Phenotypic plasticity and epigenetic marking: an assessment of evidence for genetic accommodation

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

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

Non-concordant epigenetic and transcriptional responses to acute thermal stress in western mosquitofish (Gambusia affinis)

Climate change is intensifying the frequency and severity of extreme temperatures. Understanding the molecular mechanisms underlying the ability to cope with acute thermal stress is key for predicting species' responses to extreme temperature events. While many studies have focused on the individual roles of gene expression, post-transcriptional processes and epigenetic modifications in response to acute thermal stress, the relative contribution of these molecular mechanisms remains unclear. The wide range of thermal limits of western mosquitofish (Gambusia affinis) provides an opportunity to explore this interplay. Here, we quantified changes in gene expression, alternative splicing, DNA methylation and microRNA (miRNA) expression in muscle tissue dissected from mosquitofish immediately after reaching high (CTmax) or low thermal limit (CTmin). Although the numbers of genes showing expression and splicing changes in response to acute temperature stress were small, we found a possibly larger and non-redundant role of splicing compared to gene expression, with more genes being differentially spliced (DSGs) than differentially expressed (DEGs), and little overlap between DSGs and DEGs. We also identified a small proportion of CpGs showing significant methylation change (i.e. differentially methylated cytosines, DMCs) in fish at thermal limits; however, there was no overlap between DEGs and genes annotated with DMCs in both CTmax and CTmin experiments. The weak interplay between epigenetic modifications and gene expression was further supported by our discoveries of no differentially expressed miRNAs. These findings provide novel insights into the relative role of different molecular mechanisms underlying immediate responses to extreme temperatures and demonstrate non-concordant responses of epigenetic and transcriptional mechanisms to acute temperature stress.

Genetic structure, UV-vision, wing coloration and size coincide with colour polymorphism in Fabriciana adippe butterflies

Colour polymorphisms have long served as model systems in evolutionary studies and continue to inform about processes involved in the origin and dynamics of biodiversity. Modern sequencing tools allow for evaluating whether phenotypic differences between morphs reflect genetic differentiation rather than developmental plasticity, and for investigating whether polymorphisms represent intermediate stages of diversification towards speciation. We investigated phenotypic and genetic differentiation between two colour morphs of the butterfly Fabriciana adippe using a combination of ddRAD-sequencing and comparisons of body size, colour patterns and optical properties of bright wing spots. The silvery-spotted adippe form had larger and darker wings and reflected UV light, while the yellow cleodoxa form displayed more green scales and reflected very little UV, showcasing that they constitute distinct and alternative integrated phenotypes. Genomic analyses revealed genetic structuring according to source population, and to colour morph, suggesting that the phenotypic differentiation reflects evolutionary modifications. We report 17 outlier loci associated with colour morph, including ultraviolet-sensitive visual pigment (UVRh1), which is associated with intraspecific communication and mate choice in butterflies. Together with the demonstration that the wings of the adippe (but essentially not the cleodoxa) morph reflect UV light, that UV reflectance is higher in females than males and that morphs differ in wing size, this suggests that these colour morphs might represent genetically integrated phenotypes, possibly adapted to different microhabitats. We propose that non-random mating might contribute to the differentiation and maintenance of the polymorphism.

Genome evolution and divergence in cis-regulatory architecture is associated with condition-responsive development in horned dung beetles

Phenotypic plasticity is thought to be an important driver of diversification and adaptation to environmental variation, yet the genomic mechanisms mediating plastic trait development and evolution remain poorly understood. The Scarabaeinae, or true dung beetles, are a species-rich clade of insects recognized for their highly diversified nutrition-responsive development including that of cephalic horns-evolutionarily novel, secondary sexual weapons that exhibit remarkable intra- and interspecific variation. Here, we investigate the evolutionary basis for horns as well as other key dung beetle traits via comparative genomic and developmental assays. We begin by presenting chromosome-level genome assemblies of three dung beetle species in the tribe Onthophagini (> 2500 extant species) including Onthophagus taurus, O. sagittarius, and Digitonthophagus gazella. Comparing these assemblies to those of seven other species across the order Coleoptera identifies evolutionary changes in coding sequence associated with metabolic regulation of plasticity and metamorphosis. We then contrast chromatin accessibility in developing head horn tissues of high- and low-nutrition O. taurus males and females and identify distinct cis-regulatory architectures underlying nutrition- compared to sex-responsive development, including a large proportion of recently evolved regulatory elements sensitive to horn morph determination. Binding motifs of known and new candidate transcription factors are enriched in these nutrition-responsive open chromatin regions. Our work highlights the importance of chromatin state regulation in mediating the development and evolution of plastic traits, demonstrates gene networks are highly evolvable transducers of environmental and genetic signals, and provides new reference-quality genomes for three species that will bolster future developmental, ecological, and evolutionary studies of this insect group.

Evidence of differential phenotypic plasticity in a desert mustard

Understanding the effect of the environment on trait variation is critical for ecologically and economically important plants. Here, we asked whether differences in soil moisture are a source of variation in Sahara mustard (Brassica tournefortii). We subjected common garden populations of plants derived from native, invasive, and landrace sources (ranges) to varying water addition treatments. Using principal component analysis, we generated composite variables of life history traits for ANCOVA tests and plotted norms of reaction. Planting time was included as a covariate because we observed differences in seedling emergence despite efforts to standardize germination. We also examined the population coefficient of variation of individual traits (plasticity) and the association of trait CVs with fitness. The amount of plasticity varied but was inconsistent among range sources for all composite traits. Planting time did not affect treatments, but plants from different ranges responded differently to variable planting times. With a surplus of water, plants derived from native and invasive populations plateaued in vegetative trait values but showed a continuous linear increase in reproductive trait values. Possibly as a result of domestication, moderate and high water treatments in landrace plants caused plateaus in composite trait values for flowering phenology, seed count, plant size, and branching. The ecological breadth shown by our plants is likely due to drought tolerance that evolved in Brassica tournefortii source populations.

Epigenetic drugs as new emerging therapeutics: What is the scale's orientation of application and challenges?

