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Signal theory predicts organisms should evolve signals that are conspicuous to intended receivers in natural signalling environments. Cleaner shrimps remove ectoparasites from reef fish clients and many signal their intent to clean by whipping long, white antennae. As white is a reliably conspicuous colour in aquatic environments, we hypothesized that selection has acted to increase broad-spectrum antennal reflectance in cleaners. Using scanning electron microscopy, optical models and reflectance measurements, we found that the antennae in three obligate cleaner species from two families (Palaemonidae and Lysmatidae) had thick (∼6 µm) chitinous layers or densely packed high refractive index spheres (300-400 nm diameter), which models show increase reflectance (400-700 nm). Two facultative and non-cleaning species had no visible antennae ultrastructure beyond the chitinous exoskeleton. Antennae reflectance was significantly higher in obligate cleaners than in facultative and non-cleaning species. Our results suggest that some obligate cleaners may have evolved ultrastructures that increase the conspicuousness of their antennae as signals.

The influence of light spectral properties on circadian rhythms is of substantial interest to laboratory-based investigation of the circadian system and to field-based understanding of the effects of artificial light at night. The trade-offs between intensity and spectrum regarding masking behaviors are largely unknown, even for well-studied organisms. We used a custom LED illumination system to document the response of wild-type house mice (Mus musculus) to 1-h nocturnal exposure of all combinations of four intensity levels (0.01, 0.5, 5 and 50 lx) and three correlated color temperatures (CCT; 1750, 1950 and 3000 K). Higher intensities of light (50 lx) suppressed cage activity substantially, and consistently more for the higher CCT light (91% for 3000 K, 53% for 1750 K). At the lowest intensity (0.01 lx), mean activity was increased, with the greatest increases for the lowest CCT (12.3% increase at 1750 K, 3% increase at 3000 K). Multiple linear regression confirmed the influence of both CCT and intensity on changes in activity, with the scaled effect size of intensity 3.6 times greater than that of CCT. Activity suppression was significantly lower for male than for female mice. Assessment of light-evoked cFos expression in the suprachiasmatic nucleus at 50 lx showed no significant difference between high and low CCT exposure. The significant differences by spectral composition illustrate a need to account for light spectrum in circadian studies of behavior, and confirm that spectral controls can mitigate some, but certainly not all, of the effects of light pollution on species in the wild.

Animal locomotion is the result of complex and multi-layered interactions between the nervous system, the musculo-skeletal system and the environment. Decoding the underlying mechanisms requires an integrative approach. Comparative experimental biology has allowed researchers to study the underlying components and some of their interactions across diverse animals. These studies have shown that locomotor neural circuits are distributed in the spinal cord, the midbrain and higher brain regions in vertebrates. The spinal cord plays a key role in locomotor control because it contains central pattern generators (CPGs) - systems of coupled neuronal oscillators that provide coordinated rhythmic control of muscle activation that can be viewed as feedforward controllers - and multiple reflex loops that provide feedback mechanisms. These circuits are activated and modulated by descending pathways from the brain. The relative contributions of CPGs, feedback loops and descending modulation, and how these vary between species and locomotor conditions, remain poorly understood. Robots and neuromechanical simulations can complement experimental approaches by testing specific hypotheses and performing what-if scenarios. This Review will give an overview of key knowledge gained from comparative vertebrate experiments, and insights obtained from neuromechanical simulations and robotic approaches. We suggest that the roles of CPGs, feedback loops and descending modulation vary among animals depending on body size, intrinsic mechanical stability, time required to reach locomotor maturity and speed effects. We also hypothesize that distal joints rely more on feedback control compared with proximal joints. Finally, we highlight important opportunities to address fundamental biological questions through continued collaboration between experimentalists and engineers.

The parasitoid wasp Ampulex compressa hunts down its host, the American cockroach (Periplaneta americana), and envenomates its brain to make it a behaviorally compliant food supply for its offspring. The primary target of the wasp sting is a locomotory command center called the central complex (CX). In the present study, we employ, for the first time, chronic recordings of patterned cockroach CX activity in real time as the brain is infused with wasp venom. CX envenomation is followed by sequential changes in the pattern of neuronal firing that can be divided into three distinct temporal phases during the 2 h interval after venom injection: (1) reduction in neuronal activity for roughly 10 min immediately after venom injection; (2) rebound of activity lasting up to 25 min; (3) reduction of ongoing activity for up to 2 h. Long-term reduction of CX activity after venom injection is accompanied by decreased activity of both descending interneurons projecting to thoracic locomotory circuitry (DINs) and motor output. Thus, in this study, we provide a plausible chain of events starting in the CX that leads to decreased host locomotion following brain envenomation. We propose that these events account for the onset and maintenance of the prolonged hypokinetic state observed in stung cockroaches.

Cognitive abilities, such as learning and flexibility, are hypothesized to aid behavioral adaptation to urbanization. Although growing evidence suggests that cognition may indeed facilitate persistence in urban environments, we currently lack knowledge of the cognitive abilities of many urban taxa. Recent methodological advances, including radio frequency identification (RFID), have extended automated cognitive testing into the field but have yet to be applied to a diversity of taxa. Here, we used an RFID-enabled operant conditioning device to assess the habituation, learning and cognitive flexibility of a wild population of raccoons (Procyon lotor). We examined how several biological and behavioral traits influenced participation and performance in testing. We then compared the cognitive performance of wild raccoons tested in natural conditions with that of wild-caught raccoons tested in captivity from a previous study. In natural conditions, juvenile raccoons were more likely to habituate to the testing device, but performed worse in serial reversal learning, compared with adults. We also found that docile raccoons were more likely to learn how to operate the device in natural conditions, which suggests a relationship between emotional reactivity and cognitive ability in raccoons. Although raccoons in both captive and natural conditions demonstrated rapid associative learning and flexibility, raccoons in captive conditions generally performed better, likely owing to the heightened vigilance and social interference experienced by raccoons in natural conditions. Our results have important implications for future research on urban carnivores and cognition in field settings, as well as our understanding of behavioral adaptation to urbanization and coexistence with urban wildlife.

Fish in coastal ecosystems can be exposed to acute variations in CO2 of between 0.2 and 1 kPa CO2 (2000-10,000 µatm). Coping with this environmental challenge will depend on the ability to rapidly compensate for the internal acid-base disturbance caused by sudden exposure to high environmental CO2 (blood and tissue acidosis); however, studies about the speed of acid-base regulatory responses in marine fish are scarce. We observed that upon sudden exposure to ∼1 kPa CO2, European sea bass (Dicentrarchus labrax) completely regulate erythrocyte intracellular pH within ∼40 min, thus restoring haemoglobin-O2 affinity to pre-exposure levels. Moreover, blood pH returned to normal levels within ∼2 h, which is one of the fastest acid-base recoveries documented in any fish. This was achieved via a large upregulation of net acid excretion and accumulation of HCO3- in blood, which increased from ∼4 to ∼22 mmol l-1. While the abundance and intracellular localisation of gill Na+/K+-ATPase (NKA) and Na+/H+ exchanger 3 (NHE3) remained unchanged, the apical surface area of acid-excreting gill ionocytes doubled. This constitutes a novel mechanism for rapidly increasing acid excretion during sudden blood acidosis. Rapid acid-base regulation was completely prevented when the same high CO2 exposure occurred in seawater with experimentally reduced HCO3- and pH, probably because reduced environmental pH inhibited gill H+ excretion via NHE3. The rapid and robust acid-base regulatory responses identified will enable European sea bass to maintain physiological performance during large and sudden CO2 fluctuations that naturally occur in coastal environments.

