Recommendations from people who use drugs in Philadelphia, PA about structuring point-of-care drug checking.

BACKGROUND: Adulterants, such as fentanyl and xylazine, among others, are present in a high percentage of the illicit drug supply, increasing the risk for overdose and other adverse health events among people who use drugs (PWUD). Point-of-care drug checking identifies components of a drug sample and delivers results consumers. To successfully meet the diverse needs of PWUD, more information is needed about the utility of drug checking, motivations for using services contextualized in broader comments on the drug supply, hypothesized actions to be taken after receiving drug checking results, and the ideal structure of a program. METHODS: In December 2021, semi-structured interviews were conducted with 40 PWUD who were accessing harm reduction services in Philadelphia, PA. Participants were asked about opinions and preferences for a future drug checking program. Interviews were audio recorded, transcribed and coded using content analysis to identify themes. RESULTS: Participants were primarily White (52.5%) and male (60%). Heroin/fentanyl was the most frequently reported drug used (72.5%, n = 29), followed by crack cocaine (60.0%, n = 24) and powder cocaine (47.5%, n = 19). Emerging themes from potential drug checking consumers included universal interest in using a drug checking program, intentions to change drug use actions based on drug checking results, deep concern about the unpredictability of the drug supply, engaging in multiple harm reduction practices, and concerns about privacy while accessing a service. CONCLUSIONS: We offer recommendations for sites considering point-of-care drug checking regarding staffing, safety, logistics, and cultural competency. Programs should leverage pre-existing relationships with organizations serving PWUD and hire people with lived experiences of drug use. They should work with local or state government to issue protections to people accessing drug checking programs and ensure the service is anonymous and that data collection is minimized to keep the program low-threshold. Programs will ideally operate in multiple locations and span "atmosphere" (e.g., from clinical to a drop-in culture), offer in-depth education to participants about results, engage with a community advisory board, and not partner with law enforcement.

A remote monitoring-enabled home exercise prescription for patients with interstitial lung disease at risk for exercise-induced desaturation.

RATIONALE: Alternatives to center-based pulmonary rehabilitation are needed to improve patient access to this important therapy. A critical challenge to overcome is how to maximize safety of unsupervised exercise for at-risk patients. We investigated if a novel remote monitoring-enabled mobile health (mHealth) program is safe, feasible, and effective for patients who experience exercise-induced hemoglobin desaturation. METHODS: An interstitial lung disease (ILD) commonly associated with pronounced exercise desaturation was investigated - the rare, female-predominant ILD lymphangioleiomyomatosis (LAM). Over a 12-week program, hemoglobin saturation (SpO2) was continuously recorded during all home exercise sessions. Intervention effects were assessed with 6-min walk test (6MWT), maximal cardiopulmonary exercise test (CPET), lower extremity computerized dynamometry, pulmonary function tests, and health-related quality of life (QoL) surveys. Safety was assessed by blood biomarkers of systemic inflammation and cardiac wall stress, and incidence of adverse events. RESULTS: Fifteen LAM patients enrolled and 14 completed the intervention, with high adherence to aerobic (87 ± 15%) and strength (87 ± 12%) training components. An innovative characterization of exercise training SpO2 revealed that while mild-to-moderate desaturation was common during home workouts, participants were able to self-adjust exercise intensity and supplemental oxygen levels to maintain recommended exercise parameters. Significant improvements included 6MWT distance (+36 ± 34 m, p = 0.003), CPET time (p = 0.04), muscular endurance (p = 0.008), QoL (p = 0.009 to 0.03), and fatigue (p = 0.001 to 0.03). Patient acceptability and satisfaction indicators were high, blood biomarkers remained stable (p > 0.05), and no study-related adverse events occurred. CONCLUSION: A remote monitoring-enabled home exercise program is a safe, feasible, and effective approach even for patients who experience exercise desaturation.

Population-specific responses in eastern oysters exposed to low salinity in the northern Gulf of Mexico.