Epigenetics is the study of heritable changes in gene expression or function without altering the DNA sequence. Important factors are part of epigenetic events, such as methylation, DNA histone rearrangements, nucleosome transposition, and non-coding RNAs. Dysregulated epigenetic mechanics are associated with various cancers' initiation, development, and metastasis. It is known that the occurrence and development of cancer can be controlled by regulating unexpected epigenetic events. Epi-drugs are used singly or in combination with chemotherapy and enhance antitumor activity, reduce drug resistance, and stimulate the host immune response. Despite these benefits, epigenetic therapy as a single therapy or in combination with other drugs leads to adverse effects. This review article introduces and compares the advantages, disadvantages, and side effects of using these drugs for the first time since their introduction. Also, this article describes the mechanism of action of various epigenetic drugs. Recommendations for future use of epigenetic drugs as cancer therapeutics are suggested as an overall conclusion.

Histone Demethylase Modulation: Epigenetic Strategy to Combat Cancer Progression

Epigenetic modifications are heritable, reversible changes in histones or the DNA that control gene functions, being exogenous to the genomic sequence itself. Human diseases, particularly cancer, are frequently connected to epigenetic dysregulations. One of them is histone methylation, which is a dynamically reversible and synchronously regulated process that orchestrates the three-dimensional epigenome, nuclear processes of transcription, DNA repair, cell cycle, and epigenetic functions, by adding or removing methylation groups to histones. Over the past few years, reversible histone methylation has become recognized as a crucial regulatory mechanism for the epigenome. With the development of numerous medications that target epigenetic regulators, epigenome-targeted therapy has been used in the treatment of malignancies and has shown meaningful therapeutic potential in preclinical and clinical trials. The present review focuses on the recent advances in our knowledge on the role of histone demethylases in tumor development and modulation, in emphasizing molecular mechanisms that control cancer cell progression. Finally, we emphasize current developments in the advent of new molecular inhibitors that target histone demethylases to regulate cancer progression.

The diverging epigenomic landscapes of honeybee queens and workers revealed by multiomic sequencing

The role of the epigenome in phenotypic plasticity is unclear presently. Here we used a multiomics approach to explore the nature of the epigenome in developing honey bee (Apis mellifera) workers and queens. Our data clearly showed distinct queen and worker epigenomic landscapes during the developmental process. Differences in gene expression between workers and queens become more extensive and more layered during the process of development. Genes known to be important for caste differentiation were more likely to be regulated by multiple epigenomic systems than other differentially expressed genes. We confirmed the importance of two candidate genes for caste differentiation by using RNAi to manipulate the expression of two genes that differed in expression between workers and queens were regulated by multiple epigenomic systems. For both genes the RNAi manipulation resulted in a decrease in weight and fewer ovarioles of newly emerged queens compared to controls. Our data show that the distinct epigenomic landscapes of worker and queen bees differentiate during the course of larval development.

Plasticity and Stereotypic Rewiring of the Transcriptome Upon Bacterial Evolution of Antibiotic Resistance

Bacterial evolution of antibiotic resistance frequently has deleterious side effects on microbial growth, virulence, and susceptibility to other antimicrobial agents. However, it is unclear how these trade-offs could be utilized for manipulating antibiotic resistance in the clinic, not least because the underlying molecular mechanisms are poorly understood. Using laboratory evolution, we demonstrate that clinically relevant resistance mutations in Escherichia coli constitutively rewire a large fraction of the transcriptome in a repeatable and stereotypic manner. Strikingly, lineages adapted to functionally distinct antibiotics and having no resistance mutations in common show a wide range of parallel gene expression changes that alter oxidative stress response, iron homeostasis, and the composition of the bacterial outer membrane and cell surface. These common physiological alterations are associated with changes in cell morphology and enhanced sensitivity to antimicrobial peptides. Finally, the constitutive transcriptomic changes induced by resistance mutations are largely distinct from those induced by antibiotic stresses in the wild type. This indicates a limited role for genetic assimilation of the induced antibiotic stress response during resistance evolution. Our work suggests that diverse resistance mutations converge on similar global transcriptomic states that shape genetic susceptibility to antimicrobial compounds.

A Green Light to Switch on Genes: Revisiting Trithorax on Plants

The Trithorax Group (TrxG) is a highly conserved multiprotein activation complex, initially defined by its antagonistic activity with the PcG repressor complex. TrxG regulates transcriptional activation by the deposition of H3K4me3 and H3K36me3 marks. According to the function and evolutionary origin, several proteins have been defined as TrxG in plants; nevertheless, little is known about their interactions and if they can form TrxG complexes. Recent evidence suggests the existence of new TrxG components as well as new interactions of some TrxG complexes that may be acting in specific tissues in plants. In this review, we bring together the latest research on the topic, exploring the interactions and roles of TrxG proteins at different developmental stages, required for the fine-tuned transcriptional activation of genes at the right time and place. Shedding light on the molecular mechanism by which TrxG is recruited and regulates transcription.

Stochastic models of Mendelian and reverse transcriptional inheritance in state-structured cancer populations

Recent evidence suggests that a polyaneuploid cancer cell (PACC) state may play a key role in the adaptation of cancer cells to stressful environments and in promoting therapeutic resistance. The PACC state allows cancer cells to pause cell division and to avoid DNA damage and programmed cell death. Transition to the PACC state may also lead to an increase in the cancer cell’s ability to generate heritable variation (evolvability). One way this can occur is through evolutionary triage. Under this framework, cells gradually gain resistance by scaling hills on a fitness landscape through a process of mutation and selection. Another way this can happen is through self-genetic modification whereby cells in the PACC state find a viable solution to the stressor and then undergo depolyploidization, passing it on to their heritably resistant progeny. Here, we develop a stochastic model to simulate both of these evolutionary frameworks. We examine the impact of treatment dosage and extent of self-genetic modification on eco-evolutionary dynamics of cancer cells with aneuploid and PACC states. We find that under low doses of therapy, evolutionary triage performs better whereas under high doses of therapy, self-genetic modification is favored. This study generates predictions for teasing apart these biological hypotheses, examines the implications of each in the context of cancer, and provides a modeling framework to compare Mendelian and non-traditional forms of inheritance.

