Evolutionary rescue in a changing world

Some reef-building corals only disperse metres per generation

Understanding the dispersal potential of different species is essential for predicting recovery trajectories following local disturbances and the potential for adaptive loci to spread to populations facing extreme environmental changes. However, dispersal distances have been notoriously difficult to estimate for scleractinian corals, where sexually (as gametes or larvae) or asexually (as fragments or larvae) derived propagules disperse through vast oceans. Here, we demonstrate that generational dispersal distances for sexually produced propagules can be indirectly inferred for corals using individual-based isolation-by-distance (IbD) analyses by combining reduced-representation genomic sequencing with photogrammetric spatial mapping. Colonies from the genus Agaricia were densely sampled across plots at four locations and three depths in Curaçao. Seven cryptic taxa were found among the three nominal species (Agaricia agaricites, Agaricia humilis and Agaricia lamarcki), with four taxa showing generational dispersal distances within metres (two taxa within A. agaricites and two within A. humilis). However, no signals of IbD were found in A. lamarcki taxa and thus these taxa probably disperse relatively longer distances. The short distances estimated here imply that A. agaricites and A. humilis populations are reliant on highly localized replenishment and demonstrate the need to estimate dispersal distances quantitatively for more coral species.

Understanding evolutionary rescue and parallelism in response to environmental stress

Evolutionary rescue, the process by which populations facing environmental stress avoid extinction through genetic adaptation, is a critical area of study in evolutionary biology. The order in which mutations arise and get established will be relevant to the population's rescue. This study investigates the degree of parallel evolution at the genotypic level between independent populations facing environmental stress and subject to different demographic regimes. Under density regulation, 2 regimes exist: In the first, the population can restore positive growth rates by adjusting its population size or through adaptive mutations, whereas in the second regime, the population is doomed to extinction unless a rescue mutation occurs. Analytical approximations for the likelihood of evolutionary rescue are obtained and contrasted with simulation results. We show that the initial level of maladaptation and the demographic regime significantly affect the level of parallelism. There is an evident transition between these 2 regimes. Whereas in the first regime, parallelism decreases with the level of maladaptation, it displays the opposite behavior in the rescue/extinction regime. These findings have important implications for understanding population persistence and the degree of parallelism in evolutionary responses as they integrate demographic effects and evolutionary processes.

The role of epistasis in evolutionary rescue

The process by which adaptive evolution preserves a population threatened with extinction due to environmental changes is known as evolutionary rescue. Several factors determine the fate of those populations, including demography and genetic factors, such as standing genetic variation, gene flow, availability of de novo mutations, and so on. Despite the extensive debate about evolutionary rescue in the current literature, a study about the role of epistasis and the topography of the fitness landscape on the fate of dwindling populations is missing. In the current work, we aim to fill this gap and study the influence of epistasis on the probability of extinction of populations. We present simulation results, and analytical approximations are derived. Counterintuitively, we show that the likelihood of extinction is smaller when the degree of epistasis is higher. The reason underneath is twofold: first, higher epistasis can promote mutations of more significant phenotypic effects, but also, the incongruence between the maps genotype-phenotype and phenotype-fitness turns the fitness landscape at low epistasis more rugged, thus curbing some of its advantages.

Coping with stress: Salt type, concentration, and exposure history limit life history tradeoffs in response to road salt salinization

Substantial increases in the salinity of freshwater ecosystems has occurred around the globe from causes such as climate change, industrial operations, and the application of road deicing salts. We know very little about how plastic responses in life history traits or rapid evolution of new traits among freshwater organisms could promote stability in ecological communities affected by salinization. We performed a cohort life history analysis from birth to death with 180 individuals of a ubiquitous freshwater zooplankter to understand how life history traits are affected by exposure to two common salt types causing salinization-sodium chloride (NaCl) and calcium chloride (CaCl2)-across two environmentally relevant concentrations. We also tested if a multi-generational exposure history to high salinity altered life-history responses. We tracked and measured lifespan, time to maturation, brood size, brood interval, and body size. We found smaller brood sizes but slightly longer lifespans occurred at a low concentration of NaCl (230 mg Cl-/L). The longer lifespans led to more, albeit smaller broods, which generated a similar lifetime reproductive output compared to the no-salt control populations. At higher concentrations of NaCl and CaCl2, we found lifetime reproductive output was reduced by 23 % to 83 % relative to control populations because no tradeoff among life history traits occurred. In CaCl2, we observed shorter life spans, longer time intervals between smaller broods, and smaller body sizes leading to reduced lifetime reproductive output. We also found that a multi-generational exposure to the salt types did not convey any advantages for lifetime reproductive output. In some cases, the exposure history worsened the life history trait responses suggesting maladaptation. Our findings suggest that life history tradeoffs for freshwater species can occur in response to salinization, but these tradeoffs will largely depend on salt type and concentration, which will have implications for biodiversity and ecological stability.

Conserving Evolutionary Potential: Combining Landscape Genomics with Established Methods to Inform Plant Conservation

Biodiversity conservation requires conserving evolutionary potential-the capacity for wild populations to adapt. Understanding genetic diversity and evolutionary dynamics is critical for informing conservation decisions that enhance adaptability and persistence under environmental change. We review how emerging landscape genomic methods provide plant conservation programs with insights into evolutionary dynamics, including local adaptation and its environmental drivers. Landscape genomic approaches that explore relationships between genomic variation and environments complement rather than replace established population genomic and common garden approaches for assessing adaptive phenotypic variation, population structure, gene flow, and demography. Collectively, these approaches inform conservation actions, including genetic rescue, maladaptation prediction, and assisted gene flow. The greatest on-the-ground impacts from such studies will be realized when conservation practitioners are actively engaged in research and monitoring. Understanding the evolutionary dynamics shaping the genetic diversity of wild plant populations will inform plant conservation decisions that enhance the adaptability and persistence of species in an uncertain future.

Immigration allows population persistence and maintains genetic diversity despite an attempted experimental extinction

Widespread fragmentation and degradation of habitats make organisms increasingly vulnerable to declines in population size. Immigration is a key process potentially affecting the rescue and persistence of populations in the face of such pressures. Field research addressing severe demographic declines in the context of immigration among interconnected local populations is limited owing to difficulties in detecting such demographic events and the need for long-term monitoring of populations. In a 17-subpopulation metapopulation of the butterfly, Parnassius smintheus, all adults observed in two adjacent patches were removed over eight consecutive generations. Despite this severe and long-term reduction in survival and reproduction, the targeted populations did not go extinct. Here, we use genetic data to assess the role of immigration versus in situ reproduction in allowing the persistence of these populations. We genotyped 471 samples collected from the targeted populations throughout the removal experiment at 152 single nucleotide polymorphisms. We found no reduction in the genetic diversity of the targeted populations over time, but a decrease in the number of loci in Hardy-Weinberg equilibrium, consistent with a high level of immigration from multiple surrounding populations. Our results highlight the role of connectivity and movement in making metapopulations resilient to even severe and protracted localized population reductions.