Among fishes in the family Poeciliidae, signals such as colour patterns, ornaments and courtship displays play important roles in mate choice and male-male competition. Despite this, visual capabilities in poeciliids are understudied, in particular, visual acuity, the ability to resolve detail. We used three methods to quantify visual acuity in male and female green swordtails (Xiphophorus helleri), a species in which body size and the length of the male's extended caudal fin ('sword') serve as assessment signals during mate choice and agonistic encounters. Topographic distribution of retinal ganglion cells (RGCs) was similar in all individuals and was characterized by areas of high cell densities located centro-temporally and nasally, as well as a weak horizontal streak. Based on the peak density of RGCs in the centro-temporal area, anatomical acuity was estimated to be approximately 3 cycles per degree (cpd) in both sexes. However, a behavioural optomotor assay found significantly lower mean acuity in males (0.8 cpd) than females (3.0 cpd), which was not explained by differences in eye size between males and females. An additional behavioural assay, in which we trained individuals to discriminate striped gratings from grey stimuli of the same mean luminance, also showed lower acuity in males (1-2 cpd) than females (2-3 cpd). Thus, although retinal anatomy predicts identical acuity in males and females, two behavioural assays found higher acuity in females than males, a sexual dimorphism that is rare outside of invertebrates. Overall, our results have implications for understanding how poeciliids perceive visual signals during mate choice and agonistic encounters.

In true color vision, animals discriminate between light wavelengths, regardless of intensity, using at least two photoreceptors with different spectral sensitivity peaks. Heliconius butterflies have duplicate UV opsin genes, which encode ultraviolet and violet photoreceptors, respectively. In Heliconius erato, only females express the ultraviolet photoreceptor, suggesting females (but not males) can discriminate between UV wavelengths. We tested the ability of H. erato, and two species lacking the violet receptor, Heliconius melpomene and Eueides isabella, to discriminate between 380 and 390 nm, and between 400 and 436 nm, after being trained to associate each stimulus with a sugar reward. We found that only H. erato females have color vision in the UV range. Across species, both sexes show color vision in the blue range. Models of H. erato color vision suggest that females have an advantage over males in discriminating the inner UV-yellow corollas of Psiguria flowers from their outer orange petals. Moreover, previous models ( McCulloch et al., 2017) suggested that H. erato males have an advantage over females in discriminating Heliconius 3-hydroxykynurenine (3-OHK) yellow wing coloration from non-3-OHK yellow wing coloration found in other heliconiines. These results provide some of the first behavioral evidence for female H. erato UV color discrimination in the context of foraging, lending support to the hypothesis ( Briscoe et al., 2010) that the duplicated UV opsin genes function together in UV color vision. Taken together, the sexually dimorphic visual system of H. erato appears to have been shaped by both sexual selection and sex-specific natural selection.

Most animals shift gaze by a 'fixate and saccade' strategy, where the fixation phase stabilizes background motion. A logical prerequisite for robust detection and tracking of moving foreground objects, therefore, is to suppress the perception of background motion. In a virtual reality magnetic tether system enabling free yaw movement, Drosophila implemented a fixate and saccade strategy in the presence of a static panorama. When the spatial wavelength of a vertical grating was below the Nyquist wavelength of the compound eyes, flies drifted continuously and gaze could not be maintained at a single location. Because the drift occurs from a motionless stimulus - thus any perceived motion stimuli are generated by the fly itself - it is illusory, driven by perceptual aliasing. Notably, the drift speed was significantly faster than under a uniform panorama, suggesting perceptual enhancement as a result of aliasing. Under the same visual conditions in a rigid-tether paradigm, wing steering responses to the unresolvable static panorama were not distinguishable from those to a resolvable static pattern, suggesting visual aliasing is induced by ego motion. We hypothesized that obstructing the control of gaze fixation also disrupts detection and tracking of objects. Using the illusory motion stimulus, we show that magnetically tethered Drosophila track objects robustly in flight even when gaze is not fixated as flies continuously drift. Taken together, our study provides further support for parallel visual motion processing and reveals the critical influence of body motion on visuomotor processing. Motion illusions can reveal important shared principles of information processing across taxa.

The origins of novel trophic specialization, in which organisms begin to exploit resources for the first time, may be explained by shifts in behavior such as foraging preferences or feeding kinematics. One way to investigate behavioral mechanisms underlying ecological novelty is by comparing prey capture kinematics among species. We investigated the contribution of kinematics to the origins of a novel ecological niche for scale-eating within a microendemic adaptive radiation of pupfishes on San Salvador Island, Bahamas. We compared prey capture kinematics across three species of pupfish while they consumed shrimp and scales in the lab, and found that scale-eating pupfish exhibited peak gape sizes twice as large as in other species, but also attacked prey with a more obtuse angle between their lower jaw and suspensorium. We then investigated how this variation in feeding kinematics could explain scale-biting performance by measuring bite size (surface area removed) from standardized gelatin cubes. We found that a combination of larger peak gape and more obtuse lower jaw and suspensorium angles resulted in approximately 40% more surface area removed per strike, indicating that scale-eaters may reside on a performance optimum for scale biting. To test whether feeding performance could contribute to reproductive isolation between species, we also measured F1 hybrids and found that their kinematics and performance more closely resembled generalists, suggesting that F1 hybrids may have low fitness in the scale-eating niche. Ultimately, our results suggest that the evolution of strike kinematics in this radiation is an adaptation to the novel niche of scale eating.

Vector-borne diseases, such as dengue, Zika and malaria, are a major cause of morbidity and mortality worldwide. These diseases have proven difficult to control and currently available management tools are insufficient to eliminate them in many regions. Gene drives have the potential to revolutionize vector-borne disease control. This suite of technologies has advanced rapidly in recent years as a result of the availability of new, more efficient gene editing technologies. Gene drives can favorably bias the inheritance of a linked disease-refractory gene, which could possibly be exploited (i) to generate a vector population incapable of transmitting disease or (ii) to disrupt an essential gene for viability or fertility, which could eventually eliminate a population. Importantly, gene drives vary in characteristics such as their transmission efficiency, confinability and reversibility, and their potential to develop resistance to the drive mechanism. Here, we discuss recent advancements in the gene drive field, and contrast the benefits and limitations of a variety of technologies, as well as approaches to overcome these limitations. We also discuss the current state of each gene drive technology and the technical considerations that need to be addressed on the pathway to field implementation. While there are still many obstacles to overcome, recent progress has brought us closer than ever before to genetic-based vector modification as a tool to support vector-borne disease elimination efforts worldwide.

