Physiology evolves convergently but lags behind warming in cities

Cities, through the generation of urban heat islands, provide a venue for exploring contemporary convergent evolution to climatic warming. We quantified how repeatable the evolution of heat tolerance, cold tolerance, and body size were among diverse lineages in response to urban heat islands. Our study revealed significant shifts towards higher heat tolerance and diminished cold tolerance among urban populations. We further found that the magnitude of trait divergence was significantly and positively associated with the magnitude of the urban heat island, suggesting that temperature played a major role in the observed divergence in thermal tolerance. Despite these trends, the magnitude of trait responses lagged behind environmental warming. Heat tolerance responses exhibited a deficit of 0.84°C for every 1°C increase in warming, suggesting limits on adaptive evolution and consequent adaptational lags. Other moderators were predictive of greater divergence in heat tolerance, including lower baseline tolerance and greater divergence in body size. Although terrestrial species did not exhibit systematic shifts towards larger or smaller body size, aquatic species exhibited significant shifts towards smaller body size in urban habitats. Our study demonstrates how cities can be used to address long-standing questions in evolutionary biology regarding the repeatability of evolution. Importantly, this work also shows how cities can be used as forecasting tools by quantifying adaptational lags and by developing trait-based associations with responses to contemporary warming.

Skeletal muscle BMAL1 is necessary for transcriptional adaptation of local and peripheral tissues in response to endurance exercise training

Objectives

In this investigation, we addressed the contribution of the core circadian clock factor, BMAL1, in skeletal muscle to both acute transcriptional responses to exercise and transcriptional remodelling in response to exercise training. Additionally, we adopted a systems biology approach to investigate how loss of skeletal muscle BMAL1 altered peripheral tissue homeostasis as well as exercise training adaptations in iWAT, liver, heart, and lung of male mice.

Methods

Combining inducible skeletal muscle specific BMAL1 knockout mice, physiological testing and standardized exercise protocols, we performed a multi-omic analysis (transcriptomics, chromatin accessibility and metabolomics) to explore loss of muscle BMAL1 on muscle and peripheral tissue responses to exercise.

Results

Muscle-specific BMAL1 knockout mice demonstrated a blunted transcriptional response to acute exercise, characterized by the lack of upregulation of well-established exercise responsive transcription factors including Nr4a3 and Ppargc1a. Six weeks of exercise training in muscle-specific BMAL1 knockout mice induced significantly greater and divergent transcriptomic and metabolomic changes in muscle. Surprisingly, liver, lung, inguinal white adipose and heart showed divergent exercise training transcriptomes with less than 5% of 'exercise-training' responsive genes shared for each tissue between genotypes.

Conclusion

Our investigation has uncovered the critical role that BMAL1 plays in skeletal muscle as a key regulator of gene expression programs for both acute exercise and training adaptations. In addition, our work has uncovered the significant impact that altered exercise response in muscle plays in the peripheral tissue adaptation to exercise training. We also note that the transcriptome adaptations to steady state training suggest that without BMAL1, skeletal muscle does not achieve the expected homeostatic program. Our work also demonstrates that if the muscle adaptations diverge to a more maladaptive state this is linked to increased inflammation across many tissues. Understanding the molecular targets and pathways contributing to health vs. maladaptive exercise adaptations will be critical for the next stage of therapeutic design for exercise mimetics.

Reproductive biology of Gazella arabica: Predictors of offspring weight and short- and long-term offspring survival

Reproductive traits are central to organismal fitness, and so the factors influencing patterns of reproduction and offspring survival are at the heart of biology. Making use of breeding data collected over 16 years at the King Khalid Wildlife Research Centre in Saudi Arabia, we investigated the reproductive biology of Arabian gazelles Gazella arabica. Offspring survival was mainly a function of birth weight, with heavier offspring having higher survival rates than lighter offspring. However, while sons were heavier than daughters, daughters had higher survival rates. We could not find evidence that giving birth to sons negatively impacts offspring weight in the following year. We uncovered large narrow-sense heritability (h2) in offspring weight at birth, while maternal effects (m2) on birth weight were of lesser importance. However, maternal effects on offspring survival were strong until weaning age, while paternal effects dominated survival to sexual maturity and first reproduction. We propose that variation in maternal postnatal care might overshadow the effects of maternal inheritance of birth weights, while the overall strong heritability of weight at birth and the paternal effects on survival illustrates strong variance in sire fitness based on genetic quality, suggesting a role for sexual selection by female mate choice in wild populations.

Single-fly assemblies fill major phylogenomic gaps across the Drosophilidae Tree of Life

Long-read sequencing is driving rapid progress in genome assembly across all major groups of life, including species of the family Drosophilidae, a longtime model system for genetics, genomics, and evolution. We previously developed a cost-effective hybrid Oxford Nanopore (ONT) long-read and Illumina short-read sequencing approach and used it to assemble 101 drosophilid genomes from laboratory cultures, greatly increasing the number of genome assemblies for this taxonomic group. The next major challenge is to address the laboratory culture bias in taxon sampling by sequencing genomes of species that cannot easily be reared in the lab. Here, we build upon our previous methods to perform amplification-free ONT sequencing of single wild flies obtained either directly from the field or from ethanol-preserved specimens in museum collections, greatly improving the representation of lesser studied drosophilid taxa in whole-genome data. Using Illumina Novaseq X Plus and ONT P2 sequencers with R10.4.1 chemistry, we set a new benchmark for inexpensive hybrid genome assembly at US $150 per genome while assembling genomes from as little as 35 ng of genomic DNA from a single fly. We present 183 new genome assemblies for 179 species as a resource for drosophilid systematics, phylogenetics, and comparative genomics. Of these genomes, 62 are from pooled lab strains and 121 from single adult flies. Despite the sample limitations of working with small insects, most single-fly diploid assemblies are comparable in contiguity (>1Mb contig N50), completeness (>98% complete dipteran BUSCOs), and accuracy (>QV40 genome-wide with ONT R10.4.1) to assemblies from inbred lines. We present a well-resolved multi-locus phylogeny for 360 drosophilid and 4 outgroup species encompassing all publicly available (as of August 2023) genomes for this group. Finally, we present a Progressive Cactus whole-genome, reference-free alignment built from a subset of 298 suitably high-quality drosophilid genomes. The new assemblies and alignment, along with updated laboratory protocols and computational pipelines, are released as an open resource and as a tool for studying evolution at the scale of an entire insect family.