Counter-gradient variation in gene expression between fish populations facilitates colonization of low-dissolved oxygen environments

The role of phenotypic plasticity during colonization remains unclear due to the shifting importance of plasticity across timescales. In the early stages of colonization, plasticity can facilitate persistence in a novel environment; but over evolutionary time, processes such as genetic assimilation may reduce variation in plastic traits such that species with a longer evolutionary history in an environment can show lower levels of plasticity than recent invaders. Therefore, comparing species in the early stages of colonization to long-established species provides a powerful approach for uncovering the role of phenotypic plasticity during different stages of colonization. We compared gene expression between low-dissolved oxygen (DO) and high-DO populations of two cyprinid fish: Enteromius apleurogramma, a species that has undergone a recent range expansion, and E. neumayeri, a long-established native species in the same region. We sampled tissue either immediately after capture from the field or after a 2-week acclimation under high-DO conditions, allowing us to test for both evolved and plastic differences in low-DO vs high-DO populations of each species. We found that most genes showing candidate-evolved differences in gene expression did not overlap with those showing plastic differences in gene expression. However, in the genes that did overlap, there was counter-gradient variation such that plastic and evolved gene expression responses were in opposite directions in both species. Additionally, E. apleurogramma had higher levels of plasticity and evolved divergence in gene expression between field populations. We suggest that the higher level of plasticity and counter-gradient variation may have allowed rapid genetic adaptation in E. apleurogramma and facilitated colonization. This study shows how counter-gradient variation may impact the colonization of divergent oxygen environments.

The limit to evolutionary rescue depends on ploidy in yeast exposed to nystatin

The number of copies of each chromosome, or ploidy, of an organism is a major genomic factor affecting adaptation. We set out to determine how ploidy can impact the outcome of evolution, as well as the likelihood of evolutionary rescue, using short-term experiments with yeast (Saccharomyces cerevisiae) in a high concentration of the fungicide nystatin. In similar experiments using haploid yeast, the genetic changes underlying evolutionary rescue were highly repeatable, with all rescued lines containing a single mutation in the ergosterol biosynthetic pathway. All of these beneficial mutations were recessive, which led to the expectation that diploids would find alternative genetic routes to adaptation. To test this, we repeated the experiment using both haploid and diploid strains and found that diploid populations did not evolve resistance. Although diploids are able to adapt at the same rate as haploids to a lower, not fully inhibitory, concentration of nystatin, the present study suggests that diploids are limited in their ability to adapt to an inhibitory concentration of nystatin, while haploids may undergo evolutionary rescue. These results demonstrate that ploidy can tip the balance between adaptation and extinction when organisms face an extreme environmental change.

Taking it with a grain of salt: tolerance to increasing salinization in Culex pipiens (Diptera: Culicidae) across a low-lying delta

BACKGROUND

Salinity, exacerbated by rising sea levels, is a critical environmental cue affecting freshwater ecosystems. Predicting ecosystem structure in response to such changes and their implications for the geographical distribution of arthropod disease vectors requires further insights into the plasticity and adaptability of lower trophic level species in freshwater systems. Our study investigated whether populations of the mosquito Culex pipiens, typically considered sensitive to salt, have adapted due to gradual exposure.

METHODS

Mesocosm experiments were conducted to evaluate responses in life history traits to increasing levels of salinity in three populations along a gradient perpendicular to the North Sea coast. Salt concentrations up to the brackish-marine transition zone (8 g/l chloride) were used, upon which no survival was expected. To determine how this process affects oviposition, a colonization experiment was performed by exposing the coastal population to the same concentrations.

RESULTS

While concentrations up to the currently described median lethal dose (LD50) (4 g/l) were surprisingly favored during egg laying, even the treatment with the highest salt concentration was incidentally colonized. Differences in development rates among populations were observed, but the influence of salinity was evident only at 4 g/l and higher, resulting in only a 1-day delay. Mortality rates were lower than expected, reaching only 20% for coastal and inland populations and 41% for the intermediate population at the highest salinity. Sex ratios remained unaffected across the tested range.

CONCLUSIONS

The high tolerance to salinity for all key life history parameters across populations suggests that Cx. pipiens is unlikely to shift its distribution in the foreseeable future, with potential implications for the disease risk of associated pathogens.

Population origin and heritable effects mediate road salt toxicity and thermal stress in an amphibian

Human impacts on wild populations are numerous and extensive, degrading habitats and causing population declines across taxa. Though these impacts are often studied individually, wild populations typically face suites of stressors acting concomitantly, compromising the fitness of individuals and populations in ways poorly understood and not easily predicted by the effects of any single stressor. Developing understanding of the effects of multiple stressors and their potential interactions remains a critical challenge in environmental biology. Here, we focus on assessing the impacts of two prominent stressors associated with anthropogenic activities that affect many organisms across the planet - elevated salinity (e.g., from road de-icing salt) and temperature (e.g. from climate change). We examined a suite of physiological traits and components of fitness across populations of wood frogs originating from ponds that differ in their proximity to roads and thus their legacy of exposure to pollution from road salt. When experimentally exposed to road salt, wood frogs showed reduced survival (especially those from ponds adjacent to roads), divergent developmental rates, and reduced longevity. Family-level effects mediated these outcomes, but high salinity generally eroded family-level variance. When combined, exposure to both temperature and salt resulted in very low survival, and this effect was strongest in roadside populations. Taken together, these results suggest that temperature is an important stressor capable of exacerbating impacts from a prominent contaminant confronting many freshwater organisms in salinized habitats. More broadly, it appears likely that toxicity might often be underestimated in the absence of multi-stressor approaches.

Population-specific responses to pollution exposure suggest local adaptation of invasive red swamp crayfish Procambarus clarkii along the Mediterranean French coastline

Anthropogenic stressors can have an impact in a broad range of physiological processes and can be a major selective force leading to rapid evolution and local population adaptation. In this study, three populations of the invasive crayfish Procambarus clarkii were investigated. They are geographically separated for at least 20 years, and live in different abiotic environments: a freshwater inland lake (Salagou lake) with no major anthropogenic influence and two other coastal wetlands regularly polluted by pesticides along the Mediterranean coast (Camargue region and Bages-Sigean lagoon). Collected adults were genetically characterized using the mitochondrial COI gene and haplotype frequencies were analyzed for genetic variability within and between populations. Results revealed a higher genetic diversity for these invasive populations than any previous report in France, with more than seven different haplotypes in a single population. The contrasting genetic diversity between the Camargue and the other two populations suggest different times and sources of introduction. To identify differences in key physiological responses between these populations, individuals from each population were maintained in controlled conditions. Data on oxygen consumption rates indicate that the Salagou and Bages-Sigean populations possess a high inter-individual variability compared to the Camargue population. The low individual variability of oxygen consumption and low genetic diversity suggest a specific local adaptation for the Camargue population. Population-specific responses were identified when individuals were exposed to a pesticide cocktail containing azoxystrobin and oxadiazon at sublethal concentrations. The Salagou population was the only one with altered hydro-osmotic balance due to pollutant exposure and a change in protease activity in the hepatopancreas. These results revealed different phenotypic responses suggesting local adaptations at the population level.

