Journal of Experimental Zoology Part A: Ecological and Integrative Physiology

The shift to terrestrial environments in ancestrally aquatic animals is often associated with key physiological and physical changes, including shifts in respiratory physiology and in some cases, even the evolution of completely novel respiratory structures. Examining how respiration operates across a gradient of submersion states in ancestrally aquatic terrestrial animals may shed light on how complex biological traits shift under different selective regimes. In this work, we begin exploring respiration in terrestrially-adapted land crabs that still use their gills to respire while underwater. We tested the relationship between aquatic respiratory rates, body size, and sex in red devil vampire crabs (Geosesarma hagen) at two ecologically-relevant temperatures. We found small females respire more than small males at 28{degrees}C, while large females respire more than large males at 21{degrees}C. Additionally, body size is a significant factor affecting respiratory rates of both sexes at 21{degrees}C and warmer temperatures significantly increase respiration in small crabs of both sexes. Interactions between these factors also led to emerging trends that can be explained by both physiological rules, such as reproductive investment and surface-to-volume ratios and heat transfer. We also report a temperature coefficient (Q10) of 1.52 for this species, showing an expected 52% change in respiratory and metabolic rate for every 10{degrees}C increase. This work also demonstrates the importance of understanding how and to what extent biological variables like sex and body size interact with abiotic environmental factors when measuring physiological traits in ectothermic invertebrate animals.

Climate-driven warming is challenging the physiological limits of aquatic ectotherms, with cardiac performance emerging as one of the key determinants of thermal tolerance. Cardiac function relies on mitochondrial ATP production, and mitochondrial dysfunction has been linked to cardiac failure at critical temperatures. However, mitochondria are plastic and may represent a target for interventions aimed at improving thermal tolerance in fish. Exercise training improves whole-animal performance in fish, including cardiac thermal performance, and improves mitochondrial function in other taxa. However, its effects on the thermal sensitivity of cardiac mitochondria remain unknown. This study investigated whether exercise-training alters cardiac mitochondrial performance at optimal and critical temperatures in rainbow trout Oncorhynchus mykiss. Farmed rainbow trout were subjected to a four-week exercise training regime, while control fish remained under standard rearing conditions. Cardiac mitochondrial respiration was assessed in permeabilised heart fibres at 16{degrees}C (optimal growth temperature) and 26{degrees}C (temperature associated with cardiac arrhythmia) and several biochemical and nuclear indicators were measured. No significant differences were detected between treatments for any measured variable. However, trained fish generally exhibited higher maximal respiratory capacities and respiratory control ratios, particularly at the elevated temperature, suggesting subtle improvements in mitochondrial function despite considerable inter-individual variation. Temperature influenced mitochondrial performance, increasing proton leak and reducing coupling efficiency. These findings demonstrate that cardiac mitochondrial function is thermally sensitive and represents a potential targeted for improving thermal resilience in aquaculture species.

Anoxia is a major stress for most vertebrates and frequently accompanies harsh winter conditions, particularly in species that spend much of the season frozen solid. North American freeze-tolerant wood frogs (Rana sylvatica) can survive several months without oxygen and endure whole-body freezing for up to eight months of the year, with [~]70% of total body water frozen as extracellular ice, yet revive when temperatures rise in spring. Survival depends on multiple adaptations, including tolerance of prolonged oxygen deprivation while frozen, when breathing and circulation are halted. A key strategy involves hepatic glycogen mobilization, producing large amounts of glucose that are distributed to tissues where it functions both as a cryoprotectant and as a substrate for anaerobic ATP production. The present study examines the role of histone lysine methylation and demethylation in regulating liver proteins under anoxic conditions. Relative protein expression of seven histone methyltransferases (ASH2L-S, ASH2L-L, RBBP5, SETD8, SMYD2, ESET, SETD1), six lysine demethylases (KDM1A, KDM3B, KDM4A, KDM4B, KDM5A, KDM5C), and eight histone marks (H3K4me1, H3K4me2, H3K9me3, H3K27me3, H3K36me3, H3K79me3, H4K20me1, H4K20me3) were evaluated in wood frog liver under control, 4-hour, and 24-hour anoxia exposures. The data indicate that histone lysine methylation and demethylation contribute significantly to transcriptional regulation under anoxia. Specifically, H3K4, H3K36, and H3K79 methylation were associated with transcriptional activation, whereas H3K9, H3K27, and H4K20 methylation correlated with transcriptional repression. These findings highlight the dynamic role of epigenetic regulation in supporting hypometabolism and stress adaptation in freeze-tolerant wood frogs.