Female lizards (Eremias argus) reverse Bergmann's rule across altitude

The evolution of body size within and among species is predicted to be influenced by multifarious environmental factors. However, the specific drivers of body size variation have remained difficult to understand because of the wide range of proximate factors that covary with ectotherm body sizes across populations with varying local environmental conditions. Here, we used female Eremias argus lizards collected from different populations across their wide range in China, and constructed linear mixed models to assess how climatic conditions and/or available resources at different altitudes shape the geographical patterns of lizard body size across altitude. Lizard populations showed significant differences in body size across altitudes. Furthermore, we found that climatic and seasonal changes along the altitudinal gradient also explained variations in body size among populations. Specifically, body size decreased with colder and drier environmental conditions at high altitudes, reversing Bergmann's rule. Limited resources at high altitudes, measured by the low vegetative index, may also constrain body size. Therefore, our study demonstrates that multifarious environmental factors could strongly influence the intraspecific variation in organisms' body size.

An alternative mechanism for skeletal muscle dysfunction in long-term post-viral lung disease

Chronic lung disease is often accompanied by disabling extrapulmonary symptoms, notably skeletal muscle dysfunction and atrophy. Moreover, the severity of respiratory symptoms correlates with decreased muscle mass and in turn lowered physical activity and survival rates. Previous models of muscle atrophy in chronic lung disease often modeled chronic obstructive pulmonary disease (COPD) and relied on cigarette smoke exposure and LPS stimulation, but these conditions independently affect skeletal muscle even without accompanying lung disease. Moreover, there is an emerging and pressing need to understand the extrapulmonary manifestations of long-term post-viral lung disease (PVLD) as found in COVID-19. Here, we examine the development of skeletal muscle dysfunction in the setting of chronic pulmonary disease caused by infection due to the natural pathogen Sendai virus using a mouse model of PVLD. We identify a significant decrease in myofiber size when PVLD is maximal at 49 days after infection. We find no change in the relative types of myofibers, but the greatest decrease in fiber size is localized to fast-twitch-type IIB myofibers based on myosin heavy chain immunostaining. Remarkably, all biomarkers of myocyte protein synthesis and degradation (total RNA, ribosomal abundance, and ubiquitin-proteasome expression) were stable throughout the acute infectious illness and chronic post-viral disease process. Together, the results demonstrate a distinct pattern of skeletal muscle dysfunction in a mouse model of long-term PVLD. The findings thereby provide new insights into prolonged limitations in exercise capacity in patients with chronic lung disease after viral infections and perhaps other types of lung injury.NEW & NOTEWORTHY Our study used a mouse model of post-viral lung disease to study the impact of chronic lung disease on skeletal muscle. The model reveals a decrease in myofiber size that is selective for specific types of myofibers and an alternative mechanism for muscle atrophy that might be independent of the usual markers of protein synthesis and degradation. The findings provide a basis for new therapeutic strategies to correct skeletal muscle dysfunction in chronic respiratory disease.

Keep your cool: Overwintering physiology in response to urbanization in the acorn ant, Temnothorax curvispinosus

Winter presents a challenge for survival, yet temperate ectotherms have remarkable physiological adaptations to cope with low-temperature conditions. Under recent climate change, rather than strictly relaxing pressure on overwintering survival, warmer winters can instead disrupt these low-temperature trait-environment associations, with negative consequences for populations. While there is increasing evidence of physiological adaptation to contemporary warming during the growing season, the effects of winter warming on physiological traits are less clear. To address this knowledge gap, we performed a common garden experiment using relatively warm-adapted versus cold-adapted populations of the acorn ant, Temnothorax curvispinosus, sampled across an urban heat island gradient, to explore the effects of winter conditions on plasticity and evolution of physiological traits. We found no evidence of evolutionary divergence in chill coma recovery nor in metabolic rate at either of two test temperatures (4 and 10 °C). Although we found the expected plastic response of increased metabolic rate under the 10 °C acute test temperature as compared with the 4 °C test temperature, this plastic response, (i.e., the acute thermal sensitivity of metabolic rate), was not different across populations. Surprisingly, we found that winter-acclimated urban ant populations exhibited higher heat tolerance compared with rural ant populations, and that the magnitude of divergence was comparable to that observed among growing-season acclimated ants. Finally, we found no evidence of differences between populations with respect to changes in colony size from the beginning to the end of the overwintering experiment. Together, these findings indicate that despite the evolution of higher heat tolerance that is often accompanied by losses in low-temperature tolerance, urban acorn ants have retained several components of low-temperature physiological performance when assessed under ecologically relevant overwintering conditions. Our study suggests the importance of measuring physiological traits under seasonally-relevant conditions to understand the causes and consequences of evolutionary responses to contemporary warming.

Developing A Conceptual Framework for Early Intervention Vocational Rehabilitation for People Following Spinal Cord Injury

PURPOSE

Early intervention vocational rehabilitation (EIVR) can improve return to work (RTW) outcomes for people with spinal cord injury (SCI). However, mechanisms explaining how and why EIVR works are not well understood. This study aims to develop a conceptual framework describing key mechanisms of EIVR intervention effect following SCI.

METHODS

We synthesised data from a realist literature review with data from interviews of people with SCI (n = 30), a survey of people with SCI who had received EIVR (n = 37), a focus group of EIVR providers and a focus group of community vocational providers. We first synthesised the literature review and interviews to develop an initial programme theory describing the contexts in which mechanisms are activated to produce EIVR outcomes. Then we used data from the survey and focus groups to further refine the EIVR programme theory. Finally, a conceptual framework was developed to support knowledge dissemination.

RESULTS

By ensuring consistent messaging across the multi-disciplinary team, EIVR programmes establish and maintain hope that work is possible following injury. Conversations about work allow individuals to determine the priority of work following injury. These conversations can also improve self-efficacy by providing individualized support to envisage pathways toward RTW goals and maintain worker identity. The synthesised study findings highlight the contexts and resources required to trigger activation of these mechanisms.

CONCLUSIONS

EIVR key mechanisms of effect are not specific to SCI as a health condition, therefore enabling this framework to be applied to other populations who face similar impairments and return to work barriers.

