Towards a molecular explanation of the high performance of the tuna heart

The tuna heart is capable of sustaining cardiac outputs that are high relative to other active teleost species. The question as to whether there are known molecular mechanisms to explain this phenomenon is examined. Unfortunately, the evidence at present is scant but the paper attempts to put existing knowledge into a contextual framework. It is known that the high cardiac outputs in tuna are due to the maximum heart rates that are high relative to other active teleost species. While the normalized stroke volume (ml/kg body weight) in tuna is in the same range as that of trout several important points are worth noting. The stroke volume in the tuna heart is generated in the face of an afterload that is two-fold higher (due to high ventral aortic pressure) than that observed in the trout or other teleosts. Since the stroke volume is predicated on the strength of ventricular contraction, the question then arises as to whether this is a consequence of factors intrinsic or extrinsic to the design of the cardiomyocytes that make up the myocardium. Two important extrinsic factors must be noted: the substantially higher normal operating temperatures and the apparent cardiac hyperplasia in the tuna. While the merit of these factors is discussed, the paper focuses on intrinsic factors. There is very little that has been determined to date that would indicate substantive changes in the design of the myocyte in the tuna heart compared to that of trout. Are these extrinsic factors alone then sufficient to account for the impressive cardiac output capabilities in the tuna?     

Local force cues for strength and stability in a distributed robotic construction system

Construction of spatially extended, self-supporting structures requires a consideration of structural stability throughout the building sequence. For collective construction systems, where independent agents act with variable order and timing under decentralized control, ensuring stability is a particularly pronounced challenge. Previous research in this area has largely neglected considering stability during the building process. Physical forces present throughout a structure may be usable as a cue to inform agent actions as well as an indirect communication mechanism (stigmergy) to coordinate their behavior, as adding material leads to redistribution of forces which then informs the addition of further material. Here we consider in simulation a system of decentralized climbing robots capable of traversing and extending a two-dimensional truss structure, and explore the use of feedback based on force sensing as a way for the swarm to anticipate and prevent structural failures. We consider a scenario in which robots are tasked with building an unsupported cantilever across a gap, as for a bridge, where the goal is for the swarm to build any stable spanning structure rather than to construct a specific predetermined blueprint. We show that access to local force measurements enables robots to build cantilevers that span significantly farther than those built by robots without access to such information. This improvement is achieved by taking measures to maintain both strength and stability, where strength is ensured by paying attention to forces during locomotion to prevent joints from breaking, and stability is maintained by looking at how loads transfer to the ground to ensure against toppling. We show that swarms that take both kinds of forces into account have improved building performance, in both structured settings with flat ground and unpredictable environments with rough terrain.     

Synchronisation effects on the behavioural performance and information dynamics of a simulated minimally cognitive robotic agent

Oscillatory activity is ubiquitous in nervous systems, with solid evidence that synchronisation mechanisms underpin cognitive processes. Nevertheless, its informational content and relationship with behaviour are still to be fully understood. In addition, cognitive systems cannot be properly appreciated without taking into account brain-body- environment interactions. In this paper, we developed a model based on the Kuramoto Model of coupled phase oscillators to explore the role of neural synchronisation in the performance of a simulated robotic agent in two different minimally cognitive tasks. We show that there is a statistically significant difference in performance and evolvability depending on the synchronisation regime of the network. In both tasks, a combination of information flow and dynamical analyses show that networks with a definite, but not too strong, propensity for synchronisation are more able to reconfigure, to organise themselves functionally and to adapt to different behavioural conditions. The results highlight the asymmetry of information flow and its behavioural correspondence. Importantly, it also shows that neural synchronisation dynamics, when suitably flexible and reconfigurable, can generate minimally cognitive embodied behaviour.     

