Ontogeny of oxygen stores and physiological diving capability in Australian sea lions

1.For air-breathing animals in aquatic environments, foraging behaviours are often constrained by physiological capability. The development of oxygen stores and the rate at which these stores are used determine juvenile diving and foraging potential.
2. We examined the ontogeny of dive physiology in the threatened Australian sea lion Neophoca cinerea. Australian sea lions exploit benthic habitats; adult females demonstrate high field metabolic rates (FMR), maximize time spent near the benthos, and regularly exceed their calculated aerobic dive limit (cADL). Given larger animals have disproportionately greater diving capabilities; we wanted to determine the extent physiological development constrained diving and foraging in young sea lions.
3. Ten different mother/pup pairs were measured at three developmental stages (6, 15 and 23 months) at Seal Bay Conservation Park, Kangaroo Island, South Australia. Hematocrit (Hct), haemoglobin (Hb) and plasma volume were analyzed to calculate blood O2 stores and myoglobin was measured to determine muscle O₂. Additionally, FMR's for nine of the juveniles were derived from doubly-labelled water measurements.
4. Australian sea lions have the slowest documented O₂ store development among diving mammals. Although weaning typically occurs by 17·6 months, 23-month juveniles had only developed 68% of adult blood O₂. Muscle O₂ was the slowest to develop and was 60% of adult values at 23 months.
5. We divided available O₂ stores (37·11 ± 1·49 mL O₂ kg−1) by at-sea FMR (15·78 ± 1·29 mL O₂ min−1 kg−1) to determine a cADL of 2·33 ± 0·24 min for juvenile Australian sea lions. Like adults, young sea lions regularly exceeded cADL's with 67·8 ± 2·8% of dives over theoretical limits and a mean dive duration to cADL ratio of 1·23 ± 0·10.
6. Both dive depth and duration appear impacted by the slow development of oxygen stores. For species that operate close to, or indeed above their estimated physiological maximum, the capacity to increase dive depth, duration or foraging effort would be limited. Due to reduced access to benthic habitat and restricted behavioural options, young benthic foragers, such as Australian sea lions, would be particularly vulnerable to resource limitation.

The physiological and behavioural development of diving in Australian fur seal (Arctocephalus pusillus doriferus) pups

The physiological and behavioural development of diving was examined in Australian fur seal (Arctocephalus pusillus doriferus) pups to assess whether animals at weaning are capable of exploiting the same resources as adult females. Haematocrit, haemoglobin and myoglobin contents all increased throughout pup development though total body oxygen stores reached only 71% of adult female levels just prior to weaning. Oxygen storage components, however, did not develop at the same pace. Whereas blood oxygen stores had reached adult female levels by 9 months of age, muscle oxygen stores were slower to develop, reaching only 23% of adult levels by this age. Increases in diving behaviour corresponded to the physiological changes observed. Pups spent little time (<8%) in the water prior to moulting (age 1–2 months) whereas following the moult, they spent >27% of time in the water and made mid-water dives (maximum depth 35.7 ± 2.9 m) with durations of 0.35 ± 0.03 min. By 9 months (just prior to weaning), 30.5 ± 9.3% of all dives performed were U-shaped benthic dives (maximum depth 65.0 ± 6.0 m) with mean durations of 0.87 ± 0.25 min, significantly shorter than those of adult females. These results suggest that while Australian fur seal pups approaching the age of weaning are able to reach similar depths as adult females, they do not have the physiological capacity to remain at these depths for sufficient durations to exploit them to the same efficiency.

When does physiology limit the foraging behaviour of freely diving mammals?