Evolved transcriptional responses and their trade-offs after long-term adaptation of Bemisia tabaci to a marginally-suitable host

Although generalist insect herbivores can migrate and rapidly adapt to a broad range of host plants, they can face significant difficulties when accidentally migrating to novel and marginally-suitable hosts. What happens, both in performance and gene expression regulation, if these marginally-suitable hosts must be used for multiple generations before migration to a suitable host can take place, largely remains unknown. In this study, we established multigenerational colonies of the whitefly Bemisia tabaci, a generalist phloem-feeding species, adapted to a marginally-suitable host (habanero pepper) or an optimal host (cotton). We used reciprocal host tests to estimate the differences in performance of the populations on both hosts under optimal (30 oC) and mild-stressful (24 oC) temperature conditions, and documented the associated transcriptomic changes. The habanero pepper-adapted population greatly improved its performance on habanero pepper but did not reach its performance level on cotton, the original host. It also showed reduced performance on cotton, relative to the non-adapted population, and an antagonistic effect of the lower-temperature stressor. The transcriptomic data revealed that most of the expression changes, associated with long-term adaptation to habanero pepper, can be categorized as "evolved" with no initial plastic response. Three molecular functions dominated: enhanced formation of cuticle structural constituents, enhanced activity of oxidation-reduction processes involved in neutralization of phytotoxins and reduced production of proteins from the cathepsin B family. Taken together, these findings indicate that generalist insects can adapt to novel host plants by modifying the expression of a relatively small set of specific molecular functions.

Phenotypic but no genetic adaptation in zooplankton 24 years after an abrupt +10°C climate change

The climate is currently warming fast, threatening biodiversity all over the globe. Populations often adapt rapidly to environmental change, but for climate warming very little evidence is available. Here, we investigate the pattern of adaptation to an extreme +10°C climate change in the wild, following the introduction of brine shrimp Artemia franciscana from San Francisco Bay, USA, to Vinh Chau saltern in Vietnam. We use a resurrection ecology approach, hatching diapause eggs from the ancestral population and the introduced population after 13 and 24 years (∼54 and ∼100 generations, respectively). In a series of coordinated experiments, we determined whether the introduced Artemia show increased tolerance to higher temperatures, and the extent to which genetic adaptation, developmental plasticity, transgenerational effects, and local microbiome differences contributed to this tolerance. We find that introduced brine shrimp do show increased phenotypic tolerance to warming. Yet strikingly, these changes do not have a detectable additive genetic component, are not caused by mitochondrial genetic variation, and do not seem to be caused by epigenetic marks set by adult parents exposed to warming. Further, we do not find any developmental plasticity that would help cope with warming, nor any protective effect of heat‐tolerant local microbiota. The evolved thermal tolerance might therefore be entirely due to transgenerational (great)grandparental effects, possibly epigenetic marks set by parents who were exposed to high temperatures as juveniles. This study is a striking example of “missing heritability,” where a large adaptive phenotypic change is not accompanied by additive genetic effects.

A Dual Role for Behavior in Evolution and Shaping Organismal Selective Environments

The hypothesis that evolved behaviors play a determining role in facilitating and impeding the evolution of other traits has been discussed for more than 100 years with little consensus beyond an agreement that the ideas are theoretically plausible in accord with the Modern Synthesis. Many recent reviews of the genomic, epigenetic, and developmental mechanisms underpinning major behavioral transitions show how facultative expression of novel behaviors can lead to the evolution of obligate behaviors and structures that enhance behavioral function. Phylogenetic and genomic studies indicate that behavioral traits are generally evolutionarily more labile than other traits and that they help shape selective environments on the latter traits. Adaptive decision-making to encounter resources and avoid stress sources requires specific sensory inputs, which behaviorally shape selective environments by determining those features of the external world that are biologically relevant. These recent findings support the hypothesis of a dual role for behavior in evolution and are consistent with current evolutionary theory.

Adaptive Phenotypic Plasticity Stabilizes Evolution in Fluctuating Environments

Fluctuating environmental conditions are ubiquitous in natural systems, and populations have evolved various strategies to cope with such fluctuations. The particular mechanisms that evolve profoundly influence subsequent evolutionary dynamics. One such mechanism is phenotypic plasticity, which is the ability of a single genotype to produce alternate phenotypes in an environmentally dependent context. Here, we use digital organisms (self-replicating computer programs) to investigate how adaptive phenotypic plasticity alters evolutionary dynamics and influences evolutionary outcomes in cyclically changing environments. Specifically, we examined the evolutionary histories of both plastic populations and non-plastic populations to ask: (1) Does adaptive plasticity promote or constrain evolutionary change? (2) Are plastic populations better able to evolve and then maintain novel traits? And (3), how does adaptive plasticity affect the potential for maladaptive alleles to accumulate in evolving genomes? We find that populations with adaptive phenotypic plasticity undergo less evolutionary change than non-plastic populations, which must rely on genetic variation from de novo mutations to continuously readapt to environmental fluctuations. Indeed, the non-plastic populations undergo more frequent selective sweeps and accumulate many more genetic changes. We find that the repeated selective sweeps in non-plastic populations drive the loss of beneficial traits and accumulation of maladaptive alleles, whereas phenotypic plasticity can stabilize populations against environmental fluctuations. This stabilization allows plastic populations to more easily retain novel adaptive traits than their non-plastic counterparts. In general, the evolution of adaptive phenotypic plasticity shifted evolutionary dynamics to be more similar to that of populations evolving in a static environment than to non-plastic populations evolving in an identical fluctuating environment. All natural environments subject populations to some form of change; our findings suggest that the stabilizing effect of phenotypic plasticity plays an important role in subsequent adaptive evolution.

Comparative genome and transcriptome analyses reveal innate differences in response to host plants by two color forms of the two-spotted spider mite Tetranychus urticae

Background

The two-spotted spider mite, Tetranychus urticae, is a major agricultural pest with a cosmopolitan distribution, and its polyphagous habits provide a model for investigating herbivore-plant interactions. There are two body color forms of T. urticae with a different host preference. Comparative genomics and transcriptomics are used here to investigate differences in responses of the forms to host plants at the molecular level. Biological responses of the two forms sourced from multiple populations are also presented.

Results

We carried out principal component analysis of transcription changes in three red and three green T. urticae populations feeding on their original host (common bean), and three hosts to which they were transferred: cotton, cucumber and eggplant. There were differences among the forms in gene expression regardless of their host plant. In addition, different changes in gene expression were evident in the two forms when responding to the same host transfer. We further compared biological performance among populations of the two forms after feeding on each of the four hosts. Fecundity of 2-day-old adult females showed a consistent difference between the forms after feeding on bean. We produced a 90.1-Mb genome of the red form of T. urticae with scaffold N50 of 12.78 Mb. Transcriptional profiles of genes associated with saliva, digestion and detoxification showed form-dependent responses to the same host and these genes also showed host-specific expression effects.