Effect of formulation on the stability and aerosol performance of a nebulized antibody

Most monoclonal antibodies (mAbs) are administered to patients intravenously to ensure high bioavailability as rapidly as possible. The airways, however, are an attractive delivery route for mAbs for the treatment of lung diseases, making it possible to increase their concentration in the target organ while limiting their systemic passage. Several challenges must be overcome for translation into clinical practice. For example, the drug and device must be paired for the efficient and reliable deposition of a pharmacologically active and safe mAb in the lung region of interest. Mesh nebulizers appear to be the most effective aerosol-producing devices for delivering large amounts of biopharmaceutical while limiting protein instability during nebulization. We used metrological and analytic methods to analyze the effect of both antibody concentration and surfactant addition on aerosol performance and antibody integrity. These two factors had a limited effect on aerosol performance, but affected antibody aggregation. The addition of surfactants to antibody formulations at concentrations appropriate for lung administration markedly reduced the formation of medium or large aggregates, as shown by dynamic light scattering and fluorescence microscopy. Aggregation was also dependent on the type of mesh nebulizer, highlighting the need to optimize drug and device together.     

Effect of formulation on the stability and aerosol performance of a nebulized antibody

Most monoclonal antibodies (mAbs) are administered to patients intravenously to ensure high bioavailability as rapidly as possible. The airways, however, are an attractive delivery route for mAbs for the treatment of lung diseases, making it possible to increase their concentration in the target organ while limiting their systemic passage. Several challenges must be overcome for translation into clinical practice. For example, the drug and device must be paired for the efficient and reliable deposition of a pharmacologically active and safe mAb in the lung region of interest. Mesh nebulizers appear to be the most effective aerosol-producing devices for delivering large amounts of biopharmaceutical while limiting protein instability during nebulization. We used metrological and analytic methods to analyze the effect of both antibody concentration and surfactant addition on aerosol performance and antibody integrity. These two factors had a limited effect on aerosol performance, but affected antibody aggregation. The addition of surfactants to antibody formulations at concentrations appropriate for lung administration markedly reduced the formation of medium or large aggregates, as shown by dynamic light scattering and fluorescence microscopy. Aggregation was also dependent on the type of mesh nebulizer, highlighting the need to optimize drug and device together.     

Biogeography of tuna and billfish communities

Aim The aims of this study were: (1) to identify global communities of tuna and billfish species through quantitative statistical analyses of global fisheries data; (2) to describe the spatial distribution, main environmental drivers and species composition of each community detected; and (3) to determine whether the spatial distribution of each community could be linked to the environmental conditions that affect lower trophic levels by comparing the partitions identified in this study with Longhurst’s biogeochemical provinces. Location The global ocean from 60° S to 65° N. Methods We implemented a new numerical procedure based on a hierarchical clustering method and a nonparametric probabilistic test to divide the oceanic biosphere into biomes and ecoregions. This procedure was applied to a database that comprised standardized data on commercial longline catches for 15 different species of tuna and billfish over a period of more than 50 years (i.e. 1953–2007). For each ecoregion identified (i.e. characteristic tuna and billfish community), we analysed the relationships between species composition and environmental factors. Finally, we compared the biogeochemical provinces of Longhurst with the ecoregions that we identified. Results Tuna and billfish species form nine well‐defined communities across the global ocean. Each community occurs in regions with specific environmental conditions and shows a distinctive species composition. High similarity (68.8% homogeneity) between the spatial distribution of the communities of tuna and billfish and the biogeochemical provinces suggests a strong relationship between these species and the physical and chemical characteristics of the global ocean. Main conclusions Despite their high tolerance for a wide range of environmental conditions, these highly migratory species are partitioned into clear geographical communities in the ocean at a global scale. The similarity between biogeochemical and biotic divisions in the ocean suggests that the global ocean is a mosaic of large biogeographical ecosystems, each characterized by specific environmental conditions that have a strong effect on the composition of the trophic web.     

