Journal of Experimental Zoology Part A: Ecological and Integrative Physiology

Telomeres are key biomarkers of cellular ageing, yet their dynamics remain poorly studied in tropical and short-lived bat species. Here, we present the first investigation of telomere length across age in Molossus molossus, a tropical bat historically categorised as the shortest-lived bat on record. Through a multi-year mark-recapture study in Gamboa, Panama, we sampled 492 individuals (n = 317 females, 175 males) and documented a female M. molossus surviving to at least 13 years of age, more than doubling the previously reported maximum lifespan of 5.6 years. Across the population, relative telomere length (rTL) showed no overall significant decline with age. No evidence was found for sex-specific rates of telomere attrition. Rather these results suggest that males and females follow parallel age-related telomere trajectories, with any sex differences primarily reflecting differences in mean telomere length rather than ageing dynamics. Overall, the findings here challenge previous assumptions about the lifespan and ageing biology of M. molossus. They demonstrate that telomere maintenance is not limited to temperate bats, show that sex differences in telomere biology are subtle and species-specific, and reinforce the value of long-term field studies for understanding ageing processes in the wild.

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.

Climate change-induced heatwaves threaten ectotherms, whose physiology is tightly coupled to ambient temperature. Vulnerability assessments often rely on data from one or a few populations, implicitly assuming uniform thermal sensitivity across species genetic diversity. Quantifying such variation is especially important for traits with wider ecological consequences; our focus here is on immune function, which shapes disease dynamics. We addressed this knowledge gap using ten clonal lineages of the New Zealand snail Potamopyrgus antipodarum exposed to ambient (17{degrees}C) or heatwave conditions (27{degrees}C) for 4 or 8 days. We measured two complementary innate immune traits: general phenoloxidase-like (PO-like) activity, which integrates the activity of multiple phenoloxidase enzymes, and laccase activity, which targets a specific PO enzyme subclass important in mollusc immunity. Heat exposure suppressed both traits, but patterns differed across clones. While PO-like activity declined uniformly, laccase activity showed substantial among-clone variation in heatwave responses at day 4, though these differences converged by day 8. Heat-induced immune suppression is thus trait-specific, depends on genetic background, and varies with exposure duration. Together, these results demonstrate that studies limited to a single genotype, population, or timepoint risk miscalculating species-level vulnerability.

Avian haemosporidia are blood parasites that can have dramatic fitness consequences on their hosts, including largescale population declines when introduced to naive hosts. Yet the physiological effects that accompany haemosporidian infection and underlie these fitness decrements are poorly characterized in most wild birds. Because haemosporidia destroy host red blood cells and consume host hemoglobin, they are predicted to have detrimental impacts on avian blood-oxygen transport and, as a result, reduce aerobic performance. However, the documented effects of infection on avian hematological traits vary across species and no effects have been demonstrated on avian aerobic performance to date. Here we quantified the physiological effects of haemosporidian infections on wild Pink-sided Juncos (Junco hyemalis mearnsi) breeding in northwestern Wyoming, USA. We assayed hematological traits (hemoglobin concentration and hematocrit) and aerobic performance (resting and summit metabolic rates, thermogenic endurance, and aerobic scope), then screened individuals for haemosporidian infection post-hoc (n = 106 adult juncos). We found that infection status did not correlate with any of the physiological indices that we measured, suggesting there is little cost of haemosporidian infection on either junco aerobic performance or energy budgets. Our results highlight the need for more studies of haemosporidia infections in a broader range of species and in a wider array of environmental contexts.