Diving animals offer a unique opportunity to study the importance of physiological constraint and the limitation it can impose on animal's behaviour in nature. This paper examines the interaction between physiology and behaviour and its impact on the diving capability of five eared seal species (Family Otariidae; three sea lions and two fur seals). An important physiological component of diving marine mammals is the aerobic dive limit (ADL). The ADL of these five seal species was estimated from measurements of their total body oxygen stores, coupled with estimates of their metabolic rate while diving. The tendency of each species to exceed its calculated ADL was compared relative to its diving behaviour. Overall, our analyses reveal that seals which forage benthically (i.e. on the sea floor) have a greater tendency to approach or exceed their ADL compared to seals that forage epipelagically (i.e. near the sea surface). Furthermore, the marked differences in foraging behaviour and physiology appear to be coupled with a species demography. For example, benthic foraging species have smaller populations and lower growth rates compared to seal species that forage epipelagically. These patterns are relevant to the conservation and management of diving vertebrates.

Stable isotopes reveal inter-annual and inter-individual variation in the diet of female Australian fur seals

Understanding the temporal and spatial variation of foraging habits of apex predators is central to understanding their role in marine ecosystems and how their populations may respond to environmental variability. In the present study, stable isotope analysis (C and N) of blood was used to investigate inter-individual and inter-annual differences in the diet of adult female Australian fur seals Arctocephalus pusillus doriferus. Positive correlations were observed between red cell and plasma values for δ¹³C and δ¹⁵N (r² = 0.47 and r² = 0.66, respectively, p < 0.001 in both cases), suggesting relatively consistent individual prey choices over 3 or 4 foraging trips. Mean δ¹⁵N values (12.8 to 17.5%) confirm the species occupies the highest marine trophic niche in the region. A significant decrease in plasma δ¹⁵N values, corresponding to two-thirds of a trophic level (ca. 2%), was observed between the 1998 to 2000 and 2003 to 2005 sampling periods. This was associated with a significant decrease in adult female body condition and is consistent with a decline, previously documented by faecal analysis, of the proportion of red cod Pseudophysis bachus, barracouta Thyrsites atun and Gould's squid Nototodarus gouldi in the diet and an increase in redbait Emmelichthys nitidus. While substantial variation in δ¹⁵N was observed within each age cohort, a significant decrease was observed with age, suggesting individual specialisation for particular prey types is evident early in adulthood, but that its composition changes as females age. In addition, generalized linear models indicated body mass had a negative influence on δ¹⁵N, which may reflect larger total body oxygen stores, facilitating individuals hunting cryptic prey of lower trophic level (e.g. octopus) on the sea floor.

First records of dive durations for a hibernating sea turtle

The first published record, from the early 1970s, of hibernation in sea turtles is based on the reports of the indigenous Indians and fishermen from Mexico, who hunted dormant green turtles (Chelonia mydas) in the Gulf of California. However, there were no successful attempts to investigate the biology of this particular behaviour further. Hence, data such as the exact duration and energetic requirements of dormant winter submergences are lacking. We used new satellite relay data loggers to obtain the first records of up to 7 h long dives of a loggerhead turtle (Caretta caretta) overwintering in Greek waters. These represent the longest dives ever reported for a diving marine vertebrate. There is strong evidence that the dives were aerobic, because the turtle surfaced only for short intervals and before the calculated oxygen stores were depleted. This evidence suggests that the common belief that sea turtles hibernate underwater, as some freshwater turtles do, is incorrect.

The influence of body size on the diving behaviour and physiology of the bimodally respiring turtle, Elseya albagula

In aquatic vertebrates that acquire oxygen aerially dive duration scales positively with body mass, i.e. larger animals can dive for longer periods, however in bimodally respiring animals the relationship between dive duration and body mass is unclear. In this study we investigated the relationships between body size, aquatic respiration, and dive duration in the bimodally respiring turtle, Elseya albagula. Under normoxic conditions, dive duration was found to be independent of body mass. The dive durations of smaller turtles were equivalent to that of larger individuals despite their relatively smaller oxygen stores and higher mass specific metabolic rates. Smaller turtles were able to increase their dive duration through the use of aquatic respiration. Smaller turtles had a relatively higher cloacal bursae surface area than larger turtles, which allowed them to extract a relatively larger amount of oxygen from the water. By removing the ability to respire aquatically (hypoxic conditions), the dive duration of the smaller turtles significantly decreased restoring the normal positive relationship between body size and dive duration that is seen in other air-breathing vertebrates.