Conclusions

Our research revealed that forms of T. urticae differ in host-determined transcription responses and that there is form-dependent plasticity in the transcriptomic responses. These differences may facilitate the extreme polyphagy shown by spider mites, although fitness differences on hosts are also influenced by population differences unrelated to color form.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07894-7.

Adaptation to simultaneous warming and acidification carries a thermal tolerance cost in a marine copepod

The ocean is undergoing warming and acidification. Thermal tolerance is affected both by evolutionary adaptation and developmental plasticity. Yet, thermal tolerance in animals adapted to simultaneous warming and acidification is unknown. We experimentally evolved the ubiquitous copepod Acartia tonsa to future combined ocean warming and acidification conditions (OWA approx. 22°C, 2000 µatm CO2) and then compared its thermal tolerance relative to ambient conditions (AM approx. 18°C, 400 µatm CO2). The OWA and AM treatments were reciprocally transplanted after 65 generations to assess effects of developmental conditions on thermal tolerance and potential costs of adaptation. Treatments transplanted from OWA to AM conditions were assessed at the F1 and F9 generations following transplant. Adaptation to warming and acidification, paradoxically, reduces both thermal tolerance and phenotypic plasticity. These costs of adaptation to combined warming and acidification may limit future population resilience.

Long-Term m5C Methylome Dynamics Parallel Phenotypic Adaptation in the Cyanobacterium Trichodesmium

A major challenge in modern biology is understanding how the effects of short-term biological responses influence long-term evolutionary adaptation, defined as a genetically determined increase in fitness to novel environments. This is particularly important in globally important microbes experiencing rapid global change, due to their influence on food webs, biogeochemical cycles, and climate. Epigenetic modifications like methylation have been demonstrated to influence short-term plastic responses, which ultimately impact long-term adaptive responses to environmental change. However, there remains a paucity of empirical research examining long-term methylation dynamics during environmental adaptation in nonmodel, ecologically important microbes. Here, we show the first empirical evidence in a marine prokaryote for long-term m5C methylome modifications correlated with phenotypic adaptation to CO₂, using a 7-year evolution experiment (1,000+ generations) with the biogeochemically important marine cyanobacterium Trichodesmium. We identify m5C methylated sites that rapidly changed in response to high (750 µatm) CO₂ exposure and were maintained for at least 4.5 years of CO₂ selection. After 7 years of CO₂ selection, however, m5C methylation levels that initially responded to high-CO₂ returned to ancestral, ambient CO₂ levels. Concurrently, high-CO₂ adapted growth and N₂ fixation rates remained significantly higher than those of ambient CO₂ adapted cell lines irrespective of CO₂ concentration, a trend consistent with genetic assimilation theory. These data demonstrate the maintenance of CO₂-responsive m5C methylation for 4.5 years alongside phenotypic adaptation before returning to ancestral methylation levels. These observations in a globally distributed marine prokaryote provide critical evolutionary insights into biogeochemically important traits under global change.

Adaptive and nonadaptive plasticity in changing environments: Implications for sexual species with different life history strategies

Populations adapt to novel environmental conditions by genetic changes or phenotypic plasticity. Plastic responses are generally faster and can buffer fitness losses under variable conditions. Plasticity is typically modeled as random noise and linear reaction norms that assume simple one-to-one genotype-phenotype maps and no limits to the phenotypic response. Most studies on plasticity have focused on its effect on population viability. However, it is not clear, whether the advantage of plasticity depends solely on environmental fluctuations or also on the genetic and demographic properties (life histories) of populations. Here we present an individual-based model and study the relative importance of adaptive and nonadaptive plasticity for populations of sexual species with different life histories experiencing directional stochastic climate change. Environmental fluctuations were simulated using differentially autocorrelated climatic stochasticity or noise color, and scenarios of directional climate change. Nonadaptive plasticity was simulated as a random environmental effect on trait development, while adaptive plasticity as a linear, saturating, or sinusoidal reaction norm. The last two imposed limits to the plastic response and emphasized flexible interactions of the genotype with the environment. Interestingly, this assumption led to (a) smaller phenotypic than genotypic variance in the population (many-to-one genotype-phenotype map) and the coexistence of polymorphisms, and (b) the maintenance of higher genetic variation-compared to linear reaction norms and genetic determinism-even when the population was exposed to a constant environment for several generations. Limits to plasticity led to genetic accommodation, when costs were negligible, and to the appearance of cryptic variation when limits were exceeded. We found that adaptive plasticity promoted population persistence under red environmental noise and was particularly important for life histories with low fecundity. Populations producing more offspring could cope with environmental fluctuations solely by genetic changes or random plasticity, unless environmental change was too fast.

Body shape and fin size in juvenile Atlantic salmon (Salmo salar): effects of temperature during embryogenesis

Temperature during egg incubation and early development influences later life stages of fishes, potentially influencing survival. Throughout its distribution, Atlantic salmon (Salmo salar Linnaeus, 1758) have experienced population declines, and in view of ongoing global warming, we tested if temperature during the earliest developmental stages modified body shape and fin size when temperatures averaged 2.6 vs. 5.6 °C. This temperature difference simulates increases predicted in climate change scenarios. Based on previous studies, we hypothesized that salmon originating from eggs subjected to cold incubation temperatures would have slimmer bodies and larger pectoral and dorsal fins than salmon from eggs that experienced warmer temperatures. After hatching, the juveniles were raised for 1 year under identical temperatures, after which we measured their body shape and fin areas. We found no support for our hypothesis regarding body shape. Indeed, we found the opposite, with cold-incubated salmon having deeper bodies than warm-incubated salmon. For fin size, the pectoral fins of cold-incubated salmon were larger than for warm-incubated salmon as predicted, but there was no difference in dorsal fin size. These results suggest that global warming may lead to altered body shape and fin size, possibly affecting swimming performance, and thus raise questions about the ecological consequences of the changes.

Mitochondrial Short-Term Plastic Responses and Long-Term Evolutionary Dynamics in Animal Species

How do species respond or adapt to environmental changes? The answer to this depends partly on mitochondrial epigenetics and genetics, new players in promoting adaptation to both short- and long-term environmental changes. In this review, we explore how mitochondrial epigenetics and genetics mechanisms, such as mtDNA methylation, mtDNA-derived noncoding RNAs, micropeptides, mtDNA mutations, and adaptations, can contribute to animal plasticity and adaptation. We also briefly discuss the challenges in assessing mtDNA adaptive evolution. In sum, this review covers new advances in the field of mitochondrial genomics, many of which are still controversial, and discusses processes still somewhat obscure, and some of which are still quite speculative and require further robust experimentation.