In response to environmental change, organisms rely on both genetic adaptation and phenotypic plasticity to adjust key traits that are necessary for survival and reproduction. Given the accelerating rate of climate change, plasticity may be particularly important. For organisms in warming aquatic habitats, upper thermal tolerance is likely to be a key trait, and many organisms express plasticity in this trait in response to developmental or adulthood temperatures. Although plasticity at one life stage may influence plasticity at another life stage, relatively little is known about this possibility for thermal tolerance. Here, we used locally adapted populations of the copepod Tigriopus californicus to investigate these potential effects in an intertidal ectotherm. We found that low latitude populations had greater critical thermal maxima (CTmax) than high latitude populations, and variation in developmental temperature altered CTmax plasticity in adults. After development at 25°C, CTmax was plastic in adults, whereas no adulthood plasticity in this trait was observed after development at 20°C. This pattern was identical across four populations, suggesting that local thermal adaptation has not shaped this effect among these populations. Differences in the capacities to maintain ATP synthesis rates and to induce heat shock proteins at high temperatures, two likely mechanisms of local adaptation in this species, were consistent with changes in CTmax owing to phenotypic plasticity, which suggests that there is likely mechanistic overlap between the effects of plasticity and adaptation. Together, these results indicate that developmental effects may have substantial impacts on upper thermal tolerance plasticity in adult ectotherms.

The ability of animals to learn and remember is an important adaptation for coping with environmental changes. The fitness benefits provided by these cognitive skills, in conjunction with social behaviours, contribute to the success of social insects. How these abilities are shared among the different castes and the long-term persistence of memory are now being elucidated in diverse systems, work that should shed light on general principles underlying cognitive evolution. Here, we provide the first evidence of olfactory learning and long-term olfactory memory in all three castes of an Asian hornet, Vespa velutina Using the first proboscis extension reflex assay developed for hornets or wasps, we found that all hornet castes could learn and remember odours associated with a food reward. Moreover, long-lasting memory was retained without significant decay in gynes (virgin queens) and drones even up to 30 days (workers did not survive for 30 days). Drones learned and remembered simple odorant molecules and gyne sex pheromone with equal facility. These results increase our understanding of the outstanding cognitive abilities of social insects and suggest the likely importance of long-lasting memory in different castes of the same species.

Anthropogenic noise is an important issue of environmental concern owing to its wide-ranging effects on the physiology, behavior and ecology of animals. To date, research has focused on the impacts of far-field airborne noise (i.e. pressure waves) on vertebrates, with few exceptions. However, invertebrates and the other acoustic modalities they rely on, primarily near-field airborne and substrate-borne sound (i.e. particle motion and vibrations, respectively) have received little attention. Here, we review the literature on the impacts of different types of anthropogenic noise (airborne far-field, airborne near-field, substrate-borne) on terrestrial invertebrates. Using literature on invertebrate bioacoustics, we propose a framework for understanding the potential impact of anthropogenic noise on invertebrates and outline predictions of possible constraints and adaptations for invertebrates in responding to anthropogenic noise. We argue that understanding the impacts of anthropogenic noise requires us to consider multiple modalities of sound and to cultivate a broader understanding of invertebrate bioacoustics.

For many animals, evolution has selected for complex visual systems despite the high energetic demands associated with maintaining eyes and their processing structures. Therefore, the metabolic demands of visual systems make them highly sensitive to fluctuations in available oxygen. In the marine environment, oxygen changes over daily, seasonal and inter-annual time scales, and there are large gradients of oxygen with depth. Vision is linked to survival in many marine animals, particularly among the crustaceans, cephalopods and fish, and early life stages of these groups rely on vision for prey capture, predator detection and their distribution in the water column. Using in vivo electroretinogram recordings, we show that there is a decrease in retinal sensitivity to light in marine invertebrates when exposed to reduced oxygen availability. We found a 60-100% reduction in retinal responses in the larvae of cephalopods and crustaceans: the market squid (Doryteuthis opalescens), the two-spot octopus (Octopus bimaculatus), the tuna crab (Pleuroncodes planipes) and the graceful rock crab (Metacarcinus gracilis). A decline in oxygen also decreases the temporal resolution of vision in D. opalescens These results are the first demonstration that vision in marine invertebrates is highly sensitive to oxygen availability and that the thresholds for visual impairment from reduced oxygen are species-specific. Oxygen-impaired retinal function may change the visual behaviors crucial to survival in these marine larvae. These findings may impact our understanding of species' vulnerability to ocean oxygen loss and suggest that researchers conducting electrophysiology experiments should monitor oxygen levels, as even small changes in oxygen may affect the results.

Na+/K+-ATPase (NKA)- and vacuolar H+-ATPase (VHA)-rich cells in shark gills secrete excess acid and base, respectively, to seawater to maintain blood acid-base homeostasis. Both cell types are rich in mitochondria, indicating high ATP demand; however, their metabolic fuel is unknown. Here, we report that NKA- and VHA-rich cells have large glycogen stores. Glycogen abundance in NKA-rich cells was lower in starved sharks compared with 24 h post-fed sharks, reflecting higher energy demand for acid secretion during normal activity and glycogen replenishment during the post-feeding period. Conversely, glycogen abundance in VHA-rich cells was high in starved sharks and it became depleted post-feeding. Furthermore, inactive cells with cytoplasmic VHA had large glycogen stores and active cells with basolateral VHA had depleted glycogen stores. These results indicate that glycogen is a main energy source in both NKA- and VHA-rich cells, and point to differential energy use associated with net acid and net base secretion, respectively.

Colour vision mediates ecologically relevant tasks for many animals, such as mate choice, foraging and predator avoidance. However, our understanding of animal colour perception is largely derived from human psychophysics, and behavioural tests of non-human animals are required to understand how colour signals are perceived. Here, we introduce a novel test of colour vision in animals inspired by the Ishihara colour charts, which are widely used to identify human colour deficiencies. In our method, distractor dots have a fixed chromaticity (hue and saturation) but vary in luminance. Animals can be trained to find single target dots that differ from distractor dots in chromaticity. We provide MATLAB code for creating these stimuli, which can be modified for use with different animals. We demonstrate the success of this method with triggerfish, Rhinecanthus aculeatus, which quickly learnt to select target dots that differed from distractor dots, and highlight behavioural parameters that can be measured, including success of finding the target dot, time to detection and error rate. We calculated discrimination thresholds by testing whether target colours that were of increasing colour distances (ΔS) from distractor dots could be detected, and calculated discrimination thresholds in different directions of colour space. At least for some colours, thresholds indicated better discrimination than expected from the receptor noise limited (RNL) model assuming 5% Weber fraction for the long-wavelength cone. This methodology could be used with other animals to address questions such as luminance thresholds, sensory bias, effects of sensory noise, colour categorization and saliency.