O_LIBody condition is an important life history challenge that directly impacts individual fitness and is particularly important for hibernating animals, whose maintenance of adequate body fat and mass is essential for survival. C_LIO_LIIt is well documented that symbiotic microorganisms play a vital role in animal physiology and behaviour. Recent work demonstrates that gut microbes are associated with fat accumulation and obesity; Firmicutes is consistently associated with obesity while Bacteroidetes is associated with leanness both in humans and other animals. C_LIO_LIThe focus of most microbiome studies has been on human health or involved lab reared animals used as a model system. However, these microbes likely are important for individual fitness in wild populations and provide potential mechanistic insights into the adaptability and survival of wildlife. C_LIO_LIHere we test whether symbiotic microorganisms within the phyla of Firmicutes and Bacteroidetes are associated with summer mass gain in an exceptionally well-studied wild population of yellow-bellied marmots (Marmota flaviventer) by quantifying microbial abundance over five years of fecal samples (2015 - 2019) collected during their summer active season. C_LIO_LIResults show that marmots with higher mass gain rates have a greater abundance of Firmicutes. In contrast, higher abundance of Bacteroidetes was associated with lower mass gain rates, but only for marmots living in harsher environments. Similar patterns were found at the family level where Ruminococcaceae, a member of Firmicutes, was associated with higher mass gain rates, and Muribaculaceae, a member of Bacteroidetes, was associated with lower mass gain rates, and similarly in harsher environments. C_LIO_LIAlthough correlative, these results highlight the importance of symbiotic gut microbiota to mass gain in the wild, a trait associated with survival and fitness in many taxonomic groups. C_LI

U.S. quail species are vulnerable to population declines as a result climate change, habitat loss, and habitat fragmentation; all of which can induce physiological stress. Additionally, population restoration techniques (PRTs), like translocations, also induce stress. Traditional stress assessments include capturing and handling birds to extract blood, methods which are inherently stressful and can compound stress analyses. However, the stress hormone corticosterone is metabolized from the blood and excreted in feces as fecal corticosterone metabolites (FCMs). FCMs have been used as a non-invasive measurement of stress in a variety of species, but must be validated for each species. The objective of this study was to biologically validate the use of FCMs as a non-invasive measurement of stress-hormone levels in California valley quail (Callipepla californica). Reference and treatment quail were acclimated for 3 wks in an outdoor aviary. Subsequently, treatment quail were subjected to a simulated, 48-h translocation, a common and stressful PRT. Fecal samples were collected every 4 h and processed using an enzyme immunoassay. Mean FCM concentrations of treatment quail (41.50 {+/-}16.13 ng/g) were higher than reference FCM concentrations (24.07 {+/-}10.4 ng/g). These results biologically validate the use of FCMs as a non-invasive method to assess stress hormone levels in California valley quail, demonstrate diurnal variation in quail stress levels, and confirms that quail translocations are a stressful PRT. Ultimately, this research validates a new non-invasive tool for stress measurement to advance quail research, management, and conservation. Lay summaryThis study biologically validates the use of fecal corticosterone metabolites as a non-invasive method for detecting stress in quail, demonstrates diurnal variation in quail stress levels, confirms that translocations elevate stress which likely impacts success, and establishes a new non-invasive tool for stress measurement in quail research, management, and conservation.

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.

Amphibians that reproduce in early spring at northern latitudes may encounter environmental ice while migrating to their breeding sites. Due to the nucleation properties of ice, contact with environmental ice may induce rapid freezing of body tissues, which can cause irreversible damage to cells and lead to death. Although some species of salamanders are known to move over ice during early spring migration, freeze-intolerant species are expected to avoid physical contact with ice crystals to minimise the risk of freezing. Here, we documented the thermal biology of the freeze-intolerant blue-spotted salamander (Ambystoma laterale Hallowell, 1856) migrating at sub-zero temperatures in Algonquin Provincial Park, Ontario, Canada. During our surveys, we found sheltered, inactive, and migrating individuals; some in direct contact with ice. Our field measurements of skin temperature using high resolution thermal imaging suggest that A. laterale can sustain activity in a supercooled state (i.e., chilled below the freezing point of body fluids but not frozen). By migrating in a supercooled state, these salamanders may overcome the risk of freezing while simultaneously prolonging their breeding season and potentially avoiding predators.