Absorption of CO2 by global oceans is decreasing pH resulting in ocean acidification (OA). Impacts on shellfish have been documented in ecologically and commercially important species. We examined the influence of diet and OA between two populations of red abalone (Haliotis rufescens) a species of aquaculture importance and declining wild populations. Populations experience different exposure histories: strong upwelling (Van Damme, California [VD]) historically exposed to low-pH conditions and weak-intermittent upwelling (Santa Barbara, California [SB]). Abalone were cultured under control-pH or OA-conditions and fed crustose coralline algae (CCA) or diatoms used in aquaculture. We tested treatment effects of population, settlement diet, and OA-exposure on survival as influenced by larval-energy stores. Survival in both populations was enhanced by CCA when cultured under both treatment conditions; however, by later stages, this effect remained only for SB. SB had reduced post-settlement survival when cultured under OA-conditions, whereas post-settlement survival of VD was not. Diet affected the relationship between larval-energy and post-settlement survival; a positive relationship when fed diatoms and a negative relationship with CCA. The relationship between larval energy and post-settlement survival was stronger in VD. CCA enhanced juvenile growth in SB cultured abalone at both three-months and one-year post-settlement. Settlement diets can reduce the impacts of OA on early-life stages of abalone, but population differences driven by underlying energetics affect the consistency of this outcome. These findings illuminate the impacts from OA, suggesting populations may be at risk, and inform strategies for developing and sustaining shellfish aquaculture in the face of changing ocean conditions.

Sleep is a ubiquitous, yet highly variable, behavior across species. The duration and timing of sleep are influenced by ecological demands and dietary context. In the mosquito Aedes aegypti, a blood-feeding insect with specialized nutritional requirements, the relationship between feeding and sleep remains poorly understood. Here, we investigated how blood-derived dietary protein influences sleep regulation. Using postural analysis, videography, and arousal-threshold assays, we established that immobility bouts of greater than 10 minutes reliably define sleep in Ae. aegypti. Mosquitoes lacking the circadian clock gene cycle still maintained daily sleep rhythms but exhibited reduced sleep duration and heightened overall activity. Infrared activity monitoring revealed that blood-fed females showed a marked increase in sleep beginning immediately after feeding and persisting for several days, accompanied by reduced locomotor activity. Notably, this sleep elevation lasted well beyond the cessation of previously reported host-seeking phases, raising the possibility of distinct phases of opportunistic versus targeted host pursuit. To determine the dietary basis of this effect, we tested mosquitoes fed a bovine serum albumin (BSA)-based diet. BSA feeding alone was sufficient to mimic the sleep-promoting and activity-reducing effects of blood, suggesting dietary protein is a major nutritional regulator. Moreover, RNAi-mediated knockdown of the leucokinin receptor (Lkr), which has previously been associated with fluid homeostasis and feeding behavior, resulted in enhanced sleep and reduced activity, implicating mosquito LK signaling in the modulation of postprandial sleep. Together, these findings demonstrate that blood-derived proteins drive sustained increases in sleep and reductions in locomotor activity in Ae. aegypti. This work positions Ae. aegypti as a model for dissecting nutrient-specific regulation of sleep and highlights potential adaptive functions of protein-induced quiescence, such as energy conservation and predator avoidance. More broadly, it provides insight into how specialized diets shape the neural and behavioral architecture of sleep.

