Revisiting Adaptive Potential, Population Size, and Conservation

Population genetic structure in a self-compatible hermaphroditic snail is driven by drift independently of its contemporary mating system

Genetic drift, gene flow, and natural selection commonly influence population genetic diversity. In populations of self-compatible hermaphrodites, the mating system (e.g., self-fertilization) further reduces individual heterozygosity. Furthermore, selfing, as a form of inbreeding, significantly impacts genetic drift by reducing effective population size (N e). This can potentially accelerate genetic drift, particularly in small populations where self-fertilization is likely during founder events. To investigate the roles of genetic drift and contemporary mating system in populations of the freshwater snail Lymnaea stagnalis, we examined their effective population sizes (N e) and Tajima's D values, which reflect genetic drift over extended time periods, as well as estimates of within-population selfing rates and pairwise relatedness reflecting contemporary mating system. We used 4054 SNP markers obtained using restriction site associated DNA (RAD) sequencing from individuals in five snail populations originating from geographically closely located ponds. We found strong population genetic structure and differences in genetic diversity among populations. Covariation between genetic diversity and N e estimates and Tajima's D values suggested drift being an important determinant of genetic diversity and structure in these populations. However, this effect was independent of the contemporary mating system, as indicated by the similarity of selfing rates and relatedness estimates among populations. Thus, founder events (possibly including historical inbreeding) and/or drift due to small sizes of L. stagnalis populations are likely to explain their genetic structure and limit within-population genetic diversity.

Research Note: Study on the in-situ preservation of pigeons based on the level of endangerment of genetic resources

The large-scale and intensive development of the meat pigeon breeding industry have resulted in the replacement of a large number of low-performance local breeds by a few breeds with excellent production performance. However, due to the characteristics of pigeon species that are monogamous, for which the W chromosome cannot be recovered and for which semen cannot be cryopreserved, the preservation of pigeon species is still mainly based on in-situ preservation. In this study, pigeons were classified into 6 classes of endangerment based on the criteria of the 100-year inbreeding coefficient of poultry populations in the "Assessment of Endangered Poultry Genetic Resources" (NY/T 2996-2016). The results show that when the generation interval was 1.5 yr, the number of ideal populations with the same gene frequency variance or the same heterozygosity decay rate of pigeons in class 1 to 5 was ≤149, 150 to 204, 205 to 316, 317 to 649 and ≥650. In random-reserved breeding, when the generation interval was 1.5 yr, the number of male (female) pigeons corresponding to class 1 to 5 was ≤74, 75 to 102, 103 to 157, 158 to 324 and ≥325. In family-equal-reserved breeding, when the generation interval was 1.5 yr, the number of male (female) pigeons corresponding to class 1 to 5 was ≤36, 37 to 50, 51 to 78, 79 to 162 and ≥163. When the generation interval was 1.5 yr, the inbreeding increments corresponding to class 1 to 5 were ≥0.00335, 0.00244 to 0.00334, 0.00159 to 0.00243, 0.00078 to 0.00158 and ≤0.00077; with the same population size, the inbreeding coefficient and inbreeding increment decreased with the increase of generation interval; the population effective content, inbreeding coefficient and inbreeding increment of family-equal-reserved pigeons were lower than those of random-reserved pigeons. The results of this study have certain reference value for analyzing the status quo of local and endangered species, constructing live gene banks and breeding farms of poultry genetic resources, and rescuing endangered species.

Plastic and genomic change of a newly established lizard population following a founder event

Understanding how phenotypic divergence arises among natural populations remains one of the major goals in evolutionary biology. As part of competitive exclusion experiment conducted in 1971, 10 individuals of Italian wall lizard (Podarcis siculus (Rafinesque-Schmaltz, 1810)) were transplanted from Pod Kopište Island to the nearby island of Pod Mrčaru (Adriatic Sea). Merely 35 years after the introduction, the newly established population on Pod Mrčaru Island had shifted their diet from predominantly insectivorous towards omnivorous and changed significantly in a range of morphological, behavioural, physiological and ecological characteristics. Here, we combine genomic and quantitative genetic approaches to determine the relative roles of genetic adaptation and phenotypic plasticity in driving this rapid phenotypic shift. Our results show genome-wide genetic differentiation between ancestral and transplanted population, with weak genetic erosion on Pod Mrčaru Island. Adaptive processes following the founder event are indicated by highly differentiated genomic loci associating with ecologically relevant phenotypic traits, and/or having a putatively adaptive role across multiple lizard populations. Diverged traits related to head size and shape or bite force showed moderate heritability in a crossing experiment, but between-population differences in these traits did not persist in a common garden environment. Our results confirm the existence of sufficient additive genetic variance for traits to evolve under selection while also demonstrating that phenotypic plasticity and/or genotype by environment interactions are the main drivers of population differentiation at this early evolutionary stage.

The role of neutral and adaptive evolutionary processes on patterns of genetic diversity across small cave-dwelling populations of Icelandic Arctic charr (Salvelinus alpinus)

Understanding the adaptability of small populations in the face of environmental change is a central problem in evolutionary biology. Solving this problem is challenging because neutral evolutionary processes that operate on historical and contemporary timescales can override the effects of selection in small populations. We assessed the effects of isolation by colonization (IBC), isolation by dispersal limitation (IBDL) as reflected by a pattern of isolation by distance (IBD), and isolation by adaptation (IBA) and the roles of genetic drift and gene flow on patterns of genetic differentiation among 19 cave-dwelling populations of Icelandic Arctic charr (Salvelinus alpinus). We detected evidence of IBC based on the genetic affinity of nearby cave populations and the genetic relationships between the cave populations and the presumed ancestral population in the lake. A pattern of IBD was evident regardless of whether high-level genetic structuring (IBC) was taken into account. Genetic signatures of bottlenecks and lower genetic diversity in smaller populations indicate the effect of drift. Estimates of gene flow and fish movement suggest that gene flow is limited to nearby populations. In contrast, we found little evidence of IBA as patterns of local ecological and phenotypic variation showed little association with genetic differentiation among populations. Thus, patterns of genetic variation in these small populations likely reflect localized gene flow and genetic drift superimposed onto a larger-scale structure that is largely a result of colonization history. Our simultaneous assessment of the effects of neutral and adaptive processes in a tractable and replicated system has yielded novel insights into the evolution of small populations on both historical and contemporary timescales and over a smaller spatial scale than is typically studied.

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.