Eastern oysters, Crassostrea virginica, are facing rapid environmental changes in the northern Gulf of Mexico and can respond to these changes via plasticity or evolution. Plastic responses can immediately buffer against environmental changes, although this buffering may impact the organism's ability to evolve in subsequent generations. While plasticity and evolution are not mutually exclusive, the relative contribution and interaction between them remains unclear. In this study, we investigated the roles of plastic and evolved responses of C. virginica acclimated to low salinity using a common garden experiment with four populations exposed to two salinities. We used three transcriptomic analyses (edgeR, PERMANOVA and WGCNA) combined with physiology data to identify the effect of genotype (population), environment (salinity) and the genotype-environment interaction on both whole-organism and molecular phenotypes. We demonstrate that variation in gene expression is mainly driven by population, with relatively small changes in response to salinity. In contrast, the morphology and physiology data reveal that salinity has a larger influence on oyster performance than the population of origin. All analyses lacked signatures of the genotype×environment interaction and, in contrast to previous studies, we found no evidence for population-specific responses to low salinity. However, individuals from the highest salinity estuary displayed highly divergent gene expression from that of other populations, which could potentially drive population-specific responses to other stressors. Our findings suggest that C. virginica largely rely on plasticity in physiology to buffer the effects of low salinity, but that these changes in physiology do not rely on large persistent changes in gene expression.

Ethnic and racial differences in self-reported symptoms, health status, activity level, and missed work at 3 and 6 months following SARS-CoV-2 infection.

Introduction: Data on ethnic and racial differences in symptoms and health-related impacts following SARS-CoV-2 infection are limited. We aimed to estimate the ethnic and racial differences in symptoms and health-related impacts 3 and 6 months after the first SARS-CoV-2 infection. Methods: Participants included adults with SARS-CoV-2 infection enrolled in a prospective multicenter US study between 12/11/2020 and 7/4/2022 as the primary cohort of interest, as well as a SARS-CoV-2-negative cohort to account for non-SARS-CoV-2-infection impacts, who completed enrollment and 3-month surveys (N = 3,161; 2,402 SARS-CoV-2-positive, 759 SARS-CoV-2-negative). Marginal odds ratios were estimated using GEE logistic regression for individual symptoms, health status, activity level, and missed work 3 and 6 months after COVID-19 illness, comparing each ethnicity or race to the referent group (non-Hispanic or white), adjusting for demographic factors, social determinants of health, substance use, pre-existing health conditions, SARS-CoV-2 infection status, COVID-19 vaccination status, and survey time point, with interactions between ethnicity or race and time point, ethnicity or race and SARS-CoV-2 infection status, and SARS-CoV-2 infection status and time point. Results: Following SARS-CoV-2 infection, the majority of symptoms were similar over time between ethnic and racial groups. At 3 months, Hispanic participants were more likely than non-Hispanic participants to report fair/poor health (OR: 1.94; 95%CI: 1.36-2.78) and reduced activity (somewhat less, OR: 1.47; 95%CI: 1.06-2.02; much less, OR: 2.23; 95%CI: 1.38-3.61). At 6 months, differences by ethnicity were not present. At 3 months, Other/Multiple race participants were more likely than white participants to report fair/poor health (OR: 1.90; 95% CI: 1.25-2.88), reduced activity (somewhat less, OR: 1.72; 95%CI: 1.21-2.46; much less, OR: 2.08; 95%CI: 1.18-3.65). At 6 months, Asian participants were more likely than white participants to report fair/poor health (OR: 1.88; 95%CI: 1.13-3.12); Black participants reported more missed work (OR, 2.83; 95%CI: 1.60-5.00); and Other/Multiple race participants reported more fair/poor health (OR: 1.83; 95%CI: 1.10-3.05), reduced activity (somewhat less, OR: 1.60; 95%CI: 1.02-2.51; much less, OR: 2.49; 95%CI: 1.40-4.44), and more missed work (OR: 2.25; 95%CI: 1.27-3.98). Discussion: Awareness of ethnic and racial differences in outcomes following SARS-CoV-2 infection may inform clinical and public health efforts to advance health equity in long-term outcomes.

Constitutive gene expression differs in three brain regions important for cognition in neophobic and non-neophobic house sparrows (Passer domesticus).