Crown-of-thorns sea star (CoTS), Acanthaster cf. solaris, outbreaks are a major cause of hard coral cover decline across the west Pacific, threatening coral reefs. Coral taxa vary in susceptibility to CoTS predation from preferred (Acropora spp.) to non-preferred (Porites spp.), yet the mechanisms underlying these differences are poorly understood. We investigated coral defenses during an ongoing CoTS outbreak in Mo'orea, French Polynesia by examining gene expression (including putative toxin genes) in healthy and actively predated colonies of a preferred (Acropora hyacinthus) and a non-preferred (Porites sp.) coral prey species. During predation, A. hyacinthus exhibited molecular signatures of cellular stress responses involving oxidative stress signalling, inflammation, and tissue proteolysis. In contrast, Porites sp. showed enrichment of genes involved in mitochondrial metabolic adjustment and aerobic metabolism, suggesting metabolic compensation to maintain cellular function. Furthermore, A. hyacinthus demonstrated a reactive defense behaviour by differentially expressing toxins (e.g., kunitz-type neurotoxins) while Porites sp. employed constitutive expression of all putative toxins regardless of active predation, suggesting a proactive defense strategy. Together, these findings suggest that preferred and non-preferred coral prey exhibit fundamentally different molecular and defensive strategies during CoTS predation, shedding light on the evolutionary arms race between corals and their predators.

The energetic demands of courtship are central to sexual selection, but their magnitude and temporal variation remain poorly quantified in many signalling systems. We used closed-chamber respirometry and low-light video analysis to estimate courtship-associated metabolic rates in males of the bioluminescent ostracod Photeros sp. EGD. Low-activity metabolic rate varied strongly across the diel cycle: in small vessels that constrained movement, individually measured males consumed significantly more oxygen at night than during the day. We then compared oxygen consumption across vessels that differed in opportunities for movement and courtship. Metabolic rates were highest in large vessels that permitted bioluminescent courtship displays, intermediate in medium vessels that allowed swimming but not full displays, and lowest in small vessels that constrained movement. Oxygen consumption in large vessels at night was approximately 500% of small-vessel daytime rates, 280% of small-vessel nighttime rates, and 160% of medium-vessel nighttime rates. Because measurements integrated oxygen use over multi-hour intervals, these values represent time-averaged metabolic demand rather than instantaneous costs of individual light pulses or display trains. Video analyses suggested a positive association between signalling rate and oxygen consumption, although this relationship was not statistically supported in our large-vessel dataset, which had low statistical power. Together, these results show that male Photeros undergo strong diel shifts in metabolic state and that the whole-animal performance required to construct bioluminescent courtship displays may often impose substantial energetic demands.

The gut microbiome is increasingly recognized as a pivotal modulator of animal behaviour, yet its influence on wild fauna remains largely unexplored. We investigated the correlational relationship between gut microbiota, behavioural phenotypes, and management practices in 26 captive endangered Iberian lynxs (Lynx pardinus) maintained within the ex-situ Iberian breeding program facilities, in two geographically distant stations in SW Spain. Behavioural observations were intensively recorded over two years, and three personality profiles emerged, i.e., (i) anomalous (with the highest frequencies for stereotypies), and (ii) sedentary and (iii) active (with the highest frequencies for sedentarism and for locomotion and surveillance, respectively). Fecal samples were analyzed for biweekly periods by 16S rRNA gene amplicon sequencing to profile bacterial composition and predicted functional pathways, and significant associations were found for each of the behavioural phenotypes. Both breeding station and local environment influenced gut microbial communities and personality profiles, underscoring the influence of management practices and local habitat in shaping the microbiome-behaviour nexus. Specific bacterial taxa and metabolic pathways were consistently associated with each behavioural phenotype, suggesting that microbial fecal signatures could serve as non invasive biomarkers for individual personality monitoring. This work constitutes the first comprehensive, multi layered examination of the interplay among behaviour, gut microbiota, and environmental factors in a large, wild carnivore. This integrative approach may help conservation programmes to optimize management decisions and improve reintroduction success

