Cosima S. Porteus

Relative to other subdisciplines of conservation science, conservation physiology remains somewhat nascent. Although there is a growing number of successes where physiological concepts, knowledge and tools have informed conservation decisions and management actions, there also remain a number of challenges. We argue that there is a set of misconceptions that serve as de facto barriers to realizing the full potential of conservation physiology as a mission-oriented area of scholarly inquiry and practice. However, we also suggest that those misconceptions can be easily dispelled. In this paper, we identify and dispel 10 ‘myths’ in conservation physiology: (i) conservation physiology subsumes other disciplines and has no unique goals; (ii) the toolbox is too invasive; (iii) tools are too specialized; (iv) the field relies too heavily on surrogates and captive studies; (v) physiological information cannot be scaled from the individual level to the population level; (vi) baseline (i.e. control) data are too sparse; (vii) conservation physiology is too speculative; (viii) managers do not care about physiology; (ix) conservation physiology cannot engage fundamental scientists; and (x) conservation physiology cannot solve conservation problems. Given that some of these misconceptions represent ongoing barriers, we also identify opportunities for further overcoming them. In particular, embracing co-production and engaging in effective knowledge exchange are fundamental to generating relevant and actionable knowledge. Similarly, we submit that the tension between fundamental and applied science is not inherently disruptive and ensures that there is a strong foundation for evidence-based decisions. This paper is intended to open the eyes and minds of ecologists, physiologists and end-users about what conservation physiology has to offer and how to realize those opportunities. Working collectively and collaboratively to achieve the common mission of conservation physiology will not only benefit conservation science but will also benefit biodiversity and society.

Hydrogen sulfide (H₂S) plays a crucial role in various physiological processes and has been implicated in modulating aging through its impacts on oxidative stress and cellular health. This study investigates the evolutionary dynamics of the cystathionine-β-synthase (CBS), the cystathionine-ƴ-lyase (CSE), and the 3-mercaptopyruvate sulfurtransferase (3-MST) genes, involved in endogenous H₂S production. We investigated CBS, CSE, and 3-MST in long-lived mammals, focusing on the naked mole-rat (Heterocephalus glaber). We hypothesized that these genes would exhibit signs of positive selection linked to extended lifespan. Codon-based evolutionary models were used to compare these genes across 114 mammalian species. Our results revealed a relaxation of purifying selection instead of positive selection in CSE, but not CBS and 3-MST, in long-lived mammals, suggesting an accumulation of mutations that enhance physiological functions related to longevity. In the naked mole-rat, CSE exhibited clear signs of positive selection, particularly in residues G116A and T118V, associated with increased protein stability and enhanced binding affinity to the cofactor pyridoxal-5'-phosphate (PLP). These mutations possibly improve CSE catalytic efficiency and potentially H₂S production, supporting the naked mole-rat's unique adaptations to its subterranean habitat and contributing to its remarkable lifespan. Our findings indicate a potential correlation between longevity and selection on the CSE gene, but not the CBS and 3-MST genes, highlighting the complex role of H₂S in aging and cellular health. The study provides new insights into the molecular mechanisms underlying lifespan extension in long-lived mammals and underscores the potential adaptive significance of H₂S biogenesis in the naked mole-rat.

Rapidly increasing anthropogenic CO ₂ can impose physiological challenges for fish species that are thought to be tolerant. We tested the hypothesis that elevated pCO ₂ will affect the routine activity and escape response by affecting energy metabolism and/or the muscle physiology of coastal fish. We exposed threespine stickleback ( Gasterosteus aculeatus ) to pCO ₂ of ~ 700 µatm (pH 7.9 representing current levels), ~ 1400 µatm (pH 7.6 representing upwelling events) and ~ 3500 µatm (pH 7.3 representing a future predicted scenario for coastal areas) for 2 weeks. Baseline activity was significantly higher in fish exposed to 1400 µatm compared to the control at both sampling points, while the escape response was lower ( p < 0.05). Metabolic rate was not different ( p > 0.05), but lactate dehydrogenase activity was significantly higher at 3500 µatm compared to control fish after the first week ( p < 0.05), while no difference was found in muscle histology between treatments or time points. Our study demonstrates that the baseline activity and escape responses of adult marine coastal fish were temporarily affected by the current level of ocean acidification, but this was not due to changes in metabolism or muscle function, but potentially neuronal effects of high pCO ₂ . Our study shows that ocean acidification might affect predator‐prey interactions during current upwelling events and in the future.