Cross-species transcriptomics uncovers genes underlying genetic accommodation of developmental plasticity in spadefoot toads

That hardcoded genomes can manifest as plastic phenotypes responding to environmental perturbations is a fascinating feature of living organisms. How such developmental plasticity is regulated at the molecular level is beginning to be uncovered aided by the development of -omic techniques. Here, we compare the transcriptome-wide responses of two species of spadefoot toads with differing capacity for developmental acceleration of their larvae in the face of a shared environmental risk: pond drying. By comparing gene expression profiles over time and performing cross-species network analyses, we identified orthologues and functional gene pathways whose environmental sensitivity in expression have diverged between species. Genes related to lipid, cholesterol and steroid biosynthesis and metabolism make up most of a module of genes environmentally responsive in one species, but canalized in the other. The evolutionary changes in the regulation of the genes identified through these analyses may have been key in the genetic accommodation of developmental plasticity in this system.

Avenues of reef-building coral acclimatization in response to rapid environmental change

The swiftly changing climate presents a challenge to organismal fitness by creating a mismatch between the current environment and phenotypes adapted to historic conditions. Acclimatory mechanisms may be especially crucial for sessile benthic marine taxa, such as reef-building corals, where climate change factors including ocean acidification and increasing temperature elicit strong negative physiological responses such as bleaching, disease and mortality. Here, within the context of multiple stressors threatening marine organisms, I describe the wealth of metaorganism response mechanisms to rapid ocean change and the ontogenetic shifts in organism interactions with the environment that can generate plasticity. I then highlight the need to consider the interactions of rapid and evolutionary responses in an adaptive (epi)genetic continuum. Building on the definitions of these mechanisms and continuum, I also present how the interplay of the microbiome, epigenetics and parental effects creates additional avenues for rapid acclimatization. To consider under what conditions epigenetic inheritance has a more substantial role, I propose investigation into the offset of timing of gametogenesis leading to different environmental integration times between eggs and sperm and the consequences of this for gamete epigenetic compatibility. Collectively, non-genetic, yet heritable phenotypic plasticity will have significant ecological and evolutionary implications for sessile marine organism persistence under rapid climate change. As such, reef-building corals present ideal and time-sensitive models for further development of our understanding of adaptive feedback loops in a multi-player (epi)genetic continuum.

A framework for understanding gene expression plasticity and its influence on stress tolerance

Phenotypic plasticity can serve as a stepping stone towards adaptation. Recently, studies have shown that gene expression contributes to emergent stress responses such as thermal tolerance, with tolerant and susceptible populations showing distinct transcriptional profiles. However, given the dynamic nature of gene expression, interpreting transcriptomic results in a way that elucidates the functional connection between gene expression and the observed stress response is challenging. Here, we present a conceptual framework to guide interpretation of gene expression reaction norms in the context of stress tolerance. We consider the evolutionary and adaptive potential of gene expression reaction norms and discuss the influence of sampling timing, transcriptomic resilience, as well as complexities related to life history when interpreting gene expression dynamics and how these patterns relate to host tolerance. We highlight corals as a case study to demonstrate the value of this framework for non-model systems. As species face rapidly changing environmental conditions, modulating gene expression can serve as a mechanistic link from genetic and cellular processes to the physiological responses that allow organisms to thrive under novel conditions. Interpreting how or whether a species can employ gene expression plasticity to ensure short-term survival will be critical for understanding the global impacts of climate change across diverse taxa.

Assessing the effects of genotype-by-environment interaction on epigenetic, transcriptomic, and phenotypic response in a Pacific salmon

Genotype-by-environment (GxE) interactions are non-parallel reaction norms among individuals with different genotypes in response to different environmental conditions. GxE interactions are an extension of phenotypic plasticity and consequently studying such interactions improves our ability to predict effects of different environments on phenotype as well as the fitness of genetically distinct organisms and their capacity to interact with ecosystems. Growth hormone transgenic coho salmon grow much faster than non-transgenics when raised in tank environments, but show little difference in growth when reared in nature-like streams. We used this model system to evaluate potential mechanisms underlying this growth rate GxE interaction, performing RNA-seq to measure gene transcription and whole-genome bisulfite sequencing to measure gene methylation in liver tissue. Gene ontology (GO) term analysis revealed stress as an important biological process potentially influencing growth rate GxE interactions. While few genes with transcription differences also had methylation differences, in promoter or gene regions, many genes were differentially methylated between tank and stream environments. A GO term analysis of differentially methylated genes between tank and stream environments revealed increased methylation in the stream environment of more than 95% of the differentially methylated genes, many with biological processes unrelated to liver function. The lower nutritional condition of the stream environment may cause increased negative regulation of genes less vital for liver tissue function than when fish are reared in tanks with unlimited food availability. These data show a large effect of rearing environment both on gene expression and methylation, but it is less clear that the detected epigenetic marks are responsible for the observed altered growth and physiological responses.

Reconciling Non-Genetic Plasticity with Somatic Evolution in Cancer

Post-treatment progression of tumors is commonly explained by somatic Darwinian evolution (i.e., selection of cells carrying genetic mutations that create more aggressive cell traits). But cancer genome and transcriptome analyses now paint a picture far more complex, prompting us to see beyond the Darwinian scheme: non-genetic cell phenotype plasticity explained by alternative stable gene expression states ('attractors'), may also produce aggressive phenotypes that can be selected for, without mutations. Worse, treatment may even induce cell state transitions into more malignant attractors. We review recent evidence for non-genetic mechanisms of progression, explain the theoretical foundation of attractor transitions behind treatment-induced increase of aggressiveness, and provide a framework for unifying genetic and non-genetic dynamics in tumor progression.

The origin of wing polyphenism in ants: An eco-evo-devo perspective

The evolution of eusociality, where solitary individuals integrate into a single colony, is a major transition in individuality. In ants, the origin of eusociality coincided with the origin of a wing polyphenism approximately 160 million years ago, giving rise to colonies with winged queens and wingless workers. As a consequence, both eusociality and wing polyphenism are nearly universal features of all ants. Here, we synthesize fossil, ecological, developmental, and evolutionary data in an attempt to understand the factors that contributed to the origin of wing polyphenism in ants. We propose multiple models and hypotheses to explain how wing polyphenism is orchestrated at multiple levels, from environmental cues to gene networks. Furthermore, we argue that the origin of wing polyphenism enabled the subsequent evolution of morphological diversity across the ants. We finally conclude by outlining several outstanding questions for future work.

