such an advantage, even an overweight, out of shape, or injured athlete could win the gold. An analogous situation applies in evolution. Mendelian segregation, in which the two alleles carried by a heterozygous individual are passed to equal numbers of gametes, ensures that alleles compete fairly and that they succeed (or fail) on the basis of their effects on survival and fertility. Meiotic drive — the process by which alleles are not represented equally in an individual's gametes — subverts the entire process. In the best documented examples of drive, one allele may be passed on to ?100% of an organism's gametes, equivalent to a runner getting a 50-meter head start in the 100 meter dash. The overrepresentation of such alleles in gametes can more than make up for any associated deficiencies in survival and fertility. As a result, these alleles — and those closely linked to them — can rapidly spread through a population, and thus actually cause a decline in the adaptation of a species to its environment. If such an allele drives all the way to fixation, the species may end up a little less well adapted, but there would be no evidence that meiotic drive was the cause, as drive would no longer be expressed.

A Killer–Rescue system for self-limiting gene drive of anti-pathogen constructs

4238
Gould, FH, Yunxin; Legros, Mathieu; Lloyd, Alun L.,  Proceedings of the Royal Society B: Biological Sciences,  275:2823-2829. 2008-01-16 00:00:00.
A number of genetic mechanisms have been suggested for driving anti-pathogen genes into natural populations. Each of these mechanisms requires complex genetic engineering, and most are theoretically expected to permanently spread throughout the target species' geographical range. In the near term, risk issues and technical limits of molecular methods could delay the development and use of these mechanisms. We propose a gene-drive mechanism that can be self-limiting over time and space, and is simpler to build. This mechanism involves one gene that codes for toxicity (killer) and a second that confers immunity to the toxic effects (rescue). We use population-genetic models to explore cases with one or two independent insertions of the killer gene and one insertion of the rescue gene. We vary the dominance and penetrance of gene action, as well as the magnitude of fitness costs. Even with the fitness costs of 10 per cent for each gene, the proportion of mosquitoes expected to transmit the pathogen decreases below 5 per cent for over 40 generations after one 2?:?1 release (engineered?:?wild) or after four 1?:?2 releases. Both the killer and rescue genes will be lost from the population over time, if the rescue construct has any associated fitness cost. Molecular approaches for constructing strains are discussed.

Broadening the application of evolutionarily based genetic pest management

4237
Gould, F,  Evolution,  62:500-510. 2008-01-15 00:00:00.
Insect- and tick-vectored diseases such as malaria, dengue fever, and Lyme disease cause human suffering, and current approaches for prevention are not adequate. Invasive plants and animals such as Scotch broom, zebra mussels, and gypsy moths continue to cause environmental damage and economic losses in agriculture and forestry Rodents transmit diseases and cause major pre- and postharvest losses, especially in less affluent countries. Each of these problems might benefit from the developing field of Genetic Pest Management that is conceptually based on principles of evolutionary biology This article briefly describes the history of this field, new molecular tools in this field, and potential applications of those tools. There will be a need for evolutionary biologists to interact with researchers and practitioners in a variety of other fields to determine the most appropriate targets for genetic pest management, the most appropriate methods for specific targets, and the potential of natural selection to diminish the effectiveness of genetic pest management. In addition to producing environmentally sustainable pest management solutions, research efforts in this area could lead to new insights about the evolution of selfish genetic elements in natural systems and will provide students with the opportunity to develop a more sophisticated understanding of the role of evolutionary biology in solving societal problems.

Centromere-associated female meiotic drive entails male fitness costs in Monkeyflowers

4236
Fishman, LS, A.,  Science,  322:1559-1562. 2008-01-14 00:00:00.
Female meiotic drive, in which paired chromosomes compete for access to the egg, is a potentially powerful but rarely documented evolutionary force. In interspecific monkeyflower ( Mimulus) hybrids, a driving M. guttatus allele ( D) exhibits a 98: 2 transmission advantage via female meiosis. We show that extreme interspecific drive is most likely caused by divergence in centromere- associated repeat domains and document cytogenetic and functional polymorphism for drive within a population of M. guttatus. In conspecific crosses, D had a 58: 42 transmission advantage over nondriving alternative alleles. However, individuals homozygous for the driving allele suffered reduced pollen viability. These fitness effects and molecular population genetic data suggest that balancing selection prevents the fixation or loss of D and that selfish chromosomal transmission may affect both individual fitness and population genetic load.

