Scaling of Activity Space in Marine Organisms across Latitudinal Gradients

AbstractUnifying models have shown that the amount of space used by animals (e.g., activity space, home range) scales allometrically with body mass for terrestrial taxa; however, such relationships are far less clear for marine species. We compiled movement data from 1,596 individuals across 79 taxa collected using a continental passive acoustic telemetry network of acoustic receivers to assess allometric scaling of activity space. We found that ectothermic marine taxa do exhibit allometric scaling for activity space, with an overall scaling exponent of 0.64. However, body mass alone explained only 35% of the variation, with the remaining variation best explained by trophic position for teleosts and latitude for sharks, rays, and marine reptiles. Taxon-specific allometric relationships highlighted weaker scaling exponents among teleost fish species (0.07) than sharks (0.96), rays (0.55), and marine reptiles (0.57). The allometric scaling relationship and scaling exponents for the marine taxonomic groups examined were lower than those reported from studies that had collated both marine and terrestrial species data derived using various tracking methods. We propose that these disparities arise because previous work integrated summarized data across many studies that used differing methods for collecting and quantifying activity space, introducing considerable uncertainty into slope estimates. Our findings highlight the benefit of using large-scale, coordinated animal biotelemetry networks to address cross-taxa evolutionary and ecological questions.

The rise of animal biotelemetry and genetics research data integration

The advancement and availability of innovative animal biotelemetry and genomic technologies are improving our understanding of how the movements of individuals influence gene flow within and between populations and ultimately drive evolutionary and ecological processes. There is a growing body of work that is integrating what were once disparate fields of biology, and here, we reviewed the published literature up until January 2023 (139 papers) to better understand the drivers of this research and how it is improving our knowledge of animal biology. The review showed that the predominant drivers for this research were as follows: (1) understanding how individual-based movements affect animal populations, (2) analyzing the relationship between genetic relatedness and social structuring, and (3) studying how the landscape affects the flow of genes, and how this is impacted by environmental change. However, there was a divergence between taxa as to the most prevalent research aim and the methodologies applied. We also found that after 2010 there was an increase in studies that integrated the two data types using innovative statistical techniques instead of analyzing the data independently using traditional statistics from the respective fields. This new approach greatly improved our understanding of the link between the individual, the population, and the environment and is being used to better conserve and manage species. We discuss the challenges and limitations, as well as the potential for growth and diversification of this research approach. The paper provides a guide for researchers who wish to consider applying these disparate disciplines and advance the field.

Dietary shifts may underpin the recovery of a large carnivore population

Supporting the recovery of large carnivores is a popular yet challenging endeavour. Estuarine crocodiles in Australia are a large carnivore conservation success story, with the population having extensively recovered from past heavy exploitation. Here, we explored if dietary changes had accompanied this large population recovery by comparing the isotopes δ¹³C and δ¹⁵N in bones of crocodiles sampled 40 to 55 years ago (small population) with bones from contemporary individuals (large population). We found that δ¹³C and δ¹⁵N values were significantly lower in contemporary crocodiles than in the historical cohort, inferring a shift in prey preference away from marine and into terrestrial food webs. We propose that an increase in intraspecific competition within the recovering crocodile population, alongside an increased abundance of feral ungulates occupying the floodplains, may have resulted in the crocodile population shifting to feed predominantly upon terrestrial food sources. The number of feral pigs consumed to sustain and grow crocodile biomass may help suppress pig population growth and increase the flow of terrestrially derived nutrients into aquatic ecosystems. The study highlights the significance of prey availability in contributing to large carnivore population recovery.

Crocodile social environments dictated by male philopatry

Examining the social behaviors of solitary species can be challenging due to the rarity in which interactions occur and the large and often inaccessible areas which these animals inhabit. As shared space-use is a prerequisite for the expression of social behaviors, we can gain insights into the social environments of solitary species by examining the degree of spatial overlap between individuals. Over a 10-year period, we examined how spatial overlap amongst 105 estuarine crocodiles Crocodylus porosus was influenced by season, sex, and movement tactic. We discovered that crocodiles displayed highly consistent spatial overlaps with conspecifics between months and across years. Furthermore, male crocodiles that exhibited a greater degree of site fidelity displayed more stable social environments, while females and males that were less site-attached had more dynamic social environments with spatial overlaps between conspecifics peaking during the mating season. Our results demonstrate how long-term tracking of multiple individuals within the same population can be used to quantify the spatial structure and social environment of cryptic and solitary species.

Quantifying movement of multiple threatened species to inform adaptive management of environmental flows

There is a growing need for water managers to refine and optimise environmental flow strategies (e-flows) to balance water requirements for humans and nature. With increasing demands for freshwater and consequent declines in biodiversity, managers are faced with the problem of how to adaptively manage e-flows for multiple stakeholders and species whose flow requirements may overlap or vary. This study assessed the effectiveness of a regulated e-flow release strategy from a dam, aimed at providing movement opportunities and facilitating reproductive processes for multiple threatened species. Movements of 24 Mary River cod (Maccullochella mariensis), 20 Australian lungfish (Neoceratodus forsteri) and 13 Mary River turtle (Elusor macrurus) were quantified using acoustic telemetry over a three-year period. The influence of regulated e-flow releases, season, river depth, water temperature and rainfall on animal movements was assessed using Generalised linear mixed models (GLMMs). Models showed that hydraulic connectivity provided by both natural flows and regulated e-flow releases facilitated movement of all three species between pool habitats, throughout the year. Mary River turtles made extensive use of regulated e-flow releases when moving between habitats, whereas Mary River cod and Australian lungfish required additional natural rises in river height above the regulated e-flows to trigger movements. Significant movement activity was also recorded for cod and turtles during the dry season (winter and spring), broadly coinciding with breeding periods for these species. The effectiveness of, and potential improvements to, current e-flow strategies to sustain key life-history requirements of these species is discussed. Findings suggest a revised e-flow strategy with relatively minor increases in the magnitude of e-flow releases throughout winter and spring, would be effective in providing movement opportunities and supporting reproductive success for all three species. This study demonstrates that by quantifying movement behaviour in an e-flow context, ecological risk assessment frameworks can then be used to assess and provide for critical life-history requirements of multiple species within the context of a highly regulated system under increasing water use demands.