Designing eco-evolutionary experiments for restoration projects: Opportunities and constraints revealed during stickleback introductions

Eco-evolutionary experiments are typically conducted in semi-unnatural controlled settings, such as mesocosms; yet inferences about how evolution and ecology interact in the real world would surely benefit from experiments in natural uncontrolled settings. Opportunities for such experiments are rare but do arise in the context of restoration ecology-where different "types" of a given species can be introduced into different "replicate" locations. Designing such experiments requires wrestling with consequential questions. (Q1) Which specific "types" of a focal species should be introduced to the restoration location? (Q2) How many sources of each type should be used-and should they be mixed together? (Q3) Which specific source populations should be used? (Q4) Which type(s) or population(s) should be introduced into which restoration sites? We recently grappled with these questions when designing an eco-evolutionary experiment with threespine stickleback (Gasterosteus aculeatus) introduced into nine small lakes and ponds on the Kenai Peninsula in Alaska that required restoration. After considering the options at length, we decided to use benthic versus limnetic ecotypes (Q1) to create a mixed group of colonists from four source populations of each ecotype (Q2), where ecotypes were identified based on trophic morphology (Q3), and were then introduced into nine restoration lakes scaled by lake size (Q4). We hope that outlining the alternatives and resulting choices will make the rationales clear for future studies leveraging our experiment, while also proving useful for investigators considering similar experiments in the future.

Effects of urban-induced mutations on ecology, evolution and health

Increasing evidence suggests that urbanization is associated with higher mutation rates, which can affect the health and evolution of organisms that inhabit cities. Elevated pollution levels in urban areas can induce DNA damage, leading to de novo mutations. Studies on mutations induced by urban pollution are most prevalent in humans and microorganisms, whereas studies of non-human eukaryotes are rare, even though increased mutation rates have the potential to affect organisms and their populations in contemporary time. Our Perspective explores how higher mutation rates in urban environments could impact the fitness, ecology and evolution of populations. Most mutations will be neutral or deleterious, and higher mutation rates associated with elevated pollution in urban populations can increase the risk of cancer in humans and potentially other species. We highlight the potential for urban-driven increased deleterious mutational loads in some organisms, which could lead to a decline in population growth of a wide diversity of organisms. Although beneficial mutations are expected to be rare, we argue that higher mutation rates in urban areas could influence adaptive evolution, especially in organisms with short generation times. Finally, we explore avenues for future research to better understand the effects of urban-induced mutations on the fitness, ecology and evolution of city-dwelling organisms.

Defining fitness in evolutionary ecology

An understanding of biological fitness is central to theory and practice in ecology and evolution, yet fitness remains an elusive concept to define and challenging to measure accurately. Fitness reflects an individual's ability to pass its alleles on to subsequent generations. Researchers often quantify proxies for fitness, such as survival, growth or reproductive success. However, it can be difficult to determine lifetime fitness, especially for species with long lifespans. The abiotic and biotic environment strongly affects the expression of fitness, which means that fitness components can vary through both space and time. This spatial and temporal heterogeneity results in the impressive range of adaptations that we see in nature. Here, we review definitions of fitness and approaches to measuring fitness at the level of genes, individuals, genotypes, and populations and highlight that fitness is a key concept linking ecological and evolutionary thought.

Context-dependent antioxidant defense system (ADS)-based stress memory in response to recurrent environmental challenges in congeneric invasive species

Marine ecosystems are facing escalating environmental fluctuations owing to climate change and human activities, imposing pressures on marine species. To withstand recurring environmental challenges, marine organisms, especially benthic species lacking behavioral choices to select optimal habitats, have to utilize well-established strategies such as the antioxidant defense system (ADS) to ensure their survival. Therefore, understanding of the mechanisms governing the ADS-based response is essential for gaining insights into adaptive strategies for managing environmental challenges. Here we conducted a comparative analysis of the physiological and transcriptional responses based on the ADS during two rounds of 'hypersalinity-recovery' challenges in two model congeneric invasive ascidians, Ciona robusta and C. savignyi. Our results demonstrated that C. savignyi exhibited higher tolerance and resistance to salinity stresses at the physiological level, while C. robusta demonstrated heightened responses at the transcriptional level. We observed distinct transcriptional responses, particularly in the utilization of two superoxide dismutase (SOD) isoforms. Both Ciona species developed physiological stress memory with elevated total SOD (T-SOD) and glutathione (GSH) responses, while only C. robusta demonstrated transcriptional stress memory. The regulatory distinctions within the Nrf2-Keap1 signalling pathway likely explain the formation disparity of transcriptional stress memory between both Ciona species. These findings support the 'context-dependent stress memory hypothesis', emphasizing the emergence of species-specific stress memory at diverse regulatory levels in response to recurrent environmental challenges. Our results enhance our understanding of the mechanisms of environmental challenge management in marine species, particularly those related to the ADS.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42995-024-00228-y.

Tests of evolutionary and genetic rescue using flour beetles, Tribolium castaneum, experimentally evolved to thermal conditions

Small, isolated populations are often characterised by low levels of genetic diversity. This can result in inbreeding depression and reduced capacity to adapt to changes in the environment, and therefore higher risk of extinction. However, sometimes these populations can be rescued if allowed to increase in size or if migrants enter, bringing in new allelic variation and thus increasing genetic diversity. This study uses experimental manipulation of population size and migration to quantify their effects on fitness in a challenging environment to better understand genetic rescue. Using small, replicated populations of Tribolium castaneum experimentally evolved to different temperature regimes we tested genetic and demographic rescue, by performing large-scale manipulations of population size and migration and examining fitness consequences over multiple generations. We measured fitness in high temperature (38°C) thermal lines maintained at their usual 'small' population size of N = 100 individuals, and with 'large' scaled up duplicates containing N≈10,000 individuals. We compared these large lines with and without migration (m = 0.1) for 10 generations. Additionally, we assessed the effects of outcrossing at an individual level, by comparing fitness of hybrid (thermal line × stock) offspring with within-line crosses. We found that, at the population level, a rapid increase in the number of individuals in the population resulted in reduced fitness (represented by reproductive output and survival through heatwave conditions), regardless of migration. However, at an individual level, the hybrid offspring of migrants with native individuals generally demonstrated increased longevity in high temperature conditions compared with individuals from thermal selection lines. Overall, these populations showed no evidence that demographic manipulations led to genetic or evolutionary rescue. Following the effects of migration in individuals over several generations may be the next step in unravelling these conflicting results. We discuss these findings in the context of conservation intervention.

The fitness consequences of wildlife conservation translocations: a meta-analysis

Conservation translocation is a common strategy to offset mounting rates of population declines through the transfer of captive- or wild-origin organisms into areas where conspecific populations are imperilled or completely extirpated. Translocations that supplement existing populations are referred to as reinforcements and can be conducted using captive-origin animals [ex situ reinforcement (ESR)] or wild-origin animals without any captive ancestry [in situ reinforcement (ISR)]. These programs have been criticized for low success rates and husbandry practices that produce individuals with genetic and performance deficits, but the post-release performance of captive-origin or wild-origin translocated groups has not been systematically reviewed to quantify success relative to wild-resident control groups. To assess the disparity in post-release performance of translocated organisms relative to wild-resident conspecifics and examine the association of performance disparity with organismal and methodological factors across studies, we conducted a systematic review and meta-analysis of 821 performance comparisons from 171 studies representing nine animal classes (101 species). We found that translocated organisms have 64% decreased odds of out-performing their wild-resident counterparts, supporting claims of systemic issues hampering conservation translocations. To help identify translocation practices that could maximize program success in the future, we further quantified the impact of broad organismal and methodological factors on the disparity between translocated and wild-resident conspecific performance. Pre-release animal enrichment significantly reduced performance disparities, whereas our results suggest no overall effects of taxonomic group, sex, captive generation time, or the type of fitness surrogate measured. This work is the most comprehensive systematic review to date of animal conservation translocations in which wild conspecifics were used as comparators, thereby facilitating an evaluation of the overall impact of this conservation strategy and identifying specific actions to increase success. Our review highlights the need for conservation managers to include both sympatric and allopatric wild-reference groups to ensure the post-release performance of translocated animals can be evaluated. Further, our analyses identify pre-release animal enrichment as a particular strategy for improving the outcomes of animal conservation translocations, and demonstrate how meta-analysis can be used to identify implementation choices that maximize translocated animal contributions to recipient population growth and viability.