Selective sweeps in a 2-locus model for sex-ratio meiotic drive in Drosophila simulans

4235
Derome, NB, E.; Ogereau, D.; Veuille, M.; Montchamp-Moreau, C.,  Molecular Biology and Evolution,  25:409-416. 2008-01-13 00:00:00.
A way to identify loci subject to positive selection is to detect the signature of selective sweeps in given chromosomal regions. It is revealed by the departure of DNA polymorphism patterns from the neutral equilibrium predicted by coalescent theory. We surveyed DNA sequence variation in a region formerly identified as causing "sex-ratio" meiotic drive in Drosophila simulans. We found evidence that this system evolved by positive selection at 2 neighboring loci, which thus appear to be required simultaneously for meiotic drive to occur. The 2 regions are approximately 150-kb distant, corresponding to a genetic distance of 0.1 cM. The presumably large transmission advantage of chromosomes carrying meiotic drive alleles at both loci has not erased the individual signature of selection at each locus. This chromosome fragment combines a high level of linkage disequilibrium between the 2 critical regions with a high recombination rate. As a result, 2 characteristic traits of selective sweeps-the reduction of variation and the departure from selective neutrality in haplotype tests-show a bimodal pattern. Linkage disequilibrium level indicates that, in the natural population from Madagascar used in this study, the selective sweep may be as recent as 100 years.

The population genetics of using homing endonuclease genes in vector and pest management

4234
Deredec, AB, A.; Godfray, H. C. J.,  Genetics,  179:2013-2026. 2008-01-12 00:00:00.
Homing endonuclease genes (HEGs) encode proteins that in the heterozygous state cause double- strand breaks in the homologous chromosome at the precise position opposite the HFG. If the double-strand break is repaired using the homologous chromosome, the HEG becomes homozygous, and this represents it Powerful genetic drive mechanism that might he used as it tool managing vector or pest populations. HEGs may be used to decrease population fitness to drive down population densities (possibly causing local extinction) or, in disease vectors, to knock out a gene required for pathogen transmission. The relative advantages of HEGs thia target viability or fecundity, that are active in one sex or both, and whose target. is expressed before or after homing are explored. The conditions under which escape mutants arise are also analyzed. A different strategy is to place HEGs on the Y chromosome that cause one, or more breaks on the X chromosome and so disrupt. sex ratio. This strategy can cause severe sex-ratio biases with efficiencies that depend on the details of sperm Competition and zygote mortality. This strategy is probably less susceptible to escape mutants, especially when multiple X shredders are used.

Rapid evolution of yeast centromeres in the absence of drive

4233
Bensasson, DZ, M.; Burt, A.; Koufopanou, V.,  Genetics,  178:2161-2167. 2008-01-11 00:00:00.
To find the most rapidly evolving regions in the yeast genome we compared most of chromosome III from three closely related lineages of the wild yeast Saccharomyces paradoxits. Unexpectedly, the centromere appears to be the fastest-evolving part of the chromosome, evolving even faster than DNA sequences unlikely to be under selective constraint (i.e., synonymous sites after correcting for codon usage bias and remnant transposable elements). Centromeres on other chromosomes also show an elevated rate of nucleotide substitution. Rapid centromere evolution has also been reported for some plants and animals and has been attributed to selection for inclusion in the egg or the ovule at female meiosis. But Saccharomyces yeasts have symmetrical meioses with all four products surviving, thus providing no opportunity for meiotic drive. In addition, yeast centromeres show the high levels of polymorphism expected tinder a neutral model of molecular evolution. We suggest that yeast centromeres suffer an elevated rate of mutation relative to other chromosomal regions and they change through a process of "centromere drift," not drive.