Rocky escarpment versus savanna woodlands: comparing diet and body condition as indicators of habitat quality for the endangered northern quoll (Dasyurus hallucatus)

Abstract ContextUnderstanding what constitutes high-quality habitat for threatened species is critical for conservation management planning. The endangered northern quoll (Dasyurus hallucatus) has experienced an uneven range contraction among habitat types. Once common across multiple habitats of northern mainland Australia, declining populations have now contracted to rocky escarpments. AimThe island refuge of Groote Eylandt, Northern Territory, Australia, has not experienced the declines as seen on mainland Australia. Here, northern quolls persist in both rocky escarpment and savanna woodland, which provides a rare opportunity to investigate the habitat quality of rocky escarpments and savanna woodland for the northern quoll. MethodsNorthern quolls (n=111) were trapped in both rocky escarpment (n=61) and savanna woodland (n=50) habitats before the breeding season (May). We conducted body condition assessment, scat analysis, and measured trophic niche breadth of individuals occupying each habitat type. Key resultsFemale quolls occupying rocky escarpments exhibited a lower body condition than did quolls occupying savanna woodland. Quolls from rocky escarpments consumed a significantly higher proportion of mammals and fed within a narrower dietary niche than did those occupying savanna woodland. ConclusionsQuolls had adapted to the dietary resources available within each habitat type, suggesting that the lack of quolls in savanna woodland on the mainland is due to factors other than availability of dietary resources. ImplicationsGroote Eylandt is of critical conservation significance, where high numbers of northern quolls exist in both rocky escarpment and savanna woodland habitats. For population viability on the mainland, managing threats such as feral predators and inappropriate fire regimes in savanna woodland, particularly those surrounding rocky escarpment, should be prioritised.

Motivations and fears driving participation in collaborative research infrastructure for animal tracking

Anthropogenic derived environmental change is challenging earth's biodiversity. To implement effective management, it is imperative to understand how organisms are responding over broad spatiotemporal scales. Collection of these data is generally beyond the budget of individual researchers and the integration and sharing of ecological data and associated infrastructure is becoming more common. However, user groups differ in their expectations, standards of performance, and desired outputs from research investment, and accommodating the motivations and fears of potential users from the outset may lead to higher levels of participation. Here we report upon a study of the Australian ornithology community, which was instigated to better understand perceptions around participation in nationally coordinated research infrastructure for detecting and tracking the movement of birds. The community was surveyed through a questionnaire and individuals were asked to score their motivations and fears around participation. Principal Components Analysis was used to reduce the dimensionality of the data and identify groups of questions where respondents behaved similarly. Linear regressions and model selection were then applied to the principal components to determine how career stage, employment role, and years of biotelemetry experience affected the respondent's motivations and fears for participation. The analysis showed that across all sectors (academic, government, NGO) there was strong motivation to participate and belief that national shared biotelemetry infrastructure would facilitate bird management and conservation. However, results did show that a cross-sector cohort of the Australian ornithology community were keen and ready to progress collaborative infrastructure for tracking birds, and measures including data-sharing agreements could increase participation. It also informed that securing initial funding would be a significant challenge, and a better option to proceed may be for independent groups to coordinate through existing database infrastructure to form the foundation from which a national network could grow.

Cardiopulmonary exercise testing in severe osteoarthritis: a crossover comparison of four exercise modalities

Cardiopulmonary exercise testing is performed increasingly for cardiorespiratory fitness assessment and pre-operative risk stratification. Lower limb osteoarthritis is a common comorbidity in surgical patients, meaning traditional cycle ergometry-based cardiopulmonary exercise testing is difficult. The purpose of this study was to compare cardiopulmonary exercise testing variables and subjective responses in four different exercise modalities. In this crossover study, 15 patients with osteoarthritis scheduled for total hip or knee arthroplasty (mean (SD) age 68 (7) years; body mass index 31.4 (4.1) kg.m^-2 ) completed cardiopulmonary exercise testing on a treadmill, elliptical cross-trainer, cycle and arm ergometer. Mean (SD) peak oxygen consumption was 20-30% greater on the lower limb modalities (treadmill 21.5 (4.6) (p < 0.001); elliptical cross-trainer (21.2 (4.1) (p < 0.001); and cycle ergometer (19.4 (4.2) ml.min^-1 .kg^-1 (p = 0.001), respectively) than on the arm ergometer (15.7 (3.7) ml.min^-1 .kg^-1 ). Anaerobic threshold was 25-50% greater on the lower limb modalities (treadmill 13.5 (3.1) (p < 0.001); elliptical cross-trainer 14.6 (3.0) (p < 0.001); and cycle ergometer 10.7 (2.9) (p = 0.003)) compared with the arm ergometer (8.4 (1.7) ml.min^-1 .kg^-1 ). The median (95%CI) difference between pre-exercise and peak-exercise pain scores was greater for tests on the treadmill (2.0 (0.0-5.0) (p = 0.001); elliptical cross-trainer (3.0 (2.0-4.0) (p = 0.001); and cycle ergometer (3.0 (1.0-5.0) (p = 0.001)), compared with the arm ergometer (0.0 (0.0-1.0) (p = 0.406)). Despite greater peak exercise pain, cardiopulmonary exercise testing modalities utilising the lower limbs affected by osteoarthritis elicited higher peak oxygen consumption and anaerobic threshold values compared with arm ergometry.

