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Hard tissue formation patterns and rates reveal details of animal physiology, life history, and environment, but are understudied in reptiles. Here, we use fluorescence labels delivered in vivo and laser confocal scanning microscopy to study tooth and bone formation in a managed group of green iguanas (Iguana iguana , Linné 1758) kept for 1.5 years under experimentally controlled conditions and undergoing several dietary switches. We constrain rates of tooth elongation, which we observe to be slow when enamel is initially deposited (c. 9 µm/day), but then increases exponentially in the dentin root, reaching c. 55 µm/day or more after crown completion. We further constrain the total timing of tooth formation to ∼40–60 days, and observe highly variable timings of tooth resorption onset and replacement. Fluorescent labels clearly indicate cohorts of teeth recruited within Zahnreihen replacement waves, with faster sequential tooth recruitment and greater wave sizes posteriorly, where each wave initiates. Fluorescence further reveals enamel maturation after initial deposition. Rates of hard tissue formation in long bones range from 0.4 to 3.4 µm/day, correlating with animal weight gain and cortical bone recording the entire history of the experiment. We suggest additional labeling experiments to study hard tissue formation patterns in other reptiles, and propose strategies for chemical analyses of hard tissues in order to extract temporal information about past environments, behaviors, and diets from reptilian fossils throughout the Phanerozoic. [ABSTRACT FROM AUTHOR]

Pheromones are chemical signals that facilitate communication between animals, and most animals use pheromones for reproduction and other forms of social behavior. The identification of key ligands and olfactory receptors used for pheromonal communication provides insight into the sensory processing of these important cues. An individual's responses to pheromones can be plastic, as physiological status modulates behavioral outputs. In this review, we outline the mechanisms for pheromone sensation and highlight physiological mechanisms that modify pheromone-guided behavior. We focus on hormones, which regulate pheromonal communication across vertebrates including fish, amphibians, and rodents. This regulation may occur in peripheral olfactory organs and the brain, but the mechanisms remain unclear. While this review centers on research in fish, we will discuss other systems to provide insight into how hormonal mechanisms function across taxa. [ABSTRACT FROM AUTHOR]

Model organisms have long been used to characterize the vertebrate immune system, which is responsible for protecting the host from mechanical and pathogen-induced injuries, pathology, and disease development ([37]). Google Scholar Crossref Search ADS Google Preview WorldCat COPAC 59 Reiter RJ, Calvo JR, Karbownik M, Qi W, Tan DX. 2000. Google Scholar Crossref Search ADS Google Preview WorldCat COPAC 57 Pijanowski L, Jurecka P, Irnazarow I, Kepka M, Szwejser E, Verburg-van Kemenade BML, Chadzinska M. 2015. Google Scholar Crossref Search ADS PubMed WorldCat 42 Lima AS, de Figueredo AC, Floreste FR, Garcia-Neto PG, Gomes FR, Titon SCM. [Extracted from the article]

This paper reviews several aspects of immunoendocrinology and ecoimmunology in Brazilian species of anurans under investigation for more than a decade, including (1) patterns of annual covariation of circulating steroids, calling behavior and innate immunity, (2) endocrine and immune correlates of calling performance, (3) behavioral and physiological correlates of parasite load, (4) thermal sensitivity of immune function, and (5) endocrine and immunomodulation by experimental exposure to acute and chronic stressors, as well as to endocrine manipulations and simulated infections. Integrated results have shown an immunoprotective role of increased steroid plasma levels during reproductive activity in calling males. Moreover, a higher helminth parasite load is associated with changes in several behavioral and physiological traits under field conditions. We also found anuran innate immunity is generally characterized by eurythermy, with maximal performance observed in temperatures close to normal and fever thermal preferendum. Moreover, the aerobic scope of innate immune response is decreased at fever thermal preferendum. Experimental exposure to stressors results in increased corticosterone plasma levels and immune redistribution, with an impact on immune function depending on the duration of the stress exposure. Interestingly, the fate of immunomodulation by chronic stressors also depends in part on individual body condition. Acute treatment with corticosterone generally enhances immune function, while prolonged exposure results in immunosuppression. Still, the results of hormonal treatment are complex and depend on the dose, duration of treatment, and the immune variable considered. Finally, simulated infection results in complex modulation of the expression of cytokines, increased immune function, activation of the Hypothalamus-Pituitary-Interrenal axis, and decreased activity of the Hypothalamus-Pituitary-Gonadal axis, as well as reduced melatonin plasma levels, suggesting that anurans have a functional Immune-Pineal axis, homologous to that previously described for mammals. These integrated and complementary approaches have contributed to a better understanding of physiological mechanisms and processes, as well as ecological and evolutionary implications of anuran immunoendocrinology. [ABSTRACT FROM AUTHOR]

Larger animals studied during ontogeny, across populations, or across species, usually have lower mass-specific metabolic rates than smaller animals (hypometric scaling). This pattern is usually observed regardless of physiological state (e.g. basal, resting, field, and maximally active). The scaling of metabolism is usually highly correlated with the scaling of many life-history traits, behaviors, physiological variables, and cellular/molecular properties, making determination of the causation of this pattern challenging. For across-species comparisons of resting and locomoting animals (but less so for across populations or during ontogeny), the mechanisms at the physiological and cellular level are becoming clear. Lower mass-specific metabolic rates of larger species at rest are due to (a) lower contents of expensive tissues (brains, liver, and kidneys), and (b) slower ion leak across membranes at least partially due to membrane composition, with lower ion pump ATPase activities. Lower mass-specific costs of larger species during locomotion are due to lower costs for lower-frequency muscle activity, with slower myosin and Ca++ ATPase activities, and likely more elastic energy storage. The evolutionary explanation(s) for hypometric scaling remain(s) highly controversial. One subset of evolutionary hypotheses relies on constraints on larger animals due to changes in geometry with size; for example, lower surface-to-volume ratios of exchange surfaces may constrain nutrient or heat exchange, or lower cross-sectional areas of muscles and tendons relative to body mass ratios would make larger animals more fragile without compensation. Another subset of hypotheses suggests that hypometric scaling arises from biotic interactions and correlated selection, with larger animals experiencing less selection for mass-specific growth or neurolocomotor performance. An additional third type of explanation comes from population genetics. Larger animals with their lower effective population sizes and subsequent less effective selection relative to drift may have more deleterious mutations, reducing maximal performance and metabolic rates. Resolving the evolutionary explanation for the hypometric scaling of metabolism and associated variables is a major challenge for organismal and evolutionary biology. To aid progress, we identify some variation in terminology use that has impeded cross-field conversations on scaling. We also suggest that promising directions for the field to move forward include (1) studies examining the linkages between ontogenetic, population-level, and cross-species allometries; (2) studies linking scaling to ecological or phylogenetic context; (3) studies that consider multiple, possibly interacting hypotheses; and (4) obtaining better field data for metabolic rates and the life history correlates of metabolic rate such as lifespan, growth rate, and reproduction. [ABSTRACT FROM AUTHOR]

Females and males can exhibit striking differences in body size, relative trait size, physiology, and behavior. As a consequence, the sexes can have very different rates of whole-body energy use, or converge on similar rates through different physiological mechanisms. Yet many studies that measure the relationship between metabolic rate and body size only pay attention to a single sex (more often males), or do not distinguish between sexes. We present four reasons why explicit attention to energy-use between the sexes can yield insight into the physiological mechanisms that shape broader patterns of metabolic scaling in nature. First, the sexes often differ considerably in their relative investment in reproduction, which shapes much of life-history and rates of energy use. Second, males and females share a majority of their genome but may experience different selective pressures. Sex-specific energy profiles can reveal how the energetic needs of individuals are met despite the challenge of within-species genetic constraints. Third, sexual selection often pushes growth and behavior to physiological extremes. Exaggerated sexually selected traits are often most prominent in one sex, can comprise up to 50% of body mass, and thus provide opportunities to uncover energetic constraints of trait growth and maintenance. Finally, sex-differences in behavior such as mating-displays, long-distance dispersal, and courtship can lead to drastically different energy allocation among the sexes; the physiology to support this behavior can shape patterns of metabolic scaling. The mechanisms underlying metabolic scaling in females, males, and hermaphroditic animals can provide opportunities to develop testable predictions that enhance our understanding of energetic scaling patterns in nature. [ABSTRACT FROM AUTHOR]

