Controlling invasive rodents via synthetic gene drive and the role of polyandry.

House mice are a major ecosystem pest, particularly threatening island ecosystems as a non-native invasive species. Rapid advances in synthetic biology offer new avenues to control pest species for biodiversity conservation. Recently, a synthetic sperm-killing gene drive construct called t-Sry has been proposed as a means to eradicate target mouse populations owing to a lack of females. A factor that has received little attention in the discussion surrounding such drive applications is polyandry. Previous research has demonstrated that sperm-killing drivers are extremely damaging to a male's sperm competitive ability. Here, we examine the importance of this effect on the t-Sry system using a theoretical model. We find that polyandry substantially hampers the spread of t-Sry such that release efforts have to be increased three- to sixfold for successful eradication. We discuss the implications of our finding for potential pest control programmes, the risk of drive spread beyond the target population, and the emergence of drive resistance. Our work highlights that a solid understanding of the forces that determine drive dynamics in a natural setting is key for successful drive application, and that exploring the natural diversity of gene drives may inform effective gene drive design.

Rodent gene drives for conservation: opportunities and data needs.

Invasive rodents impact biodiversity, human health and food security worldwide. The biodiversity impacts are particularly significant on islands, which are the primary sites of vertebrate extinctions and where we are reaching the limits of current control technologies. Gene drives may represent an effective approach to this challenge, but knowledge gaps remain in a number of areas. This paper is focused on what is currently known about natural and developing synthetic gene drive systems in mice, some key areas where key knowledge gaps exist, findings in a variety of disciplines relevant to those gaps and a brief consideration of how engagement at the regulatory, stakeholder and community levels can accompany and contribute to this effort. Our primary species focus is the house mouse, Mus musculus, as a genetic model system that is also an important invasive pest. Our primary application focus is the development of gene drive systems intended to reduce reproduction and potentially eliminate invasive rodents from islands. Gene drive technologies in rodents have the potential to produce significant benefits for biodiversity conservation, human health and food security. A broad-based, multidisciplinary approach is necessary to assess this potential in a transparent, effective and responsible manner.

Effects of population density on corticosterone levels of prairie voles in the field.

High population density is often associated with increased levels of stress-related hormones, such as corticosterone (CORT). Prairie voles (Microtus ochrogaster) are a socially monogamous species known for their large population density fluctuations in the wild. Although CORT influences the social behavior of prairie voles in the lab, the effect of population density on CORT has not previously been quantified in this species in the field. We validated a non-invasive hormone assay for measuring CORT metabolites in prairie vole feces. We then used semi-natural enclosures to experimentally manipulate population density, and measured density effects on male space use and fecal CORT levels. Our enclosures generated patterns of space use and social interaction that were consistent with previous prairie vole field studies. Contrary to the positive relationship between CORT and density typical of other taxa, we found that lower population densities (80 animals/ha) produced higher fecal CORT than higher densities (240/ha). Combined with prior work in the lab and field, the data suggest that high prairie vole population densities indicate favorable environments, perhaps through reduced predation risk. Lastly, we found that field animals had lower fecal CORT levels than laboratory-living animals. The data emphasize the usefulness of prairie voles as models for integrating ecological, evolutionary, and mechanistic questions in social behavior.

Phylogeography of the Rickett's big-footed bat, Myotis pilosus (Chiroptera: Vespertilionidae): a novel pattern of genetic structure of bats in China.

BACKGROUND: China is characterized by complex topographic structure and dramatic palaeoclimatic changes, making species biogeography studies particularly interesting. Previous researchers have also demonstrated multiple species experienced complex population histories, meanwhile multiple shelters existed in Chinese mainland. Despite this, species phylogeography is still largely unexplored. In the present study, we used a combination of microsatellites and mitochondrial DNA (mtDNA) to investigate the phylogeography of the east Asian fish-eating bat (Myotis pilosus). RESULTS: Phylogenetic analyses showed that M. pilosus comprised three main lineages: A, B and C, which corresponded to distinct geographic populations of the Yangtze Plain (YTP), Sichuan Basin (SCB) and North and South of China (NSC), respectively. The most recent common ancestor of M. pilosus was dated as 0.25 million years before present (BP). Population expansion events were inferred for populations of Clade C, North China Plain region, Clade B and YunGui Plateau region at 38,700, 15,900, 4,520 and 4,520 years BP, respectively. Conflicting results were obtained from mtDNA and microsatellite analyses; strong population genetic structure was obtained from mtDNA data but not microsatellite data. The microsatellite data indicated that genetic subdivision fits an isolation-by-distance (IBD) model, but the mtDNA data failed to support this model. CONCLUSIONS: Our results suggested that Pleistocene climatic oscillations might have had a profound influence on the demographic history of M. pilosus. Spatial genetic structures of maternal lineages that are different from those observed in other sympatric bats species may be as a result of interactions among special population history and local environmental factors. There are at least three possible refugia for M. pilosus during glacial episodes. Apparently contradictory genetic structure patterns of mtDNA and microsatellite could be explained by male-mediated gene flow among populations. This study also provides insights on the necessity of conservation of M. pilosus populations to conserve this genetic biodiversity, especially in the areas of YTP, SCB and NSC regions.

An intergenerational androgenic mechanism of female intrasexual competition in the cooperatively breeding meerkat.

