Biomedical subjects

Jeffrey B Graham

Publications and source records attributed to Jeffrey B Graham.

8 recordsLinked to original sources

PubMed2005

Burrow air phase maintenance and respiration by the mudskipper Scartelaos histophorus (Gobiidae: Oxudercinae).

A laboratory burrow and mudflat system was used to examine aspects of burrow air-phase maintenance and utilization by the amphibious mudskipper Scartelaos histophorus. While confined to its burrow during simulated 'high tide', this species respires both aquatically and aerially, in the latter case utilizing an air phase it had established by transporting air into the burrow during simulated 'low tide'. Over the course of 'high-tide' confinement, burrow-water P(O2) declines, making the air phase more important for respiration; the burrow-water O2 tension eliciting air-phase respiration is 4.8+/-0.2 kPa. At 'low tide', when the fish has access to air, it deposits new air in the air phase by transporting gulps into the burrow and releasing them. Observed air-deposition rates for both males and females were 12.3+/-4.5 trips h(-1). All of the fish tested (N=8 individuals + 2 pairs) deposited air and responded to experimental air-phase withdrawal by replacing the air (72 of 74 tests, 97.3%). Also, repeated tests with one fish showed that experimental reduction of the air-phase P(O2) by mixing with N2 elicited a gas-expelling behavior at O2 levels less than 10.3 kPa. At O2 levels greater than 10.3 kPa, the fish left the air phase intact and added to it by depositing surface air.

Air↗

PubMed2004

A comparative echocardiographic assessment of ventricular function in five species of sharks.

A comparative echocardiographic study was carried out on five shark species that differ in heart morphology and in aspects of their behavior and natural history. The study contrasted the ventricular function in the highly active mako shark (heart type IV) and four other sharks (heart type III) that differ in activity levels (i.e. the sedentary horn and swell sharks vs. the moderately active blue and smooth-hound sharks). All five species exhibited biphasic ventricular filling characterized by an early (conduit) and late (atrial systole) phase. In the mako shark, early filling was dominant as indicated by a higher early flow peak velocity, a greater early:late velocity ratio, and a greater early velocity time integral. In contrast, the late filling phase was the more important filling agent in the other species. Indices of systolic function such as ventricular ejection fraction and ventricular fractional shortening also reflect a more efficient cardiac pumping capacity in mako shark relative to the other four sharks. The comparative echocardiographic assessment of in vivo ventricular function integrates structural and functional features with shark activity level to arrive at a new perspective blending the occurrence of biphasic filling with functional concepts based on heart morphological typology and changing views regarding the role of factors such as central filling pressure and pericardial pressure on end-diastolic ventricular volume.

Animals↗

PubMed2004

Pericardial and pericardioperitoneal canal relationships to cardiac function in the white sturgeon (Acipenser transmontanus).

Sturgeons are primitive bony fishes and their hearts have structural features found in other primitive fishes. Sturgeons have a pericardioperitoneal canal (PPC), a one-way conduit into the peritoneum. A PPC also occurs in elasmobranchs (sharks and rays) and studies with that group demonstrate that pericardial pressure and pericardial fluid loss via the PPC affect stroke volume. A study of white sturgeon (Acipenser transmontanus) heart function was conducted to test for a comparable PPC and pericardial effects. White sturgeon-elasmobranch heart-function similarities include biphasic ventricular filling, a comparable operational pericardial pressure (-0.03 kPa), and a strongly negative pressure (-0.2 to -0.6 kPa) with complete pericardial fluid withdrawal. Differences include the white sturgeon's relatively smaller atrium and ventricle but a larger conus arteriosus. Although white sturgeon heart size is also smaller, its pericardial volume is disproportionately less (2.4 to 2.7 vs. 3.5 to 5.4 ml kg(-1) in elasmobranchs), meaning it has less scope for increasing stroke volume upon PPC fluid release. These differences may reflect the phylogenetic progression from the less complex operation of the elasmobranch heart, which lacks sympathetic innervation and has a mechanically mediated (PPC) stroke volume, to the condition in the more derived bony fishes which have sympathetic and parasympathetic regulation of both stroke volume and heart rate.

Animals↗

PubMed2004

Tuna comparative physiology.