Limited genomic signatures of population collapse in the critically endangered black abalone (Haliotis cracherodii)

The black abalone, Haliotis cracherodii, is a large, long-lived marine mollusc that inhabits rocky intertidal habitats along the coast of California and Mexico. In 1985, populations were impacted by a bacterial disease known as withering syndrome (WS) that wiped out >90% of individuals, leading to the closure of all U.S. black abalone fisheries since 1993. Current conservation strategies include restoring diminished populations by translocating healthy individuals. However, population collapse on this scale may have dramatically lowered genetic diversity and strengthened geographic differentiation, making translocation-based recovery contentious. Additionally, the current prevalence of WS remains unknown. To address these uncertainties, we sequenced and analysed the genomes of 133 black abalone individuals from across their present range. We observed no spatial genetic structure among black abalone, with the exception of a single chromosomal inversion that increases in frequency with latitude. Outside the inversion, genetic differentiation between sites is minimal and does not scale with either geographic distance or environmental dissimilarity. Genetic diversity appears uniformly high across the range. Demographic inference does indicate a severe population bottleneck beginning just 15 generations in the past, but this decline is short lived, with present-day size far exceeding the pre-bottleneck status quo. Finally, we find the bacterial agent of WS is equally present across the sampled range, but only in 10% of individuals. The lack of population genetic structure, uniform diversity and prevalence of WS bacteria indicates that translocation could be a valid and low-risk means of population restoration for black abalone species' recovery.

Population genomics of flat-tailed horned lizards (Phrynosoma mcallii) informs conservation and management across a fragmented Colorado Desert landscape

Phrynosoma mcallii (flat-tailed horned lizards) is a species of conservation concern in the Colorado Desert of the United States and Mexico. We analysed ddRADseq data from 45 lizards to estimate population structure, infer phylogeny, identify migration barriers, map genetic diversity hotspots, and model demography. We identified the Colorado River as the main geographic feature contributing to population structure, with the populations west of this barrier further subdivided by the Salton Sea. Phylogenetic analysis confirms that northwestern populations are nested within southeastern populations. The best-fit demographic model indicates Pleistocene divergence across the Colorado River, with significant bidirectional gene flow, and a severe Holocene population bottleneck. These patterns suggest that management strategies should focus on maintaining genetic diversity on both sides of the Colorado River and the Salton Sea. We recommend additional lands in the United States and Mexico that should be considered for similar conservation goals as those in the Rangewide Management Strategy. We also recommend periodic rangewide genomic sampling to monitor ongoing attrition of diversity, hybridization, and changing structure due to habitat fragmentation, climate change, and other long-term impacts.

Topographic barriers drive the pronounced genetic subdivision of a range-limited fossorial rodent

Due to their limited dispersal ability, fossorial species with predominantly belowground activity usually show increased levels of population subdivision across relatively small spatial scales. This may be exacerbated in harsh mountain ecosystems, where landscape geomorphology limits species' dispersal ability and leads to small effective population sizes, making species relatively vulnerable to environmental change. To better understand the environmental drivers of species' population subdivision in remote mountain ecosystems, particularly in understudied high-elevation systems in Africa, we studied the giant root-rat (Tachyoryctes macrocephalus), a fossorial rodent confined to the afro-alpine ecosystem of the Bale Mountains in Ethiopia. Using mitochondrial and low-coverage nuclear genomes, we investigated 77 giant root-rat individuals sampled from nine localities across its entire ~1000 km2 range. Our data revealed a distinct division into a northern and southern group, with no signs of gene flow, and higher nuclear genetic diversity in the south. Landscape genetic analyses of the mitochondrial and nuclear genomes indicated that population subdivision was driven by slope and elevation differences of up to 500 m across escarpments separating the north and south, potentially reinforced by glaciation of the south during the Late Pleistocene (~42,000-16,000 years ago). Despite this landscape-scale subdivision between the north and south, weak geographic structuring of sampling localities within regions indicated gene flow across distances of at least 16 km at the local scale, suggesting high, aboveground mobility for relatively long distances. Our study highlights that despite the potential for local-scale gene flow in fossorial species, topographic barriers can result in pronounced genetic subdivision. These factors can reduce genetic variability, which should be considered when developing conservation strategies.

How Can Genomics Help or Hinder Wildlife Conservation?

Genomic data are becoming increasingly affordable and easy to collect, and new tools for their analysis are appearing rapidly. Conservation biologists are interested in using this information to assist in management and planning but are typically limited financially and by the lack of genomic resources available for non-model taxa. It is therefore important to be aware of the pitfalls as well as the benefits of applying genomic approaches. Here, we highlight recent methods aimed at standardizing population assessments of genetic variation, inbreeding, and forms of genetic load and methods that help identify past and ongoing patterns of genetic interchange between populations, including those subjected to recent disturbance. We emphasize challenges in applying some of these methods and the need for adequate bioinformatic support. We also consider the promises and challenges of applying genomic approaches to understand adaptive changes in natural populations to predict their future adaptive capacity.

Demographic history shapes North American gray wolf genomic diversity and informs species' conservation

Effective population size estimates are critical information needed for evolutionary predictions and conservation decisions. This is particularly true for species with social factors that restrict access to breeding or experience repeated fluctuations in population size across generations. We investigated the genomic estimates of effective population size along with diversity, subdivision, and inbreeding from 162,109 minimally filtered and 81,595 statistically neutral and unlinked SNPs genotyped in 437 grey wolf samples from North America collected between 1986 and 2021. We found genetic structure across North America, represented by three distinct demographic histories of western, central, and eastern regions of the continent. Further, grey wolves in the northern Rocky Mountains have lower genomic diversity than wolves of the western Great Lakes and have declined over time. Effective population size estimates revealed the historical signatures of continental efforts of predator extermination, despite a quarter century of recovery efforts. We are the first to provide molecular estimates of effective population size across distinct grey wolf populations in North America, which ranged between Ne  ~ 275 and 3050 since early 1980s. We provide data that inform managers regarding the status and importance of effective population size estimates for grey wolf conservation, which are on average 5.2-9.3% of census estimates for this species. We show that while grey wolves fall above minimum effective population sizes needed to avoid extinction due to inbreeding depression in the short term, they are below sizes predicted to be necessary to avoid long-term risk of extinction.

Limited genomic signatures of population collapse in the critically endangered black abalone (Haliotis cracherodii)

The black abalone, Haliotis cracherodii, is a large, long-lived marine mollusc that inhabits rocky intertidal habitats along the coast of California and Mexico. In 1985, populations were impacted by a bacterial disease known as withering syndrome (WS) that wiped out >90% of individuals, leading to the species' designation as critically endangered. Current conservation strategies include restoring diminished populations by translocating healthy individuals. However, population collapse on this scale may have dramatically lowered genetic diversity and strengthened geographic differentiation, making translocation-based recovery contentious. Additionally, the current prevalence of WS is unknown. To address these uncertainties, we sequenced and analyzed the genomes of 133 black abalone individuals from across their present range. We observed no spatial genetic structure among black abalone, with the exception of a single chromosomal inversion that increases in frequency with latitude. Genetic divergence between sites is minimal, and does not scale with either geographic distance or environmental dissimilarity. Genetic diversity appears uniformly high across the range. Despite this, however, demographic inference confirms a severe population bottleneck beginning around the time of WS onset, highlighting the temporal offset that may occur between a population collapse and its potential impact on genetic diversity. Finally, we find the bacterial agent of WS is equally present across the sampled range, but only in 10% of individuals. The lack of genetic structure, uniform diversity, and prevalence of WS bacteria indicates that translocation could be a valid and low-risk means of population restoration for black abalone species' recovery.