Neophobia (aversion to new objects, food, and environments) is a personality trait that affects the ability of wildlife to adapt to new challenges and opportunities. Despite the ubiquity and importance of this trait, the molecular mechanisms underlying repeatable individual differences in neophobia in wild animals are poorly understood. We evaluated wild-caught house sparrows (Passer domesticus) for neophobia in the lab using novel object tests. We then selected a subset of neophobic and non-neophobic individuals (n = 3 of each, all females) and extracted RNA from four brain regions involved in learning, memory, threat perception, and executive function: striatum, caudal dorsomedial hippocampus, medial ventral arcopallium, and caudolateral nidopallium (NCL). Our analysis of differentially expressed genes (DEGs) used 11,889 gene regions annotated in the house sparrow reference genome for which we had an average of 25.7 million mapped reads/sample. PERMANOVA identified significant effects of brain region, phenotype (neophobic vs. non-neophobic), and a brain region by phenotype interaction. Comparing neophobic and non-neophobic birds revealed constitutive differences in DEGs in three of the four brain regions examined: hippocampus (12% of the transcriptome significantly differentially expressed), striatum (4%) and NCL (3%). DEGs included important known neuroendocrine mediators of learning, memory, executive function, and anxiety behavior, including serotonin receptor 5A, dopamine receptors 1, 2 and 5 (downregulated in neophobic birds), and estrogen receptor beta (upregulated in neophobic birds). These results suggest that some of the behavioral differences between phenotypes may be due to underlying gene expression differences in the brain. The large number of DEGs in neophobic and non-neophobic birds also implies that there are major differences in neural function between the two phenotypes that could affect a wide variety of behavioral traits beyond neophobia.

Comparative transcriptomics reveals altered species interaction between the bioeroding sponge Cliona varians and the coral Porites furcata under ocean acidification.

Bioeroding sponges interact and compete with corals on tropical reefs. Experimental studies have shown global change alters this biotic interaction, often in favour of the sponge. Ocean acidification in particular increases sponge bioerosion and reduces coral calcification, yet little is known about the molecular basis of these changes. We used RNA-Seq data to understand how acidification impacts the interaction between the bioeroding sponge, Cliona varians, and the coral, Porites furcata, at the transcriptomic level. Replicate sponge and coral genets were exposed to ambient (8.1 pH) and acidified (7.6 pH) conditions in isolation and in treatments where they were joined for 48 h. The coral had a small gene expression response (tens of transcripts) to the sponge, suggesting it does little at the transcriptomic level to deter sponge overgrowth. By contrast, the sponge differentially expressed 7320 transcripts in response to the coral under ambient conditions and 3707 transcripts in response to acidification. Overlap in the responses to acidification and the coral, 2500 transcripts expressed under both treatments, suggests a similar physiological response to both cues. The sponge expressed 50× fewer transcripts in response to the coral under acidification, suggesting energetic costs of bioerosion, and other cellular processes, are lower for sponges under acidification. Our results suggest how acidification drives ecosystem-level changes in the accretion/bioerosion balance on coral reefs. This shift is not only the result of changes to the thermodynamic balance of these chemical reactions but also the result of active physiological responses of organisms to each other and their abiotic environment.

Differential DNA methylation across environments has no effect on gene expression in the eastern oyster.

It has been hypothesized that environmentally induced changes to gene body methylation could facilitate adaptive transgenerational responses to changing environments. We compared patterns of global gene expression (Tag-seq) and gene body methylation (reduced representation bisulfite sequencing) in 80 eastern oysters Crassostrea virginica from six full-sib families, common gardened for 14 months at two sites in the northern Gulf of Mexico that differed in mean salinity. At the time of sampling, oysters from the two sites differed in mass by 60% and in parasite loads by nearly two orders of magnitude. They also differentially expressed 35% of measured transcripts. However, we observed differential methylation at only 1.4% of potentially methylated loci in comparisons between individuals from these different environments, and little correspondence between differential methylation and differential gene expression. Instead, methylation patterns were largely driven by genetic differences among families, with a PERMANOVA analysis indicating nearly a two orders of magnitude greater number of genes differentially methylated between families than between environments. An analysis of CpG observed/expected values (CpG O/E) across the C. virginica genome showed a distinct bimodal distribution, with genes from the first cluster showing the lower CpG O/E values, greater methylation and higher and more stable gene expression, while genes from the second cluster showed lower methylation, and lower and more variable gene expression. Taken together, the differential methylation results suggest that only a small portion of the C. virginica genome is affected by environmentally induced changes in methylation. At this point, there is little evidence to suggest that environmentally induced methylation states would play a leading role in regulating gene expression responses to new environments.