Using individual-based movement information to identify spatial conservation priorities for mobile species

The optimal design of reserve networks and fisheries closures depends on species occurrence information and knowledge of how anthropogenic impacts interact with the species concerned. However, challenges in surveying mobile and cryptic species over adequate spatial and temporal scales can mask the importance of particular habitats, leading to uncertainty about which areas to protect to optimize conservation efforts. We investigated how telemetry-derived locations can help guide the scale and timing of fisheries closures with the aim of reducing threatened species bycatch. Forty juvenile speartooth sharks (Glyphis glyphis) were monitored over 22 months with implanted acoustic transmitters and an array of hydrophone receivers. Using the decision-support tool Marxan, we formulated a permanent fisheries closure that prioritized areas used more frequently by tagged sharks and considered areas perceived as having high value to fisheries. To explore how the size of the permanent closure compared with an alternative set of time-area closures (i.e., where different areas were closed to fishing at different times of year), we used a cluster analysis to group months that had similar arrangements of selected planning units (informed by shark movements during that month) into 2 time-area closures. Sharks were consistent in their timing and direction of migratory movements, but the number of tagged sharks made a big difference in the placement of the permanent closure; 30 individuals were needed to capture behavioral heterogeneity. The dry-season (May-January) and wet-season (February-April) time-area closures opened 20% and 25% more planning units to fishing, respectively, compared with the permanent closure with boundaries fixed in space and time. Our results show that telemetry has the potential to inform and improve spatial management of mobile species and that the temporal component of tracking data can be incorporated into prioritizations to reduce possible impacts of spatial closures on established fisheries.

Ontogenetic shifts in the nesting behaviour of female crocodiles

Body size and age are crucial factors influencing reproductive capacity and success. As females grow, their reproductive investment and success often increase due to improved overall physiological condition and experience gained through successive reproductive events. While much of this work has been conducted on birds and mammals, surprisingly little is known on how body size affects nesting decisions in other long-lived vertebrates. We monitored the movements and nesting behaviour of 57 wild female estuarine crocodiles Crocodylus porosus over a 10-year period (and across consecutive nesting seasons) using externally mounted satellite tags, implanted acoustic transmitters and a network of submerged acoustic receivers. Applying Hidden Markov models to the telemetry-derived location data revealed that female nesting behaviours could be split into three distinct states: (i) ranging movements within home ranges and at nesting sites; (ii) migrations to and from nesting sites; (iii) and nesting/nest guarding. We found that during migration events, larger females migrated further and remained away from dry season territories for longer periods than smaller individuals. Furthermore, not only were migratory movements stimulated by increases in rainfall, larger females migrated to nest sites at lower rainfall thresholds than smaller females. We provide some of the first evidence of body size influencing nesting decisions in an ectothermic vertebrate, with shifts likely resulting from an increased willingness to invest in nest protection among larger and more experienced females.

Early Career Researchers Embrace Data Sharing

A request for raw data from the corresponding authors of 771 animal biotelemetry-focused manuscripts, published between 1995 and 2015, highlighted a difference in data sharing practices across researcher career levels. Responses were positive in only 11% of requests made to corresponding authors (CAs) that were senior researchers, while 72% of responses were positive when CAs were early career researchers (ECRs), demonstrating that the majority of senior researchers perceived little benefit from the public data archiving of their published research, while they often remain the data custodian.

Continental-scale animal tracking reveals functional movement classes across marine taxa

Acoustic telemetry is a principle tool for observing aquatic animals, but coverage over large spatial scales remains a challenge. To resolve this, Australia has implemented the Integrated Marine Observing System’s Animal Tracking Facility which comprises a continental-scale hydrophone array and coordinated data repository. This national acoustic network connects localized projects, enabling simultaneous monitoring of multiple species over scales ranging from 100 s of meters to 1000 s of kilometers. There is a need to evaluate the utility of this national network in monitoring animal movement ecology, and to identify the spatial scales that the network effectively operates over. Cluster analyses assessed movements and residency of 2181 individuals from 92 species, and identified four functional movement classes apparent only through aggregating data across the entire national network. These functional movement classes described movement metrics of individuals rather than species, and highlighted the plasticity of movement patterns across and within populations and species. Network analyses assessed the utility and redundancy of each component of the national network, revealing multiple spatial scales of connectivity influenced by the geographic positioning of acoustic receivers. We demonstrate the significance of this nationally coordinated network of receivers to better reveal intra-specific differences in movement profiles and discuss implications for effective management.