Metabolism and exercise: the skeletal muscle clock takes centre stage

Circadian rhythms that influence mammalian homeostasis and overall health have received increasing interest over the past two decades. The molecular clock, which is present in almost every cell, drives circadian rhythms while being a cornerstone of physiological outcomes. The skeletal muscle clock has emerged as a primary contributor to metabolic health, as the coordinated expression of the core clock factors BMAL1 and CLOCK with the muscle-specific transcription factor MYOD1 facilitates the circadian and metabolic programme that supports skeletal muscle physiology. The phase of the skeletal muscle clock is sensitive to the time of exercise, which provides a rationale for exploring the interactions between the skeletal muscle clock, exercise and metabolic health. Here, we review the underlying mechanisms of the skeletal muscle clock that drive muscle physiology, with a particular focus on metabolic health. Additionally, we highlight the interaction between exercise and the skeletal muscle clock as a means of reinforcing metabolic health and discuss the possible implications of the time of exercise as a chronotherapeutic approach.

Time for Exercise? Exercise and Its Influence on the Skeletal Muscle Clock

Circadian rhythms drive our daily behaviors to coincide with the earth's rotation on an approximate 24-h cycle. The circadian clock mechanism present in nearly every cell is responsible for our circadian rhythms and is comprised of a transcriptional-translational feedback loop in mammals. The central clock resides in the hypothalamus responding to external light cues, whereas peripheral clocks receive signals from the central clock and are also sensitive to cues from feeding and activity. Of the peripheral clocks, the skeletal muscle clock is particularly sensitive to exercise which has shown to be an important time-cue with the ability to influence and adjust the muscle clock phase in response to exercise timing. Since the skeletal muscle clock is also involved in the expression of tissue-specific gene expression-including glucoregulatory genes-this might suggest a role for exercise timing as a therapeutic strategy in metabolic diseases, like type 2 diabetes. Notably, those with type 2 diabetes have accompanied disruptions in their skeletal muscle clock mechanism which may also be related to the increased risk of type 2 diabetes seen among shift workers. Therefore, the direct influence of exercise on the skeletal muscle clock might support the use of exercise timing to provide disease-mitigating effects. Here, we highlight the potential use of time-of-day exercise as a chronotherapeutic tool within circadian medicine to improve the metabolic profile of type 2 diabetes and support long-term glycemic control, potentially working through the skeletal muscle clock and circadian physiology.

An alternative mechanism for skeletal muscle dysfunction in long-term post-viral lung disease

Chronic lung disease is often accompanied by disabling extrapulmonary symptoms, notably skeletal muscle dysfunction and atrophy. Moreover, the severity of respiratory symptoms correlates with decreased muscle mass and in turn lowered physical activity and survival rates. Previous models of muscle atrophy in chronic lung disease often modeled COPD and relied on cigarette smoke exposure and LPS-stimulation, but these conditions independently affect skeletal muscle even without accompanying lung disease. Moreover, there is an emerging and pressing need to understand the extrapulmonary manifestations of long-term post-viral lung disease (PVLD) as found in Covid-19. Here, we examine the development of skeletal muscle dysfunction in the setting of chronic pulmonary disease using a mouse model of PVLD caused by infection due to the natural pathogen Sendai virus. We identify a significant decrease in myofiber size when PVLD is maximal at 49 d after infection. We find no change in the relative types of myofibers, but the greatest decrease in fiber size is localized to fast-twitch type IIB myofibers based on myosin heavy chain immunostaining. Remarkably, all biomarkers of myocyte protein synthesis and degradation (total RNA, ribosomal abundance, and ubiquitin-proteasome expression) were stable throughout the acute infectious illness and chronic post-viral disease process. Together, the results demonstrate a distinct pattern of skeletal muscle dysfunction in a mouse model of long-term PVLD. The findings thereby provide new insight into prolonged limitations in exercise capacity in patients with chronic lung disease after viral infections and perhaps other types of lung injury.

Urban evolution of thermal physiology in a range-expanding, mycophagous fruit fly, Drosophila tripunctata

In Drosophila spp., their often high number of annual generations, large population sizes and large amounts of standing genetic variation should predispose them to undergo contemporary adaptation to climatic warming. However, a number of laboratory experimental evolution studies in this group of organisms suggest strong limits on the rate and magnitude of contemporary thermal adaptation. Here, we explore this discrepancy by examining the potential for rapid evolutionary divergence between wild populations of Drosophila tripunctata Loew, 1862 from rural and urban sites. We performed a multi-generation common garden study and found evidence for the evolution of higher heat tolerance (critical thermal maximum) in flies from urban populations. We also detected evolutionary divergence in cold resistance (chill coma recovery time), with diminished cold resistance in flies from urban populations, although the effect was weaker than the shift in heat tolerance. Our study provides evidence of contemporary urban thermal adaptation, although the magnitude of phenotypic change lagged the magnitude of environmental temperature change across the urbanization gradient, suggesting potential limits on the evolution of urban thermal physiology.

Adaptation to urban environments

Despite widespread evidence of urban evolution, the adaptive nature of these changes is often unclear. We review different phenotypic and molecular lines of evidence used for assessing urban adaptation, discussing the benefits and limitations of each approach, and rare examples of their integration. We then provide a synthesis of local adaptation to urban and rural environments. These data were drawn from phenotypic reciprocal transplant studies, the majority of which focus on insects and other arthropods. Broadly, we found support for local adaptation to urban and rural environments. However, there was asymmetry in the evidence for local adaptation depending on population of origin, with urban adaptation being less prevalent than rural adaptation, suggesting many urban populations are still adapting to urban environments. Further, the general patterns were underlain by considerable variation among study systems; we discuss how environmental heterogeneity and costs of adaptation might explain system-specific variation in urban-rural local adaptation. We then look to the future of urban adaptation research, considering the magnitude and direction of adaptation in context of different agents of selection including urban heat islands, chemical pollutants, and biotic interactions.