Prediction of potential distributions of Morina kokonorica and Morina chinensis in China

Changes in the habitats of species can provide insights into the impact of climate change on their habitats. Species in the genus Morina (Morinoideae) are perennial herbaceous plants that are mainly distributed in the South Asian Mountains and Eastern Mediterranean. In China, there are four species and two varieties of this genus distributed across the Yunnan, Sichuan, Qinghai, and Gansu provinces. This study used the optimal MaxEnt model to simulate past, current, and future potentially suitable habitats of Morina kokonorica and Morina chinensis. Seventy data of M. kokonorica occurrences and 3 of M. chinensis were used in the model to predict potentially suitable habitats. The model prediction results indicated that both M. kokonorica and M. chinensis exhibited trends of northward migration to higher latitudes and westward migration along the Himalayas to higher elevations, suggesting that the northern valleys of Hengduan Mountains and northern and eastern parts of the Himalayas were potential refugia for M. kokonorica, and the potential refugia for M. chinensis was located in the eastern part of Qinghai-Tibet Plateau. The results of this niche analysis showed that the two species had higher levels of interspecific competition and that the environmental adaptability of M. chinensis was stronger. This research could help further understand the response pattern of Morina to environmental change, to understand the adaptability of species to the environment, and promote the protection of species.

Male harm suppresses female fitness, affecting the dynamics of adaptation and evolutionary rescue

One of the most pressing questions we face as biologists is to understand how climate change will affect the evolutionary dynamics of natural populations and how these dynamics will in turn affect population recovery. Increasing evidence shows that sexual selection favors population viability and local adaptation. However, sexual selection can also foster sexual conflict and drive the evolution of male harm to females. Male harm is extraordinarily widespread and has the potential to suppress female fitness and compromise population growth, yet we currently ignore its net effects across taxa or its influence on local adaptation and evolutionary rescue. We conducted a comparative meta-analysis to quantify the impact of male harm on female fitness and found an overall negative effect of male harm on female fitness. Negative effects seem to depend on proxies of sexual selection, increasing inversely to the female relative size and in species with strong sperm competition. We then developed theoretical models to explore how male harm affects adaptation and evolutionary rescue. We show that, when sexual conflict depends on local adaptation, population decline is reduced, but at the cost of slowing down genetic adaptation. This trade-off suggests that eco-evolutionary feedback on sexual conflict can act like a double-edged sword, reducing extinction risk by buffering the demographic costs of climate change, but delaying genetic adaptation. However, variation in the mating system and male harm type can mitigate this trade-off. Our work shows that male harm has widespread negative effects on female fitness and productivity, identifies potential mechanistic factors underlying variability in such costs across taxa, and underscores how acknowledging the condition-dependence of male harm may be important to understand the demographic and evolutionary processes that impact how species adapt to environmental change.

Evolutionary rescue from climate change: male indirect genetic effects on lay-dates and their consequences for population persistence

Changes in avian breeding phenology are among the most apparent responses to climate change in free-ranging populations. A key question is whether populations will be able to keep up with the expected rates of environmental change. There is a large body of research on the mechanisms by which avian lay-dates track temperature change and the consequences of (mal)adaptation on population persistence. Often overlooked is the role of males, which can influence the lay-date of their mate through their effect on the prelaying environment. We explore how social plasticity causing male indirect genetic effects can help or hinder population persistence when female genes underpinning lay-date and male genes influencing female's timing of reproduction both respond to climate-mediated selection. We extend quantitative genetic moving optimum models to predict the consequences of social plasticity on the maximum sustainable rate of temperature change, and evaluate our model using a combination of simulated data and empirical estimates from the literature. Our results suggest that predictions for population persistence may be biased if indirect genetic effects and cross-sex genetic correlations are not considered and that the extent of this bias depends on sex differences in how environmental change affects the optimal timing of reproduction. Our model highlights that more empirical work is needed to understand sex-specific effects of environmental change on phenology and the fitness consequences for population dynamics. While we discuss our results exclusively in the context of avian breeding phenology, the approach we take here can be generalized to many different contexts and types of social interaction.

Multi-generation genetic contributions of immigrants reveal cryptic elevated and sex-biased effective gene flow within a natural meta-population

Impacts of immigration on micro-evolution and population dynamics fundamentally depend on net rates and forms of resulting gene flow into recipient populations. Yet, the degrees to which observed rates and sex ratios of physical immigration translate into multi-generational genetic legacies have not been explicitly quantified in natural meta-populations, precluding inference on how movements translate into effective gene flow and eco-evolutionary outcomes. Our analyses of three decades of complete song sparrow (Melospiza melodia) pedigree data show that multi-generational genetic contributions from regular natural immigrants substantially exceeded those from contemporary natives, consistent with heterosis-enhanced introgression. However, while contributions from female immigrants exceeded those from female natives by up to three-fold, male immigrants' lineages typically went locally extinct soon after arriving. Both the overall magnitude, and the degree of female bias, of effective gene flow therefore greatly exceeded those which would be inferred from observed physical arrivals, altering multiple eco-evolutionary implications of immigration.

Population structure, dispersion patterns and genetic diversity of two major invasive and commensal zoonotic disease hosts (Rattus norvegicus and Rattus tanezumi) from the southeastern coast of China

Background: The invasive brownrat (Rattus norvegicus) and the Oriental rats (Rattus tanezumi) are common commensal murid that are important hosts for rodent-borne diseases in southeast Asia. Understanding their population structure and genetic diversity is essential to uncover their invasion biology and distribution dynamics that are essential for controlling rodent-borne diseases. Methods: TA total of 103 R. norvegicus and 85 R. tanezumi were collected from 13 to 9 coastal areas of six provincial monitoring sentinel sites, respectivelyto assess patterns in their microsatellite loci and their mitochondrial coxl gene region. Results: Eleven sampled populations of R. norvegicus were divided into two major clusters by region. The observed heterozygosity values of all regional populations were smaller than expected genetic diversity heterozygosity values and deviated from Hardy-Weinberg equilibrium Nine sample populations of R. tanezumi were divided into three clusters; two that included sample from Hainan and Fujian provinces, and one that included samples from the other provinces and cities. The genetic diversity of R. tanezumi was highest in samples from Jiangsu and Guangdong provinces. Conclusion: The data in this paper confirm the two invasive rodent species from the southeastern coastal region of China may have relied on maritime transport to spread from the southern region of China to the Yangtze River basin. R. tanezumi may then hanve migrated unidirectionally, along the southeastern provinces of China towards the north, while R. norvegicus spread in a complex and multidirectional manner in Hainan, Fujian, Zhejiang and Jiangsu Provinces of the country.