Genetic diversity, gene flow, and landscape resistance in a pond-breeding amphibian in agricultural and natural forested landscapes in Norway

Genetic diversity is a key part of biodiversity, threatened by human activities that lead to loss of gene flow and reduction of effective population sizes. Gene flow is a result of both landscape connectivity and demographic processes determining the number of dispersing individuals in space and time. Thus, the effect of human impact on processes determining the level of genetic diversity must be interpreted in the context of basic ecological conditions affecting survival and recruitment. When the intensity of human impact and habitat suitability correlate, the effect on genetic diversity and gene flow may be challenging to predict. We compared genetic diversity, gene flow and landscape resistance in two contrasting landscapes in Norway for the pond-breeding amphibian Triturus cristatus: a highly human-impacted, agricultural landscape with ecologically productive habitats, and a forested landscape with less productive habitats and lower levels of human impact. Our results show that genetic diversity was higher and gene flow lower within the forested landscape. Microclimatic moisture conditions and vegetation cover were important determinants of landscape resistance to gene flow within both landscapes. There were indications that landscape resistance was increased by minor roads in the forested landscape, which was not the case for the agricultural landscape, suggesting a higher vulnerability to human interference within the landscape matrix for the populations in less productive habitats. Our findings suggest that the effect of human impact on genetic diversity may not be straightforward but modulated by the ecological conditions underlying local demographic processes. Populations within both landscapes seem to be vulnerable to loss of genetic diversity, but due to different mechanisms. This has implications for the choice of relevant management actions, that is, increasing population stability may be more relevant within an agricultural landscape still permeable for dispersal, while conserving dispersal corridors may be more appropriate in the forested landscape, to avoid isolation and increased genetic drift.

Heterogeneous patterns of heterozygosity loss in isolated populations of the threatened eastern barred bandicoot (Perameles gunnii)

Identifying and analysing isolated populations is critical for conservation. Isolation can make populations vulnerable to local extinction due to increased genetic drift and inbreeding, both of which should leave imprints of decreased genome-wide heterozygosity. While decreases in heterozygosity among populations are frequently investigated, fewer studies have analysed how heterozygosity varies among individuals, including whether heterozygosity varies geographically along lines of discrete population structure or with continuous patterns analogous to isolation by distance. Here we explore geographical patterns of differentiation and individual heterozygosity in the threatened eastern barred bandicoot (Perameles gunnii) in Tasmania, Australia, using genomic data from 85 samples collected between 2008 and 2011. Our analyses identified two isolated demes undergoing significant genetic drift, and several areas of fine-scale differentiation across Tasmania. We observed discrete genetic structures across geographical barriers and continuous patterns of isolation by distance, with little evidence of recent or historical migration. Using a recently developed analytical pipeline for estimating autosomal heterozygosity, we found individual heterozygosities varied within demes by up to a factor of two, and demes with low-heterozygosity individuals also still contained those with high heterozygosity. Spatial interpolation of heterozygosity scores clarified these patterns and identified the isolated Tasman Peninsula as a location where low-heterozygosity individuals were more common than elsewhere. Our results provide novel insights into the relationship between isolation-driven genetic structure and local heterozygosity patterns. These may help improve translocation efforts, by identifying populations in need of assistance, and by providing an individualised metric for identifying source animals for translocation.

Individual-based landscape genomics for conservation: An analysis pipeline

Landscape genomics can harness environmental and genetic data to inform conservation decisions by providing essential insights into how landscapes shape biodiversity. The massive increase in genetic data afforded by the genomic era provides exceptional resolution for answering critical conservation genetics questions. The accessibility of genomic data for non-model systems has also enabled a shift away from population-based sampling to individual-based sampling, which now provides accurate and robust estimates of genetic variation that can be used to examine the spatial structure of genomic diversity, population connectivity and the nature of environmental adaptation. Nevertheless, the adoption of individual-based sampling in conservation genetics has been slowed due, in large part, to concerns over how to apply methods developed for population-based sampling to individual-based sampling schemes. Here, we discuss the benefits of individual-based sampling for conservation and describe how landscape genomic methods, paired with individual-based sampling, can answer fundamental conservation questions. We have curated key landscape genomic methods into a user-friendly, open-source workflow, which we provide as a new R package, A Landscape Genomics Analysis Toolkit in R (algatr). The algatr package includes novel added functionality for all of the included methods and extensive vignettes designed with the primary goal of making landscape genomic approaches more accessible and explicitly applicable to conservation biology.

Fish germ cell cryobanking and transplanting for conservation

The unprecedented loss of global biodiversity is linked to multiple anthropogenic stressors. New conservation technologies are urgently needed to mitigate this loss. The rights, knowledge and perspectives of Indigenous peoples in biodiversity conservation-including the development and application of new technologies-are increasingly recognised. Advances in germplasm cryopreservation and germ cell transplantation (termed 'broodstock surrogacy') techniques offer exciting tools to preserve biodiversity, but their application has been underappreciated. Here, we use teleost fishes as an exemplar group to outline (1) the power of these techniques to preserve genome-wide genetic diversity, (2) the need to apply a conservation genomic lens when selecting individuals for germplasm cryobanking and broodstock surrogacy and (3) the value of considering the cultural significance of these genomic resources. We conclude by discussing the opportunities and challenges of these techniques for conserving biodiversity in threatened teleost fish and beyond.

Earth beyond six of nine planetary boundaries

This planetary boundaries framework update finds that six of the nine boundaries are transgressed, suggesting that Earth is now well outside of the safe operating space for humanity. Ocean acidification is close to being breached, while aerosol loading regionally exceeds the boundary. Stratospheric ozone levels have slightly recovered. The transgression level has increased for all boundaries earlier identified as overstepped. As primary production drives Earth system biosphere functions, human appropriation of net primary production is proposed as a control variable for functional biosphere integrity. This boundary is also transgressed. Earth system modeling of different levels of the transgression of the climate and land system change boundaries illustrates that these anthropogenic impacts on Earth system must be considered in a systemic context.