Many different physiological changes have been observed in wild waterfowl during the flightless stage of wing moult, including a loss of body mass. Previously we established that captive barnacle geese (Branta leucopsis) underwent this characteristic decrease in body mass during their wing moult, even though they had unlimited and unrestricted access to food. In the present study we aimed to determine if this body mass loss during moult comprised mainly a reduction in fat stores, and to ascertain if the captive geese undergo pre-migratory and pre-winter fattening over a similar temporal scale to their wild conspecifics. The non-destructive technique of deuterium oxide isotope dilution was employed to provide repeated measurements of estimated fat deposition from a captive flock of fourteen barnacle geese. Birds were injected with deuterium oxide at 7 distinct intervals for one annual cycle. During the flightless period of the moult, body fat decreased by approximately 40% from the pre-moult value. During late-September and early October, body fat reached its highest point in the annual cycle, both as an absolute value and as a percentage of total body mass. We propose that while the energetic cost of wing moult is not the ultimate cause of fat loss in moulting barnacle geese, the approximate 212 g of fat catabolised during moult would provide sufficient energy to cover the cost of the replacement of the flight feathers, estimated to be 6384 kJ, over an approximate 42 day period. We conclude that the previously recorded increase in metabolism during moult in the geese, led to the use of endogenous fat reserves because the birds reduced rather than increased their food intake rates owing to the increased risk of predation when flightless. We also conclude that captive barnacle geese do undergo pre-winter and pre-migratory fattening, providing further evidence of the innate nature of these fat deposition cycles.Competing Interest StatementThe authors have declared no competing interest.View Full Text

From a conservation perspective, it is important to identify when sub-lethal temperatures begin to adversely impact an organism. However, it is unclear whether, during acute exposures, these cellular thresholds occur at similar temperatures to other physiological or behavioural changes. To test this, we estimated temperature preference (15.1 {+/-} 1.1 {degrees}C) using a shuttle box, thermal optima for aerobic scope (10-15 {degrees}C) using respirometry, agitation temperature (22.0 {+/-} 1.4 {degrees}C) as the point where a fish exhibits a behavioural avoidance response and the CTmax (28.2 {+/-} 0.4 {degrees}C) as the upper thermal limit for 1 yr old Brook Trout (Salvelinus fontinalis) acclimated to 10 {degrees}C. We then acutely exposed a different subset of fish to these temperatures and sampled tissues when they reached the target temperature or after 60 min of recovery at 10 {degrees}C. We used qPCR to estimate mRNA transcript levels of genes associated with heat shock proteins, oxidative stress, apoptosis, and inducible transcription factors. A major shift in the transcriptome response occurred near the agitation temperature, which may identify a link between the cellular stress response and the behavioural avoidance response.

Pacific Oysters (Magallana/Crassostrea gigas) are marine bivalves that are widely cultivated but increasingly experience summer mortality due to interacting stressors. Two major concerns are (1) the rising severity and frequency of marine heat waves and (2) disease outbreaks (e.g., OsHV-1). To better understand how multiple stressors influence oyster resilience and whether stress priming can improve survival, we tested the effects of parental immune challenge on offspring performance. We exposed broodstock to a Poly(I:C) immune challenge, reared their offspring to the seed stage, and assessed survival, growth, and metabolic responses under thermal stress in the lab. Offspring of immune-challenged parents showed higher growth rates during development. Under elevated temperatures, these offspring had higher survival than controls at 40{degrees}C, but lower survival at 42{degrees}C, suggesting thermal limits to priming benefits. Metabolic assays further revealed that at moderately elevated temperature (36{degrees}C), primed offspring had higher metabolic activity, whereas at higher temperature (40{degrees}C), they exhibited lower metabolic activity than controls. This pattern indicates that parental immune challenge may influence offspring metabolic flexibility, potentially enhancing thermal tolerance through an increased capacity for metabolic depression at extreme temperatures. Together, our results highlight cross-generational links between immune priming and thermal tolerance.