Why do people donate to conservation? Insights from a 'real world' campaign

Non-governmental organisations (NGOs) play a key role in biodiversity conservation. The majority of these organisations rely on public donations to fund their activities, and therefore fundraising success is a determinant of conservation outcomes. In spite of this integral relationship, the key principals for fundraising success in conservation are still guided by expert opinion and anecdotal evidence, with very few quantitative studies in the literature. Here we assessed the behaviour of monetary donors across twenty-five different species-focused conservation campaigns organised by an NGO conservation and environmental society. The Australian Geographic Society (AGS) carried out fundraising campaigns over a five and half year period using an identical methodology in thirty-four of its country-wide network of outlet shops. AGS owns and operates these shops that sell toys and games related to science and nature. We tested how the following factors influenced monetary donations from members of the public:1) campaign duration, 2) appeal and familiarity of species, 3) species geographic distribution relative to the fundraising location, 4) level of income and education of potential donors, 5) age and gender profile of potential donors. Contrary to past research, we found most of these factors did not significantly influence the amount of donations made to each campaign by members of the public. Larger animals did elicit a significantly higher amount donated per transaction than smaller animals, as did shops located in poorer neighbourhoods. Our study findings contrast with past research that has focused largely on hypothetical donations data collected via surveys, and demonstrates the complexity and case-specific nature of relationships between donor characteristics and spending patterns. The study highlights the value of assessing real-world fundraising campaigns, and illustrates how collaboration between academia and NGOs could be used to better tailor fundraising campaigns to maximise donations from individual citizens.

Cardiorespiratory responses in an Antarctic fish suggest limited capacity for thermal acclimation

Polar fishes are at high risk from increasing seawater temperatures. Characterising the physiological responses to such changes may both clarify mechanisms that permit life under extreme conditions and identify limitations in the response to continued global warming. We hypothesised that Notothenia coriiceps would show physiological compensation after an acute exposure to 5°C, and following 6 weeks warm acclimation, compared with ambient temperature (0°C). However, initial tachycardia (22.4±2.8 versus 12.8±1.1 min(-1); P<0.01) was not reversed by acclimation (21.0±1.9 min(-1)). Hyperventilation (45.5±3.1 versus 21.4±2.4 breaths min(-1); P<0.001) showed a modest reduction following acclimation (38.0±2.9 min(-1); P<0.05), while resting oxygen consumption (0.52±0.08 mmol kg(-1) h(-1)) was acutely increased at 5°C (1.07±0.10 mmol kg(-1) h(-1); P<0.001) but unchanged with acclimation. Autonomic blockade showed initial responses were mainly of vagal origin, with little subsequent withdrawal or recovery in long-term heart rate variability after 6 weeks. Given the limited cardiorespiratory capacity to withstand sustained warming, effective physiological compensation probably requires a more prolonged acclimation period.

Finding our way: On the sharing and reuse of animal telemetry data in Australasia

The presence and movements of organisms both reflect and influence the distribution of ecological resources in space and time. The monitoring of animal movement by telemetry devices is being increasingly used to inform management of marine, freshwater and terrestrial ecosystems. Here, we brought together academics, and environmental managers to determine the extent of animal movement research in the Australasian region, and assess the opportunities and challenges in the sharing and reuse of these data. This working group was formed under the Australian Centre for Ecological Analysis and Synthesis (ACEAS), whose overall aim was to facilitate trans-organisational and transdisciplinary synthesis. We discovered that between 2000 and 2012 at least 501 peer-reviewed scientific papers were published that report animal location data collected by telemetry devices from within the Australasian region. Collectively, this involved the capture and electronic tagging of 12 656 animals. The majority of studies were undertaken to address specific management questions; rarely were these data used beyond their original intent. We estimate that approximately half (~500) of all animal telemetry projects undertaken remained unpublished, a similar proportion were not discoverable via online resources, and less than 8.8% of all animals tagged and tracked had their data stored in a discoverable and accessible manner. Animal telemetry data contain a wealth of information about how animals and species interact with each other and the landscapes they inhabit. These data are expensive and difficult to collect and can reduce survivorship of the tagged individuals, which implies an ethical obligation to make the data available to the scientific community. This is the first study to quantify the gap between telemetry devices placed on animals and findings/data published, and presents methods for improvement. Instigation of these strategies will enhance the cost-effectiveness of the research and maximise its impact on the management of natural resources.

Chemical immobilisation and satellite tagging of free-living southern cassowaries

BACKGROUND

The southern cassowary (Casuarius casuarius johnsonii) attains 1.8 m in height and over 80 kg in weight. These large birds are equipped with large claws and, although not a direct threat to humans, they have caused serious injury to handlers and members of the public.

METHODS AND RESULTS

This study describes chemical immobilisation, restraint, transport and post-monitoring (satellite tracking) methodologies for adult and juvenile southern cassowaries, captured and released from their natural environment.

CONCLUSIONS

The described methods have improved the management and research opportunities for the southern cassowary and may be transferable to other species of large ratite.

Love thy neighbour: automatic animal behavioural classification of acceleration data using the K-nearest neighbour algorithm

Researchers hoping to elucidate the behaviour of species that aren't readily observed are able to do so using biotelemetry methods. Accelerometers in particular are proving particularly effective and have been used on terrestrial, aquatic and volant species with success. In the past, behavioural modes were detected in accelerometer data through manual inspection, but with developments in technology, modern accelerometers now record at frequencies that make this impractical. In light of this, some researchers have suggested the use of various machine learning approaches as a means to classify accelerometer data automatically. We feel uptake of this approach by the scientific community is inhibited for two reasons; 1) Most machine learning algorithms require selection of summary statistics which obscure the decision mechanisms by which classifications are arrived, and 2) they are difficult to implement without appreciable computational skill. We present a method which allows researchers to classify accelerometer data into behavioural classes automatically using a primitive machine learning algorithm, k-nearest neighbour (KNN). Raw acceleration data may be used in KNN without selection of summary statistics, and it is easily implemented using the freeware program R. The method is evaluated by detecting 5 behavioural modes in 8 species, with examples of quadrupedal, bipedal and volant species. Accuracy and Precision were found to be comparable with other, more complex methods. In order to assist in the application of this method, the script required to run KNN analysis in R is provided. We envisage that the KNN method may be coupled with methods for investigating animal position, such as GPS telemetry or dead-reckoning, in order to implement an integrated approach to movement ecology research.

