Gene drive that results in addiction to a temperature-sensitive version of an essential gene triggers population collapse in Drosophila

One strategy for population suppression seeks to use gene drive to spread genes that confer conditional lethality or sterility, providing a way of combining population modification with suppression. Stimuli of potential interest could be introduced by humans, such as an otherwise benign virus or chemical, or occur naturally on a seasonal basis, such as a change in temperature. Cleave and Rescue (ClvR) selfish genetic elements use Cas9 and guide RNAs (gRNAs) to disrupt endogenous versions of an essential gene while also including a Rescue version of the essential gene resistant to disruption. ClvR spreads by creating loss-of-function alleles of the essential gene that select against those lacking it, resulting in populations in which the Rescue provides the only source of essential gene function. As a consequence, if function of the Rescue, a kind of Trojan horse now omnipresent in a population, is condition dependent, so too will be the survival of that population. To test this idea, we created a ClvR in Drosophila in which Rescue activity of an essential gene, dribble, requires splicing of a temperature-sensitive intein (TS-ClvRdbe). This element spreads to transgene fixation at 23 °C, but when populations now dependent on Ts-ClvRdbe are shifted to 29 °C, death and sterility result in a rapid population crash. These results show that conditional population elimination can be achieved. A similar logic, in which Rescue activity is conditional, could also be used in homing-based drive and to bring about suppression and/or killing of specific individuals in response to other stimuli.

Whole genome resequencing reveals signatures of rapid selection in a virus affected commercial fishery

Infectious diseases are recognised as one of the greatest global threats to biodiversity and ecosystem functioning. Consequently, there is a growing urgency to understand the speed at which adaptive phenotypes can evolve and spread in natural populations to inform future management. Here we provide evidence of rapid genomic changes in wild Australian blacklip abalone (Haliotis rubra) following a major population crash associated with an infectious disease. A genome wide association study on H. rubra was conducted using pooled whole genome re-sequencing data from commercial fishing stocks varying in historical exposure to haliotid herpesvirus-1 (HaHV-1). Approximately 25,000 SNP loci associated with virus exposure were identified, many of which mapped to genes known to contribute to HaHV-1 immunity in the New Zealand pāua (H. iris) and herpesvirus response pathways in haliotids and other animal systems. These findings indicate genetic changes across a single generation in H. rubra fishing stocks decimated by HaHV-1, with stock recovery determined by rapid evolutionary changes leading to virus resistance. This is a novel example of rapid adaptation in natural populations of a non-model marine organism, highlighting the pace at which selection can potentially act to counter disease in wildlife communities.

Gene drive that results in addiction to a temperature sensitive version of an essential gene triggers population collapse in Drosophila

One strategy for population suppression seeks to use gene drive to spread genes that confer conditional lethality or sterility, providing a way of combining population modification with suppression. Stimuli of potential interest could be introduced by humans, such as an otherwise benign virus or chemical, or occur naturally on a seasonal basis, such as a change in temperature. Cleave and Rescue (ClvR) selfish genetic elements use Cas9 and gRNAs to disrupt endogenous versions of an essential gene, while also including a Rescue version of the essential gene resistant to disruption. ClvR spreads by creating loss-of-function alleles of the essential gene that select against those lacking it, resulting in populations in which the Rescue provides the only source of essential gene function. In consequence, if function of the Rescue, a kind of Trojan horse now omnipresent in a population, is condition-dependent, so too will be the survival of that population. To test this idea we created a ClvR in Drosophila in which Rescue activity of an essential gene, dribble, requires splicing of a temperature-sensitive intein (TS-ClvRdbe). This element spreads to transgene fixation at 23° C, but when populations now dependent on TS-ClvRdbe are shifted to 29° C death and sterility result in a rapid population crash. These results show that conditional population elimination can be achieved. A similar logic, in which Rescue activity is conditional, could also be used in HEG-based drive, and to bring about suppression and/or killing of specific individuals in response to other stimuli.

Boom-bust population dynamics increase diversity in evolving competitive communities

The processes and mechanisms underlying the origin and maintenance of biological diversity have long been of central importance in ecology and evolution. The competitive exclusion principle states that the number of coexisting species is limited by the number of resources, or by the species’ similarity in resource use. Natural systems such as the extreme diversity of unicellular life in the oceans provide counter examples. It is known that mathematical models incorporating population fluctuations can lead to violations of the exclusion principle. Here we use simple eco-evolutionary models to show that a certain type of population dynamics, boom-bust dynamics, can allow for the evolution of much larger amounts of diversity than would be expected with stable equilibrium dynamics. Boom-bust dynamics are characterized by long periods of almost exponential growth (boom) and a subsequent population crash due to competition (bust). When such ecological dynamics are incorporated into an evolutionary model that allows for adaptive diversification in continuous phenotype spaces, desynchronization of the boom-bust cycles of coexisting species can lead to the maintenance of high levels of diversity.