The genomic footprint of whaling and isolation in fin whale populations

Twentieth century industrial whaling pushed several species to the brink of extinction, with fin whales being the most impacted. However, a small, resident population in the Gulf of California was not targeted by whaling. Here, we analyzed 50 whole-genomes from the Eastern North Pacific (ENP) and Gulf of California (GOC) fin whale populations to investigate their demographic history and the genomic effects of natural and human-induced bottlenecks. We show that the two populations diverged ~16,000 years ago, after which the ENP population expanded and then suffered a 99% reduction in effective size during the whaling period. In contrast, the GOC population remained small and isolated, receiving less than one migrant per generation. However, this low level of migration has been crucial for maintaining its viability. Our study exposes the severity of whaling, emphasizes the importance of migration, and demonstrates the use of genome-based analyses and simulations to inform conservation strategies.

Landscape genetics reveals contrasting patterns of connectivity in two newt species (Lissotriton montandoni and L. vulgaris)

Ecologically distinct species may respond to landscape changes in different ways. In addition to basic ecological data, the extent of the geographic range has been successfully used as an indicator of species sensitivity to anthropogenic landscapes, with widespread species usually found to be less sensitive compared to range-restricted species. In this study, we investigate connectivity patterns of two closely related but ecologically distinct newt species - the range-restricted, Lissotriton montandoni and the widespread, L. vulgaris - using genomic data, a highly replicated setting (six geographic regions per species), and tools from landscape genetics. Our results show the importance of forest for connectivity in both species, but at the same time suggest differential use of forested habitat, with L. montandoni and L. vulgaris showing the highest connectivity at forest-core and forest-edges, respectively. Anthropogenic landscapes (i.e., higher crop- or urban-cover) increased resistance in both species, but the effect was one to three orders of magnitude stronger in L. montandoni than in L. vulgaris. This result is consistent with a view of L. vulgaris as an ecological generalist. Even so, currently, the negative impact of anthropogenic landscapes is mainly seen in connectivity among L. vulgaris populations, which show significantly stronger isolation and lower effective sizes relative to L. montandoni. Overall, this study emphasizes how habitat destruction is compromising genetic connectivity not only in endemic, range-restricted species of conservation concern but also in widespread generalist species, despite their comparatively lower sensitivity to anthropogenic landscape changes.

Whole-genome survey reveals extensive variation in genetic diversity and inbreeding levels among peregrine falcon subspecies

In efforts to prevent extinction, resource managers are often tasked with increasing genetic diversity in a population of concern to prevent inbreeding depression or improve adaptive potential in a changing environment. The assumption that all small populations require measures to increase their genetic diversity may be unwarranted, and limited resources for conservation may be better utilized elsewhere. We test this assumption in a case study focused on the peregrine falcon (Falco peregrinus), a cosmopolitan circumpolar species with 19 named subspecies. We used whole-genome resequencing to generate over two million single nucleotide polymorphisms (SNPs) from multiple individuals of all peregrine falcon subspecies. Our analyses revealed extensive variation among subspecies, with many island-restricted and nonmigratory populations possessing lower overall genomic diversity, elevated inbreeding coefficients (F _ROH)-among the highest reported, and extensive runs of homozygosity (ROH) compared to mainland and migratory populations. Similarly, the majority of subspecies that are either nonmigratory or restricted to islands show a much longer history of low effective population size (N _e). While mutational load analyses indicated an increased proportion of homozygous-derived deleterious variants (i.e., drift load) among nonmigrant and island populations compared to those that are migrant or reside on the mainland, no significant differences in the proportion of heterozygous deleterious variants (i.e., inbreeding load) was observed. Our results provide evidence that high levels of inbreeding may not be an existential threat for some populations or taxa. Additional factors such as the timing and severity of population declines are important to consider in management decisions about extinction potential.

Seasonal specialization drives divergent population dynamics in two closely related butterflies

Seasons impose different selection pressures on organisms through contrasting environmental conditions. How such seasonal evolutionary conflict is resolved in organisms whose lives span across seasons remains underexplored. Through field experiments, laboratory work, and citizen science data analyses, we investigate this question using two closely related butterflies (Pieris rapae and P. napi). Superficially, the two butterflies appear highly ecologically similar. Yet, the citizen science data reveal that their fitness is partitioned differently across seasons. Pieris rapae have higher population growth during the summer season but lower overwintering success than do P. napi. We show that these differences correspond to the physiology and behavior of the butterflies. Pieris rapae outperform P. napi at high temperatures in several growth season traits, reflected in microclimate choice by ovipositing wild females. Instead, P. rapae have higher winter mortality than do P. napi. We conclude that the difference in population dynamics between the two butterflies is driven by seasonal specialization, manifested as strategies that maximize gains during growth seasons and minimize harm during adverse seasons, respectively.

Non-random mating within an Island rookery of Hawaiian hawksbill turtles: demographic discontinuity at a small coastline scale

Hawksbill sea turtles (Eretmochelys imbricata) from the Hawaiian archipelago form a small and genetically isolated population, consisting of only a few tens of individuals breeding annually. Most females nest on the island of Hawai'i, but little is known about the demographics of this rookery. This study used genetic relatedness, inferred from 135 microhaplotype markers, to determine breeding sex-ratios, estimate female nesting frequency and assess relationships between individuals nesting on different beaches. Samples were collected during the 2017 nesting season and final data included 13 nesting females and 1002 unhatched embryos, salvaged from 41 nests, of which 13 had no observed mother. Results show that most females used a single nesting beach laying 1-5 nests each. From female and offspring alleles, the paternal genotypes of 12 breeding males were reconstructed and many showed high relatedness to their mates. Pairwise relatedness of offspring revealed one instance of polygyny but otherwise suggested a 1 : 1 breeding-sex ratio. Relatedness analysis and spatial-autocorrelation of genotypes indicate that turtles from different nesting areas do not regularly interbreed, suggesting that strong natal homing tendencies in both sexes result in non-random mating across the study area. Complexes of nearby nesting beaches also showed unique patterns of inbreeding across loci, further indicating that Hawaiian hawksbill turtles have demographically discontinuous nesting populations separated by only tens of km.

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.