Genetic Determinism Exists for the Global DNA Methylation Rate in Sheep

Recent studies showed that epigenetic marks, including DNA methylation, influence production and adaptive traits in plants and animals. So far, most studies dealing with genetics and epigenetics considered DNA methylation sites independently. However, the genetic basis of the global DNA methylation rate (GDMR) remains unknown. The main objective of the present study was to investigate genetic determinism of GDMR in sheep. The experiment was conducted on 1,047 Romane sheep allocated into 10 half-sib families. After weaning, all the lambs were phenotyped for global GDMR in blood as well as for production and adaptive traits. GDMR was measured by LUminometric Methylation Analysis (LUMA) using a pyrosequencing approach. Association analyses were conducted on some of the lambs (n = 775) genotyped by using the Illumina OvineSNP50 BeadChip. Blood GDMR varied among the animals (average 70.7 ± 6.0%). Female lambs had significantly higher GDMR than male lambs. Inter-individual variability of blood GDMR had an additive genetic component and heritability was moderate (h² = 0.20 ± 0.05). No significant genetic correlation was found between GDMR and growth or carcass traits, birthcoat, or social behaviors. Association analyses revealed 28 QTLs associated with blood GDMR. Seven genomic regions on chromosomes 1, 5, 11, 17, 24, and 26 were of most interest due to either high significant associations with GDMR or to the relevance of genes located close to the QTLs. QTL effects were moderate. Genomic regions associated with GDMR harbored several genes not yet described as being involved in DNA methylation, but some are already known to play an active role in gene expression. In addition, some candidate genes, CHD1, NCO3A, KDM8, KAT7, and KAT6A have previously been described to be involved in epigenetic modifications. In conclusion, the results of the present study indicate that blood GDMR in domestic sheep is under polygenic influence and provide new insights into DNA methylation genetic determinism.

Genetic assimilation and accommodation: Models and mechanisms

Genetic assimilation and genetic accommodation are mechanisms by which novel phenotypes are produced and become established in a population. Novel characters may be fixed and canalized so they are insensitive to environmental variation, or can be plastic and adaptively responsive to environmental variation. In this review we explore the various theories that have been proposed to explain the developmental origin and evolution of novel phenotypes and the mechanisms by which canalization and phenotypic plasticity evolve. These theories and models range from conceptual to mathematical and have taken different views of how genes and environment contribute to the development and evolution of the properties of phenotypes. We will argue that a deeper and more nuanced understanding of genetic accommodation requires a recognition that phenotypes are not static entities but are dynamic system properties with no fixed deterministic relationship between genotype and phenotype. We suggest a mechanistic systems-view of development that allows one to incorporate both genes and environment in a common model, and that enables both quantitative analysis and visualization of the evolution of canalization and phenotypic plasticity.

Heat-responsive and time-resolved transcriptome and metabolome analyses of Escherichia coli uncover thermo-tolerant mechanisms

Current understanding of heat shock response has been complicated by the fact that heat stress is inevitably accompanied by changes in specific growth rates and growth stages. In this study, a chemostat culture was successfully performed to avoid the physico-chemical and biological changes that accompany heatshock, which provided a unique opportunity to investigate the full range of cellular responses to thermal stress, ranging from temporary adjustment to phenotypic adaptation at multi-omics levels. Heat-responsive and time-resolved changes in the transcriptome and metabolome of a widely used E. coli strain BL21(DE3) were explored in which the temperature was upshifted from 37 to 42 °C. Omics profiles were categorized into early (2 and 10 min), middle (0.5, 1, and 2 h), and late (4, 8, and 40 h) stages of heat stress, each of which reflected the initiation, adaptation, and phenotypic plasticity steps of the stress response. The continued heat stress modulated global gene expression by controlling the expression levels of sigma factors in different time frames, including unexpected downregulation of the second heatshock sigma factor gene (rpoE) upon the heat stress. Trehalose, cadaverine, and enterobactin showed increased production to deal with the heat-induced oxidative stress. Genes highly expressed at the late stage were experimentally validated to provide thermotolerance. Intriguingly, a cryptic capsular gene cluster showed considerably high expression level only at the late stage, and its expression was essential for cell growth at high temperature. Granule-forming and elongated cells were observed at the late stage, which was morphological plasticity occurred as a result of acclimation to the continued heat stress. Whole process of thermal adaptation along with the genetic and metabolic changes at fine temporal resolution will contribute to far-reaching comprehension of the heat shock response. Further, the identified thermotolerant genes will be useful to rationally engineer thermotolerant microorganisms.

Evolution of Plasticity in Response to Ethanol between Sister Species with Different Ecological Histories (Drosophila melanogaster and D. simulans)

AbstractWhen populations evolve adaptive reaction norms in response to novel environments, it can occur through a process termed genetic accommodation. Under this model, the initial response to the environment is widely variable between genotypes as a result of cryptic genetic variation, which is then refined by selection to a single adaptive response. Here, I empirically test these predictions from genetic accommodation by measuring reaction norms in individual genotypes and across several time points. I compare two species of Drosophila that differ in their adaptation to ethanol (D. melanogaster and D. simulans). Both species are human commensals with a recent cosmopolitan expansion, but only D. melanogaster is adapted to ethanol exposure. Using gene expression as a phenotype and an approach that combines information about expression and alternative splicing, I find that D. simulans exhibits cryptic genetic variation in the response to ethanol, while D. melanogaster has almost no genotype-specific variation in reaction norm. This is evidence for adaptation to ethanol through genetic accommodation, suggesting that the evolution of phenotypic plasticity could be an important contributor to the ability to exploit novel resources.