Bivalve molluscs have been the focus of behavioral and physiological studies for over a century, due in part to the relative ease with which their traits can be observed. The author reviews historical methods for monitoring behavior and physiology in bivalves, and how modern methods with electronic sensors can allow for a number of parameters to be measured in a variety of conditions using low-cost components and open-source tools. Open-source hardware and software tools can allow researchers to design and build custom monitoring systems to sample organismal processes and the environment, systems that can be tailored to the particular needs of a research program. The ability to leverage shared hardware and software can streamline the development process, providing greater flexibility to researchers looking to expand the number of traits they can measure, the frequency and duration of sampling, and the number of replicate devices they can afford to deploy. [ABSTRACT FROM AUTHOR]

Nature provides the parameters, or boundaries, within which organisms must cope in order to survive. Therefore, ecological conditions have an unequivocal influence on the ability of organisms to perform the necessary functions for survival. Biomechanics brings together physics and biology to understand how an organism will function under a suite of conditions. Despite a relatively rich recent history linking physiology and morphology with ecology, less attention has been paid to the linkage between biomechanics and ecology. This linkage, however, could provide key insights into patterns and processes of evolution. Ecomechanics, also known as ecological biomechanics or mechanical ecology, is not necessarily new, but has received far less attention than ecophysiology or ecomorphology. Here, we briefly review the history of ecomechanics, and then identify what we believe are grand challenges for the discipline and how they can inform some of the most pressing questions in science today, such as how organisms will cope with global change. [ABSTRACT FROM AUTHOR]

Ecological physiologists and biomechanists have investigated swimming performance in a diversity of fishes; however, the connection between form, function, and energetics of locomotion has been rarely evaluated in the same system and under climate change scenarios. In this perspective, I argue that working within the framework of "EcoPhysioMechanics," i.e. integrating energetics and biomechanics tools, to measure locomotor performance and behavior under different abiotic factors, improves our understanding of the mechanisms, limits and costs of movement. To demonstrate how EcoPhysioMechanics can be applied to locomotor studies, I outline how linking biomechanics and physiology allows us to understand how fishes may modulate their movement to achieve high speeds or reduce the costs of locomotion. I also discuss how the framework is necessary to quantify swimming capacity under climate change scenarios. Finally, I discuss current dearth of integrative studies and gaps in empirical datasets that are necessary to understand fish swimming under changing environments. [ABSTRACT FROM AUTHOR]

It has long been known that the outcome of species interactions depends on the environmental context in which they occur. Climate change research has sparked a renewed interest in context-dependent species interactions because rapidly changing abiotic environments will cause species interactions to occur in novel contexts and researchers must incorporate this in their predictions of species' responses to climate change. Here, we argue that predicting how the environment will alter the outcome of species interactions requires an integrative biology approach that focuses on the traits, mechanisms, and processes that bridge disciplines such as physiology, biomechanics, ecology, and evolutionary biology. Specifically, we advocate for quantifying how species differ in their tolerance and performance to both environmental challenges independent of species interactions, and in interactions with other species as a function of the environment. Such an approach increases our understanding of the mechanisms underlying outcomes of species interactions across different environmental contexts. This understanding will help determine how the outcome of species interactions affects the relative abundance and distribution of the interacting species in nature. A general theme that emerges from this perspective is that species are unable to maintain high levels of performance across different environmental contexts because of trade-offs between physiological tolerance to environmental challenges and performance in species interactions. Thus, an integrative biology paradigm that focuses on the trade-offs across environments, the physiological mechanisms involved, and how the ecological context impacts the outcome of species interactions provides a stronger framework to understand why species interactions are context dependent. [ABSTRACT FROM AUTHOR]

Female competitive behaviors during courtship can have substantial fitness consequences, yet we know little about the physiological and social mechanisms underlying these behaviors—particularly for females of polygynous lek mating species. We explored the hormonal and social drivers of female intersexual and intrasexual behavior during courtship by males in a captive population of Indian peafowl. We investigated whether (1) female non-stress induced circulating estradiol (E2) and corticosterone (CORT) levels or (2) female dominance status in a dyad predicts female solicitation behavior. We also tested whether female circulating E2 and CORT predict dominant females' aggressive behaviors toward subordinate females in the courtship context. Our findings demonstrate that females with higher levels of circulating E2 as well as higher levels of circulating CORT solicit more courtships from males. Dominant females also solicit more courtships from males than subordinate females. Female intrasexual aggressive behaviors during courtship, however, were not associated with circulating levels of E2 or CORT. Overall, we conclude that circulating steroid hormones in conjunction with social dominance might play a role in mediating female behaviors associated with competition for mates. Experimental manipulation and measures of hormonal flexibility throughout the breeding season in relation to competitive and sexual behaviors will be necessary to further examine the link between hormonal mechanisms and female behavior in polygynous lekking systems. [ABSTRACT FROM AUTHOR]

As environments become urbanized, tolerant species become more prevalent. The physiological, behavioral and life-history mechanisms associated with the success of such species in urbanized habitats are not well understood, especially in freshwater ecosystems. Here, we examined the glucocorticoid (GC) profiles, life-history traits, and behavior of two species of fish across a gradient of urbanization to understand coping capacity and associated trade-offs. We studied the tolerant live-bearing Western Mosquitofish (Gambusia affinis) for two years and the slightly less tolerant, egg-laying, Blacktail Shiner (Cyprinella venusta) for one year. We used a water-borne hormone method to examine baseline, stress-induced, and recovery cortisol release rates across six streams with differing degrees of urbanization. We also measured life-history traits related to reproduction, and for G. affinis , we measured shoaling behavior and individual activity in a novel arena. Both species showed a trend for reduced stress responsiveness in more urbanized streams, accompanied by higher reproductive output. Although not all populations fit this trend, these results suggest that GC suppression may be adaptive for coping with urban habitats. In G. affinis , GC recovery increased with urbanization, and individuals with the lowest stress response and highest recovery had the greatest reproductive allotment, suggesting that rapid return to baseline GC levels is also an important coping mechanism. In G. affinis , urban populations showed altered life-history trade-offs whereas behavioral traits did not vary systematically with urbanization. Thus, these tolerant species of fish may cope with anthropogenically modified streams by altering their GC profiles and life-history trade-offs. These results contribute to understanding the mechanisms driving species-specific adaptations and thereby community structure in freshwater systems associated with land-use converted areas. [ABSTRACT FROM AUTHOR]

Eastern oysters (Crassostrea virginica) have long been recognized as model organisms of extreme environmental tolerance, showing resilience to variation in temperature, salinity, hypoxia, and microbial pathogens. These phenotypic responses, however, show variability between geographic locations or habitats (e.g. tidal). Physiological, morphological, and genetic differences occur in populations throughout a species' geographical range, which may have been shaped by regional abiotic and biotic variations. Few studies of C. virginica have explored the combined factors of physiological mechanisms of divergent phenotypes between locations and the genetic relationships of individuals between these locations. To characterize genetic relationships of four locations with aquacultured oysters along the North Carolina and Virginia coast, we sequenced a portion of cytochrome oxidase subunit I (COI) that revealed significant variation in haplotype distribution between locations. We then measured mitochondrial physiology and expression of the innate immunity response of hemocytes to lab acclimation and combined stress conditions to compare basal expression and stress response in oysters between these locations. For stress sensing genes, toll-like receptors had the strongest location-specific response to hypoxia and Vibrio , whereas mannose receptor and a stress-receptor were specific to hypoxia and bacteria, respectively. The expression of stress response genes also showed location-specific and stressor-specific changes in expression, particularly for big defensin and the complement gene Cq3. Our results further suggested that genetic similarity of oysters from different locations was not clearly related to physiological and molecular responses. These results are informative for understanding the range of physiological plasticity for stress responses in this commercially important oyster species. They also have implications in the oyster farming industry as well as conservation efforts to restore endangered native oyster beds. [ABSTRACT FROM AUTHOR]