Temperatures in aquatic ecosystems have been affected by anthropogenic activities such as agricultural and industrial water use, and climate change caused by greenhouse gas emissions. Changes in water temperature directly affect the cellular and organismal physiology of fishes because most fishes are ectotherms. These effects can take different forms, such as increased cellular stress and reactive oxygen species (ROS) production. However, the type and magnitude of response depend on the duration and the frequency of the exposure to elevated water temperature. In this study, we investigated the long-term effects of exposure to daily thermal fluctuations occurring during early-life stages of zebrafish, Danio rerio, on gene expression and CTmax in later developmental stages. To do so, wild-type zebrafish were exposed daily to a + 5{degrees}C fluctuation in temperature from ambient (28 {degrees}C) to 33 {degrees}C over the first 30 days post fertilization (dpf), before being held until 90 dpf at ambient temperature. The fish that experienced daily thermal fluctuation were compared to a control group that was kept at 28 {degrees}C throughout the experiment and sampled at the same timepoints. Samples were collected at 18 (larval), 30, 60 (juvenile), and 90 (adult) dpf to study the expression of heat shock proteins and oxidative stress genes. The thermotolerance of fish was tested using CTmax trials at 60 and 90 dpf. Daily thermal fluctuation over the first 30 dpf led to a significant increase in the expression of hsp47, gstp1a, sod1, and sod2 genes at 60 dpf, and hsp47, hsp90aa1, hsp90ab1, cat, glulb, gstp1a, sod1, and sod2 genes at 90 dpf. The only significant increase detected during the larval stage was glulb at 18 dpf. Fish that experienced thermal fluctuation also had a higher CTmax at 60 dpf, but this increased thermotolerance significantly decreased from 60 to 90 dpf, where it was not different between treatments. Overall, our study demonstrates that early-life thermal stress increased cellular stress responses and thermotolerance in zebrafish into later ontological stages.

Birds maintain unusually high circulating glucose levels compared with other vertebrates without developing the diabetic complications observed in mammals, yet the mechanisms underlying this resistance remain unclear. We investigated the effects of chronic glucose and methylglyoxal supplementation on physiological condition in zebra finches (Taeniopygia guttata), with particular emphasis on sex- and season-dependent variation in plasma biochemistry, haematology and immune traits. Ninety zebra finches (45 males, 45 females) were randomly assigned to control, glucose-supplemented (50 g/L), or methylglyoxal (8.33 g/L) drinking treatments. Over one year, we analysed plasma proteins, metabolites (glucose, uric acid, bile acids), tissue damage markers (AST, CK), electrolytes, and immune parameters (leukocyte profiles). Both supplementations increased plasma glucose concentrations, with methylglyoxal producing the strongest effect. More importantly, both treatments disrupted seasonal plasma protein dynamics, preventing the increase in total proteins and globulins normally observed in females during the reproductive period, which suggests alterations in reproductive-related protein metabolism. Glucose supplementation elevated the heterophil-to-lymphocyte (H/L) ratio in May and August, consistent with elevated physiological stress. In contrast, methylglyoxal supplementation reduced the H/L ratio in November and unexpectedly lowered plasma AST and CK concentrations in May, suggesting context-dependent protective effects on tissue integrity despite its well-established pro-oxidative properties, potentially through hormetic mechanisms. Supplementation also modified the calcium/phosphate balance, further supporting treatment effects on seasonal (reproductive) physiology. Overall, our findings demonstrate that glucose and methylglyoxal reshape physiological regulation in zebra finches in a strongly sex- and season-dependent manner rather than simply inducing generalized metabolic damage. These results provide new insights into avian resistance to glucose-associated physiological challenges and highlight the importance of considering both biological context and standardized haematological reference values when investigating glucose metabolism in birds.

1. Increases in ultraviolet radiation (UVR) correlate spatially and temporally with global amphibian population declines and interact with other stressors such as disease and temperature. Declines have largely occurred in high-altitude areas associated with greater UVR and cooler temperatures. 2. UVR is a powerful mutagenic harming organisms largely by damaging DNA. When acutely exposed to UVR at cool temperatures, amphibian larvae have increased levels of DNA damage. Amphibians may be able to compensate for the depressive effects of temperature on DNA damage through thermal acclimatisation, but it is unknown whether they or other ectotherms have this capacity. 3. We reared striped marsh frog larvae (Limnodynastes peronii) in warm (25{degrees}C) and cool (15{degrees}C) temperatures under either a low or moderate daily dose of UVR (10 and 40 {micro}W cm-2 UV-B for 1 h at midday, respectively) for 18-20 days and then measured immediate DNA damage resulting from an acute high UVR dose (80 {micro}W cm-2 UV-B for 1.5 h) at a range of test temperatures (10, 15, 20, 25, and 30{degrees}C). 4. Larvae acclimated to 15{degrees}C and exposed to UVR at 15{degrees}C completely compensated UVR-induced DNA damage compared with 25{degrees}C acclimated larvae exposed to UVR at 25{degrees}C. Additionally, warm-acclimated larvae had higher CPDs than cold-acclimated larvae across test temperatures, which indicated a cost of living in warmer temperatures. In contrast, larvae reared under chronic elevated UVR levels showed no evidence of UVR acclimation resulting in lower DNA damage following an acute high UVR exposure. 5. Our finding that thermal acclimation in L. peronii larvae compensated UVR-induced DNA damage at low temperatures suggested that aquatic ectotherms living in cool temperatures may be more resilient to high UVR than previously realised. 6. We suggested individuals or species with less capacity for thermal acclimation of DNA repair mechanisms may be more at risk if exposed to changing thermal and UVR exposure regimes but cautioned that thermal acclimation of DNA repair mechanisms may not always be beneficial.