Genetic compensation rather than genetic assimilation drives the evolution of plasticity in response to mild warming across latitudes in a damselfly

Global warming is causing plastic and evolutionary changes in the phenotypes of ectotherms. Yet, we have limited knowledge on how the interplay between plasticity and evolution shapes thermal responses and underlying gene expression patterns. We assessed thermal reaction norm patterns across the transcriptome and identified associated molecular pathways in northern and southern populations of the damselfly Ischnura elegans. Larvae were reared in a common garden experiment at the mean summer water temperatures experienced at the northern (20°C) and southern (24°C) latitudes. This allowed a space-for-time substitution where the current gene expression levels at 24°C in southern larvae are a proxy for the expected responses of northern larvae under gradual thermal evolution to the predicted 4°C warming. Most differentially expressed genes showed fixed differences across temperatures between latitudes, suggesting that thermal genetic adaptation will mainly evolve through changes in constitutive gene expression. Northern populations also frequently showed plastic responses in gene expression to mild warming, while southern populations were much less responsive to temperature. Thermal responsive genes in northern populations showed to a large extent a pattern of genetic compensation, namely gene expression that was induced at 24°C in northern populations remained at a lower constant level in southern populations, and were associated with metabolic and translation pathways. There was instead little evidence for genetic assimilation of an initial plastic response to mild warming. Our data therefore suggest that genetic compensation rather than genetic assimilation may drive the evolution of plasticity in response to mild warming in this damselfly species.

Genetic Constraints, Transcriptome Plasticity, and the Evolutionary Response to Climate Change

In situ adaptation to climate change will be critical for the persistence of many ectotherm species due to their relative lack of dispersal capacity. Climate change is causing increases in both the mean and the variance of environmental temperature, each of which may act as agents of selection on different traits. Importantly, these traits may not be heritable or have the capacity to evolve independently from one another. When genetic constraints prevent the "baseline" values of thermal performance traits from evolving rapidly, phenotypic plasticity driven by gene expression might become critical. We review the literature for evidence that thermal performance traits in ectotherms are heritable and have genetic architectures that permit their unconstrained evolution. Next, we examine the relationship between gene expression and both the magnitude and duration of thermal stress. Finally, we identify genes that are likely to be important for adaptation to a changing climate and determine whether they show patterns consistent with thermal adaptation. Although few studies have measured narrow-sense heritabilities of thermal performance traits, current evidence suggests that the end points of thermal reaction norms (tolerance limits) are moderately heritable and have the potential to evolve rapidly. By contrast, performance at intermediate temperatures has substantially lower evolutionary potential. Moreover, evolution in many species appears to be constrained by genetic correlations such that populations can adapt to either increases in mean temperature or temperature variability, but not both. Finally, many species have the capacity for plastic expression of the transcriptome in response to temperature shifts, with the number of differentially expressed genes increasing with the magnitude, but not the duration, of thermal stress. We use these observations to develop a conceptual model that describes the likely trajectory of genome evolution in response to changes in environmental temperature. Our results indicate that extreme weather events, rather than gradual increases in mean temperature, are more likely to drive genetic and phenotypic change in wild ectotherms.

Plasticity leaves a phenotypic signature during local adaptation

Phenotypic responses to a novel or extreme environment are initially plastic, only later to be followed by genetic change. Whether or not environmentally induced phenotypes are sufficiently recurrent and fit to leave a signature in adaptive evolution is debated. Here, we analyze multivariate data from 34 plant reciprocal transplant studies to test: (1) if plasticity is an adaptive source of developmental bias that makes locally adapted populations resemble the environmentally induced phenotypes of ancestors; and (2) if plasticity, standing phenotypic variation and genetic divergence align during local adaptation. Phenotypic variation increased marginally in foreign environments but, as predicted, the direction of ancestral plasticity was generally well aligned with the phenotypic difference between locally adapted populations, making plasticity appear to "take the lead" in adaptive evolution. Plastic responses were sometimes more extreme than the phenotypes of locally adapted plants, which can give the impression that plasticity and evolutionary adaptation oppose each other; however, environmentally induced and locally adapted phenotypes were rarely misaligned. Adaptive fine‐tuning of phenotypes—genetic accommodation—did not fall along the main axis of standing phenotypic variation or the direction of plasticity, and local adaptation did not consistently modify the direction or magnitude of plasticity. These results suggest that plasticity is a persistent source of developmental bias that shapes how plant populations adapt to environmental change, even when plasticity does not constrain how populations respond to selection.

Developmental plasticity shapes social traits and selection in a facultatively eusocial bee

Developmental processes are an important source of phenotypic variation, but the extent to which this variation contributes to evolutionary change is unknown. We used integrative genomic analyses to explore the relationship between developmental and social plasticity in a bee species that can adopt either a social or solitary lifestyle. We find genes regulating this social flexibility also regulate development, and positive selection on these genes is influenced by their function during development. This suggests that developmental plasticity may influence the evolution of sociality. Our additional finding of genetic variants linked to differences in social behavior sheds light on how phenotypic variation derived from development may become encoded into the genome, and thus contribute to evolutionary change.

Developmental plasticity generates phenotypic variation, but how it contributes to evolutionary change is unclear. Phenotypes of individuals in caste-based (eusocial) societies are particularly sensitive to developmental processes, and the evolutionary origins of eusociality may be rooted in developmental plasticity of ancestral forms. We used an integrative genomics approach to evaluate the relationships among developmental plasticity, molecular evolution, and social behavior in a bee species (Megalopta genalis) that expresses flexible sociality, and thus provides a window into the factors that may have been important at the evolutionary origins of eusociality. We find that differences in social behavior are derived from genes that also regulate sex differentiation and metamorphosis. Positive selection on social traits is influenced by the function of these genes in development. We further identify evidence that social polyphenisms may become encoded in the genome via genetic changes in regulatory regions, specifically in transcription factor binding sites. Taken together, our results provide evidence that developmental plasticity provides the substrate for evolutionary novelty and shapes the selective landscape for molecular evolution in a major evolutionary innovation: Eusociality.

Transgenerational acclimation to changes in ocean acidification in marine invertebrates

The rapid pace of increasing oceanic acidity poses a major threat to the fitness of the marine ecosystem, as well as the buffering capacity of the oceans. Disruption in chemical equilibrium in the ocean leads to decreased carbonate ion precipitation, resulting in calcium carbonate saturation. If these trends continue, calcifying invertebrates will experience difficultly maintaining their calcium carbonate exoskeleton and shells. Because malfunction of exoskeleton formation by calcifiers in response to ocean acidification (OA) will have non-canonical biological cascading results in the marine ecosystem, many studies have investigated the direct and indirect consequences of OA on ecosystem- and physiology-related traits of marine invertebrates. Considering that evolutionary adaptation to OA depends on the duration of OA effects, long-term exposure to OA stress over multi-generations may result in adaptive mechanisms that increase the potential fitness of marine invertebrates in response to OA. Transgenerational studies have the potential to elucidate the roles of acclimation, carryover effects, and evolutionary adaptation within and over generations in response to OA. In particular, understanding mechanisms of transgenerational responses (e.g., antioxidant responses, metabolic changes, epigenetic reprogramming) to changes in OA will enhance our understanding of marine invertebrate in response to rapid climate change.