Thunniform swimming, the capacity to conserve metabolic heat in red muscle and other body regions (regional endothermy), an elevated metabolic rate and other physiological rate functions, and a frequency-modulated cardiac output distinguish tunas from most other fishes. These specializations support continuous, relatively fast swimming by tunas and minimize thermal barriers to habitat exploitation, permitting niche expansion into high latitudes and to ocean depths heretofore regarded as beyond their range.

Animals↗

PubMed2003

Vascular anatomy of the gills in a high energy demand teleost, the skipjack tuna (Katsuwonus pelamis).

Tunas (family: Scombridae, Tribe: Thunnini) exhibit anatomical, physiological, and biochemical adaptations that dramatically increase the ability of their cardiorespiratory systems to transfer oxygen from the water to the tissues. In the present study the vascular anatomy of the skipjack tuna, Katsuwonus pelamis, gill was examined by light and scanning electron microscopic analysis of methyl methacrylate vascular corrosion replicas prepared under physiological pressure. The gill filament contains three distinct blood pathways, respiratory, interlamellar, and nutrient. The respiratory, or arterio-arterial (AA) pathway, is the site of gas exchange and consists of the afferent and efferent filamental arteries (AFA and EFA) and arterioles (ALA and ELA) and the lamellae. Each ALA in the basal filament supplies ten or more lamellae and they anastomose with their neighbor to form a continuous vascular arcade. Four modifications in the lamellar circulation appear to enhance gas exchange efficiency. 1) The ALA deliver blood directly to the outer margin of the lamellae where unstirred boundary layer effects are predicted to be minimal and water PO2 highest. 2) Pillar cells are closely aligned along the outer boundary of the inlet side and the inner boundary of the outlet side of the lamellae to form multiple distributing and receiving blood channels. 3) Elsewhere in the lamella, pillar cells are aligned to form diagonal channels that direct blood from the outer to the inner lamellar margins, thereby reducing vascular resistance. 4) The lamellar sinusoid is especially widened near the efferent end to augment oxygen saturation of blood flowing through the inner margin. These adaptations, plus the presence of a bow-shaped interlamellar septum, and a thinned filament core appear to decrease gill vascular resistance and maximize gas-exchange efficiency. The interlamellar (IL) and nutrient systems originate from post-lamellar vessels and are arterio-venous (AV) pathways. IL vessels form an extensive ladder-like lattice on both sides of the filamental cartilage and are supplied in part by narrow-bore vessels from the medial wall of the EFA. Their function is unknown. Nutrient vessels are formed from the confluence of a myriad of tortuous, narrow-bore vessels arising from the basal region of the EFA and from efferent branchial arteries. They re-enter the filament and eventually drain into the IL system or filamental veins. As these AV pathways are retained despite considerable reduction in filamental tissue, it is evident that they are integral components of other non-respiratory homeostatic activities of the gill.

Animals↗

PubMed2003

Swimming performance studies on the eastern Pacific bonito Sarda chiliensis, a close relative of the tunas (family Scombridae) II. Kinematics.

The swimming kinematics of the eastern Pacific bonito Sarda chiliensis at a range of sustained speeds were analyzed to test the hypothesis that the bonito's swimming mode differs from the thunniform locomotor mode of tunas. Eight bonito (fork length FL 47.5+/-2.1 cm, mass 1.25+/-0.15 kg) (mean +/- S.D.) swam at speeds of 50-130 cm s(-1) at 18+/-2 degrees C in the same temperature-controlled water tunnel that was used in previous studies of tunas. Kinematics variables, quantified from 60 Hz video recordings and analyzed using a computerized, two-dimensional motion analysis system, were compared with published data for similar sized tunas at comparable speeds. Bonito tailbeat frequency, tailbeat amplitude and stride length all increased significantly with speed. Neither yaw (6.0+/-0.6%FL) nor propulsive wavelength (120+/-65% fish total length) varied with speed, and there were no mass or body-length effects on the kinematics variables for the size range of bonitos used. Relative to similar sized yellowfin (Thunnus albacares) and skipjack (Katsuwonus pelamis) tunas at similar speeds, the bonito has a lower tailbeat frequency, a higher yaw and a greater stride length. The lateral displacement and bending angle of each intervertebral joint during a complete tailbeat cycle were determined for the bonito at a swimming speed of 90 cm s(-1). The pattern of mean maximum lateral displacement (z(max)) and mean maximum bending angle (beta(max)) along the body in the bonito differed from that of both chub mackerel Scomber japonicus and kawakawa tuna Euthynnus affinis; z(max) was highest in the bonito. This study verifies that S. chiliensis is a carangiform swimmer and supports the hypothesis that the thunniform locomotor mode is a derived tuna characteristic associated with changes in this group's myotomal architecture. The finding that yaw and z(max) were greater in the bonito than in both mackerels and tunas suggests that swimming kinematics in the bonito is not intermediate between that of tunas and mackerels, as would be predicted on the basis of morphological characteristics.