Evolutionary and demographic processes such as selection, drift and migration shape the genetic variation of populations. Genetic diversity is often lower in populations toward higher latitudes. This decrease potentially threatens their survival as several factors are putting more pressure on the populations, including the spread of infectious diseases. In this study, we combined whole-genome re-sequencing with MHC class II genotyping and skin microbiome profiling in Bufo bufo and B. spinosus, two closely related European toad species. We investigated the underlying immunogenetic and microbial variation resulting from different demographic histories and environmental conditions to identify their potential impact on infection outcomes in these two species. We found lower immunogenetic diversity in B. bufo compared to B. spinosus, with highly significant differences in genes related to adaptive and innate immunity. We found lower overall MHC class II diversity and skin microbiome diversity at the species level in B. bufo, compared with B. spinosus. In contrast, at the individual level, B. bufo showed higher MHC allelic diversity and greater diversity in the core skin microbiota than B. spinosus. Together, our findings suggest that divergence in immunogenetic background and host-associated microbial communities may underlie differences in susceptibility to emerging infectious diseases. This integrative framework provides new insight into how host genetics and microbial communities jointly influence disease outcomes across environmental gradients.

The moonfish Mene maculata (Bloch and Schneider, 1801), the sole extant species of the family Menidae, is widely distributed in the Indo-West Pacific. Although its spawning season has previously been inferred from seasonal variation in the gonadosomatic index (GSI), the histological basis for interpreting GSI as an indicator of spawning-capable status remains limited. Here we describe the gonadal structure of male and female M. maculata and evaluate how GSI and standard length relate to spawning-capable status based on germ cell development. The testis was lobular and exhibited an unrestricted spermatogonial distribution, a structure widely observed among neoteleosts, indicating that the phylogenetic distinctiveness of M. maculata was not associated with a distinctive testicular structure. In the spawning-capable female, oocytes at multiple developmental stages, from primary growth to oocyte maturation, co-occurred within the ovary, indicating asynchronous ovarian development. This finding suggests that M. maculata may be a batch spawner rather than a total spawner as previously inferred. The spawning-capable female had a GSI consistent with previously inferred spawning season estimates. By contrast, histologically examined males were spawning capable at GSI values lower than those previously associated with the inferred spawning season, suggesting that male spawning-capable status may persist beyond the period inferred from elevated GSI alone. This study provides the first histological description of reproductive biology in the phylogenetically distinctive M. maculata and establishes a histological basis for interpreting GSI as a reproductive indicator.

Untargeted metabolomics offers a powerful lens for quantifying high-dimensional phenotypic variation within and among species in nature, but has yet to be widely adopted in evolutionary ecology. Some important initial questions are whether metabolome composition differs among populations, and to what extent such variation is genetic or plastic. Here, we use untargeted liquid chromatography tandem mass spectrometry to characterize the relative abundance of 5,939 molecular features of the threespine stickleback (Gasterosteus aculeatus) liver metabolome. Native lake populations differ in metabolome composition, reflecting effects of sex, size, geography, and population ecotype (benthic versus limnetic). Stickleback from these lakes were translocated to found new populations in nine recently fishless lakes, permuting fish ecotypes across benthic and limnetic lake habitats. Several generations later, metabolomes in these experimental populations reflect effects both of their genetic ancestry (e.g., taurocholic acid, a cholane steroid bile acid, was elevated in limnetic-ancestries), as well as their present habitat (e.g., acylcarnitines). Additionally, ecotypes transplanted into a habitat to which they were maladapted exhibited a distinctive metabolomic profile. We conclude that stickleback exhibit both heritable and plastic among-population differences in liver metabolome, which could represent an important phenotypic basis of rapid evolution, population divergence, and perhaps local adaptation.