The blowfly Chrysomya latifrons inhabits fragmented rainforests, but shows no population structure

Climate change and deforestation are causing rainforests to become increasingly fragmented, placing them at heightened risk of biodiversity loss. Invertebrates constitute the greatest proportion of this biodiversity, yet we lack basic knowledge of their population structure and ecology. There is a compelling need to develop our understanding of the population dynamics of a wide range of rainforest invertebrates so that we can begin to understand how rainforest fragments are connected, and how they will cope with future habitat fragmentation and climate change. Blowflies are an ideal candidate for such research because they are widespread, abundant, and can be easily collected within rainforests. We genotyped 188 blowflies (Chrysomya latifrons) from 15 isolated rainforests and found high levels of gene flow, a lack of genetic structure between rainforests, and low genetic diversity - suggesting the presence of a single large genetically depauperate population. This highlights that: (1) the blowfly Ch. latifrons inhabits a ~ 1000 km stretch of Australian rainforests, where it plays an important role as a nutrient recycler; (2) strongly dispersing flies can migrate between and connect isolated rainforests, likely carrying pollen, parasites, phoronts, and pathogens along with them; and (3) widely dispersing and abundant insects can nevertheless be genetically depauperate. There is an urgent need to better understand the relationships between habitat fragmentation, genetic diversity, and adaptive potential-especially for poorly dispersing rainforest-restricted insects, as many of these may be particularly fragmented and at highest risk of local extinction.

Spatial variation in the evolutionary potential and constraints of basal metabolic rate and body mass in a wild bird

An organism's energy budget is strongly related to resource consumption, performance, and fitness. Hence, understanding the evolution of key energetic traits, such as basal metabolic rate (BMR), in natural populations is central for understanding life-history evolution and ecological processes. Here we used quantitative genetic analyses to study evolutionary potential of BMR in two insular populations of the house sparrow (Passer domesticus). We obtained measurements of BMR and body mass (M_b ) from 911 house sparrows on the islands of Leka and Vega along the coast of Norway. These two populations were the source populations for translocations to create an additional third, admixed 'common garden' population in 2012. With the use of a novel genetic group animal model concomitant with a genetically determined pedigree, we differentiate genetic and environmental sources of variation, thereby providing insight into the effects of spatial population structure on evolutionary potential. We found that the evolutionary potential of BMR was similar in the two source populations, whereas the Vega population had a somewhat higher evolutionary potential of M_b than the Leka population. BMR was genetically correlated with M_b in both populations, and the conditional evolutionary potential of BMR (independent of body mass) was 41% (Leka) and 53% (Vega) lower than unconditional estimates. Overall, our results show that there is potential for BMR to evolve independently of M_b , but that selection on BMR and/or M_b may have different evolutionary consequences in different populations of the same species.

A field theoretic approach to non-equilibrium population genetics in the strong selection regime

Natural populations are virtually never observed in equilibrium, yet equilibrium approximations comprise the majority of our understanding of population genetics. Using standard tools from statistical physics, a formalism is presented that re-expresses the stochastic equations describing allelic evolution as a partition functional over all possible allelic trajectories ('paths') governed by selection, mutation, and drift. A perturbative field theory is developed for strong additive selection, relevant to disease variation, that facilitates the straightforward computation of closed-form approximations for time-dependent moments of the allele frequency distribution across a wide range of non-equilibrium scenarios; examples are presented for constant population size, exponential growth, bottlenecks, and oscillatory size, all of which align well to simulations and break down just above the drift barrier. Equilibration times are computed and, even for static population size, generically extend beyond the order 1/s timescale associated with exponential frequency decay. Though the mutation load is largely robust to variable population size, perturbative drift-based corrections to the deterministic trajectory are readily computed. Under strong selection, the variance of a new mutation's frequency (related to homozygosity) is dominated by drift-driven dynamics and a transient increase in variance often occurs prior to equilibrating. The excess kurtosis over skew squared is roughly constant (i.e., independent of selection, provided 2Ns ≳ 5) for static population size, and thus potentially sensitive to deviation from equilibrium. These insights highlight the value of such closed-form approximations, naturally generated from Feynman diagrams in a perturbative field theory, which can simply and accurately capture the parameter dependences describing a variety of non-equilibrium population genetic phenomena of interest.

Genomic signatures of inbreeding depression for a threatened Aotearoa New Zealand passerine

For small and isolated populations, the increased chance of mating between related individuals can result in a substantial reduction in individual and population fitness. Despite the increasing availability of genomic data to measure inbreeding accurately across the genome, inbreeding depression studies for threatened species are still scarce due to the difficulty of measuring fitness in the wild. Here, we investigate inbreeding and inbreeding depression for the extensively monitored Tiritiri Mātangi island population of a threatened Aotearoa New Zealand passerine, the hihi (Notiomystis cincta). First, using a custom 45 k single nucleotide polymorphism (SNP) array, we explore genomic inbreeding patterns by inferring homozygous segments across the genome. Although all individuals have similar levels of ancient inbreeding, highly inbred individuals are affected by recent inbreeding, which can probably be explained by bottleneck effects such as habitat loss after European arrival and their translocation to the island in the 1990s. Second, we investigate genomic inbreeding effects on fitness, measured as lifetime reproductive success, and its three components, juvenile survival, adult annual survival and annual reproductive success, in 363 hihi. We find that global inbreeding significantly affects juvenile survival but none of the remaining fitness traits. Finally, we employ a genome-wide association approach to test the locus-specific effects of inbreeding on fitness, and identify 13 SNPs significantly associated with lifetime reproductive success. Our findings suggest that inbreeding depression does impact hihi, but at different genomic scales for different traits, and that purging has therefore failed to remove all variants with deleterious effects from this population of conservation concern.

Genetic variation of endangered Jankowski’s Bunting (Emberiza jankowskii): High connectivity and a moderate history of demographic decline

Introduction

Continued discovery of “mismatch” patterns between population size and genetic diversity, involving wild species such as insects, amphibians, birds, mammals, and others, has raised issues about how population history, especially recent dynamics under human disturbance, affects currently standing genetic variation. Previous studies have revealed high genetic diversity in endangered Jankowski’s Bunting. However, it is unclear how the demographic history and recent habitat changes shape the genetic variation of Jankowski’s Bunting.

Methods

To explore the formation and maintenance of high genetic diversity in endangered Jankowski’s Bunting, we used a mitochondrial control region (partial mtDNA CR) and 15 nuclear microsatellite markers to explore the recent demographic history of Jankowski’s Bunting, and we compared the historical and contemporary gene flows between populations to reveal the impact of habitat change on population connectivity. Specifically, we aimed to test the following hypotheses: (1) Jankowski’s Bunting has a large historical Ne and a moderate demographic history; and (2) recent habitat change might have no significant impact on the species’ population connectivity.

Results

The results suggested that large historical effective population size, as well as severe but slow population decline, may partially explain the high observable genetic diversity. Comparison of historical (over the past 4Ne generations) and contemporary (1–3 generations) gene flow indicated that the connectivity between five local populations was only marginally affected by landscape changes.

Discussion

Our results suggest that high population connectivity and a moderate history of demographic decline are powerful explanations for the rich genetic variation in Jankowski’s Bunting. Although there is no evidence that the genetic health of Jankowski’s Bunting is threatened, the time-lag effects on the genetic response to recent environmental changes is a reminder to be cautious about the current genetic characteristics of this species. Where possible, factors influencing genetic variation should be integrated into a systematic framework for conducting robust population health assessments. Given the small contemporary population size, inbreeding, and ecological specialization, we recommend that habitat protection be maintained to maximize the genetic diversity and population connectivity of Jankowski’s Bunting.