Tolerance of northern Gulf of Mexico eastern oysters to chronic warming at extreme salinities.

The eastern oyster, Crassostrea virginica, provides critical ecosystem services and supports valuable fishery and aquaculture industries in northern Gulf of Mexico (nGoM) subtropical estuaries where it is grown subtidally. Its upper critical thermal limit is not well defined, especially when combined with extreme salinities. The cumulative mortalities of the progenies of wild C. virginica from four nGoM estuaries differing in mean annual salinity, acclimated to low (4.0), moderate (20.0), and high (36.0) salinities at 28.9 °C (84 °F) and exposed to increasing target temperatures of 33.3 °C (92 °F), 35.6 °C (96 °F) or 37.8 °C (100 °F), were measured over a three-week period. Oysters of all stocks were the most sensitive to increasing temperatures at low salinity, dying quicker (i.e., lower median lethal time, LT50) than at the moderate and high salinities and resulting in high cumulative mortalities at all target temperatures. Oysters of all stocks at moderate salinity died the slowest with high cumulative mortalities only at the two highest temperatures. The F1 oysters from the more southern and hypersaline Upper Laguna Madre estuary were generally more tolerant to prolonged higher temperatures (higher LT50) than stocks originating from lower salinity estuaries, most notably at the highest salinity. Using the measured temperatures oysters were exposed to, 3-day median lethal Celsius degrees (LD50) were estimated for each stock at each salinity. The lowest 3-day LD50 (35.1-36.0 °C) for all stocks was calculated at a salinity of 4.0, while the highest 3-day LD50 (40.1-44.0 °C) was calculated at a salinity of 20.0.

Limited plasticity in thermally tolerant ectotherm populations: evidence for a trade-off.

Many species face extinction risks owing to climate change, and there is an urgent need to identify which species' populations will be most vulnerable. Plasticity in heat tolerance, which includes acclimation or hardening, occurs when prior exposure to a warmer temperature changes an organism's upper thermal limit. The capacity for thermal acclimation could provide protection against warming, but prior work has found few generalizable patterns to explain variation in this trait. Here, we report the results of, to our knowledge, the first meta-analysis to examine within-species variation in thermal plasticity, using results from 20 studies (19 species) that quantified thermal acclimation capacities across 78 populations. We used meta-regression to evaluate two leading hypotheses. The climate variability hypothesis predicts that populations from more thermally variable habitats will have greater plasticity, while the trade-off hypothesis predicts that populations with the lowest heat tolerance will have the greatest plasticity. Our analysis indicates strong support for the trade-off hypothesis because populations with greater thermal tolerance had reduced plasticity. These results advance our understanding of variation in populations' susceptibility to climate change and imply that populations with the highest thermal tolerance may have limited phenotypic plasticity to adjust to ongoing climate warming.

Divergence in salinity tolerance of northern Gulf of Mexico eastern oysters under field and laboratory exposure.

The eastern oyster, Crassostrea virginica, is a foundation species within US Gulf of Mexico (GoM) estuaries that has experienced substantial population declines. As changes from management and climate are expected to continue to impact estuarine salinity, understanding how local oyster populations might respond and identifying populations with adaptations to more extreme changes in salinity could inform resource management, including restoration and aquaculture programs. Wild oysters were collected from four estuarine sites from Texas [Packery Channel (PC): 35.5, annual mean salinity, Aransas Bay (AB): 23.0] and Louisiana [Calcasieu Lake (CL): 16.2, Vermilion Bay (VB): 7.4] and spawned. The progeny were compared in field and laboratory studies under different salinity regimes. For the field study, F1 oysters were deployed at low (6.4) and intermediate (16.5) salinity sites in Alabama. Growth and mortality were measured monthly. Condition index and Perkinsus marinus infection intensity were measured quarterly. For the laboratory studies, mortality was recorded in F1 oysters that were exposed to salinities of 2.0, 4.0, 20.0/22.0, 38.0 and 44.0 with and without acclimation. The results of the field study and laboratory study with acclimation indicated that PC oysters are adapted to high-salinity conditions and do not tolerate very low salinities. The AB stock had the highest plasticity as it performed as well as the PC stock at high salinities and as well as Louisiana stocks at the lowest salinity. Louisiana stocks did not perform as well as the Texas stocks at high salinities. Results from the laboratory studies without salinity acclimation showed that all F1 stocks experiencing rapid mortality at low salinities when 3-month oysters collected at a salinity of 24 were used and at both low and high salinities when 7-month oysters collected at a salinity of 14.5 were used.