Giant clams (genus Tridacna) are the largest living bivalves and, like reef-building corals, host symbiotic dinoflagellate algae (Symbiodinium) that significantly contribute to their energy budget. In turn, Symbiodinium rely on the host to supply inorganic carbon (Ci) for photosynthesis. In corals, host 'proton pump' vacuolar-type H+-ATPase (VHA) is part of a carbon-concentrating mechanism (CCM) that promotes Symbiodinium photosynthesis. Here, we report that VHA in the small giant clam (Tridacna maxima) similarly promotes Symbiodinium photosynthesis. VHA was abundantly expressed in the apical membrane of epithelial cells of T. maxima's siphonal mantle tubule system, which harbors Symbiodinium Furthermore, application of the highly specific pharmacological VHA inhibitors bafilomycin A1 and concanamycin A significantly reduced photosynthetic O2 production by ∼40%. Together with our observation that exposure to light increased holobiont aerobic metabolism ∼5-fold, and earlier estimates that translocated fixed carbon exceeds metabolic demand, we conclude that VHA activity in the siphonal mantle confers strong energetic benefits to the host clam through increased supply of Ci to algal symbionts and subsequent photosynthetic activity. The convergent role of VHA in promoting Symbiodinium photosynthesis in the giant clam siphonal mantle tubule system and coral symbiosome suggests that VHA-driven CCM is a common exaptation in marine photosymbioses that deserves further investigation in other taxa.

Feeding kinematic studies inform our understanding of behavioral diversity and provide a framework for studying the flexibility and constraints of different prey acquisition strategies. However, little is known about the feeding behaviors used by many marine mammals. We characterized the feeding behaviors and associated kinematics of captive bearded (Erignathus barbatus), harbor (Phoca vitulina), ringed (Pusa hispida) and spotted (Phoca largha) seals through controlled feeding trials. All species primarily used a suction feeding strategy but were also observed using a biting strategy, specifically pierce feeding. Suction feeding was distinct from pierce feeding and was characterized by significantly faster feeding times, smaller gapes and gape angles, smaller gular depressions and fewer jaw motions. Most species showed higher variability in suction feeding performance than in pierce feeding, indicating that suction feeding is a behaviorally flexible strategy. Bearded seals were the only species for which there was strong correspondence between skull and dental morphology and feeding strategy, providing further support for their classification as suction feeding specialists. Harbor, ringed and spotted seals have been classified as pierce feeders based on skull and dental morphologies. Our behavioral and kinematic analyses show that suction feeding is also an important feeding strategy for these species, indicating that skull morphology alone does not capture the true diversity of feeding behaviors used by pinnipeds. The ability of all four species to use more than one feeding strategy is likely advantageous for foraging in spatially and temporally dynamic marine ecosystems that favor opportunistic predators.

As the primary source of colony reproduction, social insect queens play a vital role. However, the cognitive abilities of queens are not well understood, although queen learning and memory are essential in multiple species such as honey bees, in which virgin queens must leave the nest and then successfully learn to navigate back over repeated nuptial flights. Honey bee queen learning has never been previously demonstrated. We therefore tested olfactory learning in queens and workers and examined the role of DNA methylation, which plays a key role in long-term memory formation. We provide the first evidence that honey bee queens have excellent learning and memory. The proportion of honey bee queens that exhibited learning was 5-fold higher than that of workers at every tested age and, for memory, 4-fold higher than that of workers at a very young age. DNA methylation may play a key role in this queen memory because queens exhibiting remote memory had a more consistent elevation in Dnmt3 gene expression as compared with workers. Both castes also showed excellent remote memory (7 day memory), which was reduced by 14-20% by the DNA methylation inhibitor zebularine. Given that queens live approximately 10-fold longer than workers, these results suggest that queens can serve as an excellent long-term reservoir of colony memory.

Leaf-cutting ant queens mate with multiple males during a single nuptial flight and store sperm for up to two decades. During mating, males transfer sperm from their accessory testes to the queen bursa copulatrix from where it enters the spermatheca, an insect sperm storage organ that has become highly specialized in long-lived ant queens who never re-mate later in life. Long-term storage without the possibility to obtain new sperm creates an immune defence dilemma, because recognition of non-self cells eliminates infections but may also target irreplaceable sperm and reduce lifetime reproductive success. We therefore hypothesized that non-specific immune responses, like pathogen melanization, should be silenced in the spermatheca, because they rely on general non-self recognition, and that specific responses such as antimicrobial peptides are activated instead as they specifically target pathogenic bacteria and/or fungi. The maintenance of uninfected sperm cells by males before mating is not constrained by non-self recognition, meaning immune regulation might be more liberal in male reproductive organs. To test this hypothesis, we measured gene expression of two antimicrobial peptides, abaecin and defensin, and prophenoloxidase, an important enzyme of the melanization pathway, in male accessory glands and testes and in queen bursae copulatrix and spermathecae of Acromyrmex echinatior and Atta colombica leaf-cutting ants. As expected, prophenoloxidase expression was low in reproductive organs that sustain prolonged contact with sperm, whereas antimicrobial peptides showed average to high expression, indicating that leaf-cutting ants invest in specific rather than generalist immune defences for pathogen protection in organs that store sperm.

There is growing recognition of the need to understand the mechanisms underlying organismal resilience (i.e. tolerance, acclimatization) to environmental change to support the conservation management of sensitive and economically important species. Here, we discuss how functional genomics can be used in conservation biology to provide a cellular-level understanding of organismal responses to environmental conditions. In particular, the integration of transcriptomics with physiological and ecological research is increasingly playing an important role in identifying functional physiological thresholds predictive of compensatory responses and detrimental outcomes, transforming the way we can study issues in conservation biology. Notably, with technological advances in RNA sequencing, transcriptome-wide approaches can now be applied to species where no prior genomic sequence information is available to develop species-specific tools and investigate sublethal impacts that can contribute to population declines over generations and undermine prospects for long-term conservation success. Here, we examine the use of transcriptomics as a means of determining organismal responses to environmental stressors and use key study examples of conservation concern in fishes to highlight the added value of transcriptome-wide data to the identification of functional response pathways. Finally, we discuss the gaps between the core science and policy frameworks and how thresholds identified through transcriptomic evaluations provide evidence that can be more readily used by resource managers.

The nectar of the thunder god vine, Tripterygium hypoglaucum, contains a terpenoid, triptolide (TRP), that may be toxic to the sympatric Asian honey bee, Apis cerana, because honey produced from this nectar is toxic to bees. However, these bees will forage on, recruit for, and pollinate this plant during a seasonal dearth of preferred food sources. Olfactory learning plays a key role in forager constancy and pollination, and we therefore tested the effects of acute and chronic TRP feeding on forager olfactory learning, using proboscis extension reflex conditioning. At concentrations of 0.5-10 µg TRP ml-1, there were no learning effects of acute exposure. However, memory retention (1 h after the last learning trial) significantly decreased by 56% following acute consumption of 0.5 µg TRP ml-1 Chronic exposure did not alter learning or memory, except at high concentrations (5 and 10 µg TRP ml-1). TRP concentrations in nectar may therefore not significantly harm plant pollination. Surprisingly, TRP slightly increased bee survival, and thus other components in T. hypoglaucum honey may be toxic. Long-term exposure to TRP could have colony effects but these may be ameliorated by the bees' aversion to T. hypoglaucum nectar when other food sources are available and, perhaps, by detoxification mechanisms. The co-evolution of this plant and its reluctant visitor may therefore likely illustrate a classic compromise between the interests of both actors.