Increases in atmospheric carbon dioxide accelerate ocean acidification (OA), which has been shown to alter olfactory behaviours in marine organisms. Coastal regions currently experience partial pressure of carbon dioxide ( pCO ₂ ) greater than end-of-century open ocean predictions with daily and seasonal fluctuations. Therefore, we hypothesized that marine organisms inhabiting the coastal regions are tolerant to the effects of OA. The acute, static, and fluctuating effects of acidification on the olfactory system were investigated in the coastal yellow shore crab ( Hemigrapsus oregonensis (Dana, 1851)). After exposures, the olfactory behaviour to a food cue, putrescine, was measured, and changes in olfactory sensory receptors and neurons (OSNs) were determined using immunohistochemistry. Crabs took three times longer to locate the odorant and preferred it less after acute (minutes) and long-term (14 days) static exposures to OA. This impairment was correlated with a 16%–30% decrease in olfactory receptor protein (ionotropic receptor 25a (IR25a)) immunoreactivity and a 20% decrease in OSN volume. Crabs exposed to daily fluctuating pCO ₂ (7 days) displayed behavioural responses intermediate to crabs in control or static acidification conditions, and showed no changes in IR25a. These results indicate that despite their variable natural environment, yellow shore crabs are affected by acidification, being particularly vulnerable during sustained upwelling events (long-term static high pCO ₂ ).

Background There are a variety of published standard methods and water chemistry recommendations for zebrafish (Danio rerio) husbandry, but empirical evidence for their justification is often lacking, as is information on some variables that have important biological effects on fish. Importantly, these different recommendations could contribute to variability in results and fish welfare between or within institutions. Methods Here we document the current range of water chemistry used by various research institutions around the world and report initial findings on their effects on the development and growth of zebrafish. Over 40 institutes responded to a survey that revealed a large variation in water chemistry used for zebrafish husbandry including differences in the set-points and acceptable ranges for temperature, pH and conductivity. In subsequent experiments, zebrafish (D. rerio, WIK) embryos/larvae exposed to a large range of salt concentrations (50μM to 10mM Na+ or 30 – 2500 μS/cm) and CO2 levels (400 – 8,000 μatm). Results Larvae exposed to the lowest salt concentration (5 μM Na+ or < 30μS/cm) had a slower response to touch and their swim bladders were not inflated. Larvae exposed to 5-100 μM Na+ were 5 % shorter in total body length than those exposed to higher salt concentrations (>100 μM Na+). Zebrafish embryo/larvae exposed to intermediate pCO2 values (~2000 μatm) were 1 to 3.5% longer than those exposed to either ambient (400 μatm) or higher (4000 μatm) pCO2, but pCO2 did not affect developmental endpoints up to 4 dpf. Conclusions Overall, we highlight the magnitude of variation in water chemistry used within zebrafish research and provide some empirical evidence to show that not all of these water conditions might be optimal for developing zebrafish and reproducibility of research, although further research is necessary to determine longer-term effects of water chemistry on older larvae, juveniles and adults.

Coastal marine environments are characterized by daily, seasonal and long-term changes in both O₂ and CO₂, driven by local biotic and abiotic factors. The neuroepithelial cells (NECs) of fish are thought to be the putative chemoreceptors for sensing oxygen and CO₂, and, thus, NECs play a key role in detecting these environmental changes. However, the role of NECs as chemosensors in marine fish remains largely understudied. In this study, the NECs of marine threespine sticklebacks (Gasterosteus aculeatus) were characterized using immunohistochemistry. We then determined if there were changes in NEC size and density, and in gill morphology in response to either mild (10 kPa) or moderate (6.8 kPa) hypoxia and two levels of elevated CO₂ (1,500 and 3,000 µatm). We found that the NECs of stickleback contained synaptic vesicles and were innervated, and were 50–300% larger and 2 to 4 times more abundant than in other similar sized freshwater fishes. NEC size and density were largely unaffected by exposure to hypoxia, but there was a 50% decrease in interlamellar cell mass (ILCM) in response to mild and moderate hypoxia. NECs increased in size, but not abundance in response to elevated CO₂. Moreover, fish exposed to moderate or elevated CO₂ had 53–78% larger ILCMs compared to control fish. Our results demonstrated that adult marine sticklebacks have NECs that can respond to environmentally relevant pCO₂ and likely hypoxia, which highlights the importance of NECs in marine fishes under the heterogeneity of environmental conditions in coastal areas.