Ecology is a diverse field with many researchers interested in drivers and consequences of variability within populations. Two aspects of variability that have been addressed are behavioral and physiological. While these have been shown to separately influence ecological outcomes such as survival, reproductive success, and fitness, combined they could better predict within-population variability in survival and fitness. Recently there has been a focus on potential fitness outcomes of consistent behavioral traits that are referred to as personality or temperament (e.g. boldness, sociability, and exploration). Given this recent focus, it is an optimal time to identify areas to supplement in this field, particularly in determining the relationship between temperament and physiological traits. To maximize progress, in this perspective paper, we propose that the following two areas be addressed: (1) increased diversity of species and (2) increased number of physiological processes studied, with an eye toward using more representative and relatively consistent measures across studies. We first highlight information that has been gleaned from species that are frequently studied to determine how animal personality relates to physiology and/or survival/fitness. We then shine a spotlight on important taxa that have been understudied and that can contribute meaningful, complementary information to this area of research. And last, we propose a brief array of physiological processes to relate to temperament, and that can significantly impact fitness, and that may be accessible in field studies. [ABSTRACT FROM AUTHOR]

Investigating how animals navigate space and time is key to understanding communication. Small differences in spatial positioning or timing can mean the difference between a message received and a missed connection. However, these spatio-temporal dynamics are often overlooked or are subject to simplifying assumptions in investigations of animal signaling. This special issue addresses this significant knowledge gap by integrating work from researchers with disciplinary backgrounds in neuroscience, cognitive ecology, sensory ecology, computer science, evolutionary biology, animal behavior, and philosophy. This introduction to the special issue outlines the novel questions and approaches that will advance our understanding of spatio-temporal dynamics of animal communication. We highlight papers that consider the evolution of spatio-temporal dynamics of behavior across sensory modalities and social contexts. We summarize contributions that address the neural and physiological mechanisms in senders and receivers that shape communication. We then turn to papers that introduce cutting edge technologies that will revolutionize our ability to track spatio-temporal dynamics of individuals during social encounters. The interdisciplinary collaborations that gave rise to these papers emerged in part from a novel workshop-symposium model, which we briefly summarize for those interested in fostering syntheses across disciplines. [ABSTRACT FROM AUTHOR]

Life on earth has evolved during the past several billion years under relatively bright days and dark nights. Virtually all organisms on the planet display an internal representation of the solar days in the form of circadian rhythms driven by biological clocks. Nearly every aspect of physiology and behavior is mediated by these internal clocks. The widespread adoption of electric lights during the past century has exposed animals, including humans, to significant light at night (LAN) for the first time in our evolutionary history. Importantly, endogenous circadian clocks depend on light for synchronization with the external daily environment. Thus, LAN can derange temporal adaptations. Indeed, disruption of natural light–dark cycles results in several physiological and behavioral changes. In this review, we highlight recent evidence demonstrating how LAN exposure can have serious implications for adaptive physiology and behavior, including immune, endocrine, and metabolic function, as well as reproductive, foraging, and migratory behavior. Lastly, strategies to mitigate the consequences of LAN on behavior and physiology will be considered. [ABSTRACT FROM AUTHOR]

She earned her bachelors degrees and PhD from the University of Michigan and did her postdoctoral work at the Smithsonian Tropical Research Institute in Panama and at UC Berkeley. He received his PhD in 2017 from the University of South Florida where he investigated frog jumping and salamander tongue projection with Professor Steve Deban. He received his PhD in 2017 from the University of California - Berkeley, where he studied the ecology and biomechanics of kelp with Professor Mimi Koehl. [Extracted from the article]

Embryo implantation is a hallmark of the female reproductive biology of eutherian (placental) mammals and does not exist in a sustainable form in any other vertebrate group. Implantation is the initial process that leads to a sustained fetal-maternal unit engendering a complex functional relationship between the mother and the embryo/fetus. The nature of this relationship is often portrayed as one of conflict between an aggressive embryo and a passive or defensive maternal organism. Recent progress in elucidating the evolutionary origin of eutherian pregnancy leads to a different picture. The emerging scenario suggests that the very initial stages in the evolution of embryo implantation required evolutionary changes to the maternal physiology which modified an ancestral generic mucosal inflammation in response to the presence of the embryo into an active embedding process. This "female-first" evolutionary scenario also explains the role of endometrial receptivity in human pregnancy. On the marsupial side, where in most animals the fetal–maternal interaction is short and does not lead to a long term sustainable placentation, the relationship is mutual. In these mammals, uterine inflammation is followed by parturition in short order. The inflammatory signaling pathways, however, are cooperative, i.e. they are performed by both the fetus and the mother and therefore we call this relationship "cooperative inflammation." Based on these discoveries we reconceive the narrative of the maternal–fetal relationship. [ABSTRACT FROM AUTHOR]

Over the last 100 years, fishes native to the Southwestern United States have faced a myriad of biotic and abiotic pressures which has resulted in most being federally listed as endangered or threatened. Most notably, water diversions and the introduction of non-native fishes have been the primary culprits in causing the downfall of native fish populations. We describe how recent studies of morphology, physiology, and behavior yield insights into the failed (occasionally successful) management of this vanishing biota. We describe how understanding locomotor morphologies, physiologies, and behaviors unique to Southwestern native fishes can be used to create habitats that favor native fishes. Additionally, through realizing differences in morphologies and behaviors between native and non-native fishes, we describe how understanding predator–prey interactions might render greater survivorship of native fishes when stocked into the wild from repatriation programs. Understanding fundamental form–function relationships is imperative for managers to make educated decisions on how to best recover species of concern in the Southwestern United States and worldwide. [ABSTRACT FROM AUTHOR]

Anthropogenic change has well-documented impacts on stress physiology and behavior across diverse taxonomic groups. Within individual organisms, physiological and behavioral traits often covary at proximate and ultimate timescales. In the context of global change, this means that impacts on physiology can have downstream impacts on behavior, and vice versa. Because all organisms interact with members of their own species and other species within their communities, the effects of humans on one organism can impose indirect effects on one or more other organisms, resulting in cascading effects across interaction networks. Human-induced changes in the stress physiology of one species and the downstream impacts on behavior can therefore interact with the physiological and behavioral responses of other organisms to alter emergent ecological phenomena. Here, we highlight three scenarios in which the stress physiology and behavior of individuals on different sides of an ecological relationship are interactively impacted by anthropogenic change. We discuss host–parasite/pathogen dynamics, predator–prey relationships, and beneficial partnerships (mutualisms and cooperation) in this framework, considering cases in which the effect of stressors on each type of network may be attenuated or enhanced by interactive changes in behavior and physiology. These examples shed light on the ways that stressors imposed at the level of one individual can impact ecological relationships to trigger downstream consequences for behavioral and ecological dynamics. Ultimately, changes in stress physiology on one or both sides of an ecological interaction can mediate higher-level population and community changes due in part to their cascading impacts on behavior. This framework may prove useful for anticipating and potentially mitigating previously underappreciated ecological responses to anthropogenic perturbations in a rapidly changing world. [ABSTRACT FROM AUTHOR]