Repeated evolution of herbicide resistance in Lolium multiflorum revealed by haplotype-resolved analysis of acetyl-CoA carboxylase

Herbicide resistance in weeds is one of the greatest challenges in modern food production. The grass species Lolium multiflorum is an excellent model species to investigate evolution under similar selection pressure because populations have repeatedly evolved resistance to many herbicides, utilizing a multitude of mechanisms to neutralize herbicide damage. In this work, we investigated the gene that encodes acetyl-CoA carboxylase (ACCase), the target site of the most successful herbicide group available for grass weed control. We sampled L. multiflorum populations from agricultural fields with history of intense herbicide use, and studied their response to three ACCase-inhibiting herbicides. To elucidate the mechanisms of herbicide resistance and the genetic relationship among populations, we resolved the haplotypes of 97 resistant and susceptible individuals by sequencing ACCase amplicons using long-read DNA sequencing technologies. Our dose-response data indicated the existence of many, often unpredictable, resistance patterns to ACCase-inhibiting herbicides, where populations exhibited as much as 37-fold reduction in herbicide response. The majority of the populations exhibited resistance to all three herbicides studied. Phylogenetic and molecular genetic analyses revealed multiple evolutionary origins of resistance-endowing ACCase haplotypes, as well as widespread admixture in the region regardless of cropping system. The amplicons generated were diverse, with haplotypes exhibiting 26-110 polymorphisms. Polymorphisms included insertions and deletions 1-31 bp in length, none of which were associated with the resistance phenotype based on an association analysis. We also found evidence that some populations have multiple mechanisms of resistance. Our results highlight the astounding genetic diversity in L. multiflorum populations, and the potential for repeated evolution of herbicide resistance across the landscape that challenges weed management approaches and jeopardizes sustainable weed control practices. We provide an in-depth discussion of the evolutionary and practical implications of our results.

How density dependence, genetic erosion and the extinction vortex impact evolutionary rescue

Following severe environmental change that reduces mean population fitness below replacement, populations must adapt to avoid eventual extinction, a process called evolutionary rescue. Models of evolutionary rescue demonstrate that initial size, genetic variation and degree of maladaptation influence population fates. However, many models feature populations that grow without negative density dependence or with constant genetic diversity despite precipitous population decline, assumptions likely to be violated in conservation settings. We examined the simultaneous influences of density-dependent growth and erosion of genetic diversity on populations adapting to novel environmental change using stochastic, individual-based simulations. Density dependence decreased the probability of rescue and increased the probability of extinction, especially in large and initially well-adapted populations that previously have been predicted to be at low risk. Increased extinction occurred shortly following environmental change, as populations under density dependence experienced more rapid decline and reached smaller sizes. Populations that experienced evolutionary rescue lost genetic diversity through drift and adaptation, particularly under density dependence. Populations that declined to extinction entered an extinction vortex, where small size increased drift, loss of genetic diversity and the fixation of maladaptive alleles, hindered adaptation and kept populations at small densities where they were vulnerable to extinction via demographic stochasticity.

Coral Reef Population Genomics in an Age of Global Change

Coral reefs are both exceptionally biodiverse and threatened by climate change and other human activities. Here, we review population genomic processes in coral reef taxa and their importance for understanding responses to global change. Many taxa on coral reefs are characterized by weak genetic drift, extensive gene flow, and strong selection from complex biotic and abiotic environments, which together present a fascinating test of microevolutionary theory. Selection, gene flow, and hybridization have played and will continue to play an important role in the adaptation or extinction of coral reef taxa in the face of rapid environmental change, but research remains exceptionally limited compared to the urgent needs. Critical areas for future investigation include understanding evolutionary potential and the mechanisms of local adaptation, developing historical baselines, and building greater research capacity in the countries where most reef diversity is concentrated.

Rapid hyperthyroidism-induced adaptation of salmonid fish in response to environmental pollution

The streams draining volcanic landscapes are often characterized by a complex series of factors that negatively affect hydrobionts and lead to declines in their populations. However, in a number of cases, a range of rapid adaptive changes ensure the resilience of hydrobiont populations. Here, we present both field and experimental data shedding light on the physiological basis of adaptation to heavy metal contamination in populations of Dolly Varden charr (Salvelinus malma) differing in duration of isolation in volcanic streams. The study reveals that isolated populations have a physiological phenotype that distinguishes them from populations inhabiting clean waters. They are characterized by a hyperthyroid status accompanied by an increased metabolic rate, elevated activity of antioxidant enzymes, decreased ionic conductivity of tissues and reduced stored energy reserves. Our experimental data reveal that hyperthyroidism is an adaptive characteristic enhancing the resistance to heavy metal contamination and shaping the evolution of these populations. The similarity of physiological, developmental and morphological changes in isolated populations suggests a common source and mechanisms underpinning this case of 'evolutionary rescue'. Thus, populations of S. malma trapped in volcanic streams represent a genuine case of rapid endocrine-driven adaptation to changing environmental stimuli.

Evolutionary rescue under demographic and environmental stochasticity

Populations suffer two types of stochasticity: demographic stochasticity, from sampling error in offspring number, and environmental stochasticity, from temporal variation in the growth rate. By modelling evolution through phenotypic selection following an abrupt environmental change, we investigate how genetic and demographic dynamics, as well as effects on population survival of the genetic variance and of the strength of stabilizing selection, differ under the two types of stochasticity. We show that population survival probability declines sharply with stronger stabilizing selection under demographic stochasticity, but declines more continuously when environmental stochasticity is strengthened. However, the genetic variance that confers the highest population survival probability differs little under demographic and environmental stochasticity. Since the influence of demographic stochasticity is stronger when population size is smaller, a slow initial decline of genetic variance, which allows quicker evolution, is important for population persistence. In contrast, the influence of environmental stochasticity is population-size-independent, so higher initial fitness becomes important for survival under strong environmental stochasticity. The two types of stochasticity interact in a more than multiplicative way in reducing the population survival probability. Our work suggests the importance of explicitly distinguishing and measuring the forms of stochasticity during evolutionary rescue.

Contrasting genomic consequences of anthropogenic reintroduction and natural recolonization in high-arctic wild reindeer

Anthropogenic reintroduction can supplement natural recolonization in reestablishing a species' distribution and abundance. However, both reintroductions and recolonizations can give rise to founder effects that reduce genetic diversity and increase inbreeding, potentially causing the accumulation of genetic load and reduced fitness. Most current populations of the endemic high-arctic Svalbard reindeer (Rangifer tarandus platyrhynchus) originate from recent reintroductions or recolonizations following regional extirpations due to past overharvesting. We investigated and compared the genomic consequences of these two paths to reestablishment using whole-genome shotgun sequencing of 100 Svalbard reindeer across their range. We found little admixture between reintroduced and natural populations. Two reintroduced populations, each founded by 12 individuals around four decades (i.e. 8 reindeer generations) ago, formed two distinct genetic clusters. Compared to the source population, these populations showed only small decreases in genome-wide heterozygosity and increases in inbreeding and lengths of runs of homozygosity. In contrast, the two naturally recolonized populations without admixture possessed much lower heterozygosity, higher inbreeding and longer runs of homozygosity, possibly caused by serial population founder effects and/or fewer or more genetically related founders than in the reintroduction events. Naturally recolonized populations can thus be more vulnerable to the accumulation of genetic load than reintroduced populations. This suggests that in some organisms even small-scale reintroduction programs based on genetically diverse source populations can be more effective than natural recolonization in establishing genetically diverse populations. These findings warrant particular attention in the conservation and management of populations and species threatened by habitat fragmentation and loss.