Female intrasexual competition can be intense in cooperatively breeding species, with some dominant breeders (matriarchs) limiting reproduction in subordinates via aggression, eviction or infanticide. In males, such tendencies bidirectionally link to testosterone, but in females, there has been little systematic investigation of androgen-mediated behaviour within and across generations. In 22 clans of wild meerkats (Suricata suricatta), we show that matriarchs 1) express peak androgen concentrations during late gestation, 2) when displaying peak feeding competition, dominance behaviour, and evictions, and 3) relative to subordinates, produce offspring that are more aggressive in early development. Late-gestation antiandrogen treatment of matriarchs 4) specifically reduces dominance behaviour, is associated with infrequent evictions, decreases social centrality within the clan, 5) increases aggression in cohabiting subordinate dams, and 6) reduces offspring aggression. These effects implicate androgen-mediated aggression in the operation of female sexual selection, and intergenerational transmission of masculinised phenotypes in the evolution of meerkat cooperative breeding.

Population genomics of invasive rodents on islands: Genetic consequences of colonization and prospects for localized synthetic gene drive.

Introduced rodent populations pose significant threats worldwide, with particularly severe impacts on islands. Advancements in genome editing have motivated interest in synthetic gene drives that could potentially provide efficient and localized suppression of invasive rodent populations. Application of such technologies will require rigorous population genomic surveys to evaluate population connectivity, taxonomic identification, and to inform design of gene drive localization mechanisms. One proposed approach leverages the predicted shifts in genetic variation that accompany island colonization, wherein founder effects, genetic drift, and island-specific selection are expected to result in locally fixed alleles (LFA) that are variable in neighboring nontarget populations. Engineering of guide RNAs that target LFA may thus yield gene drives that spread within invasive island populations, but would have limited impacts on nontarget populations in the event of an escape. Here we used pooled whole-genome sequencing of invasive mouse (Mus musculus) populations on four islands along with paired putative source populations to test genetic predictions of island colonization and characterize locally fixed Cas9 genomic targets. Patterns of variation across the genome reflected marked reductions in allelic diversity in island populations and moderate to high degrees of differentiation from nearby source populations despite relatively recent colonization. Locally fixed Cas9 sites in female fertility genes were observed in all island populations, including a small number with multiplexing potential. In practice, rigorous sampling of presumptive LFA will be essential to fully assess risk of resistance alleles. These results should serve to guide development of improved, spatially limited gene drive design in future applications.

Development of an Online Experiment Platform for High School Biology.

We developed a novel online platform, Rex (Real experiments) that immerses students in a scientific investigative process. Rex is a virtual web-based biological science experiment platform, hosted by real scientists, and uses actual lab experiments that generate real data for students to collect, analyze, and interpret. Seven neuroscience experiments use zebrafish and rats as model systems to study the effects of drugs such as tetrahydrocannabinol (THC), caffeine, alcohol, and cigarette smoke, which are of interest to high school students. We carried out a small field-test of Rex in a variety of high school biology classrooms (e.g., standard, honors, AP, anatomy/physiology) to obtain student and teacher feedback about the implementation and usability of the program. We also assessed student situational interest (SI) to determine whether the Rex experiment captured students' attention, and whether it was an enjoyable and meaningful experience. Overall, students reported a moderate level of SI after participating in the Rex experiments. Situational interest did not differ across teachers, class section, class level, or the type of experiment. In addition, we present details of the technical issues encountered in the classroom, and we provide guidance to readers who may want to use the resource in their classrooms.

Locally Fixed Alleles: A method to localize gene drive to island populations.

Invasive species pose a major threat to biodiversity on islands. While successes have been achieved using traditional removal methods, such as toxicants aimed at rodents, these approaches have limitations and various off-target effects on island ecosystems. Gene drive technologies designed to eliminate a population provide an alternative approach, but the potential for drive-bearing individuals to escape from the target release area and impact populations elsewhere is a major concern. Here we propose the "Locally Fixed Alleles" approach as a novel means for localizing elimination by a drive to an island population that exhibits significant genetic isolation from neighboring populations. Our approach is based on the assumption that in small island populations of rodents, genetic drift will lead to alleles at multiple genomic loci becoming fixed. In contrast, multiple alleles are likely to be maintained in larger populations on mainlands. Utilizing the high degree of genetic specificity achievable using homing drives, for example based on the CRISPR/Cas9 system, our approach aims at employing one or more locally fixed alleles as the target for a gene drive on a particular island. Using mathematical modeling, we explore the feasibility of this approach and the degree of localization that can be achieved. We show that across a wide range of parameter values, escape of the drive to a neighboring population in which the target allele is not fixed will at most lead to modest transient suppression of the non-target population. While the main focus of this paper is on elimination of a rodent pest from an island, we also discuss the utility of the locally fixed allele approach for the goals of population suppression or population replacement. Our analysis also provides a threshold condition for the ability of a gene drive to invade a partially resistant population.

Effects of acute corticosterone treatment on male prairie voles (Microtus ochrogaster): Territorial aggression does not accompany induced social preference.

Corticosterone (CORT) is a stress-related steroid hormone found in vertebrates, and is known to interact with behavior. In the socially monogamous prairie vole (Microtus ochrogaster), acute stress and specifically acute CORT administration have been shown to facilitate male social preference for a familiar female, and this effect has been described as facilitation of the monogamous pair bond. It is possible, however, that the effects of stress on social preference may initially represent a short-term coping strategy. Here we test whether the effect of acute CORT administration extends to territoriality, a defining component of the prairie vole monogamous suite of behaviors. Onset of territoriality would provide further support for an induced pair bond, whereas no increase in aggression would suggest an initial coping response. Using acute exogenous CORT injections followed by behavioral trials, we found a facilitation of social preference, but we did not find increased aggression. This result suggests that the social preference that develops in response to CORT is at least in part a coping response rather than facilitation of comprehensive monogamous pair bond behavior. Our results are consistent with previous studies both within prairie voles and across other taxa that suggest that social contact may be involved in the regulation of stress responses. (PsycINFO Database Record