Eukaryotes are the outcome of an ancient symbiosis and as such, eukaryotic cells fundamentally possess two genomes. As a consequence, gene products encoded by both nuclear and mitochondrial genomes must interact in an intimate and precise fashion to enable aerobic respiration in eukaryotes. This genomic architecture of eukaryotes is proposed to necessitate perpetual coevolution between the nuclear and mitochondrial genomes to maintain coadaptation, but the presence of two genomes also creates the opportunity for intracellular conflict. In the collection of papers that constitute this symposium volume, scientists working in diverse organismal systems spanning vast biological scales address emerging topics in integrative, comparative biology in light of mitonuclear interactions. [ABSTRACT FROM AUTHOR]

The eastern oyster, Crassostrea virginica , forms reefs that provide critical services to the surrounding ecosystem. These reefs are at risk from climate change, in part because altered rainfall patterns may amplify local fluctuations in salinity, impacting oyster recruitment, survival, and growth. As in other marine organisms, warming water temperatures might interact with these changes in salinity to synergistically influence oyster physiology. In this study, we used comparative transcriptomics, measurements of physiology, and a field assessment to investigate what phenotypic changes C. virginica uses to cope with combined temperature and salinity stress in the Gulf of Mexico. Oysters from a historically low salinity site (Sister Lake, LA) were exposed to fully crossed temperature (20°C and 30°C) and salinity (25, 15, and 7 PSU) treatments. Using comparative transcriptomics on oyster gill tissue, we identified a greater number of genes that were differentially expressed (DE) in response to low salinity at warmer temperatures. Functional enrichment analysis showed low overlap between genes DE in response to thermal stress compared with hypoosmotic stress and identified enrichment for gene ontologies associated with cell adhesion, transmembrane transport, and microtubule-based process. Experiments also showed that oysters changed their physiology at elevated temperatures and lowered salinity, with significantly increased respiration rates between 20°C and 30°C. However, despite the higher energetic demands, oysters did not increase their feeding rate. To investigate transcriptional differences between populations in situ , we collected gill tissue from three locations and two time points across the Louisiana Gulf coast and used quantitative PCR to measure the expression levels of seven target genes. We found an upregulation of genes that function in osmolyte transport, oxidative stress mediation, apoptosis, and protein synthesis at our low salinity site and sampling time point. In summary, oysters altered their phenotype more in response to low salinity at higher temperatures as evidenced by a higher number of DE genes during laboratory exposure, increased respiration (higher energetic demands), and in situ differential expression by season and location. These synergistic effects of hypoosmotic stress and increased temperature suggest that climate change will exacerbate the negative effects of low salinity exposure on eastern oysters. [ABSTRACT FROM AUTHOR]

Phenotypic plasticity is not universally adaptive. In certain cases, plasticity can result in phenotypic shifts that reduce fitness relative to the un-induced state. A common cause of such maladaptive plasticity is the co-option of ancestral developmental and physiological response systems to meet novel challenges. Because these systems evolved to meet specific challenges in an ancestral environment (e.g. localized and transient hypoxia), their co-option to meet a similar, but novel, stressor (e.g. reductions in ambient pO2 at high elevation) can lead to misdirected responses that reduce fitness. In such cases, natural selection should act to remodel phenotypic plasticity to suppress the expression of these maladaptive responses. Because these maladaptive responses reduce the fitness of colonizers in new environments, this remodeling of ancestral plasticity may be among the earliest steps in adaptive walks toward new local optima. Genetic compensation has been proposed as a general form of adaptive evolution that leads to the suppression of maladaptive plasticity to restore the ancestral trait value in the face of novel stimuli. Given their central role in the regulation of basic physiological functions, we argue that genetic compensation may often be achieved by modifications of homeostatic regulatory systems. We further suggest that genetic compensation to modify homeostatic systems can be achieved by two alternative strategies that differ in their mechanistic underpinnings; to our knowledge, these strategies have not been formally recognized by previous workers. We then consider how the mechanistic details of these alternative strategies may constrain their evolution. These considerations lead us to argue that genetic compensation is most likely to evolve by compensatory physiological changes that safeguard internal homeostatic conditions to prevent the expression of maladaptive portions of conserved reaction norms, rather than direct evolution of plasticity itself. Finally, we outline a simple experimental framework to test this hypothesis. Our goal is to stimulate research aimed at providing a deeper mechanistic understanding of whether and how phenotypic plasticity can be remodeled following environmental shifts that render ancestral responses maladaptive, an issue with increasing importance in our current era of rapid environmental change. [ABSTRACT FROM AUTHOR]

Sensory hair cells are specialized secondary sensory cells that mediate our senses of hearing, balance, linear acceleration, and angular acceleration (head rotation). In addition, hair cells in fish and amphibians mediate sensitivity to water movement through the lateral line system, and closely related electroreceptive cells mediate sensitivity to low-voltage electric fields in the aquatic environment of many fish species and several species of amphibian. Sensory hair cells share many structural and functional features across all vertebrate groups, while at the same time they are specialized for employment in a wide variety of sensory tasks. The complexity of hair cell structure is large, and the diversity of hair cell applications in sensory systems exceeds that seen for most, if not all, sensory cell types. The intent of this review is to summarize the more significant structural features and some of the more interesting and important physiological mechanisms that have been elucidated thus far. Outside vertebrates, hair cells are only known to exist in the coronal organ of tunicates. Electrical resonance, electromotility, and their exquisite mechanical sensitivity all contribute to the attractiveness of hair cells as a research subject. [ABSTRACT FROM AUTHOR]

In striated muscle, the giant protein titin spans the entire length of a half-sarcomere and extends from the backbone of the thick filament, reversibly attaches to the thin filaments, and anchors to the dense protein network of the z-disk capping the end of the half-sarcomere. However, little is known about the relationship between the basic mechanical properties of titin and muscle contractility. Here, we build upon our previous multi-filament, spatially explicit computational model of the half-sarcomere by incorporating the nonlinear mechanics of titin filaments in the I-band. We vary parameters of the nonlinearity to understand the effects of titin stiffness on contraction dynamics and efficiency. We do so by simulating isometric contraction for a range of sarcomere lengths (SLs; 1.6–3.25 µm). Intermediate values of titin stiffness accurately reproduce the passive force–SL relation for skeletal muscle. The maximum force–SL relation is not affected by titin for SL≤2.5 µm. However, as titin stiffness increases, maximum force for the four thick filament system at SL = 3.0 µm significantly decreases from 103.2 ± 2 to 58.8 ± 1 pN. Additionally, by monitoring ATP consumption, we measure contraction efficiency as a function of titin stiffness. We find that at SL = 3.0 µm, efficiency significantly decreases from 13.9 ± 0.4 to 7.0 ± 0.3 pN/ATP when increasing titin stiffness, with little or no effect below 2.5 µm. Taken together, our results suggest that, despite an increase in the fraction of motors bound to actin along the descending limb when titin is stiffer, the force-generating capacity of the motors is reduced. These results suggest that titin stiffness has the potential to affect contractile efficiency. [ABSTRACT FROM AUTHOR]

During rapid locomotion, the vestibular inner ear provides head-motion signals that stabilize posture, gaze, and heading. Afferent nerve fibers from central and peripheral zones of vestibular sensory epithelia use temporal and rate encoding, respectively, to emphasize different aspects of head motion: central afferents adapt faster to sustained head position and favor higher stimulus frequencies, reflecting specializations at each stage from motion of the accessory structure to spike propagation to the brain. One specialization in amniotes is an unusual nonquantal synaptic mechanism by which type I hair cells transmit to large calyceal terminals of afferent neurons. The reduced synaptic delay of this mechanism may have evolved to serve reliable and fast input to reflex pathways that ensure stable locomotion on land. [ABSTRACT FROM AUTHOR]