Animals↗

PubMedDate not supplied

Evolution and consequences of endothermy in fishes.

Regional endothermy, the conservation of metabolic heat by vascular countercurrent heat exchangers to elevate the temperature of the slow-twitch locomotor muscle, eyes and brain, or viscera, has evolved independently among several fish lineages, including lamnid sharks, billfishes, and tunas. All are large, active, pelagic species with high energy demands that undertake long-distance migrations and move vertically within the water column, thereby encountering a range of water temperatures. After summarizing the occurrence of endothermy among fishes, the evidence for two hypothesized advantages of endothermy in fishes, thermal niche expansion and enhancement of aerobic swimming performance, is analyzed using phylogenetic comparisons between endothermic fishes and their ectothermic relatives. Thermal niche expansion is supported by mapping endothermic characters onto phylogenies and by combining information about the thermal niche of extant species, the fossil record, and paleoceanographic conditions during the time that endothermic fishes radiated. However, it is difficult to show that endothermy was required for niche expansion, and adaptations other than endothermy are necessary for repeated diving below the thermocline. Although the convergent evolution of the ability to elevate slow-twitch, oxidative locomotor muscle temperatures suggests a selective advantage for that trait, comparisons of tunas and their ectothermic sister species (mackerels and bonitos) provide no direct support of the hypothesis that endothermy results in increased aerobic swimming speeds, slow-oxidative muscle power, or energetic efficiency. Endothermy is associated with higher standard metabolic rates, which may result from high aerobic capacities required by these high-performance fishes to conduct many aerobic activities simultaneously. A high standard metabolic rate indicates that the benefits of endothermy may be offset by significant energetic costs.

Adaptation, Physiological↗

PubMedDate not supplied

Breathing air in air: in what ways might extant amphibious fish biology relate to prevailing concepts about early tetrapods, the evolution of vertebrate air breathing, and the vertebrate land transition?

The air-breathing fishes have heuristic importance as possible models for the Paleozoic evolution of vertebrate air breathing and the transition to land. A recent hypothesis about this transition suggests that the diverse assemblage of marine amphibious fishes occurring primarily in tropical, high intertidal zone habitats are analogs of early tetrapods and that the intertidal zone, not tropical freshwater lowlands, was the springboard habitat for the Devonian land transition by vertebrates. Here we argue that selection pressures imposed by life in the intertidal zone are insufficient to have resulted in the requisite aerial respiratory capacity or the degree of separation from water required for the vertebrate land transition. The extant marine amphibious fishes, which occur mainly on rocky shores or mudflats, have reached the limit of their niche expansion onto land and remain tied to water by respiratory structures that are less efficient in air and more vulnerable to desiccation than lungs. We further argue that evolutionary contingencies actuated by the Devonian origin of the tetrapods marked a critical point of divergence for a way of life in which selection pressures would operate on the physiology, morphology, and natural history of the different vertebrate groups. While chronically hypoxic and shallow water conditions in the habitats of some primitive bony fishes and some amphibians appear similar to the conditions that prevailed in the Devonian, markedly different selection pressures have operated on other amphibians and bony fishes over the 300 million years since the vertebrate land transition. For example, both egg development and larval metamorphosis in extant amphibians are geared mainly toward compensating for the uncertainty of habitat water quality or even the absence of water by minimizing the time required to develop there. In contrast, reproduction by most intertidal (and amphibious) fishes, all of which are teleosts, remains dependent on a planktonic larval phase and is characterized by specializations (brooding) that minimize overdispersal and maximize recruitment back to the littoral habitat.

Adaptation, Physiological↗