A Theory of City Biogeography and the Origin of Urban Species

Many of the choices humans make with regard to infrastructure, urban planning and other phenomena have impacts that will last thousands of years. This can readily be seen in modern cities in which contemporary streets run along street grids that were laid out thousands of years prior or even in which ancient viaducts still play a role. However, rarely do evolutionary biologists explicitly consider the future of life likely to be associated with the decisions we are making today. Here, we consider the evolutionary future of species in cities with a focus on the origin of lineages and species. We do so by adjusting evolutionary predictions from the theory of island biogeography so as to correspond to the unique features of cities as islands. Specifically, the species endemic to cities tend to be associated with the gray habitats in cities. Those habitats tend to be dominated by human bodies, pet bodies and stored food. It is among such species where the origin of new lineages is most likely, although most research on evolution in cities has focused on green habitats. We conclude by considering a range of scenarios for the far future and their implications for the origin of lineages and species.

Evolution in Cities

Although research performed in cities will not uncover new evolutionary mechanisms, it could provide unprecedented opportunities to examine the interplay of evolutionary forces in new ways and new avenues to address classic questions. However, while the variation within and among cities affords many opportunities to advance evolutionary biology research, careful alignment between how cities are used and the research questions being asked is necessary to maximize the insights that can be gained. In this review, we develop a framework to help guide alignment between urban evolution research approaches and questions. Using this framework, we highlight what has been accomplished to date in the field of urban evolution and identify several up-and-coming research directions for further expansion. We conclude that urban environments can be used as evolutionary test beds to tackle both new and long-standing questions in evolutionary biology.

Natural Selection on Adults Has Trait-Dependent Consequences for Juvenile Evolution in Dragonflies

AbstractAlthough natural selection often fluctuates across ontogeny, it remains unclear what conditions enable selection in one life-cycle stage to shape evolution in others. Organisms that undergo metamorphosis are useful for addressing this topic because their highly specialized life-cycle stages cannot always evolve independently despite their dramatic life-history transition. Using a comparative study of dragonflies, we examined three conditions that are hypothesized to allow selection in one stage to affect evolution in others. First, we tested whether lineages with less dramatic metamorphosis (e.g., hemimetabolous insects) lack the capacity for stage-specific evolution. Rejecting this hypothesis, we found that larval body shape evolves independently from selection on adult shape. Next, we evaluated whether stage-specific evolution is limited for homologous and/or coadapted structures. Indeed, we found that selection for larger wings is associated with the evolution of coadapted larval sheaths that store developing wing tissue. Finally, we assessed whether stage-specific evolution is restricted for traits linked to a single biochemical pathway. Supporting this hypothesis, we found that species with more wing melanization in the adult stage have evolved weaker melanin immune defenses in the larval stage. Thus, our results collectively show that natural selection in one stage imposes trait-dependent constraints on evolution in others.

In a nutshell, a reciprocal transplant experiment reveals local adaptation and fitness trade-offs in response to urban evolution in an acorn-dwelling ant

Urban-driven evolution is widely evident, but whether these changes confer fitness benefits and thus represent adaptive urban evolution is less clear. We performed a multiyear field reciprocal transplant experiment of acorn-dwelling ants across urban and rural environments. Fitness responses were consistent with local adaptation: we found a survival advantage of the "home" and "local" treatments compared to "away" and "foreign" treatments. Seasonal bias in survival was consistent with evolutionary patterns of gains and losses in thermal tolerance traits across the urbanization gradient. Rural ants in the urban environment were more vulnerable in the summer, putatively due to low heat tolerance, and urban ants in the rural environment were more vulnerable in winter, putatively due to an evolved loss of cold tolerance. The results for fitness via fecundity were also generally consistent with local adaptation, if somewhat more complex. Urban-origin ants produced more alates in their home versus away environment, and rural-origin ants had a local advantage in the rural environment. Overall, the magnitude of local adaptation was lower for urban ants in the novel urban environment compared with rural ants adapted to the ancestral rural environment, adding further evidence that species might not keep pace with anthropogenic change.

Physiological adaptation to cities as a proxy to forecast global-scale responses to climate change

Cities are emerging as a new venue to overcome the challenges of obtaining data on compensatory responses to climatic warming through phenotypic plasticity and evolutionary change. In this Review, we highlight how cities can be used to explore physiological trait responses to experimental warming, and also how cities can be used as human-made space-for-time substitutions. We assessed the current literature and found evidence for significant plasticity and evolution in thermal tolerance trait responses to urban heat islands. For those studies that reported both plastic and evolved components of thermal tolerance, we found evidence that both mechanisms contributed to phenotypic shifts in thermal tolerance, rather than plastic responses precluding or limiting evolved responses. Interestingly though, for a broader range of studies, we found that the magnitude of evolved shifts in thermal tolerance was not significantly different from the magnitude of shift in those studies that only reported phenotypic results, which could be a product of evolution, plasticity, or both. Regardless, the magnitude of shifts in urban thermal tolerance phenotypes was comparable to more traditional space-for-time substitutions across latitudinal and altitudinal clines in environmental temperature. We conclude by considering how urban-derived estimates of plasticity and evolution of thermal tolerance traits can be used to improve forecasting methods, including macrophysiological models and species distribution modelling approaches. Finally, we consider areas for further exploration including sub-lethal performance traits and thermal performance curves, assessing the adaptive nature of trait shifts, and taking full advantage of the environmental thermal variation that cities generate.

Evidence for the evolution of thermal tolerance, but not desiccation tolerance, in response to hotter, drier city conditions in a cosmopolitan, terrestrial isopod

Cities are often hotter and drier compared with nearby undeveloped areas, but how organisms respond to these multifarious stressors associated with urban heat islands is largely unknown. Terrestrial isopods are especially susceptible to temperature and aridity stress as they have retained highly permeable gills from their aquatic ancestors. We performed a two temperature common garden experiment with urban and rural populations of the terrestrial isopod, Oniscus asellus, to uncover evidence for plastic and evolutionary responses to urban heat islands. We focused on physiological tolerance traits including tolerance of heat, cold, and desiccation. We also examined body size responses to urban heat islands, as size can modulate physiological tolerances. We found that different mechanisms underlie responses to urban heat islands. While evidence suggests urban isopods may have evolved higher heat tolerance, urban and rural isopods had statistically indistinguishable cold and desiccation tolerances. In both populations, plasticity to warmer rearing temperature diminished cold tolerance. Although field-collected urban and rural isopods were the same size, rearing temperature positively affected body size. Finally, larger size improved desiccation tolerance, which itself was influenced by rearing temperature. Our study demonstrates how multifarious changes associated with urban heat islands will not necessarily contribute to contemporary evolution in each of the corresponding physiological traits.