The vertebrate lateral line system comprises a mechanosensory division, with neuromasts containing hair cells that detect local water movement (“distant touch”); and an electrosensory division, with electrosensory organs that detect the weak, low-frequency electric fields surrounding other animals in water (primarily used for hunting). The entire lateral line system was lost in the amniote lineage with the transition to fully terrestrial life; the electrosensory division was lost independently in several lineages, including the ancestors of frogs and of teleost fishes. (Electroreception with different characteristics subsequently evolved independently within two teleost lineages.) Recent gene expression studies in a non-teleost actinopterygian fish suggest that electroreceptor ribbon synapses employ the same transmission mechanisms as hair cell ribbon synapses, and show that developing electrosensory organs express transcription factors essential for hair cell development, including Atoh1 and Pou4f3. Previous hypotheses for electroreceptor evolution suggest either that electroreceptors and hair cells evolved independently in the vertebrate ancestor from a common ciliated secondary cell, or that electroreceptors evolved from hair cells. The close developmental and putative physiological similarities implied by the gene expression data support the latter hypothesis, i.e. that electroreceptors evolved in the vertebrate ancestor as a “sister cell-type” to lateral line hair cells. [ABSTRACT FROM AUTHOR]

Tunicates, the sister group of vertebrates, possess a mechanoreceptor organ, the coronal organ, which is considered the best candidate to address the controversial issue of vertebrate hair cell evolution. The organ, located at the base of the oral siphon, controls the flow of seawater into the organism and can drive the “squirting” reaction, i.e. the rapid body muscle contraction used to eject dangerous particles during filtration. Coronal sensory cells are secondary mechanoreceptors and share morphological, developmental, and molecular traits with vertebrate hair cells. In the colonial tunicate Botryllus schlosseri, we described coronal organ differentiation during asexual development. Moreover, we showed that the ototoxic aminoglycoside gentamicin caused morphological and mechanosensorial impairment in coronal cells. Finally, fenofibrate had a strong protective effect on coronal sensory cells due to gentamicin-induced toxicity, as occurs in vertebrate hair cells. Our results reinforce the hypothesis of homology between vertebrate hair cells and tunicate coronal sensory cells. [ABSTRACT FROM AUTHOR]

To relate in vivo behavior of fascicle segments within a muscle to their in vitro force-length relationships, we examined the strain behavior of paired segments within each of three vertebrate muscles. After determining in vivo muscle activity patterns and length changes of in-series segments within the semimembranosus muscle (SM) in the American Toad (Bufo americanus) during hopping and within the sternohyoid (SH) muscle in the rat (Rattus rattus) during swallowing, and of spatially separated fascicles within the medial gastrocnemius (MG) muscle in the rat during trotting, we measured their corresponding in vitro (toad) or in situ (rat) force–length relationships (FLRs). For all three muscles, in vivo strain heterogeneity lasted for about 36–57% of the behavior cycle, during which one segment or fascicle shortened while the other segment or fascicle simultaneously lengthened. In the toad SM, the proximal segment shortened from the descending limb across the plateau of its FLR from 1.12 to 0.91 of its optimal length (L o), while the distal segment lengthened (by 0.04 ± 0.04 L o) before shortening down the ascending limb from 0.94 to 0.83 L o. In the rat SH muscle, the proximal segment tended to shorten on its ascending limb from 0.90 to 0.85 L o while the distal segment tended to lengthen across L o (0.96–1.12 L o). In the rat MG muscle, in vivo strains of proximal fascicles ranged from 0.72 to 1.02 L o, while the distal fascicles ranged from 0.88 to 1.11 L o. Even though the timing of muscle activation patterns were similar between segments, the heterogeneous strain patterns of fascicle segments measured in vivo coincided with different operating ranges across their FLRs simultaneously, implying differences in force–velocity behavior as well. The three vertebrate skeletal muscles represent a diversity of fiber architectures and functions and suggest that patterns of in vivo contractile strain and the operating range over the FLR in one muscle region does not necessarily represent other regions within the same muscle. [ABSTRACT FROM AUTHOR]

Evolving from filter feeding chordate ancestors, vertebrates adopted a more active life style. These ecological and behavioral changes went along with an elaboration of the vertebrate head including novel complex paired sense organs such as the eyes, inner ears, and olfactory epithelia. However, the photoreceptors, mechanoreceptors, and chemoreceptors used in these sense organs have a long evolutionary history and homologous cell types can be recognized in many other bilaterians or even cnidarians. After briefly introducing some of the major sensory cell types found in vertebrates, this review summarizes the phylogenetic distribution of sensory cell types in metazoans and presents a scenario for the evolutionary history of various sensory cell types involving several cell type diversification and fusion events. It is proposed that the evolution of novel cranial sense organs in vertebrates involved the redeployment of evolutionarily ancient sensory cell types for building larger and more complex sense organs. [ABSTRACT FROM AUTHOR]

Despite the pressing need for accurate forecasts of ecological and evolutionary responses to environmental change, commonly used modeling approaches exhibit mixed performance because they omit many important aspects of how organisms respond to spatially and temporally variable environments. Integrating models based on organismal phenotypes at the physiological, performance, and fitness levels can improve model performance. We summarize current limitations of environmental data and models and discuss potential remedies. The paper reviews emerging techniques for sensing environments at fine spatial and temporal scales, accounting for environmental extremes, and capturing how organisms experience the environment. Intertidal mussel data illustrate biologically important aspects of environmental variability. We then discuss key challenges in translating environmental conditions into organismal performance including accounting for the varied timescales of physiological processes, for responses to environmental fluctuations including the onset of stress and other thresholds, and for how environmental sensitivities vary across lifecycles. We call for the creation of phenotypic databases to parameterize forecasting models and advocate for improved sharing of model code and data for model testing. We conclude with challenges in organismal biology that must be solved to improve forecasts over the next decade. [ABSTRACT FROM AUTHOR]

Human-induced global change has triggered the sixth major extinction event on earth with profound consequences for humans and other species. A scientifically literate public is necessary to find and implement approaches to prevent or slow species loss. Creating science-inspired art can increase public understanding of the current anthropogenic biodiversity crisis and help people connect emotionally to difficult concepts. In spite of the pressure to avoid advocacy and emotion, there is a rich history of scientists who make art, as well as art–science collaborations resulting in provocative work that engages public interest; however, such interdisciplinary partnerships can often be challenging to initiate and navigate. Here we explore the goals, impacts, cascading impacts, and lessons learned from art–science collaborations, as well as ideas for collaborative projects. Using three case studies based on Harrower’s scientific research into species interactions, we illustrate the importance of artists as a primary audience and the potential for a combination of art and science presentations to influence public understanding and concern related to species loss. [ABSTRACT FROM AUTHOR]

Maternal stress can prenatally influence offspring phenotypes and there are an increasing number of ecological studies that are bringing to bear biomedical findings to natural systems. This is resulting in a shift from the perspective that maternal stress is unanimously costly, to one in which maternal stress may be beneficial to offspring. However, this adaptive perspective is in its infancy with much progress to still be made in understanding the role of maternal stress in natural systems. Our aim is to emphasize the importance of the ecological and evolutionary context within which adaptive hypotheses of maternal stress can be evaluated. We present five primary research areas where we think future research can make substantial progress: (1) understanding maternal and offspring control mechanisms that modulate exposure between maternal stress and subsequent offspring phenotype response; (2) understanding the dynamic nature of the interaction between mothers and their environment; (3) integrating offspring phenotypic responses and measuring both maternal and offspring fitness outcomes under real-life (either free-living or semi-natural) conditions; (4) empirically testing these fitness outcomes across relevant spatial and temporal environmental contexts (both pre- and post-natal environments); (5) examining the role of maternal stress effects in human-altered environments--i.e., do they limit or enhance fitness. To make progress, it is critical to understand the role of maternal stress in an ecological context and to do that, we must integrate across physiology, behavior, genetics, and evolution. [ABSTRACT FROM AUTHOR]