Guidance for contained field trials of vector mosquitoes engineered to contain a gene drive system: Recommendations of a scientific working group

4232
Benedict, MDA, P.; Dobson, S.; Gottlieb, M.; Harrington, L.; Higgs, S.; James, A.; James, S.; Knols, B.; Lavery, J.; O'Neill, S.; Scott, T.; Takken, W.; Toure, Y.; Core Working Grp Guidance, Containe,  Vector-Borne and Zoonotic Diseases,  8:127-166. 2008-01-10 00:00:00.
The following recommendations represent the response of a group of involved scientists to the need for guidance to aid researchers, government authorities, and community leaders as they consider the design and implementation of field trials to assess the safety and efficacy of genetic strategies for reducing the transmission of diseases by mosquito vectors. Guidance is provided for contained (caged) field trials of genetically-engineered (GE) vector mosquitoes that are fertile and contain novel genetic constructs designed to spread through natural mosquito populations (“gene drive systems”). An effort is made to raise the practical issues that must be considered in advance of such testing, provide generalized recommendations based on currently available information, and identify “points to consider” regarding additional information that may be required in order to make informed decisions on a case-by-case basis. This guidance is intended to clarify the pathway for further assessment of the potential utility of such GE mosquitoes as a tool for the improvement of public health in disease-endemic regions.

Targeting the X chromosome during spermatogenesis induces Y chromosome transmission ratio distortion and early dominant embryo lethality in Anopheles gambiae

4247
Windbichler, NP, P. A.; Crisanti, A.,  PLOS Genetics,  4:1-9. 2008-01-05 00:00:00.
We have exploited the high selectivity of the homing endonuclease I-PpoI for the X-linked Anopheles gambiae 28S ribosomal genes to selectively target X chromosome carrying spermatozoa. Our data demonstrated that in heterozygous males, the expression of I-PpoI in the testes induced a strong bias toward Y chromosome-carrying spermatozoa. Notably, these male mosquitoes also induced complete early dominant embryo lethality in crosses with wild-type females. Morphological and molecular data indicated that all spermatozoa, irrespectively of the inheritance of the transgene, carried a substantial amount of I-PpoI protein that could attack the maternally inherited chromosome X of the embryo. Besides the obvious implications for implementing vector control measures, our data demonstrated the feasibility of generating synthetic sex distorters and revealed the intriguing possibility of manipulating maternally inherited genes using wild-type sperm cells carrying engineered endonucleases.

Meiotic drive and sex determination: molecular and cytological mechanisms of sex ratio adjustment in birds

4246
Rutkowska, JB, A. V.,  Philosophical Transactions of the Royal Society B-Biological Sciences,  363:1675-1686. 2008-01-04 00:00:00.
Differences in relative fitness of male and female offspring across ecological and social environments should favour the evolution of sex-determining mechanisms that enable adjustment of brood sex ratio to the context of breeding. Despite the expectation that genetic sex determination should not produce consistent bias in primary sex ratios, extensive and adaptive modifications of offspring sex ratio in relation to social and physiological conditions during reproduction are often documented. Such discordance emphasizes the need for empirical investigation of the proximate mechanisms for modifying primary sex ratios, and suggests epigenetic effects on sex-determining mechanisms as the most likely candidates. Birds, in particular, are thought to have an unusually direct opportunity to modify offspring sex ratio because avian females are heterogametic and because the sex-determining division in avian meiosis occurs prior to ovulation and fertilization. However, despite evidence of strong epigenetic effects on sex determination in pre-ovulatory avian oocytes, the mechanisms behind such effects remain elusive. Our review of molecular and cytological mechanisms of avian meiosis uncovers a multitude of potential targets for selection on biased segregation of sex chromosomes, which may reflect the diversity of mechanisms and levels on which such selection operates in birds. Our findings indicate that pronounced differences between sex chromosomes in size, shape, size of protein bodies, alignment at the meiotic plate, microtubule attachment and epigenetic markings should commonly produce biased segregation of sex chromosomes as the default state, with secondary evolution of compensatory mechanisms necessary to maintain unbiased meiosis. We suggest that it is the epigenetic effects that modify such compensatory mechanisms that enable context-dependent and precise adjustment of primary sex ratio in birds. Furthermore, we highlight the features of avian meiosis that can be influenced by maternal hormones in response to environmental stimuli and may account for the precise and adaptive patterns of offspring sex ratio adjustment observed in some species.

