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Symmorphosis

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Symmorphosis

When the formation of elements are regulated to meet the needs of the requirements of a functional system is the principle of symmorphosis within a physiological system.[1] In biological organisms, symmorphosis is when a quantitative match of design and function within an organism defined within a functional system[2]. This proposes that if organs were matched structurally and functionally paired with the correct energy and minerals would lead to optimal organ design.[3] Some examples of this in the human body could be how bones are structured to withstand stress, how blood vessels are designed to distribute blood throughout the body without using a lot of energy or even how as a person becomes more physically fit or endures more cardio their body has adjusted to maintain higher functioning demands.[2]

Symmorphosis was proposed by Ewald Weibel and Charles Taylor in 1981. A common form of testing symmorphosis between species of mammals is to use comparative biology. The first system to use the proposed theory for symmorphosis is the oxygen pathway for mammals. [3]

Three Predictions of Symmorphosis

Symmorphosis occurs when the three predictions occur at one time. These three work together to allow an organ to function to its full potential.

Prediction One: Structural Design

When looking at the theory of symmorphosis one must consider if the design in the organism is fully optimized. [3] The structural design in terms of symmorphosis means that the organ is designed to allow full capacity of its function and can allow for adjustments to occur when necessary. [4]

Prediction Two: Functional Capacity

The functional capacity is when all functional units work together to determine the the maximal capacity.[4] Functional capacity is overall determined by the structural design. Once the design is optimized in terms of biological materials, then the structure must be taken into account. The structure of an organ will determine the maximal capacity and adjustments in order to allow morphogenesis, the process in which causes an organism to create its shape, to occur. [3]

Prediction Three: Functional Performance

The third prediction states that if prediction two works in intermediate steps to create a function of an individual organ than each step will also help create the upper limitation of the function as well. [3]

Symmorphosis with the Respiratory System

Recently, symmorphosis has received attention as it has been applied to the oxygen utilization in mammals. The original experimental method for symmorphosis was used to show if the design of the organs were relative to the static demands of the mammalian respiratory system. The oxygen pathway is the first used because it represents a good model for mammals of most species. This pathway is a good model because it involves several organs that are linked together as well as the overall function has a measurable upper limit.[3] In particular, this testing would help identify structural elements that differed in order to cary the maximal amount of oxygen throughout the body. [1]

The respiratory system is a good example to study due to having one main function, the function has a measurable limit, the limit is variable between individuals of a species, has a sequence of structure, and each step of the sequence has functional parameters that are not fixed. [2] The upper limit for the oxygen pathway is called the Vo2max. Vo2max is the maximal oxygen capacity that systems can take in, transport, and use oxygen. [5][3] Vo2max can vary among individuals due to allometric variation (the differences in body mass) , adaptive variation (differences in lifestyles) , and the induced variation (amount of cardio exercise). The O2 cascade is one way that can put a limit and can help determine the Vo2max by components such as oxygen supply to the skeletal muscle mitochondria and the demand of oxygen by these skeletal muscle mitochondria.[6]

To test the hypothesis of symmorphosis researchers must be able to measure Vo2max by recording this when the organism being tested is running.[2] Running will allow majority of oxygen consumption to occur.

Critiques of Symmorphosis

An issue with symmorphosis is that there is issues with having an optimal design for an organ if the organ contains multiple functions. [1] When an organ is performing multiple functions it must compromise its optimal performance of one function in order to perform another. As these complex components all add together it dramatically decreases the chance that everything will optimally match. [1] An example of this in mammals would be the lungs. Researchers now claim that the lungs are an exception when considering the Lungs typically are only partially adjusted to maximal oxygen capacity in terms of adaptive and allometric variation and cause a fluctuation in these values.[3]

In terms of symmorphosis, the capacity of each step of the oxygen cascade should match the demand of Vmax. [6] In most cases this theory holds true with the exception of when an individual exceeds the Vmax. When Vmax is exceeded there then becomes developmental constraints as well as design constraints in terms of symmorphosis[7]. When this occurs there is an unmatched capacity, although they maybe similar they do not aline with the predictions for symmorphosis. [1]

In terms of evolution, natural selection can hinder the design when looking at the guidelines for symmorphosis. Natural selection can alter the phenotype in order to increase the fitness of a species. In doing this natural selection can cause adaptations that can change the optimal structural design.[1]

References

  1. ^ a b c d e f Dudley, R., Gans, C. (1991). A Critique of Symmorphosis and Optimality Models of Physiology. Division of Comparative Physiology and Biochemistry, Society for Integrative and Comparative Biology. 64(3), 627-637.
  2. ^ a b c d Weibel, E., Taylor, C., Hoppeler, H. (1991). The concept of symmorphosis: A testable hypothesis of structure-function relationship. Proceedings of the National Academy of Sciences of the United States of America. 88(22), 10357-61.
  3. ^ a b c d e f g h Canals, M., Figueroa, D., Sabat, P. (2010).  Symmorphosis in the proximal pathway for oxygen in the leaf-eared mouse Phyllotis darwini. Biological Research. 43(1). 75-81.
  4. ^ a b Weibel,E, Taylor, C. Bolis, L. (1998). Principles of animal design. The optimization and symmorphosis debate. Cambridge University Press, Cambridge.
  5. ^ Smirmaul BP, Bertucci DR, Teixeira IP. Is the VO2max that we measure really maximal?. Front Physiol. 2013;4:203. Published 2013 Aug 5. doi:10.3389/fphys.2013.00203
  6. ^ a b Gifford, Jayson R.; Garten, Ryan S.; Nelson, Ashley D.; Trinity, Joel D.; Layec, Gwenael; Witman, Melissa A. H.; Weavil, Joshua C.; Mangum, Tyler; Hart, Corey (2016). "Symmorphosis and skeletal muscle : in vivo and in vitro measures reveal differing constraints in the exercise-trained and untrained human". The Journal of Physiology. 594 (6): 1741–1751. doi:10.1113/JP271229. ISSN 1469-7793. PMC 4799962. PMID 26614395.{{cite journal}}: CS1 maint: PMC format (link)
  7. ^ Diamond, J. (1992). The Red Flag of Optimality. Nature.355(6357), 205.

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