Predicting the effects of climate change on species and communities remains a pre-eminent challenge for biologists. Critical among this is understanding the indirect effects of climate change, which arise when the direct, physiological effects of climate on one species change the outcome of its interaction with a second species, altering the success of the second species. A diverse array of approaches to predicting indirect effects exists from mechanistic models, which attempt to build-up from physiological changes to ecological consequences, to ecological models that focus solely on the ecological scale. Here I review studies of the indirect effects of temperature on two predator-prey systems in rocky intertidal habitats. Laboratory and field studies have shown that temperature can indirectly affect interactions through both physiological and behavioral changes in predator and prey, but no model yet captures the full range of these effects. The three main categories of changes are metabolic rate effects, stress effects, and behavioral avoidance. Mechanistic models best capture the first two of these three dynamics, while ecological models have focused mainly on the last two. The challenge remains to correctly identify a species' vulnerability to climate change, which differs from its physiological sensitivity. The best approach may be to use detailed physiological-scale studies of indirect effect in a few systems to ground truth simpler models that can be applied more broadly. Model development and testing is also hampered by the small number of field studies of indirect effects in natural systems, particularly studies that examine natural temporal or spatial variation in climate. [ABSTRACT FROM AUTHOR]

Venomous organisms used in research were historically chosen based on size and availability. This opportunitydriven strategy created a species bias in which snakes, scorpions, and spiders became the primary subjects of venom research. Increasing technological advancements have enabled interdisciplinary studies using genomics, transcriptomics, and proteomics to expand venom investigation to animals that produce small amounts of venom or lack traditional venom producing organs. One group of non-traditional venomous organisms that have benefitted from the rise of -omic technologies is the Conoideans. The Conoidean superfamily of venomous marine snails includes, the Terebridae, Turridae (s.l), and Conidae. Conoidea venom is used for both predation and defense, and therefore under strong selection pressures. The need for conoidean venom peptides to be potent and specific to their molecular targets has made them important tools for investigating cellular physiology and bioactive compounds that are beneficial to improving human health. A convincing case for the potential of Conoidean venom is made with the first commercially available conoidean venom peptide drug Ziconotide (Prialt®), an analgesic derived from Conus magus venom that is used to treat chronic pain in HIV and cancer patients. Investigation of conoidean venom using -omics technology provides significant insights into predator-driven diversification in biodiversity and identifies novel compounds for manipulating cellular communication, especially as it pertains to disease and disorders. [ABSTRACT FROM AUTHOR]

Fan worms (Annelida: Sabellidae) possess some of the strangest eyes in nature. Their eponymous fans are composed of two sets of radiolar tentacles that project from the head up out of the worm's protective tube into the water column. Primarily used for respiration and feeding, these radioles are also often involved in photoreception. They display a surprising diversity of eyes of varying levels of sophistication, ranging from scattered single ocelli to compound eyes with up to hundreds of facets. These photoreceptors could represent a relatively recent evolutionary development to cope with a sessile, tube-dwelling lifestyle, and the primary cerebral eyes (haplessly positioned within the tube most of the time) amount to little more than minute pigment cups with scant visual potential. The radiolar eyes on the other hand, appear to function as visual burglar alarms for detecting looming predators and eliciting a startle response for the worm to rapidly retreat within its fortified tube. Despite sometimes resembling arthropod compound eyes, the radiolar photoreceptors have many canonically vertebrate-like physiological characteristics. Considering the unusual and apparently recently evolved nature of the fan worm radiolar photoreceptors, these animals are an excellent case for examining the emergence of novel visual systems, the development of rudimentary visually guided behaviors, and the function of distributed sensory systems. Here, we review over 100 years of investigations into the anatomical diversity of sabellid radiolar photoreceptors and eyes in an evolutionary and functional context. We provide new information on radiolar eye structure in several species of fan worms, and we attempt to organize the various eye types and ocellar structures into meaningful hierarchies. We discuss the developmental, evolutionary, and functional significance of the radiolar eyes and highlight areas of future interest in deciphering their unique nature. [ABSTRACT FROM AUTHOR]

The ocean's midwaters (the mesopelagic and bathypelagic zones) make up the largest living space on the planet, but are undersampled and relatively poorly understood. The true distribution of many midwater species, let alone the abiotic factors most important in determining that distribution, is not well known. Because collecting specimens and data from the deep ocean is expensive and logistically difficult, it would be useful to be able to predict where species of interest are likely to occur so that sampling effort can be concentrated in appropriate areas. The distribution of two representative midwater fishes, the gulper eel Eurypharynx pelecanoides and the bobtail eel Cyema atrum (Teleostei: Saccopharyngiformes), were modeled with MaxEnt software to examine the viability of species distribution modeling (SDM) for globally distributed midwater fishes using currently available environmental data from the ocean surface and bottom. These species were chosen because they are relatively abundant, easily recognized, and unlikely to have been misidentified in database records, and are true midwater fishes, not known to undertake significant vertical diurnal migration. Models for both species show a generally worldwide distribution with some exceptions, including the Southern Ocean and Bering Sea. Variable contributions show that surface and bottom environmental variables correlate with species presence. Both species are more likely to be found in areas with low levels of silicate. SDM is a promising method for better understanding the ecology of midwater organisms. [ABSTRACT FROM AUTHOR]

Embryos of the annual killifish Austrofundulus limnaeus are routinely exposed to oxygen limitation during development and are extremely tolerant of anoxia. Importantly, tolerance of anoxia is not strictly associated with entrance into metabolic dormancy associated with diapause II, but rather any embryo will respond to anoxia by entering into a state of anoxia-induced quiescence. Hypoxia causes a reduction in the rate of development, reduced heart rates, and reduced capacities for metabolic enzyme activity in both aerobic and anaerobic pathways. Embryos of A. limnaeus begin life as oxyconformers, and transition into oxyregulators near the completion of embryonic development. As this transition occurs, extreme anoxia tolerance is lost. The rate of early development is independent of oxygen partial pressure, despite the fact that the embryos are oxyconformers. This suggests a contribution from anaerobic pathways to support early development. However, the specific pathways supporting this metabolism are unknown. The response of A. limnaeus embryos to hypoxia and anoxia is unique compared to other fishes and most other vertebrates, and thus future studies on this species may lend insight into novel mechanisms that support survival during prolonged oxygen limitation. [ABSTRACT FROM AUTHOR]

Daily rhythms for hormonal traits are likely widespread and important aspects of organismal (e.g., life history) adaptation. Yet they remain substantially understudied, especially with respect to variable rhythms within species. The cricket, Gryllus firmus, exhibits a genetically polymorphic circadian rhythm for the blood titer of the key hormone, juvenile hormone (JH). Gryllus firmus is also wing-polymorphic, consisting of a dispersing morph that delays reproduction and a flightless morph with substantially enhanced egg production. JH circadian phenotype strongly covaries with morph type: The blood JH titer is strongly rhythmic in multiple populations artificially-selected for the dispersing morph (LW(f)=long wings with functional flight muscles) and is essentially arrhythmic in populations selected for the SW (short-winged) morph. Association between JH titer cycle and LW(f) morph is also found in natural populations of G. firmus and in several related species in the field. This is one of the very few studies of endocrine titer variation in natural populations of an insect. The morph-specific cycle is underlain by a circadian rhythm in hormone biosynthesis, which in turn is underlain by a rhythm in a brain neuropeptide regulator of JH biosynthesis. The morph-specific JH titer circadian cycle is also strongly correlated with a morph-specific daily rhythm in global gene expression. This is currently the only example of a genetically-variable hormone circadian rhythm in both the laboratory and field that is strongly associated with an ecologically important polymorphism. The extensive information on the underlying causes of the morph-specific JH titer rhythm, coupled with the strong association between the JH circadian rhythm and wing polymorphism makes this system in G. firmus an exceptional experimental model to investigate the mechanisms underlying circadian hormonal adaptations. Genetic polymorphism for the JH titer circadian rhythm in G. firmus is discussed in context of circadian rhythms for endocrine traits reported for vertebrates and insects. Consequences of the failure to identify endocrine circadian rhythms on the accuracy of estimation of quantitative-genetic parameters, such as heritability and correlations between hormonal and fitness-related traits, are also discussed. [ABSTRACT FROM AUTHOR]