Regional variability in diving physiology and behavior in a widely distributed air-breathing marine predator, the South American sea lion Otaria byronia

Our understanding of how air-breathing marine predators cope with environmental variability is limited by our inadequate knowledge of their ecological and physiological parameters. Due to their wide distribution along both coasts of the sub-continent, South American sea lions (Otaria byronia) provide a valuable opportunity to study the behavioral and physiological plasticity of a marine predator in different environments. We measured the oxygen stores and diving behavior of South American sea lions throughout most of its range, allowing us to demonstrate that diving ability and behavior vary across its range. We found no significant differences in mass-specific blood volumes of sea lions among field sites and a negative relationship between mass-specific oxygen storage and size, which suggests that exposure to different habitats and geographical locations better explains oxygen storage capacities and diving capability in South American sea lions than body size alone. The largest animals in our study (individuals from Uruguay) were the most shallow and short duration divers, and had the lowest mass-specific total body oxygen stores, while the deepest and longest duration divers (individuals from Southern Chile) had significantly larger mass-specific oxygen stores, despite being much smaller animals.Our study suggests that the physiology of air-breathing diving predators is not fixed, but that it can be adjusted, to a certain extent, depending on the ecological setting and or habitat. These adjustments can be thought of as a "training effect" as the animal continues to push its physiological capacity through greater hypoxic exposure, its breath holding capacity increases.

Patterns of oxygen consumption during establishment of cephalocaudal polarity in the early chick embryo.

Oxygen uptake was studied during the establishment of cephalocaudal polarity in the very early chick embryo, i.e., 10 hr before (stage VI) and at laying (stage X). Oxygen fluxes in minute regions of the intact blastoderms were measured in vitro by scanning microspectrophotometry in the presence or absence of glucose. The oxygen consumption of the whole blastoderm remained constant (6 nmol O2 X hr-1) throughout the period studied, although the number of cells increased more than twofold. The regional oxygen fluxes varied from 0.41 to 1.13 nmol O2 X hr-1 X mm-2 at stage VI and from 0.42 to 0.70 nmol O2 X hr-1 X mm-2 at stage X. At stage VI, the oxygen flux in the center of the blastoderm was significantly higher than that in its periphery. This pattern remained evident when the values were corrected for cell number or for cytoplasmic volume. At stage X, there was a tendency for the oxygen fluxes to decrease from the posterior to the anterior regions of the area pellucida. Thus the pattern of oxidative metabolism in the late uterine embryos seems to change from radial to bilateral. This change of symmetry probably reflects the process of formation of the embryonic axis. In addition, the fact that the oxygen uptake was similar in the presence or absence of glucose suggests that early chick embryos metabolize essentially intracellular stores.

A three species model to simulate application of hyperbaric oxygen therapy to chronic wounds

Chronic wounds are a significant socioeconomic problem for governments worldwide. Approximately 15% of people who suffer from diabetes will experience a lower-limb ulcer at some stage of their lives, and 24% of these wounds will ultimately result in amputation of the lower limb. Hyperbaric Oxygen Therapy (HBOT) has been shown to aid the healing of chronic wounds; however, the causal reasons for the improved healing remain unclear and hence current HBOT protocols remain empirical. Here we develop a three-species mathematical model of wound healing that is used to simulate the application of hyperbaric oxygen therapy in the treatment of wounds. Based on our modelling, we predict that intermittent HBOT will assist chronic wound healing while normobaric oxygen is ineffective in treating such wounds. Furthermore, treatment should continue until healing is complete, and HBOT will not stimulate healing under all circumstances, leading us to conclude that finding the right protocol for an individual patient is crucial if HBOT is to be effective. We provide constraints that depend on the model parameters for the range of HBOT protocols that will stimulate healing. More specifically, we predict that patients with a poor arterial supply of oxygen, high consumption of oxygen by the wound tissue, chronically hypoxic wounds, and/or a dysfunctional endothelial cell response to oxygen are at risk of nonresponsiveness to HBOT. The work of this paper can, in some way, highlight which patients are most likely to respond well to HBOT (for example, those with a good arterial supply), and thus has the potential to assist in improving both the success rate and hence the costeffectiveness of this therapy.