Population Rescue through an Increase in the Selfing Rate under Pollen Limitation: Plasticity versus Evolution

AbstractIncreased rates of self-fertilization offer reproductive assurance when plant populations experience pollen limitation, but self-fertilization may reduce fitness by exposing deleterious mutations. If an environmental change responsible for pollen limitation also induces plastic mating system shifts toward self-pollination, the reproductive assurance benefit and inbreeding depression cost of increased self-fertilization occur immediately, while the benefit and cost happen more gradually when increased self-fertilization occur through evolution. I built eco-evolutionary models to explore the demographic and genetic conditions in which higher self-fertilization by plasticity and/or evolution rescues populations, following deficits due to a sudden onset of pollen limitation. Rescue is most likely under an intermediate level of selfing rate increase, either through plasticity or evolution, and this critical level of selfing rate increase is higher under stronger pollen limitation. Generally, rescue is more likely through plasticity than through evolution. Under weak pollen limitation, rescue by enhanced self-fertilization may mainly occur through purging of deleterious mutations rather than reproductive assurance. The selfing rate increase conferring the highest rescue probability is lower when the initial population size is smaller. This article shows the importance of plasticity during plant population rescue and offers insights for future studies of the evolution of mating system plasticity.

Tropical Trees Will Need to Acclimate to Rising Temperatures-But Can They?

For tropical forests to survive anthropogenic global warming, trees will need to avoid rising temperatures through range shifts and "species migrations" or tolerate the newly emerging conditions through adaptation and/or acclimation. In this literature review, we synthesize the available knowledge to show that although many tropical tree species are shifting their distributions to higher, cooler elevations, the rates of these migrations are too slow to offset ongoing changes in temperatures, especially in lowland tropical rainforests where thermal gradients are shallow or nonexistent. We also show that the rapidity and severity of global warming make it unlikely that tropical tree species can adapt (with some possible exceptions). We argue that the best hope for tropical tree species to avoid becoming "committed to extinction" is individual-level acclimation. Although several new methods are being used to test for acclimation, we unfortunately still do not know if tropical tree species can acclimate, how acclimation abilities vary between species, or what factors may prevent or facilitate acclimation. Until all of these questions are answered, our ability to predict the fate of tropical species and tropical forests-and the many services that they provide to humanity-remains critically impaired.

Predicting the Responses of Functional Leaf Traits to Global Warming: An In Situ Temperature Manipulation Design Using Iris pumila L

Phenotypic plasticity is widely acknowledged as one of the most common solutions for coping with novel environmental conditions following climate change. However, it is less known whether the current amounts of trait plasticity, which is sufficient for matching with the contemporary climate, will be adequate when global temperatures exceed historical levels. We addressed this issue by exploring the responses of functional and structural leaf traits in Iris pumila clonal individuals to experimentally increased temperatures (~1.5 °C) using an open top chamber (OTC) design. We determined the phenotypic values of the specific leaf area, leaf dry matter content, specific leaf water content, and leaf thickness in the leaves sampled from the same clone inside and outside of the OTC deployed on it, over seasons and years within two natural populations. We analyzed the data using a repeated multivariate analysis of variance, which primarily focusses on the profiles (reaction norms (RNs)) of a variable gathered from the same individual at several different time points. We found that the mean RNs of all analyzed traits were parallel regardless of experienced temperatures, but differed in the level and the shape. The populations RNs were similar as well. As the amount of plasticity in the analyzed leaf trait was adequate for coping with elevated temperatures inside the OTCs, we predict that it will be also sufficient for responding to increased temperatures if they exceed the 1.5 °C target.

Genetic Incompatibilities and Evolutionary Rescue by Wild Relatives Shaped Grain Amaranth Domestication

Crop domestication and the subsequent expansion of crops have long been thought of as a linear process from a wild ancestor to a domesticate. However, evidence of gene flow from locally adapted wild relatives that provided adaptive alleles into crops has been identified in multiple species. Yet, little is known about the evolutionary consequences of gene flow during domestication and the interaction of gene flow and genetic load in crop populations. We study the pseudo-cereal grain amaranth that has been domesticated three times in different geographic regions of the Americas. We quantify the amount and distribution of gene flow and genetic load along the genome of the three grain amaranth species and their two wild relatives. Our results show ample gene flow between crop species and between crops and their wild relatives. Gene flow from wild relatives decreased genetic load in the three crop species. This suggests that wild relatives could provide evolutionary rescue by replacing deleterious alleles in crops. We assess experimental hybrids between the three crop species and found genetic incompatibilities between one Central American grain amaranth and the other two crop species. These incompatibilities might have created recent reproductive barriers and maintained species integrity today. Together, our results show that gene flow played an important role in the domestication and expansion of grain amaranth, despite genetic species barriers. The domestication of plants was likely not linear and created a genomic mosaic by multiple contributors with varying fitness effects for today's crops.

Population demographic history and evolutionary rescue: Influence of a bottleneck event

Rapid environmental change presents a significant challenge to the persistence of natural populations. Rapid adaptation that increases population growth, enabling populations that declined following severe environmental change to grow and avoid extinction, is called evolutionary rescue. Numerous studies have shown that evolutionary rescue can indeed prevent extinction. Here, we extend those results by considering the demographic history of populations. To evaluate how demographic history influences evolutionary rescue, we created 80 populations of red flour beetle, Tribolium castaneum, with three classes of demographic history: diverse populations that did not experience a bottleneck, and populations that experienced either an intermediate or a strong bottleneck. We subjected these populations to a new and challenging environment for six discrete generations and tracked extinction and population size. Populations that did not experience a bottleneck in their demographic history avoided extinction entirely, while more than 20% of populations that experienced an intermediate or strong bottleneck went extinct. Similarly, among the extant populations at the end of the experiment, adaptation increased the growth rate in the novel environment the most for populations that had not experienced a bottleneck in their history. Taken together, these results highlight the importance of considering the demographic history of populations to make useful and effective conservation decisions and management strategies for populations experiencing environmental change that pushes them toward extinction.

Hidden genetic variation in plasticity provides the potential for rapid adaptation to novel environments

Rapid environmental change is forcing populations into environments where plasticity will no longer maintain fitness. When populations are exposed to novel environments, evolutionary theory predicts that genetic variation in fitness will increase and should be associated with genetic differences in plasticity. If true, then genetic variation in plasticity can increase adaptive potential in novel environments, and population persistence via evolutionary rescue is more likely. To test whether genetic variation in fitness increases in novel environments and is associated with plasticity, we transplanted 8149 clones of 314 genotypes of a Sicilian daisy (Senecio chrysanthemifolius) within and outside its native range, and quantified genetic variation in fitness, and plasticity in leaf traits and gene expression. Although mean fitness declined by 87% in the novel environment, genetic variance in fitness increased threefold and was correlated with plasticity in leaf traits. High fitness genotypes showed greater plasticity in gene expression, but lower plasticity in most leaf traits. Interestingly, genotypes with the highest fitness in the novel environment had the lowest fitness at the native site. These results suggest that standing genetic variation in plasticity could help populations to persist and adapt to novel environments, despite remaining hidden in native environments.