Synopsis All organisms must anticipate and balance energetic demands and available resources in order to maximize fitness. As hormones coordinate many interactions between an organism's internal condition and the external environment, they may be key in mediating the allocation of resources to meet these demands. However, given that individuals differ considerably in how they react to changes in energetic demand, we asked whether variations in endocrine traits also correspond with life history variation. We tested whether natural variation in glucocorticoid hormone levels, oxidative stress measurements, and condition related to reproductive effort in a free-living songbird, the tree swallow, Tachycineta bicolor. We then tested whether any of these traits predicted the probability of a particular individual's return to the local population in the following two years, an indicator of survival in this philopatric species. We found that males and females with longer telomeres had lighter nestlings. Moreover, individuals with lower plasma antioxidant capacity and higher reactive oxygen metabolites (i.e., greater oxidative stress) were less likely to return to the population. However, none of these traits were related to glucocorticoid levels. Our findings suggest a trade-off between reproduction and survival, with individuals with shorter telomeres having heavier nestlings but potentially paying a cost in terms of higher oxidative stress and lower survival. Interestingly, the evidence of this trade-off was unrelated to natural variation in glucocorticoids. [ABSTRACT FROM AUTHOR]

Migratory animals undergo extreme physiological changes to prepare for and sustain energetically costly movements; one potential change is reduced investment in immune defenses. However, because some migrants have evolved to minimize the energetic demands of movement (for example, through the temporary atrophy of non-essential organs such as those involved in reproduction), migratory animals could potentially avoid immunosuppression during long-distance journeys. In this study, we used a tethered flight mill to examine immune consequences of experimentally induced powered flight in eastern North American monarch butterflies. These butterflies undergo an annual two-way long-distance migration each year from as far north as Canada to wintering sites in Central Mexico. We quantified immune measures as a function of categorical flight treatment (flown versus control groups) and continuous measures of flight effort (e.g., flight distance, duration, and measures of efficiency). We also examined whether relationships between flight and immune measures depended on reproductive investment by experimentally controlling whether monarchs were reproductive or in state of reproductive diapause (having atrophied reproductive organs) prior to flight. Of the three immune responses we measured, hemocyte concentration (the number of immune cells) was lower in flown monarchs relative to controls but increased with flight distance among flown monarchs; the other two immune measures showed no relationship to monarch flight. We also found that monarchs that were reproductively active were less efficient fliers, as they exerted more power during flight than monarchs in reproductive diapause. However, reproductive status did not modify relationships between flight and immune measures. Results of this study add to a growing body of work suggesting that migratory monarchs—like some other animals that travel vast distances—can complete their journeys with efficient use of resources and minimal costs. [ABSTRACT FROM AUTHOR]

Maximal whole-organism performance traits measured in the laboratory and the levels of performance expressed in the field often exhibit a mismatch, complicating our understanding of the selection pressures influencing the evolution of performance traits. To better understand the evolution of locomotor performance, we built an individual-based simulation to test hypotheses about selection on locomotor performance. Starting with a population of individuals with two correlated but variable performance traits, we simulated these individuals surviving and reproducing in a complex environment, presenting each individual with successive ecological challenges requiring specific performance capabilities over their lifespan. While most challenges require sub-maximal speeds, intermittent bouts requiring increased performance, such as escape from predators, introduce strong, but infrequent, selection for maximal performance. By comparing the results of simulations run with individuals that only perform at their maximum levels versus those that adjust this effort, we show that intra-individual variation in speed confers a selective advantage, regardless of the extent of that variation. We also show that the direction and strength of the correlation between the two performance traits affects the evolutionary trajectory of phenotypic change. Ultimately, this model allows us to simulate the evolution of movement speeds over a range of selective contexts, offering insight into the factors affecting the evolutionary relationship between optimal and maximal performance. [ABSTRACT FROM AUTHOR]

Behavioral studies performed in natural habitats provide a context for the development of hypotheses and the design of experiments relevant both to biomechanics and to evolution. In particular, predator-prey interactions are a model system for integrative study because success or failure of predation has a direct effect on fitness and drives the evolution of specialized performance in both predator and prey. Although all predators share the goal of capturing prey, and all prey share the goal of survival, the behavior of predators and prey are diverse in nature. This article presents studies of some predator-prey interactions sharing common predation strategies that reveal general principles governing the behaviors of predator and prey, even in distantly related taxa. Studies of predator-prey interactions also reveal that maximal performance observed in a laboratory setting is not necessarily the performance that determines fitness. Thus, considering locomotion in the context of predation ecology can aid in evolutionarily relevant experimental design. Classification by strategy reveals that displaying unpredictable trajectories is a relevant anti-predator behavior in response to multiple predation strategies. A predator's perception and pursuit of prey can be affected indirectly by divergent locomotion of similar animals that share an ecosystem. Variation in speed and direction of locomotion that directly increases the unpredictability of a prey's trajectory can be increased through genetic mutation that affects locomotor patterns, musculoskeletal changes that affect maneuverability, and physical interactions between an animal and the environment. By considering the interconnectedness of ecology, physical constraints, and the evolutionary history of behavior, studies in biomechanics can be designed to inform each of these fields. [ABSTRACT FROM AUTHOR]

The ability for prey to escape a pursuing predator is dependent both on the prey's speed away from the threat and on their ability to rapidly change directions, or maneuverability. Given that the biomechanical trade-off between speed and maneuverability limits the simultaneous maximization of both performance traits, animals should not select their fastest possible speeds when running away from a pursuing predator but rather a speed that maximizes the probability of successful escape. We explored how variation in the relationship between speed and maneuverability—or the shape of the trade-off—affects the optimal choice of speed for escaping predators. We used tablet-based games that simulated interactions between predators and prey (human subjects acting as predators attempting to capture "prey" moving across a screen). By defining a specific relationship between speed and maneuverability, we could test the survival of each of the possible behavioral choices available to this phenotype, i.e., the best combination of speed and maneuverability for prey fitness, based on their ability to escape. We found that the shape of the trade-off function affected the prey's optimal speed for success in escaping, the prey's maximum performance in escaping, and the breadth of speeds over which the prey's performance was high. The optimal speed for escape varied only when the trade-off between speed and maneuverability was non-linear. Phenotypes possessing trade-off functions for which maneuverability was only compromised at high speeds exhibited lower optimal speeds. Phenotypes that exhibited greater increases in maneuverability for any decrease in speed were more likely to have broader ranges of performance, meaning that individuals could attain their maximum performance across a broader range of speeds. We also found that there was a differential response of the subject's learning to these different components of locomotion. With increased experience through repeated trials, subjects were able to successfully catch faster and faster dots. However, no improvement was observed in the subject's ability to capture more maneuverable prey. Our work highlights the costs of high-speed movement on other traits, including maneuverability, which make the use of an animal's fastest speeds unlikely, even when attempting to escape predators. By investigating the shape of the trade-off functions between speed and maneuverability and the way the environment and morphology mediates this trade-off, we can begin to understand why animals choose to move at the speeds they do when they are running away from predators or attempting to capture prey. [ABSTRACT FROM AUTHOR]

Speed of movement is fundamental to animal behavior—defining the intensity of a task, the time needed to complete it, and the likelihood of success—but how does an animal decide how fast to move? Most studies of animal performance measure maximum capabilities, but animals rarely move at their maximum in the wild. It was the goal of our symposium to develop a conceptual framework to explore the choices of speed in nature. A major difference between our approach and previous work is our move toward understanding optimal rather than maximal speeds. In the following series of papers, we provide a starting point for future work on animal movement speeds, including a conceptual framework, a simple optimality model, an evolutionary context, and an exploration of the various biomechanical and energetic constraints on speed. By applying a cross-disciplinary approach to the study of the choice of speed—as we have done here—we can reveal much about the way animals use habitats, interact with conspecifics, avoid predators, obtain food, and negotiate human-modified landscapes. [ABSTRACT FROM AUTHOR]