Fat accumulation and use is critical for sustaining life. Most insects show a typical response to feeding where fat is accumulated when sufficient sugars and other carbohydrates are consumed. Parasitoid insects are an exception, because most species do not accumulate fat when feeding on a sugar-rich diet. Studies on fat metabolism generally measure fat content early in life without considering lipid metabolism as a dynamic process that is expected to change as life progresses. In this paper, we compared fat accumulation and use throughout the lives of adult female Drosophila melanogaster and females of 5 inbred lines of the parasitoid wasp Leptopilina heterotoma. We expected that fat accumulation would take place irrespective of teneral fat content in D. melanogaster. We found that fat D. melanogaster initially used fat reserves, while lean flies economized on fat stores. Both lean and fat flies started accumulating fat after 7 days of life, indeed showing a typical response for insects. Unlike other parasitoids, L. heterotoma populations differs in fat accumulation patterns that we expected to observe also between inbred lines. In none of the inbred lines, however, did fat accumulation take place. Our results did reveal that inbred lines differed in the rate at which fat was used mainly later during life. We further confirmed that D. melanogaster pupal size was highly correlated with adult female size for both D. melanogaster and L. heterotoma. Overall, our findings for L. heterotoma provide strong evidence that genetic background has a major impact on the rate at which fat is used over a lifetime.

One challenge of reintroduction programs is ensuring that captive individuals are prepared for life in the wild, including having the ability to forage on wild resources. Foraging proficiency can be especially challenging to foster in species with a wide dietary breadth or reliance on ephemerally available resources. A relatively unexplored obstacle to release readiness may be an animals hesitancy to approach or consume unfamiliar foods, i.e. their neophobia and dietary conservatism. In this study, we examined the responses of a conservation breeding population of the extinct-in-the-wild alal[a] (Corvus hawaiiensis), a dietary generalist, to novel and familiar native and non-native fruits. Birds were similarly willing to contact both novel and familiar fruits, suggesting little aversion to the presence and appearance of novel food items. However, birds showed a clear preference for contacting non-native fruits over native fruits, regardless of familiarity. Additionally, while birds were willing to contact novel items, they were less likely to consume novel native fruits, suggesting that dietary conservatism may limit incorporation of these resources in the wild. Finally, juvenile birds were less likely to approach the testing setup and contact items, suggesting that neophobia may constrain their exploration of novel environments and resources. We discuss the implications of alal[a] preferences for non-native foods and reluctance to consume novel native items for pre-release preparations and the goal of wild species recovery.

O_LIThermal performance curves (TPCs) predict species vulnerability to climate change, but standard respirometry assumes that measured oxygen consumption reflects physiological state. Sessile invertebrates that retract their tentacles and contract under thermal stress violate this assumption, with unmeasured consequences for thermal limit estimates. C_LIO_LIWe tested this behavioral confound in an undescribed cold-water intertidal anemone (Urticina sp.) in the Northwest Atlantic by integrating a negative binomial encounter-rate regression, a maximum entropy species distribution model (both from effort-corrected iNaturalist data), and closed-chamber respirometry across seven temperatures (1-30{degrees}C, 18 individuals, 126 trials). C_LIO_LIThe strongest distributional predictors were cloud cover and coastal urbanization, with a weaker association with winter minimum SST; direct evidence for warm-edge thermal limitation came from the experiment. Anemone expansion state (scored 0-1 from fully closed to fully expanded) was variable and without a clear trend across the coldest treatments but declined above 20{degrees}C before collapsing at the 30{degrees}C treatment, which proved lethal to all individuals. C_LIO_LIStandard TPC models extrapolated the thermal maximum far beyond the lethal bracket ([~]74{degrees}C symmetric Gaussian; 45.9{degrees}C asymmetric). A Bayesian multiplicative model that separated physiology from behavior showed that physiology continued to track temperature while expansion state declined above 20{degrees}C; a fully expanded anemone respired about twice as fast as a fully closed one at the same temperature. The decline in measured respiration is therefore both behavioral and physiological, and disentangling the two requires recording expansion state alongside oxygen consumption. C_LIO_LIBecause a closed anemone cannot feed or exchange gases, the ecologically relevant thermal limit is the temperature at which the animal can no longer maintain its normal expanded posture, not a curve-fitted thermal maximum. That behavioral threshold leaves warm-edge populations within a few degrees of functional thermal failure. C_LIO_LIFuture thermal physiology studies of organisms capable of modulating oxygen consumption through behavior should incorporate quantitative behavioral covariates to separate physiological from behavioral components of the metabolic response. C_LI