Despite its prominent role as an intracellular messenger in all organisms, cytosolic free calcium ([Ca2+]i) has never been quantified in corals or cnidarians in general. Ratiometric calcium dyes and cell imaging have been key methods in successful research on [Ca2+]i in model systems, and could be applied to corals. Here, we developed a procedure to quantify [Ca2+]i in isolated cells from the model coral species Stylophora pistillata using Indo-1 and confocal microscopy. We quantified [Ca2+]i in coral cells with and without intracellular dinoflagellate symbionts, and verified our procedure on cultured mammalian cells. We then used our procedure to measure changes in [Ca2+]i in coral cells exposed to a classic inhibitor of [Ca2+]i regulation, thapsigargin, and also used it to record elevations in [Ca2+]i in coral cells undergoing apoptosis. Our procedure paves the way for future studies into intracellular calcium in corals and other cnidarians., (© 2024. Published by The Company of Biologists Ltd.)

Organisms regularly adjust their physiology and energy balance in response to predictable seasonal environmental changes. Stressors and contaminants have the potential to disrupt these critical seasonal transitions. No studies have investigated how simultaneous exposure to the ubiquitous toxin methylmercury (MeHg) and food stress affects birds' physiological performance across seasons. We quantified several aspects of energetic performance in song sparrows, Melospiza melodia, exposed or not to unpredictable food stress and MeHg in a 2×2 experimental design, over 3 months during the breeding season, followed by 3 months post-exposure. Birds exposed to food stress had reduced basal metabolic rate and non-significant higher factorial metabolic scope during the exposure period, and had a greater increase in lean mass throughout most of the experimental period. Birds exposed to MeHg had increased molt duration, and increased mass:length ratio of some of their primary feathers. Birds exposed to the combined food stress and MeHg treatment often had responses similar to the stress-only or MeHg-only exposure groups, suggesting these treatments affected physiological performance through different mechanisms and resulted in compensatory or independent effects. Because the MeHg and stress variables were selected in candidate models with a ΔAICc lower than 2 but the 95% confidence interval of these variables overlapped zero, we found weak support for MeHg effects on all measures except basal metabolic rate, and for food stress effects on maximum metabolic rate, factorial metabolic scope and feather mass:length ratio. This suggests that MeHg and food stress effects on these measures are statistically identified but not simple and/or were too weak to be detected via linear regression. Overall, combined exposure to ecologically relevant MeHg and unpredictable food stress during the breeding season does not appear to induce extra energetic costs for songbirds in the post-exposure period. However, MeHg effects on molt duration could carry over across multiple annual cycle stages., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2024. Published by The Company of Biologists Ltd.)

Much of our understanding of the thermal physiology of intertidal organisms comes from experiments with animals acclimated under constant conditions and exposed to a single heat stress. In nature, however, the thermal environment is more complex. Aerial exposure and the unpredictable nature of thermal stress during low tides may be critical factors in defining the thermal physiology of intertidal organisms. In the fingered limpet, Lottia digitalis, we investigated whether upper temperature tolerance and thermal sensitivity were influenced by the pattern of fluctuation with which thermal stress was applied. Specifically, we examined whether there was a differential response (measured as cardiac performance) to repeated heat stress of a constant and predictable magnitude compared with heat stress applied in a stochastic and unpredictable nature. We also investigated differences in cellular metabolism and damage following immersion for insights into biochemical mechanisms of tolerance. Upper temperature tolerance increased with aerial exposure, but no significant differences were found between predictable treatments of varying magnitudes (13°C versus 24°C versus 32°C). Significant differences in thermal tolerance were found between unpredictable trials with different heating patterns. There were no significant differences among treatments in basal citrate synthase activity, glycogen content, oxidative stress or antioxidants. Our results suggest that aerial exposure and recent thermal history, paired with relief from high low-tide temperatures, are important factors modulating the capacity of limpets to deal with thermal stress.

Extended periods of skeletal muscle disuse can cause a significant loss of contractile proteins, which compromises the ability to generate force, mechanical work or power, thus compromising locomotor performance. Several hibernating organisms can resist muscle atrophy despite months of inactivity. This resistance has been attributed to a reduction in body temperature and metabolic rate and activation of physiological pathways that counteract pathways of protein degradation. However, in these systems, such strategies are not mutually exclusive and the effects of these mechanisms can be difficult to separate. In this study, we used the western fence lizard, Sceloporus occidentalis, as an ectothermic model to determine whether a reduction in metabolic rate is sufficient to resist muscle atrophy. We induced atrophy through sciatic denervation of the gastrocnemius muscle and housed lizards at either 15 or 30°C for 6-7 weeks. Following treatment, we used muscle ergometry to measure maximum isometric force, the force-velocity relationship and contractile dynamics in the gastrocnemius. This approach allowed us to relate changes in the size and morphology to functional metrics of contractile performance. A subset of samples was used to histologically determine muscle fiber types. At 30°C, denervated muscles had a larger reduction in muscle mass, physiological cross-sectional area and maximum isometric force than at 15°C. Maximum shortening velocity of the muscle decreased slightly in animals housed at 30°C but did not change in those housed at 15°C. Our results suggest that metabolic rate alone can influence the rate of muscle atrophy and that ectothermic vertebrates may have an intrinsic mechanism to resist muscle atrophy during seasonal periods of inactivity.

During flight, insect wings bend and twist under the influence of aerodynamic and inertial forces. We tested whether wing resonance of honeybees (Apis mellifera) matches the wingbeat frequency, against the 'stiff element' hypothesis that the wing's first longitudinal mode exceeds the wingbeat frequency. Six bees were immobilized with their right wing pair outspread, and stimulated with a shaker while the normal modes were recorded with a scanning Doppler laser vibrometer. The lowest normal mode of the wings was the first longitudinal bending mode and, at 602±145 Hz, was greater than the wingbeat frequency of 234±13.9 Hz. Higher-order normal modes of the wing tended to incorporate nodal lines in the chordwise direction of the trailing edge, suggesting that their mode shape did not strongly resemble wing deformation during flapping flight. These results support the stiff element hypothesis for Apis mellifera.

Experimental exposure to ocean and freshwater acidification affects the behaviour of multiple aquatic organisms in laboratory tests. One proposed cause involves an imbalance in plasma chloride and bicarbonate ion concentrations as a result of acid-base regulation, causing the reversal of ionic fluxes through GABAA receptors, which leads to altered neuronal function. This model is exclusively based on differential effects of the GABAA receptor antagonist gabazine on control animals and those exposed to elevated CO2 However, direct measurements of actual chloride and bicarbonate concentrations in neurons and their extracellular fluids and of GABAA receptor properties in aquatic organisms are largely lacking. Similarly, very little is known about potential compensatory mechanisms, and about alternative mechanisms that might lead to ocean acidification-induced behavioural changes. This article reviews the current knowledge on acid-base physiology, neurobiology, pharmacology and behaviour in relation to marine CO2-induced acidification, and identifies important topics for future research that will help us to understand the potential effects of predicted levels of aquatic acidification on organisms.