Creating a behavioural classification module for acceleration data: using a captive surrogate for difficult to observe species

Distinguishing specific behavioural modes from data collected by animal-borne tri-axial accelerometers can be a time-consuming and subjective process. Data synthesis can be further inhibited when the tri-axial acceleration data cannot be paired with the corresponding behavioural mode through direct observation. Here, we explored the use of a tame surrogate (domestic dog) to build a behavioural classification module, and then used that module to accurately identify and quantify behavioural modes within acceleration collected from other individuals/species. Tri-axial acceleration data were recorded from a domestic dog whilst it was commanded to walk, run, sit, stand and lie-down. Through video synchronisation, each tri-axial acceleration sample was annotated with its associated behavioural mode; the feature vectors were extracted and used to build the classification module through the application of support vector machines (SVMs). This behavioural classification module was then used to identify and quantify the same behavioural modes in acceleration collected from a range of other species (alligator, badger, cheetah, dingo, echidna, kangaroo and wombat). Evaluation of the module performance, using a binary classification system, showed there was a high capacity (>90%) for behaviour recognition between individuals of the same species. Furthermore, a positive correlation existed between SVM capacity and the similarity of the individual's spinal length-to-height above the ground ratio (SL:SH) to that of the surrogate. The study describes how to build a behavioural classification module and highlights the value of using a surrogate for studying cryptic, rare or endangered species.

Branchial osmoregulation in the euryhaline bull shark, Carcharhinus leucas: a molecular analysis of ion transporters

Bull sharks, Carcharhinus leucas, are one of only a few species of elasmobranchs that live in both marine and freshwater environments. Osmoregulation in euryhaline elasmobranchs is achieved through the control and integration of various organs (kidney, rectal gland and liver) in response to changes in environmental salinity. However, little is known regarding the mechanisms of ion transport in the gills of euryhaline elasmobranchs and how they are affected by osmoregulatory challenges. This study was conducted to gain insight into the branchial ion and acid-base regulatory mechanisms of C. leucas by identifying putative ion transporters and determining whether their expression is influenced by environmental salinity. We hypothesised that expression levels of the Na+/K+-ATPase (NKA) pump, Na+/H+ exchanger 3 (NHE3), vacuolar-type H+-ATPase (VHA) and anion exchanger pendrin (PDN) would be upregulated in freshwater (FW) C. leucas. Immunohistochemistry was used to localise all four ion transporters in gills of bull sharks captured in both FW and estuarine/seawater (EST/SW) environments. NHE3 immunoreactivity occurred in the apical region of cells with basolateral NKA expression whereas PDN was apically expressed in cells that also exhibited basolateral VHA immunoreactivity. In accordance with our hypotheses, quantitative real-time PCR showed that the mRNA expression of NHE3 and NKA was significantly upregulated in gills of FW-captured C. leucas relative to EST/SW-captured animals. These data suggest that NHE3 and NKA together may be important in mediating branchial Na+ uptake in freshwater environments, whereas PDN and VHA might contribute to Cl-/HCO3- transport in marine and freshwater bull shark gills.

Diving through the thermal window: implications for a warming world

Population decline and a shift in the geographical distribution of some ectothermic animals have been attributed to climatic warming. Here, we show that rises in water temperature of a few degrees, while within the thermal window for locomotor performance, may be detrimental to diving behaviour in air-breathing ectotherms (turtles, crocodilians, marine iguanas, amphibians, snakes and lizards). Submergence times and internal and external body temperature were remotely recorded from freshwater crocodiles (Crocodylus johnstoni) while they free-ranged throughout their natural habitat in summer and winter. During summer, the crocodiles' mean body temperature was 5.2±0.1°C higher than in winter and the largest proportion of total dive time was composed of dive durations approximately 15 min less than in winter. Diving beyond 40 min during summer required the crocodiles to exponentially increase the time they spent on the surface after the dive, presumably to clear anaerobic debt. The relationship was not as significant in winter, even though a greater proportion of dives were of a longer duration, suggesting that diving lactate threshold (DLT) was reduced in summer compared with winter. Additional evidence for a reduced DLT in summer was derived from the stronger influence body mass exerted upon dive duration, compared to winter. The results demonstrate that the higher summer body temperature increased oxygen demand during the dive, implying that thermal acclimatization of the diving metabolic rate was inadequate. If the study findings are common among air-breathing diving ectotherms, then long-term warming of the aquatic environment may be detrimental to behavioural function and survivorship.

Hibernation in an antarctic fish: on ice for winter

Active metabolic suppression in anticipation of winter conditions has been demonstrated in species of mammals, birds, reptiles and amphibians, but not fish. This is because the reduction in metabolic rate in fish is directly proportional to the decrease in water temperature and they appear to be incapable of further suppressing their metabolic rate independently of temperature. However, the Antarctic fish (Notothenia coriiceps) is unusual because it undergoes winter metabolic suppression irrespective of water temperature. We assessed the seasonal ecological strategy by monitoring swimming activity, growth, feeding and heart rate (f_H) in N. coriiceps as they free-ranged within sub-zero waters. The metabolic rate of wild fish was extrapolated from f_H recordings, from oxygen consumption calibrations established in the laboratory prior to fish release. Throughout the summer months N. coriiceps spent a considerable proportion of its time foraging, resulting in a growth rate (G_w) of 0.18±0.2% day⁻¹. In contrast, during winter much of the time was spent sedentary within a refuge and fish showed a net loss in G_w (−0.05±0.05% day⁻¹). Whilst inactive during winter, N. coriiceps displayed a very low f_H, reduced sensory and motor capabilities, and standard metabolic rate was one third lower than in summer. In a similar manner to other hibernating species, dormancy was interrupted with periodic arousals. These arousals, which lasted a few hours, occurred every 4–12 days. During arousal activity, f_H and metabolism increased to summer levels. This endogenous suppression and activation of metabolic processes, independent of body temperature, demonstrates that N. coriiceps were effectively ‘putting themselves on ice’ during winter months until food resources improved. This study demonstrates that at least some fish species can enter a dormant state similar to hibernation that is not temperature driven and presumably provides seasonal energetic benefits.