Effects of immunostimulants on ranched southern bluefin tuna Thunnus maccoyii: immune response, health and performance

Ranched southern bluefin tuna Thunnus maccoyii were fed baitfishes supplemented with vitamins (predominantly E and C) or vitamins and immunostimulants, nucleotides and β-glucans, over 12 weeks after transfer and monitored for enhancement in immune response, health and performance through their 19 week grow-out period. Fish from two different tows were sampled separately at three different sampling points: at transfer to grow-out pontoons, at 8 weeks post-transfer and at harvest, 19 weeks post-transfer. Lysozyme activity was enhanced during vitamin supplementation compared to control fish. Performance (i.e. survival, condition index and crude fat), health (i.e. blood plasma variables including pH, osmolality, cortisol, lactate and glucose) and alternative complement activity were not commonly improved through diet supplementation. There were some tow-specific improvements in performance through vitamin supplementation including survival, selected parasite prevalence and intensity, and alternative complement activity. Immunostimulant supplementation also showed a tow-specific improvement in plasma cortisol level. Tow-specific responses may suggest that life history, previous health condition and husbandry can affect the success of vitamin and immunostimulant enhancement of immune response, health and performance of ranched T. maccoyii.     

Crosslinking of enzymes for improved stability and performance.

Stabilization of enzymes without diminishing and diluting their activity is crucial for their use as industrial catalysts. One practically proven approach involves crystallization of the enzyme (size 1-200 microm) followed by subsequent crosslinking. In many cases, the resulting crosslinked enzyme crystals exhibit increased storage stability as well as stability in applications. The technology is complementary to protein engineering methods that aim at boosting the inherent stability of the enzyme.     

Influence of swimming speed on metabolic rates of juvenile pacific bluefin tuna and yellowfin tuna

Bluefin tuna are endothermic and have higher temperatures, heart rates, and cardiac outputs than tropical tuna. We hypothesized that the increased cardiovascular capacity to deliver oxygen in bluefin may be associated with the evolution of higher metabolic rates. This study measured the oxygen consumption of juvenile Pacific bluefin Thunnus orientalis and yellowfin tuna Thunnus albacares swimming in a swim-tunnel respirometer at 20 degrees C. Oxygen consumption (Mo2) of bluefin (7.1-9.4 kg) ranged from 235+/-38 mg kg(-1) h(-1) at 0.85 body length (BL) s(-1) to 498+/-55 mg kg(-1) h(-1) at 1.80 BL s(-1). Minimal metabolic rates of swimming bluefin were 222+/-24 mg O(2) kg(-1) h(-1) at speeds of 0.75 to 1.0 BL s(-1). Mo2 of T. albacares (3.7-7.4 kg) ranged from 164+/-18 mg kg(-1) h(-1) at 0.65 BL s(-1) to 405+/-105 mg kg(-1) h(-1) at 1.8 BL s(-1). Bluefin tuna had higher metabolic rates than yellowfin tuna at all swimming speeds tested. At a given speed, bluefin had higher metabolic rates and swam with higher tailbeat frequencies and shorter stride lengths than yellowfin. The higher M dot o2 recorded in Pacific bluefin tuna is consistent with the elevated cardiac performance and enhanced capacity for excitation-contraction coupling in cardiac myocytes of these fish. These physiological traits may underlie thermal-niche expansion of bluefin tuna relative to tropical tuna species.     

Diversity of protists and bacteria determines predation performance and stability

Predation influences prey diversity and productivity while it effectuates the flux and reallocation of organic nutrients into biomass at higher trophic levels. However, it is unknown how bacterivorous protists are influenced by the diversity of their bacterial prey. Using 456 microcosms, in which different bacterial mixtures with equal initial cell numbers were exposed to single or multiple predators (Tetrahymena sp., Poterioochromonas sp. and Acanthamoeba sp.), we showed that increasing prey richness enhanced production of single predators. The extent of the response depended, however, on predator identity. Bacterial prey richness had a stabilizing effect on predator performance in that it reduced variability in predator production. Further, prey richness tended to enhance predator evenness in the predation experiment including all three protists predators (multiple predation experiment). However, we also observed a negative relationship between prey richness and predator production in multiple predation experiments. Mathematical analysis of potential ecological mechanisms of positive predator diversity—functioning relationships revealed predator complementarity as a factor responsible for both enhanced predator production and prey reduction. We suggest that the diversity at both trophic levels interactively determines protistan performance and might have implications in microbial ecosystem processes and services.     