Lack of genotype-by-environment interaction suggests limited potential for evolutionary changes in plasticity in the eastern oyster, Crassostrea virginica.

Eastern oysters in the northern Gulf of Mexico are facing rapid environmental changes and can respond to this change via plasticity or evolution. Plasticity can act as an immediate buffer against environmental change, but this buffering could impact the organism's ability to evolve in subsequent generations. While plasticity and evolution are not mutually exclusive, the relative contribution and interaction between them remains unclear. In this study, we investigate the roles of plastic and evolved responses to environmental variation and Perkinsus marinus infection in Crassostrea virginica by using a common garden experiment with 80 oysters from six families outplanted at two field sites naturally differing in salinity. We use growth data, P. marinus infection intensities, 3' RNA sequencing (TagSeq) and low-coverage whole-genome sequencing to identify the effect of genotype, environment and genotype-by-environment interaction on the oyster's response to site. As one of first studies to characterize the joint effects of genotype and environment on transcriptomic and morphological profiles in a natural setting, we demonstrate that C. virginica has a highly plastic response to environment and that this response is parallel among genotypes. We also find that genes responding to genotype have distinct and opposing profiles compared to genes responding to environment with regard to expression levels, Ka/Ks ratios and nucleotide diversity. Our findings suggest that C. virginica may be able to buffer the immediate impacts of future environmental changes by altering gene expression and physiology, but the lack of genetic variation in plasticity suggests limited capacity for evolved responses.

Selection Experiments in the Sea: What Can Experimental Evolution Tell Us About How Marine Life Will Respond to Climate Change?

AbstractRapid evolution may provide a buffer against extinction risk for some species threatened by climate change; however, the capacity to evolve rapidly enough to keep pace with changing environments is unknown for most taxa. The ecosystem-level consequences of climate adaptation are likely to be the largest in marine ecosystems, where short-lived phytoplankton with large effective population sizes make up the bulk of primary production. However, there are substantial challenges to predicting climate-driven evolution in marine systems, including multiple simultaneous axes of change and considerable heterogeneity in rates of change, as well as the biphasic life cycles of many marine metazoans, which expose different life stages to disparate sources of selection. A critical tool for addressing these challenges is experimental evolution, where populations of organisms are directly exposed to controlled sources of selection to test evolutionary responses. We review the use of experimental evolution to test the capacity to adapt to climate change stressors in marine species. The application of experimental evolution in this context has grown dramatically in the past decade, shedding light on the capacity for evolution, associated trade-offs, and the genetic architecture of stress-tolerance traits. Our goal is to highlight the utility of this approach for investigating potential responses to climate change and point a way forward for future studies.

Evolutionary Change in the Eastern Oyster, Crassostrea Virginica, Following Low Salinity Exposure.

The presence of standing genetic variation will play a role in determining a population's capacity to adapt to environmentally relevant stressors. In the Gulf of Mexico, extreme climatic events and anthropogenic changes to local hydrology will expose productive oyster breeding grounds to stressful low salinity conditions. We identified genetic variation for performance under low salinity (due to the combined effects of low salinity and genetic load) using a single-generation selection experiment on larvae from two populations of the eastern oyster, Crassostrea virginica. We used pool-sequencing to test for allele frequency differences at 152 salinity-associated genes for larval families pre- and post-low salinity exposure. Our results have implications for how evolutionary change occurs during early life history stages at environmentally relevant salinities. Consistent with observations of high genetic load observed in oysters, we demonstrate evidence for purging of deleterious alleles at the larval stage in C. virginica. In addition, we observe increases in allele frequencies at multiple loci, suggesting that natural selection for low salinity performance at the larval stage can act as a filter for genotypes found in adult populations.