Conservation genomics of an endangered arboreal mammal following the 2019-2020 Australian megafire

The impacts of a changing climate threaten species, populations and ecosystems. Despite these significant and large-scale impacts on threatened species, many remain understudied and have little to no genetic information available. The greater glider, Petauroides volans, is an endangered species highly sensitive to the predicted changes in temperature under a changing climate and was recently severely impacted by a megafire natural disaster (85% estimated population loss). Baseline genetic data is essential for conservation management and for detecting detrimental changes in fire-effected populations. We collected genetic samples within 2 years post the 2019-2020 catastrophic Australian bushfires to examine adaptive potential, baseline genetic diversity and population structure, across their southern range in the state of New South Wales. Population genomic analyses were conducted using 8493 genome-wide SNPs for 86 greater glider individuals across 14 geographic locations. Substantial genetic structure was detected across locations, with low genetic diversity and effective population sizes observed in isolated areas. Additionally, we found signals of putative adaptation in response to temperature in greater gliders using a genotype-environment association analysis. These findings have important implications for the management of greater glider populations by identifying at-risk populations and identifying adaptive potential. We demonstrate the importance of baseline genetic information for endangered species as a practical approach to conservation. This is particularly important given the threat that changes in temperatures and megafire events, as predicted under a changing climate, poses for this species.

Genomic analyses reveal range-wide devastation of sea otter populations

The genetic consequences of species-wide declines are rarely quantified because the timing and extent of the decline varies across the species' range. The sea otter (Enhydra lutris) is a unique model in this regard. Their dramatic decline from thousands to fewer than 100 individuals per population occurred range-wide and nearly simultaneously due to the 18th-19th century fur trade. Consequently, each sea otter population represents an independent natural experiment of recovery after extreme population decline. We designed sequence capture probes for 50 Mb of sea otter exonic and neutral genomic regions. We sequenced 107 sea otters from five populations that span the species range to high coverage (18-76×) and three historical Californian samples from ~1500 and ~200 years ago to low coverage (1.5-3.5×). We observe distinct population structure and find that sea otters in California are the last survivors of a divergent lineage isolated for thousands of years and therefore warrant special conservation concern. We detect signals of extreme population decline in every surviving sea otter population and use this demographic history to design forward-in-time simulations of coding sequence. Our simulations indicate that this decline could lower the fitness of recovering populations for generations. However, the simulations also demonstrate how historically low effective population sizes prior to the fur trade may have mitigated the effects of population decline on genetic health. Our comprehensive approach shows how demographic inference from genomic data, coupled with simulations, allows assessment of extinction risk and different models of recovery.

Eco-evolutionary causes and consequences of rarity in plants: a meta-analysis

Species differ dramatically in their prevalence in the natural world, with many species characterized as rare due to restricted geographic distribution, low local abundance and/or habitat specialization. We investigated the ecoevolutionary causes and consequences of rarity with phylogenetically controlled metaanalyses of population genetic diversity, fitness and functional traits in rare and common congeneric plant species. Our syntheses included 252 rare species and 267 common congeners reported in 153 peer-reviewed articles published from 1978 to 2020 and one manuscript in press. Rare species have reduced population genetic diversity, depressed fitness and smaller reproductive structures than common congeners. Rare species also could suffer from inbreeding depression and reduced fertilization efficiency. By limiting their capacity to adapt and migrate, these characteristics could influence contemporary patterns of rarity and increase the susceptibility of rare species to rapid environmental change. We recommend that future studies present more nuanced data on the extent of rarity in focal species, expose rare and common species to ecologically relevant treatments, including reciprocal transplants, and conduct quantitative genetic and population genomic analyses across a greater array of systems. This research could elucidate the processes that contribute to rarity and generate robust predictions of extinction risks under global change.

Tracking population genetic signatures of local extinction with herbarium specimens

BACKGROUND AND AIMS

Habitat degradation and landscape fragmentation dramatically lower population sizes of rare plant species. Decreasing population sizes may, in turn, negatively affect genetic diversity and reproductive fitness, which can ultimately lead to local extinction of populations. Although such extinction vortex dynamics have been postulated in theory and modelling for decades, empirical evidence from local extinctions of plant populations is scarce. In particular, comparisons between current vs. historical genetic diversity and differentiation are lacking despite their potential to guide conservation management.

METHODS

We studied the population genetic signatures of the local extinction of Biscutella laevigata subsp. gracilis populations in Central Germany. We used microsatellites to genotype individuals from 15 current populations, one ex situ population, and 81 herbarium samples from five extant and 22 extinct populations. In the current populations, we recorded population size and fitness proxies, collected seeds for a germination trial and conducted a vegetation survey. The latter served as a surrogate for habitat conditions to study how habitat dissimilarity affects functional connectivity among the current populations.

KEY RESULTS

Bayesian clustering revealed similar gene pool distribution in current and historical samples but also indicated that a distinct genetic cluster was significantly associated with extinction probability. Gene flow was affected by both the spatial distance and floristic composition of population sites, highlighting the potential of floristic composition as a powerful predictor of functional connectivity which may promote decision-making for reintroduction measures. For an extinct population, we found a negative relationship between sampling year and heterozygosity. Inbreeding negatively affected germination.

CONCLUSIONS

Our study illustrates the usefulness of historical DNA to study extinction vortices in threatened species. Our novel combination of classical population genetics together with data from herbarium specimens, an ex situ population and a germination trial underlines the need for genetic rescue measures to prevent extinction of B. laevigata in Central Germany.

Coral-bleaching responses to climate change across biological scales

The global impacts of climate change are evident in every marine ecosystem. On coral reefs, mass coral bleaching and mortality have emerged as ubiquitous responses to ocean warming, yet one of the greatest challenges of this epiphenomenon is linking information across scientific disciplines and spatial and temporal scales. Here we review some of the seminal and recent coral-bleaching discoveries from an ecological, physiological, and molecular perspective. We also evaluate which data and processes can improve predictive models and provide a conceptual framework that integrates measurements across biological scales. Taking an integrative approach across biological and spatial scales, using for example hierarchical models to estimate major coral-reef processes, will not only rapidly advance coral-reef science but will also provide necessary information to guide decision-making and conservation efforts. To conserve reefs, we encourage implementing mesoscale sanctuaries (thousands of km² ) that transcend national boundaries. Such networks of protected reefs will provide reef connectivity, through larval dispersal that transverse thermal environments, and genotypic repositories that may become essential units of selection for environmentally diverse locations. Together, multinational networks may be the best chance corals have to persist through climate change, while humanity struggles to reduce emissions of greenhouse gases to net zero.