A seasonally dependent change in the distribution and physiological condition of Caiman crocodilus yacare in the Paraguay River Basin

The distribution and physiological condition of 116 Caiman crocodilus yacare was assessed over one year in the Southern Pantanal. Body mass and intermediary plasma metabolites were measured at three different time periods, representing large differences in the abundance of surface water. During the wet season the study site was completely submerged under water and C.c. yacare were distributed evenly throughout. High levels of [glucose] and [triglyceride] in the plasma indicated regular feeding. As the dry season progressed C.c. yacare became increasingly crowded around the remaining ponds. They showed a reduction in plasma [glucose] and [triglyceride], and an increase in plasma [β-hydroxy-butyrate], signifying that they were feeding less and utilising fat reserves. At this sampling period, ~40% of the male C. c. yacare that were >10 years old inhabited dry grassland and did not have access to water. These animals were significantly lighter than males of a similar length that had immediate water access, and plasma [uric acid] indicated that they had not fed for a long time and were metabolising tissue proteins. Essentially, the adult male C.c. yacare that inhabited dry grassland were in a state of energy deficiency. This was so severe in some animals that recovery seemed unlikely. The study suggests that fluctuations in the abundance of surface ground water may influence the size and structure of the C. c. yacare population in the Pantanal.

The vagus nerve mediates cardio-respiratory coupling that changes with metabolic demand in a temperate nototheniod fish

The extent and efficiency of cardio-respiratory coupling (CRC) in teleost fishes is unclear. We simultaneously monitored heart rate (fH) and ventilation rate (fV) in Paranotothenia angustata, and applied modern power spectral analysis (PSA) mathematics to examine the rate association under varying levels of oxygen consumption(ṀO2). At low ṀO2 (0.94 mmol O2 kg–1 h–1) there was a correspondingly low fH and fV(25.5±2.4 min–1 and 29.2±2.6 min–1, respectively). Heart rate variability (HRV) consisted of oscillatory components caused by periodic vagal inhibition of the heart beat. Cross-spectral analysis showed that fH and fV were coupled, with the response lag in heart beat being approximately one seventh of each ventilation cycle. Ingestion of food elevated ṀO2(1.99±0.02 mmol O2 kg–1h–1) and increased both fH and fV (45±2.3 min–1 and 52±2 min–1, respectively, P&lt;0.05), but CRC was maintained despite a reduction in HRV. The elevated stress caused by handling and placement of fish into respirometry chambers raised fHand fV to a similar rate as observed after feeding,although high-frequency (&gt;0.2 Hz) oscillations in fHwere lacking and ṀO2 was lower(1.82±0.03 mmol O2 kg–1h–1, P&lt;0.05). Subsequent cardiac vagotomy elevated fH and fV (55.5±0.8 min–1 and 48.2±0.7 min–1,respectively; P&lt;0.05) but abolished all HRV and CRC, although ṀO2 was significantly less for a given fH and fV compared to intact fish. Thus, P. angustataexhibits vagally mediated CRC, and the association between fH and fV varies according to oxygen demand.

Does respiratory sinus arrhythmia occur in fishes?

The hypothesis that respiratory modulation of heart rate variability (HRV) or respiratory sinus arrhythmia (RSA) is restricted to mammals was tested on four Antarctic and four sub-Antarctic species of fish, that shared close genotypic or ecotypic similarities but, due to their different environmental temperatures, faced vastly different selection pressures related to oxygen supply. The intrinsic heart rate (fH) for all the fish species studied was approximately 25% greater than respiration rate (fV), but vagal activity successively delayed heart beats, producing a resting fH that was synchronized with fV in a progressive manner. Power spectral statistics showed that these episodes of relative bradycardia occurred in a cyclical manner every 2-4 heart beats in temperate species but at >4 heart beats in Antarctic species, indicating a more relaxed selection pressure for cardio-respiratory coupling. This evidence that vagally mediated control of fH operates around the ventilatory cycle in fish demonstrates that influences similar to those controlling RSA in mammals operate in non-mammalian vertebrates.

Coupling of the Respiratory Rhythm in Fish with Activity in Hypobranchial Nerves and with Heartbeat

Fish have a central respiratory pattern generator (CRPG) in the brain stem that initiates activity in a series of cranial nerves innervating respiratory muscles. These nerves burst sequentially in the order of their rostrocaudal distribution in the central nervous system. When respiratory drive is high, this activity spreads caudally to occipital and anterior spinal neurons that project via the hypobranchial nerves to stimulate hypaxial muscles, causing active jaw abduction. The CRPG may also recruit the heart. Fish, like mammals, show respiratory components in the intrinsic variability of heart rate (HRV). Cardiorespiratory synchrony in the dogfish is driven by bursting activity in the cardiac branches of the vagus nerve, which emanates from preganglionic neurons in the dorsal vagal motor nucleus. A respiratory component in HRV is difficult to discriminate in other species, requiring the use of power spectral analysis and the subsequent elimination of aliased components.