Toxic Heliconius butterflies have yellow hindwing bars that - unlike those of their closest relatives - reflect ultraviolet (UV) and long wavelength light, and also fluoresce. The pigment in the yellow scales is 3-hydroxy-dl-kynurenine (3-OHK), which is found in the hair and scales of a variety of animals. In other butterflies like pierids with color schemes characterized by independent sources of variation in UV and human-visible yellow/orange, behavioral experiments have generally implicated the UV component as most relevant to mate choice. This has not been addressed in Heliconius butterflies, where variation exists in analogous color components, but moreover where fluorescence due to 3-OHK could also contribute to yellow wing coloration. In addition, the potential cost due to predator visibility is largely unknown for the analogous well-studied pierid butterfly species. In field studies with butterfly paper models, we show that both UV and 3-OHK yellow act as signals for H. erato when compared with models lacking UV or resembling ancestral Eueides yellow, respectively, but attack rates by birds do not differ significantly between the models. Furthermore, measurement of the quantum yield and reflectance spectra of 3-OHK indicates that fluorescence does not contribute to the visual signal under broad-spectrum illumination. Our results suggest that the use of 3-OHK pigmentation instead of ancestral yellow was driven by sexual selection rather than predation.

Animals may improve camouflage by both dynamic colour change and local evolutionary adaptation of colour but we have little understanding of their relative importance in colour-changing species. We tested for differences in colour change in response to background colour and light intensity in two populations of central bearded dragon lizards (Pogona vitticeps) representing the extremes in body coloration and geographical range. We found that bearded dragons change colour in response to various backgrounds and that colour change is affected by illumination intensity. Within-individual colour change was similar in magnitude in the two populations but varied between backgrounds. However, at the endpoints of colour change, each population showed greater similarity to backgrounds that were representative of the local habitat compared with the other population, indicating local adaptation to visual backgrounds. Our results suggest that even in species that change colour, both phenotypic plasticity and geographic divergence of coloration may contribute to improved camouflage.

In colonial organisms, alarm pheromones can provide a key fitness advantage by enhancing colony defence and warning of danger. Learning which species use alarm pheromone and the key compounds involved therefore enhances our understanding of how this important signal has evolved. However, our knowledge of alarm pheromones is more limited in the social wasps and hornets compared with the social bees and ants. Vespa velutina is an economically important and widespread hornet predator that attacks honey bees and humans. This species is native to Asia and has now invaded Europe. Despite growing interest in V. velutina, it was unknown whether it possessed an alarm pheromone. We show that these hornets use sting venom as an alarm pheromone. Sting venom volatiles were strongly attractive to hornet workers and triggered attacks. Two major venom fractions, consisting of monoketones and diketones, also elicited attack. We used gas chromatography coupled to electroantennographic detection (GC-EAD) to isolate 13 known and 3 unknown aliphatic ketones and alcohols in venom that elicited conspicuous hornet antennal activity. Two of the unknown compounds may be an undecen-2-one and an undecene-2,10-dinone. Three major compounds (heptan-2-one, nonan-2-one and undecan-2-one) triggered attacks, but only nonan-2-one did so at biologically relevant levels (10 hornet equivalents). Nonan-2-one thus deserves particular attention. However, the key alarm releasers for V. velutina remain to be identified. Such identification will help to illuminate the evolution and function of alarm compounds in hornets.

Robust adhesion to wet, salt-encrusted, corroded and slimy surfaces has been an essential adaptation in the life histories of sessile marine organisms for hundreds of millions of years, but it remains a major impasse for technology. Mussel adhesion has served as one of many model systems providing a fundamental understanding of what is required for attachment to wet surfaces. Most polymer engineers have focused on the use of 3,4-dihydroxyphenyl-l-alanine (Dopa), a peculiar but abundant catecholic amino acid in mussel adhesive proteins. The premise of this Review is that although Dopa does have the potential for diverse cohesive and adhesive interactions, these will be difficult to achieve in synthetic homologs without a deeper knowledge of mussel biology; that is, how, at different length and time scales, mussels regulate the reactivity of their adhesive proteins. To deposit adhesive proteins onto target surfaces, the mussel foot creates an insulated reaction chamber with extreme reaction conditions such as low pH, low ionic strength and high reducing poise. These conditions enable adhesive proteins to undergo controlled fluid-fluid phase separation, surface adsorption and spreading, microstructure formation and, finally, solidification.

There is an accumulating body of evidence suggesting that the sub-zero Antarctic marine environment places physiological constraints on protein homeostasis. Levels of ubiquitin (Ub)-conjugated proteins, 20S proteasome activity and mRNA expression of many proteins involved in both the Ub tagging of damaged proteins as well as the different complexes of the 26S proteasome were measured to examine whether there is thermal compensation of the Ub-proteasome pathway in Antarctic fishes to better understand the efficiency of the protein degradation machinery in polar species. Both Antarctic (Trematomus bernacchii, Pagothenia borchgrevinki) and non-Antarctic (Notothenia angustata, Bovichtus variegatus) notothenioids were included in this study to investigate the mechanisms of cold adaptation of this pathway in polar species. Overall, there were significant differences in the levels of Ub-conjugated proteins between the Antarctic notothenioids and B. variegatus, with N. angustata possessing levels very similar to those of the Antarctic fishes. Proteasome activity in the gills of Antarctic fishes demonstrated a high degree of temperature compensation such that activity levels were similar to activities measured in their temperate relatives at ecologically relevant temperatures. A similar level of thermal compensation of proteasome activity was not present in the liver of two Antarctic fishes. Higher gill proteasome activity is likely due in part to higher cellular levels of proteins involved in the Ub-proteasome pathway, as evidenced by high mRNA expression of relevant genes. Reduced activity of the Ub-proteasome pathway does not appear to be the mechanism responsible for elevated levels of denatured proteins in Antarctic fishes, at least in the gills.

Social bonds are necessary for many mammals to survive and reproduce successfully. These bonds (i.e. pair-bonds, friendships, filial bonds) are characterized by different periods of development, longevity and strength. Socially monogamous species display certain behaviors not seen in many other mammals, such as adult pair-bonding and male parenting. In our studies of prairie voles (Microtus ochrogaster) and titi monkeys (Callicebus cupreus), we have examined the neurohormonal basis of these bonds. Here, we discuss the evidence from voles that aspects of adolescent and adult social behavior are shaped by early experience, including changes to sensory systems and connections, neuropeptide systems such as oxytocin and vasopressin, and alterations in stress responses. We will compare this with what is known about these processes during development and adulthood in other mammalian species, both monogamous and non-monogamous, and how our current knowledge in voles can be used to understand the development of and variation in social bonds. Humans are endlessly fascinated by the variety of social relationships and family types displayed by animal species, including our own. Social relationships can be characterized by directionality (either uni- or bi-directional), longevity, developmental epoch (infant, juvenile or adult) and strength. Research on the neurobiology of social bonds in animals has focused primarily on 'socially monogamous' species, because of their long-term, strong adult affiliative bonds. In this Review, we attempt to understand how the ability and propensity to form these bonds (or lack thereof), as well as the display of social behaviors more generally, are transmitted both genomically and non-genomically via variation in parenting in monogamous and non-monogamous species.