Carryover effects and the evolution of polyphenism

An individual’s early-life environment and phenotype often influence its traits and performance as an adult. We investigated whether such ‘carryover effects’ are associated with alternative, environmentally-induced phenotypes (‘polyphenism’), and, if so, whether they influence the evolution of polyphenism. To do so, we studied Mexican spadefoot toads, Spea multiplicata, which have evolved a polyphenism consisting of two, dramatically different forms: a carnivore morph and an omnivore morph. We sampled both morphs from a fast-drying and a slow-drying pond and reared them to sexual maturity. Larval environment (pond) strongly influenced survival as well as age and size at metamorphosis and sexual maturity; i.e. environment-dependent carryover effects were present. By contrast, larval phenotype (morph) did not affect life-history traits at sexual maturity; i.e. phenotype-dependent carryover effects were absent. These results are consistent with theory, which suggests that by amplifying selective trade-offs in heterogenous environments, environment-dependent carryover effects might foster the evolution of polyphenism. At the same time, by freeing selection to refine a novel phenotype without altering the existing form, the absence of phenotype-dependent carryover effects might enable polyphenism to evolve in the first place. Generally, carryover effects might play an underappreciated role in the evolution of polyphenism.

Myogenic Cell Expression of Intercellular Adhesion Molecule-1 Contributes to Muscle Regeneration after Injury

This study investigated intercellular adhesion molecule-1 (ICAM-1), a membrane protein that mediates cell-to-cell adhesion and communication, as a mechanism through which the inflammatory response facilitates muscle regeneration after injury. Toxin-induced muscle injury to tibialis anterior muscles of wild-type mice caused ICAM-1 to be expressed by a population of satellite cells/myoblasts and myofibers. Myogenic cell expression of ICAM-1 contributed to the restoration of muscle structure after injury, as regenerating myofibers were more abundant and myofiber size was larger for wild-type compared with Icam1^-/- mice during 28 days of recovery. Contrastingly, restoration of muscle function after injury was similar between the genotypes. ICAM-1 facilitated the restoration of muscle structure after injury through mechanisms involving the regulation of myofiber branching, protein synthesis, and the organization of nuclei within myofibers after myogenic cell fusion. These findings provide support for a paradigm in which ICAM-1 expressed by myogenic cells after muscle injury augments their adhesive and fusogenic properties, which, in turn, facilitates regenerative and hypertrophic processes that restore structure to injured muscle.

Evolution is a double-edged sword, not a silver bullet, to confront global change

Although there is considerable optimism surrounding adaptive evolutionary responses to global change, relatively little attention has been paid to maladaptation in this context. In this review, we consider how global change might lead populations to become maladapted. We further consider how populations can evolve to new optima, fail to evolve and therefore remain maladapted, or become further maladapted through trait-driven or eco-evo-driven mechanisms after being displaced from their fitness optima. Our goal is to stimulate thinking about evolution as a "double-edged sword" that comprises both adaptive and maladaptive responses, rather than as a "silver bullet" or a purely adaptive mechanism to combat global change. We conclude by discussing how a better appreciation of environmentally driven maladaptation and maladaptive responses might improve our current understanding of population responses to global change and our ability to forecast future responses.

Remarkable insensitivity of acorn ant morphology to temperature decouples the evolution of physiological tolerance from body size under urban heat islands

Environmental temperature can alter body size and thermal tolerance, yet the effects of temperature rise on the size-tolerance relationship remain unclear. Terrestrial ectotherms with larger body sizes typically exhibit greater tolerance of high (and low) temperatures. However, while warming tends to increase tolerance of high temperatures through phenotypic plasticity and evolutionary change, warming tends to decrease body size through these mechanisms and thus might indirectly contribute to worse tolerance of high temperatures. These contrasting effects of warming on body size, thermal tolerance, and their relationship are increasingly important in light of global climate change. Here, we used replicated urban heat islands to explore the size-tolerance relationship in response to warming. We performed a common garden experiment with a small acorn-dwelling ant species collected from urban and rural populations across three different cities and reared under five laboratory rearing temperatures from 21 to 29 °C. We found that acorn ant body size was remarkably insensitive to laboratory rearing temperature (ant workers exhibited no phenotypic plasticity in body size across rearing temperature) and among populations experiencing cooler rural versus warmer urban environmental temperatures (no evolved differences in body size between urban and rural populations). Further, this insensitivity of body size to temperature was highly consistent across each of the three cities we examined. Because body size was robust to temperature variation, previously described plastic and evolved shifts in heat (and cold) tolerance in acorn ant responses to urbanization were shown to be independent of shifts in body size. Indeed, genetic (colony-level) correlations between heat and cold tolerance traits and body size revealed no significant association between size and tolerance. Our results show how typical trait correlations, such as between size and thermal tolerance, might be decoupled as populations respond to contemporary environmental change.

On the evolution of carry-over effects

The environment experienced early in life often affects the traits that are developed after an individual has transitioned into new life stages and environments. Because the phenotypes induced by earlier environments are then screened by later ones, these 'carry-over effects' influence fitness outcomes across the entire life cycle. While the last two decades have witnessed an explosion of studies documenting the occurrence of carry-over effects, little attention has been given to how they adapt and diversify. To aid future research in this area, we present a framework for the evolution of carry-over effects. Carry-over effects can evolve in two ways. First, the expression of traits later in life may become more or less dependent on the developmental processes of earlier stages (e.g., 'adaptive decoupling'). Genetic correlations between life stages then either strengthen or weaken. Alternatively, those influential developmental processes that begin early in life may become more or less sensitive to that earlier environment. Here, plasticity changes in all the traits that share those developmental pathways across the whole life cycle. Adaptive evolution of a carry-over effect is governed by selection on the induced phenotypes in the later stage, and also by selection on any developmentally linked traits in the earlier life stage. When these selective pressures conflict, the evolution of the carry-over effect will be biased towards maximizing performance in the life stage with stronger selection. Because life stages often contribute unequally to total fitness, the strength of selection in any one stage depends on: (a) the relationship between the traits and the stage-specific fitness components (e.g., juvenile survival, adult mating success), and (b) the reproductive value of the life stage. Considering the evolution of carry-over effects reveals several intriguing features of the evolution of life histories and phenotypic plasticity more generally. For instance, carry-over effects that manifest as maladaptive plasticity in one life stage may represent an adaptive strategy for maximizing fitness in stages with stronger selection. Additionally, adaptation to novel environments encountered early in the life cycle may be faster in the presence of carry-over effects that influence sexually selected traits.