Evidence for a respiratory component, similar to mammalian respiratory sinus arrhythmia, in the heart rate variability signal from the rattlesnake,Crotalus durissus terrificus

Autonomic control of heart rate variability and the central location of vagal preganglionic neurones (VPN) were examined in the rattlesnake(Crotalus durissus terrificus), in order to determine whether respiratory sinus arrhythmia (RSA) occurred in a similar manner to that described for mammals. Resting ECG signals were recorded in undisturbed snakes using miniature datalogging devices, and the presence of oscillations in heart rate (fh) was assessed by power spectral analysis (PSA). This mathematical technique provides a graphical output that enables the estimation of cardiac autonomic control by measuring periodic changes in the heart beat interval. At fh above 19 min-1spectra were mainly characterised by low frequency components, reflecting mainly adrenergic tonus on the heart. By contrast, at fhbelow 19 min-1 spectra typically contained high frequency components, demonstrated to be cholinergic in origin. Snakes with a fh &gt;19 min-1 may therefore have insufficient cholinergic tonus and/or too high an adrenergic tonus acting upon the heart for respiratory sinus arrhythmia (RSA) to develop. A parallel study monitored fh simultaneously with the intraperitoneal pressures associated with lung inflation. Snakes with a fh&lt;19 min-1 exhibited a high frequency (HF) peak in the power spectrum,which correlated with ventilation rate (fv). Adrenergic blockade by propranolol infusion increased the variability of the ventilation cycle, and the oscillatory component of the fh spectrum broadened accordingly. Infusion of atropine to effect cholinergic blockade abolished this HF component, confirming a role for vagal control of the heart in matching fh and fv in the rattlesnake. A neuroanatomical study of the brainstem revealed two locations for vagal preganglionic neurones (VPN). This is consistent with the suggestion that generation of ventilatory components in the heart rate variability (HRV)signal are dependent on spatially distinct loci for cardiac VPN. Therefore,this study has demonstrated the presence of RSA in the HRV signal and a dual location for VPN in the rattlesnake. We suggest there to be a causal relationship between these two observations.

A new method in applying power spectral statistics to examine cardio-respiratory interactions in fish

Power spectral analysis (PSA) provides a powerful tool for determining frequency oscillations in time signals, and it is accepted that mammals can show distinct components in the heart rate (fH) spectrum that are synchronous with ventilatory frequency (fV). Using similar signal processing techniques, these fundamental components at fV are not apparent in the spectrum calculated from fish fH. Here we compare conventional PSA on the R-R interval tachogram generated from ECG traces recorded in rats and fish, with PSA on the raw ECG waveform. The rat R-R tachogram showed a defined sigmoidal component, whereas the fish R-R tachogram was a more chaotic waveform. In agreement with the literature, PSA of these respective waveforms produced a component at the same frequency as ventilation in the rat, but of lower frequency than ventilation for the fish. Applying PSA to the rat ECG produced a spectrum with a fundamental component of similar frequency to that observed in the R-R tachogram spectrum, indicating that the latter adequately contained heart rate variability (HRV) oscillations. However, PSA of the ECG in fish contrasted with that from the R-R tachogram, with components observed in the latter spectrum being absent from the former. This suggests that the frequency components determined by PSA on the fish R-R tachogram were not true components, but were aliased (or folded-back) from higher up in the spectrum. Using established aliasing equations, recalculation of these peaks showed that their true frequency was similar to that of the ventilatory frequency for individual fish. The extent of cardio-respiratory interaction, resulting in fV < f(H/2) in rats but fV > f(H/2) in fish, is suggested to be the origin of the differences observed.

Shifts in a Fish’s Resource Holding Power during a Contact Paired Interaction: The Influence of a Copper‐Contaminated Diet in Rainbow Trout

The influence of sublethal chronic dietary copper (Cu) exposure on the dominant-subordinate relationship between pairs of juvenile rainbow trout (Oncorhynchus mykiss) was examined. Fish were fed either a normal (11 mg Cu kg(-1) food) or Cu-contaminated (721 mg Cu kg(-1) food) diet for 8 wk. Paired interactions were observed--control versus control, Cu-exposed versus Cu-exposed, and control versus Cu-exposed fish--using a computer-aided video tracking system to measure duration of interactions, total distance moved, and the number of encounters during each contest. In concurrence with game theory, each interaction became escalated with a lesser size disparity between contestants. However, in Cu-exposed versus Cu-exposed fish interactions, the dominant-subordinate relationship was decided sooner and with less aggression than a control versus control fish interaction with fish of a similar relative body mass disparity. During control versus Cu-exposed fish interactions, control fish would normally dominate interactions (12 out of 16 bouts) unless the Cu-exposed fish had a 15% body mass advantage. Muscle glycogen and lactate levels after each contest reflected the duration of bouts and winners of the contests, irrespective of Cu exposure. We conclude that Cu-contaminated fish are less able to compete and have lower resource holding power than controls and will withdraw from a contest at a lower level of interaction, unless a size advantage in the Cu-exposed fish increases the probability of winning.