Onset of alcohol use disorder among alcohol initiates by race/ethnicity.

Prevalence of alcohol use disorders (AUD) varies across racial/ethnic groups. It remains unclear whether rapid transition from first-time alcohol use to developing AUD varies by race and ethnicity. In this study, we investigate racial/ethnic differences in AUD onset among first-time alcohol drinkers and identify specific predictors of AUD onset by racial/ethnic group. The study population was non-institutionalized US residents aged 12 and older. Within four nationally representative probability samples (n ∼70,000/year) drawn from the 2015-2018 National Surveys on Drug Use and Health, we identified 9,381 individuals who initiated alcohol use within 1-12 months prior to the survey. The probability of AUD after initiation was estimated for the entire sample, followed by racial/ethnic group stratification. Bivariate and multivariable logistic regression models were used to identify predictors of AUD onset among alcohol initiates. The overall incidence estimate of AUD among alcohol initiates was 3.7% (95% CI = 3.0%, 4.6%). There was no significant variation in the incidence of AUD between racial/ethnic groups. Drug use, drug use disorders, and major depressive episode were significant predictors of AUD onset among all alcohol initiates. However, these predictors were not significant among non-Hispanic/Latinx Black individuals. Drug use and drug use disorders were strong predictors of AUD onset among alcohol initiates, except among non-Hispanic/Latinx Black individuals. These findings strengthen the importance of focusing on the co-use of alcohol and other drugs and the need to further investigate the risk profile differences between racial/ethnic groups.

Transgenerational plasticity and the capacity to adapt to low salinity in the eastern oyster, Crassostrea virginica.

Salinity conditions in oyster breeding grounds in the Gulf of Mexico are expected to drastically change due to increased precipitation from climate change and anthropogenic changes to local hydrology. We determined the capacity of the eastern oyster, Crassostrea virginica, to adapt via standing genetic variation or acclimate through transgenerational plasticity (TGP). We outplanted oysters to either a low- or medium-salinity site in Louisiana for 2 years. We then crossed adult parents using a North Carolina II breeding design, and measured body size and survival of larvae 5 dpf raised under low or ambient salinity. We found that TGP is unlikely to significantly contribute to low-salinity tolerance since we did not observe increased growth or survival in offspring reared in low salinity when their parents were also acclimated at a low-salinity site. However, we detected genetic variation for body size, with an estimated heritability of 0.68 ± 0.25 (95% CI). This suggests there is ample genetic variation for this trait to evolve, and that evolutionary adaptation is a possible mechanism through which oysters will persist with future declines in salinity. The results of this experiment provide valuable insights into successfully breeding low-salinity tolerance in this commercially important species.

Transcriptomic signatures of temperature adaptation in the eastern oyster Crassostrea virginica.

The large geographic distribution of the eastern oyster, Crassostrea virginica, makes it an ideal species to test how populations have adapted to latitudinal gradients in temperature. Despite inhabiting distinct thermal regimes, populations of C. virginica near the species' southern and northern geographic range show no population differences in their physiological response to temperature. In this study, we used comparative transcriptomics to understand how oysters from either end of the species' range maintain enantiostasis across three acclimation temperatures (10, 20, and 30°C). With this approach, we identified genes that were differentially expressed in response to temperature between individuals of C. virginica collected from New Brunswick, Canada and Louisiana, USA. We observed a core set of genes whose expression responded to temperature in both populations, but also an even larger set of genes with expression patterns that were unique to each population. Intriguingly, the genes with population-specific responses to temperature had elevated FST and Ka/Ks ratios compared to the genome-wide average. In contrast, genes showing only a response to temperature were found to only have elevated FST values suggesting that divergent FST may be due to selection on linked regulatory regions rather than positive selection on protein coding regions. Taken together, our results suggest that, despite coarse-scale physiological similarities, natural selection has shaped divergent gene expression responses to temperature in geographically separated populations of this broadly eurythermal marine invertebrate.

An Experimental Test of Adaptive Introgression in Locally Adapted Populations of Splash Pool Copepods.