Evolution, not transgenerational plasticity, explains the adaptive divergence of acorn ant thermal tolerance across an urban-rural temperature cline

Although studies increasingly disentangle phenotypic plasticity from evolutionary responses to environmental change, few test for transgenerational plasticity in this context. Here, we evaluate whether phenotypic divergence of acorn ants in response to urbanization is driven by transgenerational plasticity rather than evolution. F2 generation worker ants (offspring of laboratory-born queens) exhibited similar divergence among urban and rural populations as field-born worker ants, suggesting that evolutionary divergence rather than transgenerational plasticity was primarily responsible for shifts toward higher heat tolerance and diminished cold tolerance in urban acorn ants. Hybrid offspring from matings between urban and rural populations also indicated that evolutionary divergence was likely the primary mechanism underlying population differences in thermal tolerance. Specifically, thermal tolerance traits were not inherited either maternally or paternally in the hybrid pairings as would be expected for strong parental or grandparental effects mediated through a single sex. Urban-rural hybrid offspring provided further insight into the genetic architecture of thermal adaptation. Heat tolerance of hybrids more resembled the urban-urban pure type, whereas cold tolerance of hybrids more resembled the rural-rural pure type. As a consequence, thermal tolerance traits in this system appear to be influenced by dominance rather than being purely additive traits, and heat and cold tolerance might be determined by separate genes. Though transgenerational plasticity does not appear to explain divergence of acorn ant thermal tolerance, its role in divergence of other traits and across other urbanization gradients merits further study.

A roadmap for urban evolutionary ecology

Urban ecosystems are rapidly expanding throughout the world, but how urban growth affects the evolutionary ecology of species living in urban areas remains largely unknown. Urban ecology has advanced our understanding of how the development of cities and towns change environmental conditions and alter ecological processes and patterns. However, despite decades of research in urban ecology, the extent to which urbanization influences evolutionary and eco-evolutionary change has received little attention. The nascent field of urban evolutionary ecology seeks to understand how urbanization affects the evolution of populations, and how those evolutionary changes in turn influence the ecological dynamics of populations, communities, and ecosystems. Following a brief history of this emerging field, this Perspective article provides a research agenda and roadmap for future research aimed at advancing our understanding of the interplay between ecology and evolution of urban-dwelling organisms. We identify six key questions that, if addressed, would significantly increase our understanding of how urbanization influences evolutionary processes. These questions consider how urbanization affects nonadaptive evolution, natural selection, and convergent evolution, in addition to the role of urban environmental heterogeneity on species evolution, and the roles of phenotypic plasticity versus adaptation on species' abundance in cities. Our final question examines the impact of urbanization on evolutionary diversification. For each of these six questions, we suggest avenues for future research that will help advance the field of urban evolutionary ecology. Lastly, we highlight the importance of integrating urban evolutionary ecology into urban planning, conservation practice, pest management, and public engagement.

Urban heat islands advance the timing of reproduction in a social insect

For many species, the timing of life cycle events is advancing under contemporary global climate change. However, much less is known regarding phenological shifts as a result of other sources of anthropogenic change, such as urban warming. In both cases, progress has been hampered by a focus on phenological traits such as the timing of emergence, rather than the phenology of more directly related fitness traits such as the timing of reproduction. Here we explore how urban heat island effects shape the timing of reproduction in an acorn-dwelling ant. We used a common garden experiment with acorn ants collected from three cities in the eastern United States along a latitudinal gradient and reared long-term in the laboratory under five temperature treatments. This allowed us to quantify the effects of temperature on reproductive phenology across three scales-a biogeographic temperature cline, three urban vs. rural temperature comparisons, and five laboratory rearing temperatures. At our northernmost and southernmost cities (spanning 6° of latitude), we found both urbanization and warmer laboratory rearing temperature significantly advanced reproductive phenology; ants from the lowest latitude city also had earlier reproductive phenology compared with the higher latitude cities. In the field, the differences in urban versus rural acorn ant reproductive phenology translate to approximately one month earlier reproduction in the urban populations. For insects with synchronous mating events, such as ants, shifts in the already short window of time to reproduce could limit mating across environments, potentially leading to reproductive isolation between urban and rural populations.

Temperature shapes the costs, benefits and geographic diversification of sexual coloration in a dragonfly

The environment shapes the evolution of secondary sexual traits by determining how their costs and benefits vary across the landscape. Given the thermal properties of dark coloration generally, temperature should crucially influence the costs, benefits and geographic diversification of many secondary sexual colour patterns. We tested this hypothesis using sexually selected wing coloration in a dragonfly. We find that greater wing coloration heats males - the magnitude of which improves flight performance under cool conditions but dramatically reduces it under warm conditions. In a colder region of the species' range, behavioural observations of a wild population show that these thermal effects translate into greater territorial acquisition on thermally variable days. Finally, geo-referenced photographs taken by citizen scientists reveal that this sexually selected wing coloration is dramatically reduced in the hottest portions of the species' range. Collectively, our results underscore temperature's capacity to promote and constrain the evolution of sexual coloration.

A meta-analysis of the agents of selection on floral traits

Floral traits are hypothesized to evolve primarily in response to selection by pollinators. However, selection can also be mediated by other environmental factors. To understand the relative importance of pollinator-mediated selection and its variation among trait and pollinator types, we analyzed directional selection gradients on floral traits from experiments that manipulated the environment to identify agents of selection. Pollinator-mediated selection was stronger than selection by other biotic factors (e.g., herbivores), but similar in strength to selection by abiotic factors (e.g., soil water), providing partial support for the hypothesis that floral traits evolve primarily in response to pollinators. Pollinator-mediated selection was stronger on pollination efficiency traits than on other trait types, as expected if efficiency traits affect fitness via interactions with pollinators, but other trait types also affect fitness via other environmental factors. In addition to varying among trait types, pollinator-mediated selection varied among pollinator taxa: selection was stronger when bees, long-tongued flies, or birds were the primary visitors than when the primary visitors were Lepidoptera or multiple animal taxa. Finally, reducing pollinator access to flowers had a relatively small effect on selection on floral traits, suggesting that anthropogenic declines in pollinator populations would initially have modest effects on floral evolution.

