Counter-Current Vascular Heat Exchange in the Fins of Whales

689

585

Life is almost certainly the most complex and diverse physical system in the universe, covering more than 27 orders of magnitude in mass, from the molecules of the genetic code and metabolic process up to whales and sequoias. Organisms themselves span a mass range of over 21 orders of magnitude, ranging from the smallest microbes (10 -13 ·g) to the largest mammals and plants (10 8 ·g). This vast range exceeds that of the Earth's mass relative to that of the galaxy (which is 'only' 18 orders of magnitude) and is comparable to the mass of an electron relative to that of a cat. Similarly, the metabolic power required to support life over this immense range spans more than 21 orders of magnitude. Despite this amazing diversity and complexity, many of the most fundamental biological processes manifest an extraordinary simplicity when viewed as a function of size, regardless of the class or taxonomic group being considered. Indeed, we shall argue that mass, and to a lesser extent temperature, is the prime determinant of variation in physiological behaviour when different organisms are compared over many orders of magnitude.Scaling with size typically follows a simple power law behaviour of the form:where Y is some observable biological quantity, Y 0 is a normalization constant, and M b is the mass of the organism (Calder, 1984;McMahon and Bonner, 1983;Niklas, 1994;Peters, 1986;Schmidt-Nielsen, 1984). An additional simplification is that the exponent, b, takes on a limited set of values, which are typically simple multiples of 1/4. Among the many variables that obey these simple quarter-power allometric scaling laws are nearly all biological rates, times, and dimensions; they include metabolic rate (bഠ3/4), lifespan (bഠ1/4), growth rate (bഠ-1/4), heart rate (bഠ-1/4), DNA nucleotide substitution rate (bഠ-1/4), lengths of aortas and heights of trees (bഠ1/4), radii of aortas and tree trunks Life is the most complex physical phenomenon in the Universe, manifesting an extraordinary diversity of form and function over an enormous scale from the largest animals and plants to the smallest microbes and subcellular units. Despite this many of its most fundamental and complex phenomena scale with size in a surprisingly simple fashion. For example, metabolic rate scales as the 3/4-power of mass over 27 orders of magnitude, from molecular and intracellular levels up to the largest organisms. Similarly, time-scales (such as lifespans and growth rates) and sizes (such as bacterial genome lengths, tree heights and mitochondrial densities) scale with exponents that are typically simple powers of 1/4. The universality and simplicity of these relationships suggest that fundamental universal principles underly much of the coarse-grained generic structure and organisation of living systems. We have proposed a set of principles based on the observation that almost all life is sustained by hierarchical branching networks, which we assume have invariant terminal units, are space-filling and are optimised by the process of natural selection. W...

Section: Discussionmentioning

confidence: 99%

The origin of allometric scaling laws in biology from genomes to ecosystems: towards a quantitative unifying theory of biological structure and organization

West

Brown

2005

689

585

“…Third, their stratification in blubber may be prevented by their containment in adipocytes as well as the highly structured nature of adipocytes in the blubber tissue. Finally, cetaceans are known to have fine vascular control to their appendages and to the periphery of their body (Elsner et al, 1974;Kvadsheim and Folkow, 1997;Ling, 1974;Meagher et al, 2002;Pabst et al, 1999b;Scholander and Schevill, 1955). Intermittent heat loads could be applied to the blubber through shunting of warm blood to the blubber layer, followed by periods of vasoconstriction.…”

Section: Phylogenetic and Methodological Comparisons Of Blubber's Thementioning

confidence: 99%

The ontogenetic changes in the thermal properties of blubber from Atlantic bottlenose dolphinTursiops truncatus

Dunkin

McLellan

Blum

et al. 2005

136

139

categories, while that of emaciated animals was significantly higher (0.24 ± 0.04·W·m·deg.-1 ) than all other categories. Blubber from sub-adults and pregnant females had the highest insulation values while fetuses and emaciated animals had the lowest. In nutritionally dependant life history categories, changes in blubber's thermal insulation were characterized by stable blubber quality (i.e. conductivity) and increased blubber quantity (i.e. thickness). In nutritionally independent animals, blubber quantity remained stable while blubber quality varied. A final, unexpected observation was that heat flux measurements at the deep blubber surface were significantly higher than that at the superficial surface, a pattern not observed in control materials. This apparent ability to absorb heat, coupled with blubber's fatty acid composition, suggest that dolphin integument may function as a phase change material.

“…As early as 1955, Irving and Krog (1955) demonstrated that the feet of Arctic dogs, reindeer and seagulls may be at near-freezing temperatures while core body temperature is maintained at low ambient temperature. The anatomical arrangement of the heat exchangers that make this possible varies between species, but the general structure consists of arteries running in close contact with veins (Scholander and Schevill, 1955;Blix et al, 2010). The result is two concentric conduits, where the warm arterial blood is cooled by the venous blood, which has been chilled in the legs or flippers.…”

Section: Physiological Defencesmentioning

confidence: 99%

Adaptations to polar life in mammals and birds

Blix

2016

141

This Review presents a broad overview of adaptations of truly Arctic and Antarctic mammals and birds to the challenges of polar life. The polar environment may be characterized by grisly cold, scarcity of food and darkness in winter, and lush conditions and continuous light in summer. Resident animals cope with these changes by behavioural, physical and physiological means. These include responses aimed at reducing exposure, such as 'balling up', huddling and shelter building; seasonal changes in insulation by fur, plumage and blubber; and circulatory adjustments aimed at preservation of core temperature, to which end the periphery and extremities are cooled to increase insulation. Newborn altricial animals have profound tolerance to hypothermia, but depend on parental care for warmth, whereas precocial mammals are well insulated and respond to cold with non-shivering thermogenesis in brown adipose tissue, and precocial birds shiver to produce heat. Most polar animals prepare themselves for shortness of food during winter by the deposition of large amounts of fat in times of plenty during autumn. These deposits are governed by a sliding set-point for body fatness throughout winter so that they last until the sun reappears in spring. Polar animals are, like most others, primarily active during the light part of the day, but when the sun never sets in summer and darkness prevails during winter, high-latitude animals become intermittently active around the clock, allowing opportunistic feeding at all times. The importance of understanding the needs of the individuals of a species to understand the responses of populations in times of climate change is emphasized.