As species struggle to keep pace with the rapidly warming climate, adaptive introgression of beneficial alleles from closely related species or populations provides a possible avenue for rapid adaptation. We investigate the potential for adaptive introgression in the copepod, Tigriopus californicus, by hybridizing two populations with divergent heat tolerance limits. We subjected hybrids to strong heat selection for 15 generations followed by whole-genome resequencing. Utilizing a hybridize evolve and resequence (HER) technique, we can identify loci responding to heat selection via a change in allele frequency. We successfully increased the heat tolerance (measured as LT50) in selected lines, which was coupled with higher frequencies of alleles from the southern (heat tolerant) population. These repeatable changes in allele frequencies occurred on all 12 chromosomes across all independent selected lines, providing evidence that heat tolerance is polygenic. These loci contained genes with lower protein-coding sequence divergence than the genome-wide average, indicating that these loci are highly conserved between the two populations. In addition, these loci were enriched in genes that changed expression patterns between selected and control lines in response to a nonlethal heat shock. Therefore, we hypothesize that the mechanism of heat tolerance divergence is explained by differential gene expression of highly conserved genes. The HER approach offers a unique solution to identifying genetic variants contributing to polygenic traits, especially variants that might be missed through other population genomic approaches.

Population epigenetic divergence exceeds genetic divergence in the Eastern oyster Crassostrea virginica in the Northern Gulf of Mexico.

Populations may respond to environmental heterogeneity via evolutionary divergence or phenotypic plasticity. While evolutionary divergence occurs through DNA sequence differences among populations, plastic divergence among populations may be generated by changes in the epigenome. Here, we present the results of a genome-wide comparison of DNA methylation patterns and genetic structure among four populations of Eastern oyster (Crassostrea virginica) in the northern Gulf of Mexico. We used a combination of restriction site-associated DNA sequencing (RADseq) and reduced representation bisulfite sequencing (RRBS) to explore population structure, gene-wide averages of F ST, and DNA methylation differences between oysters inhabiting four estuaries with unique salinity profiles. This approach identified significant population structure despite a moderately low F ST (0.02) across the freshwater boundary of the Mississippi river, a finding that may reflect recent efforts to restore oyster stock populations. Divergence between populations in CpG methylation was greater than for divergence in F ST, likely reflecting environmental effects on DNA methylation patterns. Assessment of CpG methylation patterns across all populations identified that only 26% of methylated DNA was intergenic; and, only 17% of all differentially methylated regions (DMRs) were within these same regions. DMRs within gene bodies between sites were associated with genes known to be involved in DNA damage repair, ion transport, and reproductive timing. Finally, when assessing the correlation between genomic variation and DNA methylation between these populations, we observed population-specific DNA methylation profiles that were not directly associated with single nucleotide polymorphisms or broader gene-body mean F ST trends. Our results suggest that C. virginica may use DNA methylation to generate environmentally responsive plastic phenotypes and that there is more divergence in methylation than divergence in allele frequencies.

Adaptation to climate change through genetic accommodation and assimilation of plastic phenotypes.

Theory suggests that evolutionary changes in phenotypic plasticity could either hinder or facilitate evolutionary rescue in a changing climate. Nevertheless, the actual role of evolving plasticity in the responses of natural populations to climate change remains unresolved. Direct observations of evolutionary change in nature are rare, making it difficult to assess the relative contributions of changes in trait means versus changes in plasticity to climate change responses. To address this gap, this review explores several proxies that can be used to understand evolving plasticity in the context of climate change, including space for time substitutions, experimental evolution and tests for genomic divergence at environmentally responsive loci. Comparisons among populations indicate a prominent role for divergence in environmentally responsive traits in local adaptation to climatic gradients. Moreover, genomic comparisons among such populations have identified pervasive divergence in the regulatory regions of environmentally responsive loci. Taken together, these lines of evidence suggest that divergence in plasticity plays a prominent role in adaptation to climatic gradients over space, indicating that evolving plasticity is also likely to play a key role in adaptive responses to climate change through time. This suggests that genetic variation in plastic responses to the environment (G × E) might be an important predictor of species' vulnerabilities to climate-driven decline or extinction. This article is part of the theme issue 'The role of plasticity in phenotypic adaptation to rapid environmental change'.