For many endotherms, communal roosting saves energy in cold conditions, but how this might affect social dynamics or breeding phenology is not well understood. Using chestnut-crowned babblers (Pomatostomus ruficeps), we studied the effects of nest use and group size on roosting energy costs. These 50 g cooperatively breeding passerine birds of outback Australia breed from late winter to early summer and roost in huddles of up to 20 in single-chambered nests. We measured babbler metabolism at three ecologically relevant temperatures: 5°C (similar to minimum nighttime temperatures during early breeding), 15°C (similar to nighttime temperatures during late breeding) and 28°C (thermal neutrality). Nest use alone had modest effects: even for solitary babblers at 5°C, it reduced nighttime energy expenditures by

The excretion of nitrogenous waste products in the form of ammonia (NH3) and ammonium (NH4 (+)) is a fundamental process in aquatic organisms. For mytilid bivalves, little is known about the mechanisms and sites of excretion. This study investigated the localization and the mechanisms of ammonia excretion in mytilid mussels. An Rh protein was found to be abundantly expressed in the apical cell membrane of the plicate organ, which was previously described as a solely respiratory organ. The Rh protein was also expressed in the gill, although at significantly lower concentrations, but was not detectable in mussel kidney. Furthermore, NH3/NH4 (+) was not enriched in the urine, suggesting that kidneys are not involved in active NH3/NH4 (+) excretion. Exposure to elevated seawater pH of 8.5 transiently reduced NH3/NH4 (+) excretion rates, but they returned to control values following 24 h acclimation. These mussels had increased abundance of V-type H(+)-ATPase in the apical membranes of plicate organ cells; however, NH3/NH4 (+) excretion rates were not affected by the V-type H(+)-ATPase specific inhibitor concanamycin A (100 nmol l(-1)). In contrast, inhibition of ciliary beating with dopamine and increased seawater viscosity significantly reduced NH3 excretion rates under control pH (8.0). These results suggest that NH3/NH4 (+) excretion in mytilid mussels takes place by passive NH3 diffusion across respiratory epithelia via the Rh protein, facilitated by the water current produced for filter feeding, which prevents accumulation of NH3 in the boundary layer. This mechanism would be energy efficient for sessile organisms, as they already generate water currents for filter feeding.

The vacuolar-type H(+)-ATPase (VHA) is a multi-subunit enzyme that uses the energy from ATP hydrolysis to transport H(+) across biological membranes. VHA plays a universal role in essential cellular functions, such as the acidification of lysosomes and endosomes. In addition, the VHA-generated H(+)-motive force can drive the transport of diverse molecules across cell membranes and epithelia for specialized physiological functions. Here, I discuss diverse physiological functions of VHA in marine animals, focusing on recent discoveries about base secretion in shark gills, potential bone dissolution by Osedax bone-eating worms and its participation in a carbon-concentrating mechanism that promotes coral photosynthesis. Because VHA is evolutionarily conserved among eukaryotes, it is likely to play many other essential physiological roles in diverse marine organisms. Elucidating and characterizing basic VHA-dependent mechanisms could help to determine species responses to environmental stress, including (but not limited to) that resulting from climate change.

Climate change and associated increases in water temperatures may impact physiological performance in ectotherms and exacerbate endangered species declines. We used an integrative approach to assess the impact of elevated water temperature on two fishes of immediate conservation concern in a large estuary system, the threatened longfin smelt (Spirinchus thaleichthys) and endangered delta smelt (Hypomesus transpacificus). Abundances have reached record lows in California, USA, and these populations are at imminent risk of extirpation. California is currently impacted by a severe drought, resulting in high water temperatures, conditions that will become more common as a result of climate change. We exposed fish to environmentally relevant temperatures (14°C and 20°C) and used RNA sequencing to examine the transcriptome-wide responses to elevated water temperature in both species. Consistent with having a lower temperature tolerance, longfin smelt exhibited a pronounced cellular stress response, with an upregulation of heat shock proteins, after exposure to 20°C that was not observed in delta smelt. We detected an increase in metabolic rate in delta smelt at 20°C and increased expression of genes involved in metabolic processes and protein synthesis, patterns not observed in longfin smelt. Through examination of responses across multiple levels of biological organization, and by linking these responses to habitat distributions in the wild, we demonstrate that longfin smelt may be more susceptible than delta smelt to increases in temperatures, and they have little room to tolerate future warming in California. Understanding the species-specific physiological responses of sensitive species to environmental stressors is crucial for conservation efforts and managing aquatic systems globally.

Skeletal muscles power a broad diversity of animal movements, despite only being able to produce high forces over a limited range of velocities. Pennate muscles use a range of gear ratios, the ratio of muscle shortening velocity to fiber shortening velocity, to partially circumvent these force-velocity constraints. Muscles operate with a high gear ratio at low forces; fibers rotate to greater angles of pennation, enhancing velocity but compromising force. At higher forces, muscles operate with a lower gear ratio; fibers rotate little so limiting muscle shortening velocity, but helping to preserve force. This ability to shift gears is thought to be due to the interplay of contractile force and connective tissue constraints. In order to test this hypothesis, gear ratios were determined in the medial gastrocnemius muscles of both healthy young rats, and old rats where the interaction between contractile and connective tissue properties was assumed to be disrupted. Muscle fiber and aponeurosis stiffness increased with age (P

Most butterfly families expand the number of spectrally distinct photoreceptors in their compound eye by opsin gene duplications together with lateral filter pigments; however, most nymphalid genera have limited diversity, with only three or four spectral types of photoreceptor. Here, we examined the spatial pattern of opsin expression and photoreceptor spectral sensitivities in Heliconius erato, a nymphalid with duplicate ultraviolet opsin genes, UVRh1 and UVRh2 We found that the H. erato compound eye is sexually dimorphic. Females express the two UV opsin proteins in separate photoreceptors, but males do not express UVRh1. Intracellular recordings confirmed that females have three short wavelength-sensitive photoreceptors (λmax=356, ∼390 and 470 nm), while males have two (λmax=390 and ∼470 nm). We also found two long wavelength-sensitive photoreceptors (green, λmax∼555 nm, and red, λmax∼600 nm), which express the same LW opsin. The red cell's shifted sensitivity is probably due to perirhabdomal filtering pigments. Sexual dimorphism of the UV-absorbing rhodopsins may reflect the females' need to discriminate conspecifics from co-mimics. Red-green color vision may be used to detect differences in red coloration on Heliconius wings, or for host-plant identification. Among nymphalids so far investigated, only H. erato is known to possess five spectral classes of photoreceptor; sexual dimorphism of the eye via suppression of one class of opsin (here UVRh1 in males) has not - to our knowledge - been reported in any animal.