Evolution of thermal tolerance and its fitness consequences: parallel and non-parallel responses to urban heat islands across three cities

The question of parallel evolution-what causes it, and how common it is-has long captured the interest of evolutionary biologists. Widespread urban development over the last century has driven rapid evolutionary responses on contemporary time scales, presenting a unique opportunity to test the predictability and parallelism of evolutionary change. Here we examine urban evolution in an acorn-dwelling ant species, focusing on the urban heat island signal and the ant's tolerance of these altered urban temperature regimes. Using a common-garden experimental design with acorn ant colonies collected from urban and rural populations in three cities and reared under five temperature treatments in the laboratory, we assessed plastic and evolutionary shifts in the heat and cold tolerance of F1 offspring worker ants. In two of three cities, we found evolved losses of cold tolerance, and compression of thermal tolerance breadth. Results for heat tolerance were more complex: in one city, we found evidence of simple evolved shifts in heat tolerance in urban populations, though in another, the difference in urban and rural population heat tolerance depended on laboratory rearing temperature, and only became weakly apparent at the warmest rearing temperatures. The shifts in tolerance appeared to be adaptive, as our analysis of the fitness consequences of warming revealed that while urban populations produced more sexual reproductives under warmer laboratory rearing temperatures, rural populations produced fewer. Patterns of natural selection on thermal tolerances supported our findings of fitness trade-offs and local adaptation across urban and rural acorn ant populations, as selection on thermal tolerance acted in opposite directions between the warmest and coldest rearing temperatures. Our study provides mixed support for parallel evolution of thermal tolerance under urban temperature rise, and, importantly, suggests the promising use of cities to examine parallel and non-parallel evolution on contemporary time scales.

Immune deployment increases larval vulnerability to predators and inhibits adult life-history traits in a dragonfly

While deploying immune defences early in ontogeny can trade-off with the production and maintenance of other important traits across the entire life cycle, it remains largely unexplored how features of the environment shape the magnitude or presence of these lifetime costs. Greater predation risk during the juvenile stage may particularly influence such costs by (1) magnifying the survival costs that arise from any handicap of juvenile avoidance traits and/or (2) intensifying allocation trade-offs with important adult traits. Here, we tested for predator-dependent costs of immune deployment within and across life stages using the dragonfly, Pachydiplax longipennis. We first examined how larval immune deployment affected two traits associated with larval vulnerability to predators: escape distance and foraging under predation risk. Larvae that were induced to mount an immune response had shorter escape distances but lower foraging activity in the presence of predator cues. We also induced immune responses in larvae and reared them through emergence in mesocosms that differed in the presence of large predatory dragonfly larvae (Aeshnidae spp.). Immune-challenged larvae had later emergence overall and lower survival in pools with predators. Immune-challenged males were also smaller at emergence and developed less sexually selected melanin wing coloration, but these effects were independent of predator treatment. Overall, these results highlight how mounting an immune defence early in ontogeny can have substantial ecological and physiological costs that manifest both within and across life stages.

Trade-offs between larval survival and adult ornament development depend on predator regime in a territorial dragonfly

Trade-offs between juvenile survival and the development of sexually selected traits can cause ontogenetic conflict between life stages that constrains adaptive evolution. However, the potential for ecological interactions to alter the presence or strength of these trade-offs remains largely unexplored. Antagonistic selection over the accumulation and storage of resources could be one common cause of environment-specific trade-offs between life stages: higher condition may simultaneously enhance adult ornament development and increase juvenile vulnerability to predators. We tested this hypothesis in an ornamented dragonfly (Pachydiplax longipennis). Higher larval body condition indeed enhanced the initial development of its intrasexually selected wing coloration, but was opposed by viability selection in the presence of large aeshnid predators. In contrast, viability selection did not oppose larval body condition in pools when aeshnids were absent, and was not affected when we manipulated cannibalism risk. Trade-offs between larval survival and ornament development, mediated through the conflicting effects of body condition, therefore occurred only under high predation risk. We additionally characterized how body condition influences several traits associated with predator avoidance. Although body condition did not affect burst distance, it did increase larval abdomen size, potentially making larvae easier targets for aeshnid predators. As high body condition similarly increases vulnerability to predators in many other animals, predator-mediated costs of juvenile resource accumulation could be a common, environment-specific limitation on the elaboration of sexually selected traits.

Gut microbiome composition is associated with cardiac disease in zoo-housed western lowland gorillas (Gorilla gorilla gorilla)

Cardiac disease is a leading cause of mortality in zoo-housed western lowland gorillas (Gorilla gorilla gorilla). The gut microbiome is associated with cardiac disease in humans and similarly the gut microbiome may be associated with cardiac diseases in close relatives of humans, such as gorillas. We assessed the relationship between cardiac disease and gut bacterial composition in eight zoo-housed male western lowland gorillas (N = 4 with and N = 4 without cardiac disease) utilizing 16S rRNA gene analysis on the Illumina MiSeq sequencing platform. We found bacterial composition differences between gorillas with and without cardiac disease. Bacterial operational taxonomic units from phyla Bacteroidetes, Spirochaetes, Proteobacteria and Firmicutes were significant indicators of cardiac disease. Our results suggest that further investigations between diet and cardiac disease could improve the management and health of zoo-housed populations of this endangered species.

Mechanisms of Change for Children Participating in Therapeutic Horse Riding: A Grounded Theory

AIM

To develop a model for understanding mechanisms of change in health outcomes for riders with disabilities participating in therapeutic horse riding (THR).

METHODS

Using grounded theory methods we collected and analyzed data from interviews with 16 child riders and 18 caregivers, teachers and primary therapists, and from participant-observation during THR sessions.

RESULTS

The central concept underpinning the model illustrating mechanisms of change was "gaining the tools to go on." Riders' experiences suggested the THR landscape (i.e., "where the tools are gathered") allowed for an expanded range of experiences in which riders could participate. Riders experienced an expansion of self-concept by learning to move, succeed, connect, and adapt (i.e., "the tools gathered") within the THR landscape. Riders then iteratively translated an expanded view of self into other environments, reflecting "how and where the tools are used."