The use of power spectral analysis to determine cardiorespiratory control in the short-horned sculpinMyoxocephalus scorpius

Anaesthesia and minor surgery to place electrocardiogram recording electrodes in the short-horned sculpin caused a decrease in mean normal beat(R–R) interval and heart rate variability (HRV), measured as the standard deviation in the R–R interval (SDRR). Mean R–R interval increased to a steady state value (1.9±2.9 s) 72 h post-surgery, but SDRR took 120 h to stabilise (0.56±0.09 s). Power spectral analysis applied to recordings of instantaneous heart rate showed no spectral peaks immediately after surgery, with the development of twin peaks (at 0.02 and 0.05 Hz) that also became stable 120 h post surgery. Bilateral cardiac vagotomy abolished the variability in beat-to-beat interval, and both the high and low frequency peaks, suggesting that much of the regulation of heart rate and HRV in sculpin was under parasympathetic, cholinergic control that was withdrawn as a result of surgical and handling stress. Rate of oxygen consumption \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(({\dot{M}}_{\mathrm{O}_{2}})\) \end{document} and heart rate (fH) were monitored simultaneously and \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \({\dot{M}}_{\mathrm{O}_{2}}\) \end{document} showed a good correlation with both mean R–R interval(r2=–0.89) and SDRR (r2=0.93),although a more significant (ANCOVA, P=0.02) covariance existed between the post-surgical decrease in \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \({\dot{M}}_{\mathrm{O}_{2}}\) \end{document} and increase in SDRR. These data suggest that sculpin use fHas a way of moderating oxygen consumption, fine-tuned on a beat-to-beat basis by cholinergic control. We conclude that power spectral analysis is a useful method of determining HRV in fish, and that HRV is a more sensitive measure of recovery from disturbance than fH alone.

The CTP:phosphocholine cytidylyltransferase encoded by the licC gene of Streptococcus pneumoniae: cloning, expression, purification, and characterization

Streptococcus pneumoniae is a member of a small group of bacteria that display phosphocholine on the cell surface, covalently attached to the sugar groups of teichoic acid and lipoteichoic acid. The putative pathway for this phosphocholine decoration is, in its first two enzymes, functionally similar to the CDP-choline pathway used for phosphatidylcholine biosynthesis in eukaryotes. We show that the licC gene encodes a functional CTP:phosphocholine cytidylyltransferase (CCT). The enzyme has been expressed and purified to homogeneity. Assay conditions were optimized, particularly with respect to linearity with time, pH, Mg(2+), and ammonium sulfate concentration. The pure enzyme has K(M) values of 890+/-240 microM for CTP, and 390+/-170 microM for phosphocholine. The k(cat) is 17.5+/-4.0 s(-1). S. pneumoniae CTP:phosphocholine cytidylyltransferase (SpCCT) is specific for CTP or dCTP as the nucleotide substrate. SpCCT is strongly inhibited by Ca(2+). The IC(50) values for recombinant and native SpCCT are 0.32+/-0.04 and 0.27+/-0.03 mM respectively. The enzyme is also inhibited by all other tested divalent cations, including Mg(2+) at high concentrations. The cloning and expression of this enzyme sets the stage for design of inhibitors as possible antipneumococcal drugs.

Negative cooperativity of substrate binding but not enzyme activity in wild-type and mutant forms of CTP:glycerol-3-phosphate cytidylyltransferase

CTP:glycerol-3-phosphate cytidylyltransferase (GCT) catalyzes the synthesis of CDP-glycerol for teichoic acid biosynthesis in certain Gram-positive bacteria. This enzyme is a model for a cytidylyltransferase family that includes the enzymes that synthesize CDP-choline and CDP-ethanolamine for phosphatidylcholine and phosphatidylethanolamine biosynthesis. We have used quenching of intrinsic tryptophan fluorescence to measure binding affinities of substrates to the GCT from Bacillus subtilis. Binding of either CTP or glycerol-3-phosphate to GCT was biphasic, with two binding constants of about 0.1-0.3 and 20-40 microm for each substrate. The stoichiometry of binding was 2 molecules of substrate/enzyme dimer, so the two binding constants represented distinctly different affinities of the enzyme for the first and second molecule of each substrate. The biphasic nature of binding was observed with the wild-type GCT as well as with several mutants with altered Km or kcat values. This negative cooperativity of binding was also seen when a catalytically defective mutant was saturated with two molecules of CTP and then titrated with glycerol-3-phosphate. Despite the pronounced negative cooperativity of substrate binding, negative cooperativity of enzyme activity was not observed. These data support a mechanism in which catalysis occurs only when the enzyme is fully loaded with 2 molecules of each substrate/enzyme dimer.

Enzymatic and cellular characterization of a catalytic fragment of CTP:phosphocholine cytidylyltransferase alpha

To probe the mechanism of lipid activation of CTP:phosphocholine cytidylyltransferase (CCTalpha), we have characterized a catalytic fragment of the enzyme that lacks the membrane-binding segment. The kinetic properties of the purified fragment, CCTalpha236, were characterized, as well as the effects of expressing the fragment in cultured cells. CCTalpha236 was truncated after residue 236, which corresponds to the end of the highly conserved catalytic domain. The activity of purified CCTalpha236 was independent of lipids and about 50-fold higher than the activity of wild-type CCTalpha assayed in the absence of lipids, supporting a model in which the membrane-binding segment functions as an inhibitor of the catalytic domain. The kcat/Km values for CCTalpha236 were only slightly lower than those for lipid-activated CCTalpha. The importance of the membrane-binding segment in vivo was tested by expression of CCTalpha236 in CHO58 cells, a cell line that is temperature-sensitive for growth and CCTalpha activity. Expression of wild-type CCTalpha in these cells complemented the defective growth phenotype when the cells were cultured in complete or delipidated fetal bovine serum. Expression of CCTalpha236, however, did not complement the growth phenotype in the absence of serum lipids. These cells were capable of making phosphatidylcholine in the delipidated medium, so the inability of the cells to grow was not due to defective phosphatidylcholine synthesis. Supplementation of the delipidated medium with an unsaturated fatty acid allowed growth of CHO58 cells expressing CCTalpha236. These results indicate that the membrane-binding segment of CCTalpha has an important role in cellular lipid metabolism.