Although neural modulation of heart rate is well established among chordate animals, the Pacific hagfish (Eptatretus stoutii) lacks any cardiac innervation, yet it can increase its heart rate from the steady, depressed heart rate seen in prolonged anoxia to almost double its normal normoxic heart rate, an almost fourfold overall change during the 1-h recovery from anoxia. The present study sought mechanistic explanations for these regulatory changes in heart rate. We provide evidence for a bicarbonate-activated, soluble adenylyl cyclase (sAC)-dependent mechanism to control heart rate, a mechanism never previously implicated in chordate cardiac control.

To date, numerous studies have shown negative impacts of CO2-acidified seawater (i.e. ocean acidification, OA) on marine organisms, including calcifying invertebrates and fishes; however, limited research has been conducted on the physiological effects of OA on polar fishes and even less on the impact of OA on early developmental stages of polar fishes. We evaluated aspects of aerobic metabolism and cardiorespiratory physiology of juvenile emerald rockcod, ITALIC! Trematomus bernacchii, an abundant fish in the Ross Sea, Antarctica, to elevated partial pressure of carbon dioxide ( ITALIC! PCO2 ) [420 (ambient), 650 (moderate) and 1050 (high) μatm ITALIC! PCO2 ] over a 1 month period. We examined cardiorespiratory physiology, including heart rate, stroke volume, cardiac output and ventilation rate, whole organism metabolism via oxygen consumption rate and sub-organismal aerobic capacity by citrate synthase enzyme activity. Juvenile fish showed an increase in ventilation rate under high ITALIC! PCO2 compared with ambient ITALIC! PCO2 , whereas cardiac performance, oxygen consumption and citrate synthase activity were not significantly affected by elevated ITALIC! PCO2 Acclimation time had a significant effect on ventilation rate, stroke volume, cardiac output and citrate synthase activity, such that all metrics increased over the 4 week exposure period. These results suggest that juvenile emerald rockcod are robust to near-future increases in OA and may have the capacity to adjust for future increases in ITALIC! PCO2  by increasing acid-base compensation through increased ventilation.

The importance of dietary salt may explain why bees are often observed collecting brackish water, a habit that may expose them to harmful xenobiotics. However, the individual salt preferences of water-collecting bees were not known. We measured the proboscis extension reflex (PER) response of Apis mellifera water foragers to 0-10% w/w solutions of Na, Mg and K, ions that provide essential nutrients. We also tested phosphate, which can deter foraging. Bees exhibited significant preferences, with the most PER responses for 1.5-3% Na and 1.5% Mg. However, K and phosphate were largely aversive and elicited PER responses only for the lowest concentrations, suggesting a way to deter bees from visiting contaminated water. We then analyzed the salt content of water sources that bees collected in urban and semi-urban environments. Bees collected water with a wide range of salt concentrations, but most collected water sources had relatively low salt concentrations, with the exception of seawater and swimming pools, which had >0.6% Na. The high levels of PER responsiveness elicited by 1.5-3% Na may explain why bees are willing to collect such salty water. Interestingly, bees exhibited high individual variation in salt preferences: individual identity accounted for 32% of variation in PER responses. Salt specialization may therefore occur in water foragers.

Neonicotinoid insecticides can impair bee learning and memory--cognitive features that play a key role in colony fitness because they facilitate foraging. For example, the commonly used neonicotinoid imidacloprid reduces honey bee olfactory learning. However, no studies have previously determined whether imidacloprid can impair aversive associative learning, although such learning should enhance bee survival by allowing bees to avoid dangerous foraging sites. To mimic attempted predation of foragers, we developed an electro-mechanical predator that consistently attacked foragers with a pinching bite at a fixed force and elicited aversive olfactory learning in a sting extension response (SER) assay. We show that chronic exposure to a sublethal concentration of imidacloprid (25.6 µg l(-1)=20.8 ppb) over 4 days (mean of 1.5 ng per bee day(-1)), significantly impaired aversive short-term learning and memory retention. Imidacloprid treatment reduced short-term learning by 87% and memory retention by 85% in comparison with control bees. Imidacloprid therefore impairs the ability of honey bees to associate a naturalistic predation stimulus--biting--with floral odor compounds. Such learning should enhance bee survival, suggesting that xenobiotics could alter more complex ecological interactions such as predator-prey relationships.

A growing body of research on the mechanics and energetics of terrestrial locomotion has demonstrated that elastic elements acting in series with contracting muscle are critical components of sustained, stable and efficient gait. Far fewer studies have examined how the nervous system modulates muscle-tendon interaction dynamics to optimize 'tuning' or meet varying locomotor demands. To explore the fundamental neuromechanical rules that govern the interactions between series elastic elements (SEEs) and contractile elements (CEs) within a compliant muscle-tendon unit (MTU), we used a novel work loop approach that included implanted sonomicrometry crystals along muscle fascicles. This enabled us to decouple CE and SEE length trajectories when cyclic strain patterns were applied to an isolated plantaris MTU from the bullfrog (Lithobates catesbeianus). Using this approach, we demonstrate that the onset timing of muscle stimulation (i.e. stimulation phase) that involves a symmetrical MTU stretch-shorten cycle during active force production results in net zero mechanical power output, and maximal decoupling of CE and MTU length trajectories. We found it difficult to 'tune' the muscle-tendon system for strut-like isometric force production by adjusting stimulation phase only, as the zero power output condition involved significant positive and negative mechanical work by the CE. A simple neural mechanism - adjusting muscle stimulation phase - could shift an MTU from performing net zero to net positive (energy producing) or net negative (energy absorbing) mechanical work under conditions of changing locomotor demand. Finally, we show that modifications to the classical work loop paradigm better represent in vivo muscle-tendon function during locomotion.

Social pollinators such as honey bees face attacks from predators not only at the nest, but also during foraging. Pollinating honey bees can therefore release alarm pheromones that deter conspecifics from visiting dangerous inflorescences. However, the effect of alarm pheromone and its chemical components upon bee avoidance of dangerous food sources remains unclear. We tested the responses of giant honey bee foragers, Apis dorsata, presented with alarm pheromone at a floral array. Foragers investigated the inflorescence with natural alarm pheromone, but 3.3-fold more foragers preferred to land on the 'safe' inflorescence without alarm pheromone. Using gas chromatography-mass spectrometry analysis, we identified eight chemical components in the alarm pheromone, of which three components (1-octanol, decanal and gamma-octanoic lactone) have not previously been reported in this species. We bioassayed six major compounds and found that a synthetic mixture of these compounds elicited behaviors statistically indistinguishable from responses to natural alarm pheromone. By testing each compound separately, we show that gamma-octanoic lactone, isopentyl acetate and (E)-2-decen-1-yl acetate are active compounds that elicit significant alarm responses. Gamma-octanoic lactone elicited the strongest response to a single compound and has not been previously reported in honey bee alarm pheromone. Isopentyl acetate is widely found in the alarm pheromones of sympatric Asian honey bee species, and thus alarmed A. dorsata foragers may produce information useful for conspecifics and heterospecifics, thereby broadening the effects of alarm information on plant pollination.