Many insects enter diapause, a programmed state of developmental arrest that enables survival under adverse environmental conditions. In Drosophila melanogaster Meigen, 1830, diapause is characterized by reproductive arrest and reduced intestinal growth, accompanied by suppressed intestinal stem cell (ISC) activity. Juvenile Hormone (JH) promotes ISC proliferation under favorable conditions, but its capacity to modulate stem cell dynamics during cold-induced diapause remains unclear. Here, we investigated whether JH signaling can reactivate midgut remodeling in adult females maintained at 11. At this temperature, flies exhibited pronounced gut atrophy and elevated Phospho-histone H3 (PH3+) cell abundance, consistent with temperature-dependent G2/M phase arrest JH treatment significantly increased the proportion of Delta-positive progenitor cells in the anterior (R2) and posterior (R5) midgut regions at both 11 and 25, demonstrating that JH acts as a conserved mitogen for the ISC pool irrespective of thermal environment. A trend toward reduced PH3+ accumulation in the posterior midgut following JH treatment (p = 0.061) suggests possible facilitation of mitotic exit, though this effect did not reach statistical significance. Despite cellular-level changes, JH treatment did not restore overall gut size, indicating that the 72-84 hour exposure window was insufficient for subsequent tissue hypertrophy. Additionally, we identified a recurrent cold-induced pathology of gut distension, provisionally termed Lumen Obstruction Syndrome (LOS), which was independent of JH signaling. These findings reveal an uncoupling of JH-driven stem cell expansion from gross organ growth under diapause conditions, highlighting the selective sensitivity of the ISC compartment to endocrine signaling during environmental stress.

Understanding the genetic structure of keystone species within river networks is essential for effective conservation and management. While population differentiation of anadromous species often occurs between river systems, less research has been conducted on differentiation within rivers with smaller catchment areas. In this study, we investigated the population genetic structure of wild Atlantic salmon (Salmo salar) across the small-scale river Ronne [a] system in southernmost Sweden using Restriction-site Associated DNA sequencing (RADseq). Although the Admixture analysis did not detect clearly defined genetic clusters, significant pairwise FST values and DAPC revealed emerging population differentiation among the Ronne [a] tributaries. The observed patterns are consistent with a system characterized by connectivity, where genetic flow is present but can be reduced by behavioral and ecological factors such as spawning homing behavior and selective movements. These findings suggest that, despite overall connectivity, Atlantic salmon populations in the Ronne [a] catchment area may function as partially independent sub-populations. This highlights the importance of conservation and management strategies in fragmented river systems to consider population genetic structure to support resilient salmon populations under ongoing anthropogenic pressures.

Advances in metagenomic sequencing have transformed our understanding of host-associated microbiota, revealing critical roles in immune regulation, nutrient metabolism, and gastrointestinal (GI) homeostasis. However, the gut microbiome of large non-model species, particularly elephants, remains poorly characterized. Captivity introduces dietary, environmental, and management-related perturbations that may disrupt microbial balance and contribute to GI dysfunction. Here, we performed a longitudinal analysis of the fecal microbiome in five captive Asian elephants (Elephas maximus) at the Oregon Zoo exhibiting chronic fecal abnormalities, including mucus and inconsistent stool formation. Over 14 weeks, weekly fecal samples were collected and compared with samples from clinically normal elephants housed at three other zoological institutions. Using 16S rRNA gene sequencing, we identified marked differences in microbial community composition between affected and control elephants. Dysbiosis in Oregon Zoo elephants was characterized by enrichment of Akkermansia muciniphila and multiple members of the order Clostridiales, including taxa previously associated with gastrointestinal disorders. Administration of a commercially available probiotic formulation was associated with transient improvement in fecal characteristics and pronounced shifts in microbial composition, including a significant post-treatment reduction in overall microbial diversity and decreased abundance of several taxa linked to GI abnormalities. Notably, probiotic strains themselves were not detected, suggesting indirect or short-lived functional effects rather than durable colonization. Together, these findings provide one of the first longitudinal characterizations of gut microbiome dysbiosis in captive Asian elephants and identify candidate microbial contributors to chronic GI dysfunction in captivity, with implications for husbandry, dietary management, and microbiome-informed interventions in megafauna. Additionally, our study underscores the potential, although limited and likely indirect, benefit of probiotics when treating GI disorders in monograstric megavertebrates.