Evolving spatial conservation prioritization with intraspecific genetic data

Spatial conservation prioritization (SCP) is a planning framework used to identify new conservation areas on the basis of the spatial distribution of species, ecosystems, and their services to human societies. The ongoing accumulation of intraspecific genetic data on a variety of species offers a way to gain knowledge of intraspecific genetic diversity and to estimate several population characteristics useful in conservation, such as dispersal and population size. Here, we review how intraspecific genetic data have been integrated into SCP and highlight their potential for identifying conservation area networks that represent intraspecific genetic diversity comprehensively and that ensure the long-term persistence of biodiversity in the face of global change.

The wild ancestors of domestic animals as a neglected and threatened component of biodiversity

Domestic animals have immense economic, cultural, and practical value and have played pivotal roles in the development of human civilization. Many domesticates have, among their wild relatives, undomesticated forms representative of their ancestors. Resurgent interest in these ancestral forms has highlighted the unclear genetic status of many, and some are threatened with extinction by hybridization with domestic conspecifics. We considered the contemporary status of these ancestral forms relative to their scientific, practical, and ecological importance; the varied impacts of wild-domestic hybridization; and the challenges and potential resolutions involved in conservation efforts. Identifying and conserving ancestral forms, particularly with respect to disentangling patterns of gene flow from domesticates, is complex because of the lack of available genomic and phenotypic baselines. Comparative behavioral, ecological, and genetic studies of ancestral-type, feral, and domestic animals should be prioritized to establish the contemporary status of the former. Such baseline information will be fundamental in ensuring successful conservation efforts.

Population bottlenecks constrain host microbiome diversity and genetic variation impeding fitness

It is becoming increasingly clear that microbial symbionts influence key aspects of their host’s fitness, and vice versa. This may fundamentally change our thinking about how microbes and hosts interact in influencing fitness and adaptation to changing environments. Here we explore how reductions in population size commonly experienced by threatened species influence microbiome diversity. Consequences of such reductions are normally interpreted in terms of a loss of genetic variation, increased inbreeding and associated inbreeding depression. However, fitness effects of population bottlenecks might also be mediated through microbiome diversity, such as through loss of functionally important microbes. Here we utilise 50 Drosophila melanogaster lines with different histories of population bottlenecks to explore these questions. The lines were phenotyped for egg-to-adult viability and their genomes sequenced to estimate genetic variation. The bacterial 16S rRNA gene was amplified in these lines to investigate microbial diversity. We found that 1) host population bottlenecks constrained microbiome richness and diversity, 2) core microbiomes of hosts with low genetic variation were constituted from subsets of microbiomes found in flies with higher genetic variation, 3) both microbiome diversity and host genetic variation contributed to host population fitness, 4) connectivity and robustness of bacterial networks was low in the inbred lines regardless of host genetic variation, 5) reduced microbial diversity was associated with weaker evolutionary responses of hosts in stressful environments, and 6) these effects were unrelated to Wolbachia density. These findings suggest that population bottlenecks reduce hologenomic variation (combined host and microbial genetic variation). Thus, while the current biodiversity crisis focuses on population sizes and genetic variation of eukaryotes, an additional focal point should be the microbial diversity carried by the eukaryotes, which in turn may influence host fitness and adaptability with consequences for the persistence of populations.

It is becoming increasingly clear that organisms and the microbes that live on or in them–their microbiome–affect each other in profound ways that we are just beginning to understand. For instance, a diverse microbiome can help maintain metabolic functions or fight pathogens causing diseases. A disrupted microbiome may be especially critical for animals and plants that occur in low numbers because of threats from e.g. human exploitation or climate change, as they may already suffer from genetic challenges such as inbreeding and reduced evolutionary potential. The importance of such a reduction in population size, called a bottleneck, on the microbial diversity and the potential interactive effects on host health remains unexplored. Here we experimentally test these associations by investigating the microbiomes of 50 inbred or non-inbred populations of vinegar flies. We found that restricting the population size constrain the host’s genetic variation and simultaneously decreases the diversity of the microbiome that they harbor, and that both effects were detrimental to host fitness. The microbial communities in inbred host populations were less robust than in their non-inbred counterparts, suggesting that we should increasingly consider the microbiome diversity, which may ultimately influence the health and persistence of threatened species.

Intraspecific variability in thermal tolerance: a case study with coastal cutthroat trout

Fish physiological performance is directly regulated by their thermal environment. Intraspecific comparisons are essential to ascertain the vulnerability of fish populations to climate change and to identify which populations may be more susceptible to extirpation and which may be more resilient to continued warming. In this study, we sought to evaluate how thermal performance varies in coastal cutthroat trout (Oncorhynchus clarki clarki) across four distinct watersheds in OR, USA. Specifically, we measured oxygen consumption rates in trout from the four watersheds with variable hydrologic and thermal regimes, comparing three ecologically relevant temperature treatments (ambient, annual maximum and novel warm). Coastal cutthroat trout displayed considerable intraspecific variability in physiological performance and thermal tolerance across the four watersheds. Thermal tolerance matched the historical experience: the coastal watersheds experiencing warmer ambient temperatures had higher critical thermal tolerance compared with the interior, cooler Willamette watersheds. Physiological performance varied across all four watersheds and there was evidence of a trade-off between high aerobic performance and broad thermal tolerance. Given the evidence of climate regime shifts across the globe, the uncertainty in both the rate and extent of warming and species responses in the near and long term, a more nuanced approach to the management and conservation of native fish species must be considered.

Scale-dependent influence of the sagebrush community on genetic connectivity of the sagebrush obligate Gunnison sage-grouse

Habitat fragmentation and degradation impacts an organism's ability to navigate the landscape, ultimately resulting in decreased gene flow and increased extinction risk. Understanding how landscape composition impacts gene flow (i.e., connectivity) and interacts with scale is essential to conservation decision‐making. We used a landscape genetics approach implementing a recently developed statistical model based on the generalized Wishart probability distribution to identify the primary landscape features affecting gene flow and estimate the degree to which each component influences connectivity for Gunnison sage‐grouse (Centrocercus minimus). We were interested in two spatial scales: among distinct populations rangewide and among leks (i.e., breeding grounds) within the largest population, Gunnison Basin. Populations and leks are nested within a landscape fragmented by rough terrain and anthropogenic features, although requisite sagebrush habitat is more contiguous within populations. Our best fit models for each scale confirm the importance of sagebrush habitat in connectivity, although the important sagebrush characteristics differ. For Gunnison Basin, taller shrubs and higher quality nesting habitat were the primary drivers of connectivity, while more sagebrush cover and less conifer cover facilitated connectivity rangewide. Our findings support previous assumptions that Gunnison sage‐grouse range contraction is largely the result of habitat loss and degradation. Importantly, we report direct estimates of resistance for landscape components that can be used to create resistance surfaces for prioritization of specific locations for conservation or management (i.e., habitat preservation, restoration, or development) or as we demonstrated, can be combined with simulation techniques to predict impacts to connectivity from potential management actions.