Transgenerational plasticity of inducible defences: Combined effects of grand-parental, parental and current environments

Phenotypic plasticity can occur across generations (transgenerational plasticity) when environments experienced by the previous generations influenced offspring phenotype. The evolutionary importance of transgenerational plasticity, especially regarding within-generational plasticity, is a currently hot topic in the plasticity framework. How long an environmental effect can persist across generations and whether multigenerational effects are cumulative are primordial-for the evolutionary significance of transgenerational plasticity-but still unresolved questions. In this study, we investigated how the grand-parental, parental and offspring exposures to predation cues shape the predator-induced defences of offspring in the Physa acuta snail. We expected that the offspring phenotypes result from a three-way interaction among grand-parental, parental and offspring environments. We exposed three generations of snails without and with predator cues according to a full factorial design and measured offspring inducible defences. We found that both grand-parental and parental exposures to predator cues impacted offspring antipredator defences, but their effects were not cumulative and depended on the defences considered. We also highlighted that the grand-parental environment did alter reaction norms of offspring shell thickness, demonstrating an interaction between the grand-parental transgenerational plasticity and the within-generational plasticity. We concluded that the effects of multigenerational exposure to predator cues resulted on complex offspring phenotypic patterns which are difficult to relate to adaptive antipredator advantages.

Aged virgin adults respond to extreme heat events with phenotypic plasticity in an invasive species, Drosophila suzukii

Climate warming has increased the frequency of extreme heat events. Alien species usually invade new areas with a low-density population and often have limited mating opportunities due to the unsynchronized emergence of adults. Early-emerging virgin adults often have to wait to mate with later-emerging partners at the cost of aging, which reduces thermal tolerance. To understand the adaptive strategies of virgin males/females versus those of mated males/females in response to heat stress during aging, we conducted a fully factorial experiment to test the basal and plastic heat tolerance (CTmax, critical thermal maximum) of males and females with different mating statuses (virgin and mated) at different ages (5, 10, and 15 days after eclosion) after different acclimation regimes (null, rapid and developmental heat acclimation) in a well-known invasive species, Drosophila suzukii. We found that mating could change the heat tolerance of adults during aging. Mated females had higher basal heat tolerance than virgin females, while mated males had lower tolerance than virgin males. Mating could generally decrease the acclimation capacity (i.e., plasticity of heat tolerance) during aging. Aged virgin adults had a much higher acclimation capacity than aged mated adults. Our findings suggest that phenotypic plasticity of heat tolerance may be a main strategy used by virgin adults to cope with heat events. The phenotypic plasticity of thermal tolerance could increase the invasion success of alien species in new areas by allowing them to rapid respond to local temperature changes.

The SWI/SNF ATP-Dependent Chromatin Remodeling Complex in Arabidopsis Responds to Environmental Changes in Temperature-Dependent Manner

SWI/SNF ATP-dependent chromatin remodeling complexes (CRCs) play important roles in the regulation of transcription, cell cycle, DNA replication, repair, and hormone signaling in eukaryotes. The core of SWI/SNF CRCs composed of a SWI2/SNF2 type ATPase, a SNF5 and two of SWI3 subunits is sufficient for execution of nucleosome remodeling in vitro. The Arabidopsis genome encodes four SWI2/SNF2 ATPases, four SWI3, a single SNF5 and two SWP73 subunits. Genes of the core SWI/SNF components have critical but not fully overlapping roles during plant growth, embryogenesis, and sporophyte development. Here we show that the Arabidopsis swi3c mutant exhibits a phenotypic reversion when grown at lower temperature resulting in partial restoration of its embryo, root development and fertility defects. Our data indicates that the swi3c mutation alters the expression of several genes engaged in low temperature responses. The location of SWI3C-containing SWI/SNF CRCs on the ICE1, MYB15 and CBF1 target genes depends on the temperature conditions, and the swi3c mutation thus also influences the transcription of several cold-responsive (COR) genes. These findings, together with genetic analysis of swi3c/ice1 double mutant and enhanced freezing tolerance of swi3c plants illustrate that SWI/SNF CRCs contribute to fine-tuning of plant growth responses to different temperature regimes.

Early-exposure to new sex pheromone blends alters mate preference in female butterflies and in their offspring

While the diversity of sex pheromone communication systems across insects is well documented, the mechanisms that lead to such diversity are not well understood. Sex pheromones constitute a species-specific system of sexual communication that reinforces interspecific reproductive isolation. When odor blends evolve, the efficacy of male-female communication becomes compromised, unless preference for novel blends also evolves. We explore odor learning as a possible mechanism leading to changes in sex pheromone preferences in the butterfly Bicyclus anynana. Our experiments reveal mating patterns suggesting that mating bias for new blends can develop following a short learning experience, and that this maternal experience impacts the mating outcome of offspring without further exposure. We propose that odor learning can be a key factor in the evolution of sex pheromone blend recognition and in chemosensory speciation.

Ecological change in dynamic environments: Accounting for temporal environmental variability in studies of ocean change biology

The environmental conditions in the ocean have long been considered relatively more stable through time compared to the conditions on land. Advances in sensing technologies, however, are increasingly revealing substantial fluctuations in abiotic factors over ecologically and evolutionarily relevant timescales in the ocean, leading to a growing recognition of the dynamism of the marine environment as well as new questions about how this dynamism may influence species' vulnerability to global environmental change. In some instances, the diurnal or seasonal variability in major environmental change drivers, such as temperature, pH and seawater carbonate chemistry, and dissolved oxygen, can exceed the changes expected with continued anthropogenic global change. While ocean global change biologists have begun to experimentally test how variability in environmental conditions mediates species' responses to changes in the mean, the extensive literature on species' adaptations to temporal variability in their environment and the implications of this variability for their evolutionary responses has not been well integrated into the field. Here, we review the physiological mechanisms underlying species' responses to changes in temperature, pCO₂ /pH (and other carbonate parameters), and dissolved oxygen, and discuss what is known about behavioral, plastic, and evolutionary strategies for dealing with variable environments. In addition, we discuss how exposure to variability may influence species' responses to changes in the mean conditions and highlight key research needs for ocean global change biology.