In this review, we explore the inconsistencies in the data and gaps in our knowledge that exist in what is currently known regarding gill chemosensors which drive the cardiorespiratory reflexes in fish. Although putative serotonergic neuroepithelial cells (NEC) dominate the literature, it is clear that other neurotransmitters are involved (adrenaline, noradrenaline, acetylcholine, purines, and dopamine). And although we assume that these agents act on neurons synapsing with the NECs or in the afferent or efferent limbs of the paths between chemosensors and central integration sites, this process remains elusive and may explain current discrepancies or species differences in the literature. To date it has been impossible to link the distribution of NECs to species sensitivity to different stimuli or fish lifestyles and while the gills have been shown to be the primary sensing site for respiratory gases, the location (gills, oro-branchial cavity or elsewhere) and orientation (external/water or internal/blood sensing) of the NECs are highly variable between species of water and air breathing fish. Much of what has been described so far comes from studies of hypoxic responses in fish, however, changes in CO₂, ammonia and lactate have all been shown to elicit cardio-respiratory responses and all have been suggested to arise from stimulation of gill NECs. Our view of the role of NECs is broadening as we begin to understand the polymodal nature of these cells. We begin by presenting the fundamental picture of gill chemosensing that has developed, followed by some key unanswered questions about gill chemosensing in general.

Background There are a variety of published standard methods and water chemistry recommendations for zebrafish (Danio rerio) husbandry, but empirical evidence for their justification is often lacking, as is information on some variables that have important biological effects on fish. Importantly, these different recommendations could contribute to variability in results and fish welfare between or within institutions. Methods Here we document the current range of water chemistry used by various research institutions around the world and report initial findings on their effects on the development and growth of zebrafish. Over 40 institutes responded to a survey that revealed a large variation in water chemistry used for zebrafish husbandry including differences in the set-points and acceptable ranges for temperature, pH and conductivity. In subsequent experiments, zebrafish (D. rerio, WIK) embryos/larvae exposed to a large range of salt concentrations (50μM to 10mM Na+ or 30 – 2500 μS/cm) and CO2 levels (400 – 8,000 μatm). Results Larvae exposed to the lowest salt concentration (5 μM Na+ or < 30μS/cm) had a slower response to touch and their swim bladders were not inflated. Larvae exposed to 5-100 μM Na+ were 5 % shorter in total body length than those exposed to higher salt concentrations (>100 μM Na+). Zebrafish embryo/larvae exposed to intermediate pCO2 values (~2000 μatm) were 1 to 3.5% longer than those exposed to either ambient (400 μatm) or higher (4000 μatm) pCO2, but pCO2 did not affect developmental endpoints up to 4 dpf. Conclusions Overall, we highlight the magnitude of variation in water chemistry used within zebrafish research and provide some empirical evidence to show that not all of these water conditions might be optimal for developing zebrafish and reproducibility of research, although further research is necessary to determine longer-term effects of water chemistry on older larvae, juveniles and adults.

With the unprecedented environmental changes caused by climate change including ocean acidification, it has become crucial to understand the responses and adaptive capacity of fish to better predict directional changes in the ecological landscape of the future. We conducted a systematic literature review to examine if simulated ocean acidification (sOA) could influence growth and reproduction in fish within the dynamic energy budget theory framework. As such, we chose to examine metabolic rate, locomotion, food assimilation and growth in early life stages (i.e. larvae and juvenile) and adults. Our goal was to evaluate if acclimatization to sOA has any directional changes in these traits and to explore potential implications for energetic trade-offs in these for growth and reproduction. We found that sOA had negligible effects on energetic expenditure for maintenance and aerobic metabolism due to the robust physiological capacity regulating acid–base and ion perturbations but substantive effects on locomotion, food assimilation and growth. We demonstrated evidence that sOA significantly reduced growth performance of fish in early life stages, which may have resulted from reduced food intake and digestion efficiency. Also, our results showed that sOA may enhance reproduction with increased numbers of offspring although this may come at the cost of altered reproductive behaviours or offspring fitness. While these results indicate evidence for changes in energy budgets because of physiological acclimatization to sOA, the heterogeneity of results in the literature suggests that physiological and neural mechanisms need to be clearly elucidated in future studies. Lastly, most studies on sOA have been conducted on early life stages, which necessitates that more studies should be conducted on adults to understand reproductive success and thus better predict cohort and population dynamics under ongoing climate change.