Understanding the biology of species' ranges: when and how does evolution change the rules of ecological engagement?

Understanding processes that limit species' ranges has been a core issue in ecology and evolutionary biology for many decades, and has become increasingly important given the need to predict the responses of biological communities to rapid environmental change. However, we still have a poor understanding of evolution at range limits and its capacity to change the ecological 'rules of engagement' that define these communities, as well as the time frame over which this occurs. Here we link papers in the current volume to some key concepts involved in the interactions between evolutionary and ecological processes at species' margins. In particular, we separate hypotheses about species' margins that focus on hard evolutionary limits, which determine how genotypes interact with their environment, from those concerned with soft evolutionary limits, which determine where and when local adaptation can persist in space and time. We show how theoretical models and empirical studies highlight conditions under which gene flow can expand local limits as well as contain them. In doing so, we emphasize the complex interplay between selection, demography and population structure throughout a species' geographical and ecological range that determines its persistence in biological communities. However, despite some impressively detailed studies on range limits, particularly in invertebrates and plants, few generalizations have emerged that can predict evolutionary responses at ecological margins. We outline some directions for future work such as considering the impact of structural genetic variants and metapopulation structure on limits, and the interaction between range limits and the evolution of mating systems and non-random dispersal. This article is part of the theme issue 'Species' ranges in the face of changing environments (Part II)'.

Linking body condition and thermal physiology in limping crickets: Does limb autotomy incur costs concerning behavioral thermal tolerance?

Many ectotherms have the ability to voluntarily detach a body part, known as autotomy, usually in response to predator attacks. Autotomy can have an immediate benefit for survival, but it can also involve costs related to the individual's body condition. Even though the effects of autotomy have been studied in many ecophysiological aspects, its short-term costs on the ability to tolerate high environmental temperatures are still unexplored. Herein, we evaluated the effects of autotomy on the behavioral thermal tolerance (VT_Max ) in the cricket Gryllus assimilis. We hypothesized that, due to the increased energetic costs to maintain homeostasis, autotomized crickets have a lower VT_Max than intact ones. Additionally, we investigated differences in VT_Max between sexes, as well as the effects of heating rates and body mass on their VT_Max . Contrary to our hypothesis, we found no differences between VT_Max of autotomized and intact individuals. However, we observed that females have a higher VT_Max than males, regardless of their condition (i.e., autotomized and intact). Moreover, we detected significant effects of body mass and heating rate on behavioral thermal tolerances. The results of our study indicate that costs associated with limb autotomy at high environmental temperatures might be intricate and not immediately impactful. Furthermore, important aspects of reproduction and ecology might be responsible for differences in VT_Max between males and females. Our results contribute to understanding the ecological and physiological aspects of ectotherms and how they respond to changing climatic conditions.

Stress Resistance Traits under Different Thermal Conditions in Drosophila subobscura from Two Altitudes

Simple Summary

The global warming and rapid climate change that we are witnessing is generally influencing all of the living world, so all species must necessarily cope with these changes in order to survive. The ability to withstand environmental stress, especially during the last two decades, has been of great importance for any species’ long-term survival. For that purpose, we studied these abilities in the Drosophila subobscura species, which is known to be a good model organism for studying adaptations to environmental changes such as in temperature. We chose to investigate thermal stress responses in D. subobscura populations from two different altitudes, through four traits linked to stress tolerance: desiccation resistance, heat knock-down resistance, starvation resistance, and chill coma recovery time. Correlations between the populations’ origin and these traits were found, as well as the significant influence of the laboratory thermal conditions and sex on these traits showing that males and cold-adapted populations are expected to fare much worse in a fast-changing warming environment.

Abstract

Global warming and climate change are affecting many insect species in numerous ways. These species can develop diverse mechanisms as a response to variable environmental conditions. The rise in mean and extreme temperatures due to global warming and the importance of the population’s ability to adapt to temperature stress will further increase. In this study, we investigated thermal stress response, which is considered to be one of the crucial elements of population fitness and survival in fast-changing environments. The dynamics and variation of thermal stress resistance traits in D. subobscura flies originating from two natural populations sampled from different altitudes were analysed. Three different temperature regimes (25 °C, 19 °C, and 16 °C) were used for the F1 progeny from both localities to establish six experimental groups and investigate stress resistance traits: desiccation resistance, heat knock-down resistance, starvation resistance, and chill-coma recovery time. We detected that laboratory thermal conditions and population origin may have an effect on the analysed traits, and that sex also significantly influences stress resistance. Individuals from the lower altitude reared at higher temperatures show inferior resistance to thermal shock.

Conservation genetics as a management tool: The five best-supported paradigms to assist the management of threatened species

About 50 y ago, Crow and Kimura [An Introduction to Population Genetics Theory (1970)] and Ohta and Kimura [Genet. Res. 22, 201-204 (1973)] laid the foundations of conservation genetics by predicting the relationship between population size and genetic marker diversity. This work sparked an enormous research effort investigating the importance of population dynamics, in particular small population size, for population mean performance, population viability, and evolutionary potential. In light of a recent perspective [J. C. Teixeira, C. D. Huber, Proc. Natl. Acad. Sci. U.S.A. 118, 10 (2021)] that challenges some fundamental assumptions in conservation genetics, it is timely to summarize what the field has achieved, what robust patterns have emerged, and worthwhile future research directions. We consider theory and methodological breakthroughs that have helped management, and we outline some fundamental and applied challenges for conservation genetics.

Landscape Genomics in Tree Conservation Under a Changing Environment

Understanding the genetic basis of how species respond to changing environments is essential to the conservation of species. However, the molecular mechanisms of adaptation remain largely unknown for long-lived tree species which always have large population sizes, long generation time, and extensive gene flow. Recent advances in landscape genomics can reveal the signals of adaptive selection linking genetic variations and landscape characteristics and therefore have created novel insights into tree conservation strategies. In this review article, we first summarized the methods of landscape genomics used in tree conservation and elucidated the advantages and disadvantages of these methods. We then highlighted the newly developed method "Risk of Non-adaptedness," which can predict the genetic offset or genomic vulnerability of species via allele frequency change under multiple scenarios of climate change. Finally, we provided prospects concerning how our introduced approaches of landscape genomics can assist policymaking and improve the existing conservation strategies for tree species under the ongoing global changes.