Partial protection from fluctuating selection leads to evolution towards wider population size fluctuation and a novel mechanism of balancing selection

When a population is partially protected from fluctuating selection, as when a seed bank is present, variance in fitness will be reduced and reproductive success of the population will be promoted. This study further investigates the effect of such a 'refuge' from fluctuating selection using a mathematical model that couples demographic and evolutionary dynamics. While alleles that cause smaller fluctuations in population density should be positively selected according to classical theoretic predictions, this study finds the opposite: alleles that increase the amplitude of population size fluctuation are positively selected if population density is weakly regulated. Under strong density regulation with a constant carrying capacity, long-term maintenance of polymorphism caused by the storage effect emerges. However, if the carrying capacity of the population is oscillating, mutant alleles whose fitness fluctuates in the same direction as population size are positively selected, eventually reaching fixation or intermediate frequencies that oscillate over time. This oscillatory polymorphism, which requires fitness fluctuations that can arise with simple trade-offs in life-history traits, is a novel form of balancing selection. These results highlight the importance of allowing joint demographic and population genetic changes in models, the failure of which prevents the discovery of novel eco-evolutionary dynamics.

Slow and population specific evolutionary response to a warming environment

Adaptation to increasingly warmer environments may be critical to avoid extinction. Whether and how these adaptive responses can arise is under debate. Though several studies have tackled evolutionary responses under different thermal selective regimes, very few have specifically addressed the underlying patterns of thermal adaptation under scenarios of progressive warming conditions. Also, considering how much past history affects such evolutionary response is critical. Here, we report a long-term experimental evolution study addressing the adaptive response of Drosophila subobscura populations with distinct biogeographical history to two thermal regimes. Our results showed clear differences between the historically differentiated populations, with adaptation to the warming conditions only evident in the low latitude populations. Furthermore, this adaptation was only detected after more than 30 generations of thermal evolution. Our findings show some evolutionary potential of Drosophila populations to respond to a warming environment, but the response was slow and population specific, emphasizing limitations to the ability of ectotherms to adapt to rapid thermal shifts.

Genetic rescue from protected areas is modulated by migration, hunting rate, and timing of harvest

In terrestrial and marine ecosystems, migrants from protected areas may buffer the risk of harvest-induced evolutionary changes in exploited populations that face strong selective harvest pressures. Understanding the mechanisms favoring genetic rescue through migration could help ensure evolutionarily sustainable harvest outside protected areas and conserve genetic diversity inside those areas. We developed a stochastic individual-based metapopulation model to evaluate the potential for migration from protected areas to mitigate the evolutionary consequences of selective harvest. We parameterized the model with detailed data from individual monitoring of two populations of bighorn sheep subjected to trophy hunting. We tracked horn length through time in a large protected and a trophy-hunted populations connected through male breeding migrations. We quantified and compared declines in horn length and rescue potential under various combinations of migration rate, hunting rate in hunted areas and temporal overlap in timing of harvest and migrations, which affects the migrants' survival and chances to breed within exploited areas. Our simulations suggest that the effects of size-selective harvest on male horn length in hunted populations can be dampened or avoided if harvest pressure is low, migration rate is substantial, and migrants leaving protected areas have a low risk of being shot. Intense size-selective harvest impacts the phenotypic and genetic diversity in horn length, and population structure through changes in proportions of large-horned males, sex ratio and age structure. When hunting pressure is high and overlaps with male migrations, effects of selective removal also emerge in the protected population, so that instead of a genetic rescue of hunted populations, our model predicts undesirable effects inside protected areas. Our results stress the importance of a landscape approach to management, to promote genetic rescue from protected areas and limit ecological and evolutionary impacts of harvest on both harvested and protected populations.

Contrasting adaptive genetic consequences of stream insects under changing climate

Freshwater biodiversity undergoes degradation due to climate change. Researchers have inferred the effects of climate change on neutral genetic diversity, assuming the fixed spatial distributions of alleles. However, the adaptive genetic evolution of populations that may change the spatial distribution of allele frequencies along environmental gradients (i.e., evolutionary rescue) have largely been overlooked. We developed a modeling approach that projects the comparatively adaptive and neutral genetic diversities of four stream insects, using empirical neutral/ putative adaptive loci, ecological niche models (ENMs), and a distributed hydrological-thermal simulation at a temperate catchment under climate change. The hydrothermal model was used to generate hydraulic and thermal variables (e.g., annual current velocity and water temperature) at the present and the climatic change conditions, projected based on the eight general circulation models and the three representative concentration pathways scenarios for the two future periods (2031-2050, near future; 2081-2100, far future). The hydraulic and thermal variables were used for predictor variables of the ENMs and adaptive genetic modeling based on machine learning approaches. The increases in annual water temperature in the near- (+0.3-0.7 °C) and far-future (+0.4-3.2 °C) were projected. Of the studied species, with different ecologies and habitat ranges, Ephemera japonica (Ephemeroptera) was projected to lose rear-edge habitats (i.e., downstream) but retain the adaptive genetic diversity owing to evolutionary rescue. In contrast, the habitat range of the upstream-dwelling Hydropsyche albicephala (Trichoptera) was found to remarkably decline, resulting in decreases in the watershed genetic diversity. While the other two Trichoptera species expanded their habitat ranges, the genetic structures were homogenized over the watershed and experienced moderate decreases in gamma diversity. The findings emphasize the evolutionary rescue potential, depending on the extent of species-specific local adaptation.

Urban insect bioarks of the 21st century

Insects exhibit divergent biodiversity responses to cities. Many urban populations are not at equilibrium: biodiversity decline or recovery from environmental perturbation is often still in progress. Substantial variation in urban biodiversity patterns suggests the need to understand its mechanistic basis. In addition, current urban infrastructure decisions might profoundly influence future biodiversity trends. Although many nature-based solutions to urban climate problems also support urban insect biodiversity, trade-offs are possible and should be avoided to maximize biodiversity-climate cobenefits. Because insects are coping with the dual threats of urbanization and climate change, there is an urgent need to design cities that facilitate persistence within the city footprint or facilitate compensatory responses to global climate change as species transit through the city footprint.

Using conservation genetics to prioritise management options for an endangered songbird

Genetic data can be highly informative for answering questions relevant to practical conservation efforts, but remain one of the most neglected aspects of species recovery plans. Framing genetic questions with reference to practical and tractable conservation objectives can help bypass this limitation of the application of genetics in conservation. Using a single-nucleotide polymorphism dataset from reduced-representation sequencing (DArTSeq), we conducted a genetic assessment of remnant populations of the endangered forty-spotted pardalote (Pardalotus quadragintus), a songbird endemic to Tasmania, Australia. Our objectives were to inform strategies for the conservation of genetic diversity in the species and estimate effective population sizes and patterns of inter-population movement to identify management units relevant to population conservation and habitat restoration. We show population genetic structure and identify two small populations on mainland Tasmania as 'satellites' of larger Bruny Island populations connected by migration. Our data identify management units for conservation objectives relating to genetic diversity and habitat restoration. Although our results do not indicate the immediate need to genetically manage populations, the small effective population sizes we estimated for some populations indicate that they are vulnerable to genetic drift, highlighting the urgent need to implement habitat restoration to increase population size and to conduct genetic monitoring. We discuss how our genetic assessment can be used to inform management interventions for the forty-spotted pardalote and show that by assessing contemporary genetic aspects, valuable information for conservation planning and decision-making can be produced to guide actions that account for genetic diversity and increase chances of recovery in species of conservation concern.