CONCLUSION

Findings suggest that positive changes in health arise from riders' experiences of learning and agency within the THR therapeutic landscape, and from the influence of these experiences on a child's developing self-concept. This article considers the wider impact of THR on children's health, beyond a focus on changes in physical outcomes.

Precipitation drives global variation in natural selection

Climate change has the potential to affect the ecology and evolution of every species on Earth. Although the ecological consequences of climate change are increasingly well documented, the effects of climate on the key evolutionary process driving adaptation-natural selection-are largely unknown. We report that aspects of precipitation and potential evapotranspiration, along with the North Atlantic Oscillation, predicted variation in selection across plant and animal populations throughout many terrestrial biomes, whereas temperature explained little variation. By showing that selection was influenced by climate variation, our results indicate that climate change may cause widespread alterations in selection regimes, potentially shifting evolutionary trajectories at a global scale.

Larval body condition regulates predator-induced life-history variation in a dragonfly

Organisms with complex life cycles commonly exhibit adaptive plasticity in the timing of transitions between life stages. While the threat of predation is predicted to induce earlier transitions, empirical support has been equivocal. When predation risk affects both the propensity to transition to the next life stage and the ability to reach the energetic thresholds necessary to complete the transition, only those individuals in the best physiological condition may be able to accelerate development and emerge earlier. To test this hypothesis, we followed uniquely marked dragonfly larvae (Pachydiplax longipennis) through emergence in pools where we factorially manipulated the presence of a large heterospecific predator (Anax junius) and cannibalism risk via conspecific size variation. Consistent with our hypothesis, high-condition larvae were more likely to emerge in the presence of the heterospecific predator than in its absence, and low-condition larvae were more likely to emerge in its absence than in its presence. Moreover, high-condition larvae emerged earlier when cannibalism risk was high than when it was low. Predation risk therefore has condition-dependent effects on emergence. As predation risk frequently affects resource accumulation, similar mechanisms across taxa could commonly underlie the incongruence between empirical results and theoretical expectations for predator-induced life-history variation.

Intraspecific adaptive radiation: Competition, ecological opportunity, and phenotypic diversification within species

Intraspecific variation in resource-use traits can have profound ecological and evolutionary implications. Among the most striking examples are resource polymorphisms, where alternative morphs that utilize different resources evolve within a population. An underappreciated aspect of their evolution is that the same conditions that favor resource polymorphism-competition and ecological opportunity-might foster additional rounds of diversification within already existing morphs. We examined these issues in spadefoot toad tadpoles that develop into either a generalist "omnivore" or a specialist "carnivore" morph. Specifically, we assessed the morphological diversity of tadpoles from natural ponds and experimentally induced carnivores reared on alternative diets. We also surveyed natural ponds to determine if the strength of intramorph competition and the diversity and abundance of dietary resources (measures of ecological opportunity) influenced the diversity of within-morph variation. We found that five omnivore and four carnivore types were present in natural ponds; alternative diets led to shape differences, some of which mirrored variation in the wild; and both competition and ecological opportunity were associated with enhanced morphological diversity in natural ponds. Such fine-scale intraspecific variation might represent an underappreciated form of biodiversity and might constitute a crucible of evolutionary innovation and diversification.

Intercellular adhesion molecule-1 augments myoblast adhesion and fusion through homophilic trans-interactions

The overall objective of the study was to identify mechanisms through which intercellular adhesion molecule-1 (ICAM-1) augments the adhesive and fusogenic properties of myogenic cells. Hypotheses were tested using cultured myoblasts and fibroblasts, which do not constitutively express ICAM-1, and myoblasts and fibroblasts forced to express full length ICAM-1 or a truncated form lacking the cytoplasmic domain of ICAM-1. ICAM-1 mediated myoblast adhesion and fusion were quantified using novel assays and cell mixing experiments. We report that ICAM-1 augments myoblast adhesion to myoblasts and myotubes through homophilic trans-interactions. Such adhesive interactions enhanced levels of active Rac in adherent and fusing myoblasts, as well as triggered lamellipodia, spreading, and fusion of myoblasts through the signaling function of the cytoplasmic domain of ICAM-1. Rac inhibition negated ICAM-1 mediated lamellipodia, spreading, and fusion of myoblasts. The fusogenic property of ICAM-1-ICAM-1 interactions was restricted to myogenic cells, as forced expression of ICAM-1 by fibroblasts did not augment their fusion to ICAM-1+ myoblasts/myotubes. We conclude that ICAM-1 augments myoblast adhesion and fusion through its ability to self-associate and initiate Rac-mediated remodeling of the actin cytoskeleton.

The effect of acute aerobic exercise on hemostasis in obstructive sleep apnea

PURPOSE

Individuals with obstructive sleep apnea (OSA) have an altered hemostatic balance; however, the exercise response is less described. The purpose of this study is to determine the hemostatic response after acute aerobic exercise in obstructive sleep apnea.

METHODS

Eighteen males (nine OSA vs. nine controls) were recruited from the university and local community. Individuals with evidence of cardiovascular, pulmonary, or metabolic disease were excluded. An apnea-hypopnea index (AHI) of >5 was a criterion for OSA. Subjects performed a treadmill exercise test at 35 and 70% predicted VO₂ reserve during the morning hours. Pre-exercise blood samples were obtained after 15 min supine rest and within 2 min following exercise. Repeated measures ANOVA were performed for factor VIII antigen, tissue plasminogen activator (tPA) antigen, tPA activity, and PAI-1 activity. Correlational analysis compared resting and post-exercise hemostatic factors with age, BMI, and AHI.

RESULTS

Mean AHI was 13.00 ± 12.6. No exercise × condition interactions were observed for hemostatic markers. There was a main effect for exercise in factor VIII, tPA antigen, and tPA activity in both groups. PAI-1 activity tended to be elevated in OSA (145%) compared to controls which remained after exercise (205%) (P = 0.05). Post-exercise FVIII/Ag correlated with BMI (r = 0.52), while resting tPA/Ag correlated with AHI (r = 0.49) and age (r = 0.50).

CONCLUSION

The hemostatic response after acute aerobic exercise is unaffected in mild OSA, although PAI-1 activity seems to be elevated, reducing fibrinolytic potential. BMI seems to correlate with FVIII/Ag, while tPA/Ag is associated with AHI and age.