Sexually antagonistic “Zygotic Drive” of the sex Chromosomes

4245
Rice, WRG, S.; Friberg, U.,  PLOS Genetics,  4:e1000313. 2008-01-03 00:00:00.
Genomic conflict is perplexing because it causes the fitness of a species to decline rather than improve. Many diverse forms of genomic conflict have been identified, but this extant tally may be incomplete. Here, we show that the unusual characteristics of the sex chromosomes can, in principle, lead to a previously unappreciated form of sexual genomic conflict. The phenomenon occurs because there is selection in the heterogametic sex for sex-linked mutations that harm the sex of offspring that does not carry them, whenever there is competition among siblings. This harmful phenotype can be expressed as an antagonistic green-beard effect that is mediated by epigenetic parental effects, parental investment, and/or interactions among siblings. We call this form of genomic conflict sexually antagonistic "zygotic drive'', because it is functionally equivalent to meiotic drive, except that it operates during the zygotic and postzygotic stages of the life cycle rather than the meiotic and gametic stages. A combination of mathematical modeling and a survey of empirical studies is used to show that sexually antagonistic zygotic drive is feasible, likely to be widespread in nature, and that it can promote a genetic "arms race'' between the homo- and heteromorphic sex chromosomes. This new category of genomic conflict has the potential to strongly influence other fundamental evolutionary processes, such as speciation and the degeneration of the Y and W sex chromosomes. It also fosters a new genetic hypothesis for the evolution of enigmatic fitness-reducing traits like the high frequency of spontaneous abortion, sterility, and homosexuality observed in humans.

Selfish genetic elements promote polyandry in a fly

4244
Price, TARH, D. J.; Lewis, Z.; Hurst, G. D. D.; Wedell, N.,  Science,  322:1241-1243. 2008-01-02 00:00:00.
It is unknown why females mate with multiple males when mating is frequently costly and a single copulation often provides enough sperm to fertilize all a female's eggs. One possibility is that remating increases the fitness of offspring, because fertilization success is biased toward the sperm of high- fitness males. We show that female Drosophila pseudoobscura evolved increased remating rates when exposed to the risk of mating with males carrying a deleterious sex ratio- distorting gene that also reduces sperm competitive ability. Because selfish genetic elements that reduce sperm competitive ability are generally associated with low genetic fitness, they may represent a common driver of the evolution of polyandry.

Control of introduced species using Trojan sex chromosomes

11543
S. Cotton and C. Wedekind,  Trends in Ecology & Evolution,  22:441-443. 2007-07-20 17:25:46.
To control introduced exotic species that have predominantly genetic, but environmentally reversible, sex determination (e.g. many species of fish), Gutierrez and Teem recently modeled the use of carriers of Trojan Y chromosomes - individuals who are phenotypically sex reversed from their genotype. Repeated introduction of YY females into wild populations should produce extreme male-biased sex ratios and eventual elimination of XX females, thus leading to population extinction. Analogous dynamics are expected in systems in which sex determination is influenced by one or a few major genes on autosomes.

Homing endonuclease mediated gene targeting in Anopheles gambiae cells and embryos

4259
Windbichler, NP, P. A.; Catteruccia, F.; Ranson, H.; Burt, A.; Crisanti, A.,  Nucleic Acids Research,  35:5922-5933. 2007-01-17 00:00:00.
Homing endonuclease genes (HEGs) are selfish genetic elements that combine the capability to selectively disrupt specific gene sequences with the ability to rapidly spread from a few individuals to an entire population through homologous recombination repair events. Because of these properties, HEGs are regarded as promising candidates to transfer genetic modifications from engineered laboratory mosquitoes to wild-type populations including Anopheles gambiae the vector of human malaria. Here we show that I-SceI and I-PpoI homing endonucleases cleave their recognition sites with high efficiency inA. gambiae cells and embryos and we demonstrate HEG-induced homologous and non-homologous repair events in a variety of functional assays. We also propose a gene drive system for mosquitoes that is based on our finding that I-PpoI cuts genomic rDNA located on the X chromosome in A. gambiae, which could be used to selectively incapacitate X-carrying spermatozoa thereby imposing a severe male-biased sex ratio.