Facilitated Adaptation as A Conservation Tool in the Present Climate Change Context: A Methodological Guide

Climate change poses a novel threat to biodiversity that urgently requires the development of adequate conservation strategies. Living organisms respond to environmental change by migrating to locations where their ecological niche is preserved or by adapting to the new environment. While the first response has been used to develop, discuss and implement the strategy of assisted migration, facilitated adaptation is only beginning to be considered as a potential approach. Here, we present a review of the conceptual framework for facilitated adaptation, integrating advances and methodologies from different disciplines. Briefly, facilitated adaptation involves a population reinforcement that introduces beneficial alleles to enable the evolutionary adaptation of a focal population to pressing environmental conditions. To this purpose, we propose two methodological approaches. The first one (called pre-existing adaptation approach) is based on using pre-adapted genotypes existing in the focal population, in other populations, or even in closely related species. The second approach (called de novo adaptation approach) aims to generate new pre-adapted genotypes from the diversity present in the species through artificial selection. For each approach, we present a stage-by-stage procedure, with some techniques that can be used for its implementation. The associated risks and difficulties of each approach are also discussed.

Prepping for climate change by introgressive hybridization

Species and populations may adapt to climate change by microevolutionary processes. However, standing genetic variation can be insufficient for this to occur. An interesting new study of a system of rainbowfish species shows that intraspecific hybridization enriches gene pools with adaptive variation that may allow persistence in a changing climate.

Fast drug rotation reduces bacterial resistance evolution in a microcosm experiment

Drug rotation (cycling), in which multiple drugs are administrated alternatively, has the potential for limiting resistance evolution in pathogens. The frequency of drug alternation could be a major factor to determine the effectiveness of drug rotation. Drug rotation practices often have low frequency of drug alternation, with an expectation of resistance reversion. Here we, based on evolutionary rescue and compensatory evolution theories, suggest that fast drug rotation can limit resistance evolution in the first place. This is because fast drug rotation would give little time for the evolutionarily rescued populations to recover in population size and genetic diversity, and thus decrease the chance of future evolutionary rescue under alternate environmental stresses. We experimentally tested this hypothesis using the bacterium Pseudomonas fluorescens and two antibiotics (chloramphenicol and rifampin). Increasing drug rotation frequency reduced the chance of evolutionary rescue, and most of the finally surviving bacterial populations were resistant to both drugs. Drug resistance incurred significant fitness costs, which did not differ among the drug treatment histories. A link between population sizes during the early stages of drug treatment and the end-point fates of populations (extinction vs survival) suggested that population size recovery and compensatory evolution before drug shift increase the chance of population survival. Our results therefore advocate fast drug rotation as a promising approach to reduce bacterial resistance evolution, which in particular could be a substitute for drug combination when the latter has safety risks.

Evolutionary rescue and geographic range shifts under climate change for global amphibians

By the end of this century, human-induced climate change and habitat loss may drastically reduce biodiversity, with expected effects on many amphibian lineages. One of these effects is the shift in the geographic distributions of species when tracking suitable climates. Here, we employ a macroecological approach to dynamically model geographic range shifts by coupling ecological niche models and eco-evolutionary mechanisms, aiming to assess the probability of evolutionary rescue (i.e., rapid adaptation) and dispersal under climate change. Evolutionary models estimated the probability of population persistence by adapting to changes in the temperature influenced by precipitation in the following decades, while compensating the fitness reduction and maintaining viable populations in the new climates. In addition, we evaluated emerging patterns of species richness and turnover at the assemblage level. Our approach was able to identify which amphibian populations among 7,193 species at the global scale could adapt to temperature changes or disperse into suitable regions in the future. Without evolutionary adaptation and dispersal, 47.7% of the species could go extinct until the year 2,100, whereas adding both processes will slightly decrease this extinction rate to 36.5%. Although adaptation to climate is possible for populations in about 25.7% of species, evolutionary rescue is the only possibility to avoid extinction in 4.2% of them. Dispersal will allow geographic range shifts for 49.7% of species, but only 6.5% may avoid extinction by reaching climatically suitable environments. This reconfiguration of species distributions and their persistence creates new assemblage-level patterns at the local scale. Temporal beta-diversity across the globe showed relatively low levels of species turnover, mainly due to the loss of species. Despite limitations with obtaining data, our approach provides more realistic assessments of species responses to ongoing climate changes. It shows that, although dispersal and evolutionary rescue may attenuate species losses, they are not enough to avoid a significant reduction of species’ geographic ranges in the future. Actions that guarantee a higher potential of adaptation (e.g., genetic diversity through larger population sizes) and increased connectivity for species dispersion to track suitable climates become essential, increasing the resilience of biodiversity to climate change.

Forest Landscape Effects on Dispersal of Spruce Budworm Choristoneura fumiferana (Clemens, 1865) (Lepidoptera, Tortricidae) and Forest Tent Caterpillar Malacosoma disstria Hübner, 1820 (Lepidoptera, Lasiocampidae) Female Moths in Alberta, Canada

Leaf-rollers and tent caterpillars, the families Torticidae and Lasiocampidae, represent a significant component of the Lepidoptera, and are well-represented in the forest insect pest literature of North America. Two species in particular-spruce budworm (Choristoneura fumiferana (Clem.)) and forest tent caterpillar (Malacosoma disstria Hbn.)-are the most significant pests of the Pinaceae and Salicacae, respectively, in the boreal forest of Canada, each exhibiting periodic outbreaks of tremendous extent. Dispersal is thought to play a critical role in the triggering of population eruptions and in the synchronization of outbreak cycling, but formal studies of dispersal, in particular studies of long-range dispersal by egg-bearing adult females, are rare. Here, it is shown in two independent studies that adult females of both species tend to disperse away from sparse or defoliated forest, and toward intact or undefoliated forest, suggesting that long-range dispersal during an outbreak peak is adaptive to the species and an important factor in their population dynamics, and hence their evolutionary biology.

Eco-evolutionary extinction and recolonization dynamics reduce genetic load and increase time to extinction in highly inbred populations

Understanding how genetic and ecological effects can interact to shape genetic loads within and across local populations is key to understanding ongoing persistence of systems that should otherwise be susceptible to extinction through mutational meltdown. Classic theory predicts short persistence times for metapopulations comprising small local populations with low connectivity, due to accumulation of deleterious mutations. Yet, some such systems have persisted over evolutionary time, implying the existence of mechanisms that allow metapopulations to avoid mutational meltdown. We first hypothesize a mechanism by which the combination of stochasticity in the numbers and types of mutations arising locally (genetic stochasticity), resulting local extinction, and recolonization through evolving dispersal facilitates metapopulation persistence. We then test this mechanism using a spatially and genetically explicit individual-based model. We show that genetic stochasticity in highly structured metapopulations can result in local extinctions, which can favor increased dispersal, thus allowing recolonization of empty habitat patches. This causes fluctuations in metapopulation size and transient gene flow, which reduces genetic load and increases metapopulation persistence over evolutionary time. Our suggested mechanism and simulation results provide an explanation for the conundrum presented by the continued persistence of highly structured populations with inbreeding mating systems that occur in diverse taxa.