Genetic validation of the unexpected presence of a tropical tuna,bigeye tuna (Thunnus obesus), in the Mediterranean

Bigeye tuna (Thunnus obesus, Lowe, 1839) is one of the eight recognized species of the genus Thunnus. It is considered a tropical species distributed in the Atlantic, Pacific and Indian Oceans. To date, no validated presence of this species has been reported inside the Mediterranean Sea. This study, however, confirms, for the first time, the presence of three young individuals of this species within the Mediterranean Sea.     

Genetic Allee effects on performance, plasticity and developmental stability in a clonal plant

Negative effects of small population size on fitness, so-called Allee effects, may threaten population persistence even in intact habitat remnants. We studied genotypes of 14 isolated populations of the clonal plant Ranunculus reptans, for which molecular genetic (RAPD-) variability is higher for large than for small populations. In a competition-free greenhouse environment vegetative offspring of genotypes from large populations produced more rosettes and flowers, indicating higher fitness. Within-genotype coefficients of variation in performance traits, indicating developmental instability, were lower for genotypes from populations with higher RAPD-variability. In competition with a taller grass, we found relative reduction in leaf length less pronounced for plants from large populations, suggesting higher adaptive plasticity. Our experimental study of a plant with predominantly vegetative reproduction suggests, that negative genetic effects of recent habitat fragmentation, which so far rather were expected in plants with frequent sexual reproduction, are more severe and more common than previously acknowledged.     

Growth-promoting activity of tuna growth hormone and expression of tuna growth hormone cDNA in Escherichia coli

Tuna (Thunnus thynnus) growth hormone (GH) was purified by using a column of Sepharose 4B to which tuna GH-specific IgG was linked. The molecular weight and isoelectric point of tuna GH were 21,000 and 6.5, respectively. The growth of snapper (Pagrus major) was remarkably accelerated when the purified hormone was administered by four intraperitonial injections at intervals of 5 days: 1.5-fold in length and 1.9-fold in body weight/60 days. To produce tuna GH in Escherichia coli cells, expression plasmids pTES8 and pTES8S for tuna GH cDNA with or without the signal peptide region were constructed and GH production in E. coli cells was examined with the Maxicell system. The product specified by the plasmids in E. coli cells was immunologically identified to be tuna GH.     

Structure and function of tuna tail tendons

The caudal tendons in tunas and other scombrid fish link myotomal muscle directly to the caudal fin rays, and thus serve to transfer muscle power to the hydrofoil-like tail during swimming. These robust collagenous tendons have structural and mechanical similarity to tendons found in other vertebrates, notably the leg tendons of terrestrial mammals. Biochemical studies indicate that tuna tendon collagen is composed of the (alpha1)(2),alpha2 heterotrimer that is typical of vertebrate Type I collagen, while tuna skin collagen has the unusual alpha1,alpha2,alpha3 trimer previously described in the skin of some other teleost species. Tuna collagen, like that of other fish, has high solubility due to the presence of an acid-labile intermolecular cross-link. Unlike collagen in mammalian tendons, no differences related to cross-link maturation were detected among tendons in tuna ranging from 0.05 to 72 kg (approx. 0.25-6 years). Tendons excised post-mortem were subjected to load cycling to determine the modulus of elasticity and resilience (mean of 1.3 GPa and 90%, respectively). These material properties compare closely to those of leg tendons from adult mammals that can function as effective biological springs in terrestrial locomotion, but the breaking strength is substantially lower. Peak tendon forces recorded during steady swimming appear to impose strains of much less than 1% of tendon length, and no more than 1.5% during bursts. Thus, the caudal tendons in tunas do not appear to function as elastic storage elements, even at maximal swimming effort.     

Isolation and characterization of a new zinc-binding protein from albacore tuna plasma

The protein responsible for sequestering high levels of zinc in the plasma of the albacore tuna (Thunnus alalunga) has been isolated by sequential chromatography. The glycoprotein has a molecular weight of 66,000. Approximately 8.2% of its amino acid residues are histidines. Equilibrium dialysis experiments show it to bind 3 mol of zinc/mol of protein. The stoichiometric constant for the association of zinc with a binding site containing three histidines was determined to be 10(9.4). This protein is different from albumin and represents a previously uncharacterized zinc transport protein.