Panthera tigris jacksoni Population Crash and Impending Extinction due to Environmental Perturbation and Human-Wildlife Conflict

The critically endangered Malayan tiger (Panthera tigris jacksoni), with an estimated population of less than 200 individuals left in isolated rainforest habitats in Malaysia, is in an intermediate population crash leading to extinction in the next decade. The population has decreased significantly by illegal poaching, environmental perturbation, roadkill, and being captured during human–wildlife conflicts. Forty-five or more individuals were extracted from the wild (four animals captured due to conflict, one death due to canine distemper, one roadkilled, and 39 poached) in the 12 years between 2008–2019. The Malayan tigers are the first wildlife species to test positive for COVID-19 and are subject to the Canine Distemper Virus. These anthropogenic disturbances (poaching and human–tiger conflict) and environmental perturbation (decreasing habitat coverage and quality) have long been identified as impending extinction factors. Roadkill and infectious diseases have emerged recently as new confounding factors threatening Malayan tiger extinction in the near future. Peninsular Malaysia has an existing Malayan tiger conservation management plan; however, to enhance the protection and conservation of Malayan tigers from potential extinction, the authority should reassess the existing legislation, regulation, and management plan and realign them to prevent further population decline, and to better enable preparedness and readiness for the ongoing pandemic and future threats.

Nesting ecology of the Pacific cicada killer, Sphecius convallis Patton (Hymenoptera, Crabronidae), in the Sonoran Desert

Factors affecting the ecology of a large population of Pacific cicada killers (Sphecius convallis) occupying a field of mine tailings in Ruby, AZ, were examined. Burrows were quite dense in certain areas around the periphery of the mine tailings, but were dispersed randomly within these areas. Approximately 1600 females (based on burrow counts) and 2500 males (based on mark-recapture) were recorded, yielding a total population estimate of 5000–6000 adults. Female wasps were able to dig much more rapidly in the mine tailings than their congeners S. speciosus in soils from PA, suggesting that the habitat suitability was a large factor in this robust population. Provisioning rate was comparatively slow, however, suggesting that cicada abundance in that year was not a contributor to the high population density. The presence of a sap-producing tree may have eased the energetic and thermoregulatory demands of the wasps. Although excavations revealed that the number of burrows and cells could easily maintain the population size, the lack of cicadas probably resulted instead in a population crash the following season.

Mysterious disappearances of a large mammal in Neotropical forests

SummaryThe drivers of periodic population cycling by some animal species in northern systems remain unresolved1. Mysterious disappearances of populations of the Neotropical, herdforming white-lipped peccary (Tayassu pecari, henceforth “WLP”) have been anecdotally documented and explained as local events resulting from migratory movements or overhunting2,3,4, or as disease outbreaks5,6, and have not been considered in the context of large-scale species-specific population dynamics. Here we present evidence that WLP disappearances represent troughs in population cycles that occur with regular periodicity and are synchronized at regional and perhaps continent-wide spatial scales. Analysis of 43 disappearance events and 88 years of commercial and subsistence harvesting data reveals boom – bust population cycles lasting from 20 to 30 years, in which a rapid population crash occurring over 1 to 5 years is followed by a period of absence of 7 to12 years and then a slow growth phase. Overhunting alone cannot explain the crashes, but as in northern systems dispersal during the growth phase appears to play a key role. This is the first documentation of population cycling in a tropical vertebrate.

Boom-bust population dynamics can increase diversity in evolving competitive communities

The processes and mechanisms underlying the origin and maintenance of biological diversity have long been of central importance in ecology and evolution. The competitive exclusion principle states that the number of coexisting species is limited by the number of resources, or by the species’ similarity in resource use. Natural systems such as the extreme diversity of unicellular life in the oceans provide counter examples. It is known that mathematical models incorporating population fluctuations can lead to violations of the exclusion principle. Here we use simple eco-evolutionary models to show that a certain type of population dynamics, boom-bust dynamics, can allow for the evolution of much larger amounts of diversity than would be expected with stable equilibrium dynamics. Boom-bust dynamics are characterized by long periods of almost exponential growth (boom) and a subsequent population crash due to competition (bust). When such ecological dynamics are incorporated into an evolutionary model that allows for adaptive diversification in continuous phenotype spaces, desynchronization of the boom-bust cycles of coexisting species can lead to the maintenance of high levels of diversity.