Parasites can have profound effects on their hosts, and those effects can be altered by changing environmental conditions. The dinoflagellate Hematodinium sp. is a common and deadly parasite of the crab Chionoecetes bairdi, a species vulnerable to rising ocean temperatures. To examine the impact of parasitism under various temperature conditions, infected crabs (n = 9) were held under three temperature regimes (4{degrees}C, 7.5{degrees}C, and 10{degrees}C) for 17 days. RNAseq was performed on samples from three timepoints, and the relationships of temperature and time to gene expression were examined. Transcriptomes for C. bairdi and Alveolata symbiotes were created, and genes linked to immune function were identified within both host and parasite. Within the host, 1721 contigs were differentially expressed in response to a temperature increase, with 86% of these increased in expression. In total, 3013 contigs linked to temperature response were identified. Additionally, numerous changes in biological processes were observed in Hematodinium over the course of the experiment, including development and microtubule-based processes and ribosomal assembly. Through understanding the impact of changes in temperature on gene expression within both Hematodinium and infected C. bairdi, we provide a more complete picture of the response of these species to rising ocean temperatures.

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.

Populations of marine species that respond differently to ocean acidification offer natural reservoirs of biodiversity that can be leveraged for conservation efforts and to sustain marine food systems. The molecular and physiological traits associated with tolerance to acidification must first be identified. This study leveraged oysters from three phenotypically distinct populations of the Olympia oyster, Ostrea lurida, but that were bred and reared in common conditions for four years. We assessed their growth, reproductive development, and transcriptional response to acidification within and across generations. Responses reveal energetic trade-offs that reflect unique physiotypes previously observed among populations. The population with the slowest growth but high survival rates, oysters from Dabob Bay, mounted the largest transcriptional response to acidification without effects to growth and reproduction. A moderate response was observed in the population with fastest growth rate but lowest fecundity (Fidalgo Bay). Oyster Bay, the population with highest fecundity but lowest survival rates, did not respond at the transcript level. Oyster Bay was also the only population for which acidification negatively affected growth and reproductive development. While exposure to acidification did not affect gene expression in the next generations larval stage, it did result in larger larvae in the Oyster Bay population, which could partially alleviate negative effects of acidification in the wild for that population. Given the distinct transcriptional response of the Dabob Bay population to acidification and its high survival rates in previous studies, we then identified genes that were uniquely expressed in Dabob Bay oysters compared to the other populations. Genes involved in antibacterial and antiviral processes, metabolism, growth, and reproduction were uniquely expressed in Dabob Bay, and many similar functions were identified in both adults and larvae, which provides insight into the mechanisms behind a stress-tolerant oyster population. The population-specific physiotypes and responses to acidification illustrate the diversity of physiological strategies in O. lurida that balance the energetic demands of growth, reproduction, cellular maintenance, and offspring viability. Taken together this study reveals that there are distinct physiotypes among marine invertebrate populations on small geographic scales with implications for species resilience to acidification and other environmental stressors.