Viability effects and not meoitic drive cause dramatic departures from Mendelian inheritance for malic enzyme in hybrids of Tigriopus californicus populations

4258
Willett, CSB, J. N.,  Journal of Evolutionary Biology,  20:1196-1205. 2007-01-16 00:00:00.
The genetic basis of post-zygotic reproductive isolation is beginning to be untangled in closely related species, but less is known about the genetics of reproductive isolation between divergent populations. Here, two genes encoding malic enzyme (ME) are isolated from the copepod Tigriopus californicus and their influence upon lowered viability in F-2 hybrids of genetically divergent populations is determined. Each ME gene has diverged extensively between T. californicus populations and one gene shows evidence for a recent selective sweep. Segregation patterns of genotypes for both ME genes in adult F-2 hybrids reveal dramatic departures from Mendelian inheritance, deviations that are not seen in F-2 nauplii implying that selection is acting during development based upon the genotype at these ME genes. These results imply that selection against deleterious gene combinations and not aberrant segregation (i.e. meiotic drive) is likely to lead to dramatic departures from Mendelian inheritance observed in these crosses.

Small steps or giant leaps for male-killers? Phylogenetic constraints to male-killer host shifts

4257
Tinsley, MCM, M. E. N.,  BMC Evolutionary Biology,  7:e1000313. 2007-01-15 00:00:00.
Background: Arthropods are infected by a wide diversity of maternally transmitted microbes. Some of these manipulate host reproduction to facilitate population invasion and persistence. Such parasites transmit vertically on an ecological timescale, but rare horizontal transmission events have permitted colonisation of new species. Here we report the first systematic investigation into the influence of the phylogenetic distance between arthropod species on the potential for reproductive parasite interspecific transfer. Results: We employed a well characterised reproductive parasite, a coccinellid beetle male-killer, and artificially injected the bacterium into a series of novel species. Genetic distances between native and novel hosts were ascertained by sequencing sections of the 16S and 12S mitochondrial rDNA genes. The bacterium colonised host tissues and transmitted vertically in all cases tested. However, whilst transmission efficiency was perfect within the native genus, this was reduced following some transfers of greater phylogenetic distance. The bacterium's ability to distort offspring sex ratios in novel hosts was negatively correlated with the genetic distance of transfers. Male-killing occurred with full penetrance following within-genus transfers; but whilst sex ratio distortion generally occurred, it was incomplete in more distantly related species. Conclusion: This study indicates that the natural interspecific transmission of reproductive parasites might be constrained by their ability to tolerate the physiology or genetics of novel hosts. Our data suggest that horizontal transfers are more likely between closely related species. Successful bacterial transfer across large phylogenetic distances may require rapid adaptive evolution in the new species. This finding has applied relevance regarding selection of suitable bacteria to manipulate insect pest and vector populations by symbiont gene-drive systems.

A sex-ratio meiotic drive system in Drosophila simulans. I: An autosomal suppressor

4256
Tao, YM, J. P.; Araripe, L.; Ke, Y.; Hartl, D. L.,  PLOS Biology,  5:2560-2575. 2007-01-14 00:00:00.
Sex ratio distortion (sex-ratio for short) has been reported in numerous species such as Drosophila, where distortion can readily be detected in experimental crosses, but the molecular mechanisms remain elusive. Here we characterize an autosomal sex-ratio suppressor from D. simulans that we designate as not much yang (nmy, polytene chromosome position 87F3). Nmy suppresses an X-linked sex-ratio distorter, contains a pair of near-perfect inverted repeats of 345 bp, and evidently originated through retrotransposition from the distorter itself. The suppression is likely mediated by sequence homology between the suppressor and distorter. The strength of sex-ratio is greatly enhanced by lower temperature. This temperature sensitivity was used to assign the sex-ratio etiology to the maturation process of the Y-bearing sperm, a hypothesis corroborated by both light microscope observations and ultrastructural studies. It has long been suggested that an X-linked sex-ratio distorter can evolve by exploiting loopholes in the meiotic machinery for its own transmission advantage, which may be offset by other changes in the genome that control the selfish distorter. Data obtained in this study help to understand this evolutionary mechanism in molecular detail and provide insight regarding its evolutionary impact on genomic architecture and speciation.

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