Investigating relationships between relationship quality, customer loyalty and cooperation : an empirical study of convenience stores' franchise chain systems in Taiwan

Franchising has been widely accepted as an effective way to conduct and expand businesses. However, a franchise system is not a guarantee of success in the market. A successful franchise system should rely on a close and strong franchising relationship. Franchising is an important relationship management business. Franchising arrangements normally last for a number of years, so the franchisor and franchisee in the arrangement relationship are usually motivated to cooperate with each other. In addition, highly loyal franchisees may be obtained through a successful long-term franchising relationship. Over the last few decades, there has been a tremendous wave of interest in franchising relationships. However, little research has been conducted to determine the reasons for long-term franchising relationships. As a result, this study focuses on the important elements that might lead to a successful long-term franchising relationship. This study attempts to examine empirically three essential constructs (relationship quality, cooperation and customer loyalty), which might lead to successful long-term franchising relationships between franchisees and franchisors among the convenience stores in Taiwan. Mailed questionnaires were utilised to collect the research data. A total of 500 surveys were mailed randomly to the manager/supervisor of convenience stores’ franchisees among the four main franchisors (7-ELEVEN, Family, Hi-Life and OK) in Taiwan. The final sample size is 120, yielding a response rate of 24 per cent. The results show that relationship quality positively influences the cooperative relationships between franchisors and franchisees. Relationship quality is also positively correlated with franchisees’ loyalty. Additionally, the results indicate that the cooperative relationships between franchisors and franchisees are significantly associated with franchisees’ loyalty.

Plasma ATP concentration and venous oxygen content in the forearm during dynamic handgrip exercise

Background: It has been proposed that adenosine triphosphate (ATP) released from red blood cells (RBCs) may contribute to the tight coupling between blood flow and oxygen demand in contracting skeletal muscle. To determine whether ATP may contribute to the vasodilatory response to exercise in the forearm, we measured arterialised and venous plasma ATP concentration and venous oxygen content in 10 healthy young males at rest, and at 30 and 180 seconds during dynamic handgrip exercise at 45% of maximum voluntary contraction (MVC). Results: Venous plasma ATP concentration was elevated above rest after 30 seconds of exercise (P < 0.05), and remained at this higher level 180 seconds into exercise (P < 0.05 versus rest). The increase in ATP was mirrored by a decrease in venous oxygen content. While there was no significant relationship between ATP concentration and venous oxygen content at 30 seconds of exercise, they were moderately and inversely correlated at 180 seconds of exercise (r = -0.651, P = 0.021). Arterial ATP concentration remained unchanged throughout exercise, resulting in an increase in the venous-arterial ATP difference. Conclusions: Collectively these results indicate that ATP in the plasma originated from the muscle microcirculation, and are consistent with the notion that deoxygenation of the blood perfusing the muscle acts as a stimulus for ATP release. That ATP concentration was elevated just 30 seconds after the onset of exercise also suggests that ATP may be a contributing factor to the blood flow response in the transition from rest to steady state exercise.

Central venous oxygen saturation monitoring

It has been established that mixed venous oxygen saturation (SvO2) reflects the balance between systemic oxygen deliver y and consumption. Literature indicates that it is a valuable clinical indicator and has good prognostic value early in patient course. This article aims to establish the usefulness of SvO2 as a clinical indicator. A secondary aim was to determine whether central venous oxygen saturation (ScvO2) and SvO2 are interchangeable. Of particular relevance to cardiac nurses is the link between decreased SvO2 and cardiac failure in patients with myocardial infarction, and with decline in myocardial function, clinical shock and arrhythmias. While absolute values ScvO2 and SvO2 are not interchangeable, ScvO2 and SvO2are equivalent in terms of clinical course. Additionally, ScvO2 monitoring is a safer and less costly alternative to SvO2 monitoring. It can be concluded that continuous ScvO2 monitoring should potentially be undertaken in patients at risk of haemodynamic instability.