Maternal thyroid hormones (THs) are known to be crucial in embryonic development in humans, but their influence on other, especially wild, animals remains poorly understood. So far, the studies that experimentally investigated the consequences of maternal THs focused on short-term effects, while early organisational effects with long-term consequences, as shown for other prenatal hormones, could also be expected. In this study, we aimed at investigating both the short- and long-term effects of prenatal THs in a bird species, the Japanese quail Coturnix japonica. We experimentally elevated yolk TH content (the prohormone T4, and its active metabolite T3, as well as a combination of both hormones). We analysed hatching success, embryonic development, offspring growth and oxidative stress as well as their potential organisational effects on reproduction, moult, and oxidative stress in adulthood. We found that eggs injected with both hormones had a higher hatching success compared with control eggs, suggesting conversion of T4 into T3 by the embryo. We detected no other clear short-term or long-term effects of yolk THs. These results suggest that yolk thyroid hormones are important in the embryonic stage of precocial birds, but other short- and long-term consequences remain unclear. Research on maternal thyroid hormones will greatly benefit from studies investigating how embryos use and respond to this maternal signalling. Long-term studies on prenatal THs in other taxa in the wild are needed for a better understanding of this hormone-mediated maternal pathway.

1.The aim of this study was to investigate the effect of ocean acidification (OA) and warming (OW) as well as the transgenerational effect of OA on larval and juvenile growth and metabolism of a large economically important fish species with a long generation time. Therefore we incubated European sea bass from Brittany (France) for two generations (>5 years in total) under current and predicted OA conditions (PCO2: 650 and 1700 {micro}atm). In the F1 generation both OA condition were crossed with OW (temperature: 15-18{degrees}C and 20-23{degrees}C). We found that OA alone did not affect larval or juvenile growth and OW increased developmental time and growth rates, but OAW decreased larval size at metamorphosis. Larval routine metabolic rate (RMR) and juvenile standard metabolic rate (SMR) were significantly lower in cold compared to warm conditioned fish and also lower in F0 compared to F1 fish. We did not find any effect of OA on RMR or SMR. Juvenile PO2crit was not affected by OA, OW or OAW in both generations. We discuss the potential underlying mechanisms resulting in beneficial effects of OW on F1 larval growth and RMR and in resilience of F0 and F1 larvae and juveniles to OA, but on the other hand resulting in vulnerability of F1, but not F0 larvae to OAW.. With regard to the ecological perspective, we conclude that recruitment of larvae and early juveniles to nursery areas might decrease under OAW conditions but individuals reaching juvenile phase might benefit from increased performance at higher temperatures. Summary statementWe found that OA did not affect developmental time, growth, RMR and SMR, while OW increased these traits. OAW decreased larval size at metamorphosis. We discuss underlying mechanisms and the ecological perspective resulting from these results and conclude that recruitment to nursery areas might decrease under OAW conditions but individuals reaching juvenile phase might benefit from increased performance at higher temperatures in Atlantic waters.

In natural environments two or more abiotic parameters often vary simultaneously, and interactions between covarying parameters frequently result in unpredictable, non-additive biological responses. To better understand the mechanisms and consequences of interactions between multiple stressors it is important to study their effects on both survival and performance. The splashpool copepod Tigriopus californicus tolerates extremely variable abiotic conditions and exhibits a non-additive, antagonistic interaction resulting in higher survival when simultaneously exposed to high salinity and acute heat stress. Here, we investigated T. californicus response in activity and oxygen consumption under simultaneous manipulation of salinity and temperature to identify if this interaction also arises in these sublethal measures of performance. Oxygen consumption and activity rates decreased with increasing assay salinity. Oxygen consumption also sharply increased in response to acute transfer to lower salinities, an effect that was absent upon transfer to higher salinities. Elevated temperature led to reduced rates of activity overall, resulting in no discernible impact of increased temperature on routine metabolic rates. This suggests that swimming activity has a non-negligible effect on copepods metabolic rates and must be accounted for in metabolic studies. Temperature also interacted with assay salinity to affect activity and with acclimation salinity to affect routine metabolic rates upon acute salinity transfer, implying that the sublethal impacts of these co-varying factors are also not predictable from experiments that study them in isolation. Summary StatementTemperature and salinity interact to affect metabolic rate in the copepod Tigriopus californicus, but the stressors individual effects and their interaction are complicated by concurrent changes in activity.