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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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

4097
Pugh, 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

4096
Pieper, 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

4095
Paulraj, 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

4094
Manrique-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

4092
Lindholm, 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

4091
Laruson, 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

4090
Kubo, 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

4089
Hoang, 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

4088
Helleu, 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

4087
Hammond, 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

4106
Wu, 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

4086
Graham, 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

4105
Verspoor, 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

4085
Gantz, 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?

4104
Sutter, 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

4084
Didion, 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

11516
D. 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

11514
X. 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.

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