Age-dependent survival is central to understanding population dynamics and life-history evolution. We analysed carcass weight and age-at-harvest data from 6022 red foxes (Vulpes vulpes) collected across Sweden between 1967 and 1971 to evaluate latitudinal effects on body mass and age-dependent survival. Carcass weights decreased from south to north in both adults and sub-adults, contrary to Bergmann's rule, with southern foxes weighing approximately 1.27 times more than northern foxes. The latitudinal weight gradient exceeded the sex difference in both age classes, and no sex x region interaction was detected. The decrease in weight with latitude is consistent with reduced prey availability and harsher winter conditions in the north, which limit growth and body size during development. Using a Bayesian age-at-harvest model with region-specific population growth rates (lambda), we estimated age-dependent survival probabilities for four latitudinal regions and both sexes. Despite the strong latitudinal gradient in weight, survival did not show a corresponding pattern - regional differences were uncertain, with all credible intervals spanning zero. Regional population growth rates were consistent with slight decline in the north and near-stability in the south-central region, which suggests that body condition and population dynamics are coupled at the regional scale despite no survival gradient. The decoupling of body condition and survival across regions suggests that mortality patterns are similar across the latitudinal gradient. We discuss these patterns in terms of latitudinal productivity gradients, prey availability, and life-history trade-offs in a widely distributed carnivore.

Despite extensive research on vestibular function in microgravity, particularly during orbital and parabolic flight exposure, several gaps remain regarding the spontaneous behavior of vestibular organs under non-terrestrial gravitoinertial conditions. In particular, semicircular canal function, typically assessed through vestibulo-ocular reflex (VOR) recordings, has yielded inconsistent findings, with reports describing either no effect or reduced performance in microgravity. Moreover, many of these studies are limited by methodological constraints that reduce the interpretability of their conclusions. To clarify these discrepancies, we evaluated horizontal and vertical VOR responses during parabolic flights to assess semicircular canal function under transient weightlessness. Participants were passively rotated at a constant frequency and amplitude during normogravity and microgravity phases, centered along the head vertical or inter-aural axis. Eye movements were recorded binocularly using infrared eye-tracking in darkness to eliminate visual influences, while participants were tightly restrained to minimize proprioceptive variability. Results show a reduction in VOR gain during microgravity in both axes, despite consistent rotational stimulation across gravity conditions. In addition, VOR gain remained reduced after parabolas in the horizontal plane, whereas vertical VOR performance was preserved. These are the first results to demonstrate an immediate alteration of semicircular canal function in weightlessness. Possible sources of the reduction in VOR performance in 0g are discussed. We also propose that the observed post-flight effects reflect a down-weighting of semicircular canal inputs during multisensory integration.

Fistulobalanus albicostatus Pilsbry, 1916 (Thoracica: Balanidae) is a tropical to temperate species distributed in the NW Pacific. The previously known northernmost record of this species in Japan was from Aomori Prefecture, at the northern end of Honshu Island, Japan. However, field surveys conducted in 2023 and 2026 confirmed the occurrence of F. albicostatus in Hakodate Bay, the southern end of Hokkaido, Japan, across the Tsugaru Strait, thereby extending the northern limit of its known distribution. A line transect survey conducted in May 2026 recorded seven living individuals within an area of 128 m. F. albicostatus was rare on the mid-high shores, accounting for only 2% of all barnacle individuals in a quadrat survey. The basal diameter of the living individuals ranged from 0.76 to 1.23 cm, and all individuals possessed ovaries. Based on characteristics of both morphological and COI gene, the specimens were identified as F. albicostatus, and belonged to the same haplotype of populations that are present in Honshu Island. The establishment of F. albicostatus in Hokkaido suggests an ongoing northward range shift of this warm-water species, with the potential for further expansion under continued ocean warming.