RNA editing is a process of targeted alterations of nucleotides in all types of RNA molecules (e.g., rRNA, tRNA, mRNA, and miRNA). As a result, the transcriptional output differs from its genomic DNA template. RNA editing can be defined both by biochemical mechanisms and by enzymes that perform these reactions. There are high levels of RNA editing detected in the mammalian nervous system, suggesting that nervous systems use this mechanism to increase protein diversity, because the post-transcription modifications lead to new gene products with novel functions. By reannotating the ctenophore genomes, we found that the number of predicted RNA-editing enzymes is comparable to the numbers in mammals, but much greater than in other non-bilaterian basal metazoans. However, the overall molecular diversity of RNA-editing enzymes in ctenophores is lower, suggesting a possible "compensation" by an expansion of the ADAT1-like subfamily in this lineage. In two genera of ctenophores, Pleurobrachia and Mnemiopsis, there are high levels of expression for RNA-editing enzymes in their aboral organs, the integrative center involved in control of locomotion and geotaxis. This finding supports the hypothesis that RNA editing is correlated with the complexity of tissues and behaviors. Smaller numbers of RNA-editing enzymes in Porifera and Placozoa also correlates with the primary absence of neural and muscular systems in these lineages. In ctenophores, the expansion of the RNA-editing machinery can also provide mechanisms that support the remarkable capacity for regeneration in these animals. In summary, despite their compact genomes, a wide variety of epigenomic mechanisms employed by ctenophores and other non-bilaterian basal metazoans can provide novel insights into the evolutionary origins of biological novelties. [ABSTRACT FROM AUTHOR]

An animal's movement speed affects all behaviors and underlies the intensity of an activity, the time it takes to complete it, and the probability of successfully completing it, but which factors determine how fast or slow an animal chooses to move? Despite the critical importance of an animal's choice of speed (hereafter designated as "speed-choice"), we still lack a framework for understanding and predicting how fast animals should move in nature. In this article, we develop a framework for predicting speed that is applicable to any animal—including humans—performing any behavior where choice of speed occurs. To inspire new research in this area, we (1) detail the main factors likely to affect speedchoice, including organismal constraints (i.e., energetic, physiological, and biomechanical) and environmental constraints (i.e., predation intensity and abiotic factors); (2) discuss the value of optimal foraging theory in developing models of speed-choice; and (3) describe how optimality models might be integrated with the range of potential organismal and environmental constraints to predict speed. We show that by utilizing optimality theory it is possible to provide quantitative predictions of optimal speeds across different ecological contexts. However, the usefulness of any predictive models is still entirely dependent on being able to provide relevant mathematical functions to insert into such models. We still lack basic knowledge about how an animal's speed affects its motor control, maneuverability, observational skills, and vulnerability to predators. Studies exploring these gaps in knowledge will help facilitate the field of optimal performance and allow us to adequately parameterize models predicting the speed-choice of animals, which represents one of the most basic of all behavioral decisions. [ABSTRACT FROM AUTHOR]

Epigenetic modifications control gene expression without altering the primary DNA sequence. However, little is known about DNA methylation in invertebrates and its evolution. Here, we characterize two types of genomic DNA methylation in ctenophores, 5-methyl cytosine (5-mC) and the unconventional form of methylation 6-methyl adenine (6-mA). Using both bisulfite sequencing and an ELISA-based colorimetric assay, we experimentally confirmed the presence of 5-mC DNA methylation in ctenophores. In contrast to other invertebrates studied, Mnemiopsis leidyi has lower levels of genome-wide 5-mC methylation, but higher levels of 5-mC methylation in promoters when compared with gene bodies. Phylogenetic analysis showed that ctenophores have distinct forms of DNA methyltransferase 1 (DNMT1); the zf-CXXC domain type, which localized DNMT1 to CpG sites, and is a metazoan specific innovation. We also show that ctenophores encode the full repertoire of putative enzymes for 6-mA DNA methylation, and these genes are expressed in the aboral organ of Mnemiopsis. Using an ELISA-based colorimetric assay, we experimentally confirmed the presence of 6-mA methylation in the genomes of three different species of ctenophores, M. leidyi, Beroe abyssicola, and Pleurobrachia bachei. The functional role of this novel epigenomic mark is currently unknown. In summary, despite their compact genomes, there is a wide variety of epigenomic mechanisms employed by basal metazoans that provide novel insights into the evolutionary origins of biological novelties. [ABSTRACT FROM AUTHOR]

Despite an explosion in the amount of sequence data, phylogenomics has failed to settle controversy regarding some critical nodes on the animal tree of life. Understanding relationships among Bilateria, Ctenophora, Cnidaria, Placozoa, and Porifera is essential for studying how complex traits such as neurons, muscles, and gastrulation have evolved. Recent studies have cast doubt on the historical viewpoint that sponges are sister to all other animal lineages with recent studies recovering ctenophores as sister. However, the ctenophore-sister hypothesis has been criticized as unrealistic and caused by systematic error. We review past phylogenomic studies and potential causes of systematic error in an effort to identify areas that can be improved in future studies. Increased sampling of taxa, less missing data, and a priori removal of sequences and taxa that may cause systematic error in phylogenomic inference will likely be the most fruitful areas of focus when assembling future datasets. Ultimately, we foresee metazoan relationships being resolved with higher support in the near future, and we caution against dismissing novel hypotheses merely because they conflict with historical viewpoints of animal evolution. [ABSTRACT FROM AUTHOR]

How and why did complex brain and behavior evolve? Clues emerge from comparative studies of animals with simpler morphology, nervous system, and behavioral economics. The brains of vertebrates, arthropods, and some annelids have highly derived executive structures and function that control downstream, central pattern generators (CPGs) for locomotion, behavioral choice, and reproduction. For the vertebrates, these structures—cortex, basal ganglia, and hypothalamus— integrate topographically mapped sensory inputs with motivation and memory to transmit complex motor commands to relay stations controlling CPG outputs. Similar computations occur in the central complex and mushroom bodies of the arthropods, and in mammals these interactions structure subjective thought and socially based valuations. The simplest model systems available for comparison are opisthobranch molluscs, which have avoided selective pressure for complex bodies, brain, and behavior through potent chemical defenses. In particular, in the sea-slug Pleurobranchaea californica the functions of vertebrates' olfactory bulb and pallium are performed in the peripheral nervous system (PNS) of the chemotactile oral veil. Functions of hypothalamus and basal ganglia are combined in Pleurobranchaea's feeding motor network. The actions of basal ganglia on downstream locomotor regions and spinal CPGs are analogous to Pleurobranchaea's feeding network actions on CPGs for agonist and antagonist behaviors. The nervous systems of opisthobranch and pulmonate gastropods may conserve or reflect relations of the ancestral urbilaterian. Parallels and contrasts in neuronal circuits for action selection in Pleurobranchaea and vertebrates suggest how a basic set of decision circuitry was built upon in evolving segmentation, articulated skeletons, sociality, and highly invested reproductive strategies. They suggest (1) an origin of olfactory bulb and pallium from head-region PNS; (2) modularization of an ancestral feeding network into discrete but interacting executive modules for incentive comparison and decision (basal ganglia), and homeostatic functions (hypothalamus); (3) modification of a multifunctional premotor network for turns and locomotion, and its downstream targets for mid-brain and hind-brain motor areas and spinal CPGs; (4) condensation of a distributed serotonergic network for arousal into the raphe nuclei, with superimposed control by a peptidergic hypothalamic network mediating appetite and arousal; (5) centralization and condensation of the dopaminergic sensory afferents of the PNS, and/or the disperse dopaminergic elements of central CPGs, into the brain nuclei mediating valuation, reward, and motor arousal; and (6) the urbilaterian possessed the basic circuit relations integrating sensation, internal state, and learning for cost-benefit approach-avoidance decisions. [ABSTRACT FROM AUTHOR]