An isomorph is an organism that does not change in shape during growth. The implication is that its volume is proportional to its cubed length, and its surface area to its squared length. This holds for any shape it might have; the actual shape determines the proportionality constants.
The reason why the concept is important in the context of the
Dynamic Energy Budget
The dynamic energy budget (DEB) theory is a formal metabolic theory which provides a single quantitative framework to dynamically describe the aspects of metabolism (energy and mass budgets) of all living organisms at the individual level, based o ...
(DEB) theory is that food (
substrate) uptake is proportional to surface area, and maintenance to volume. Since volume grows faster than surface area, this controls the ultimate size of the organism.
Alfred Russel Wallace
Alfred Russel Wallace (8 January 1823 – 7 November 1913) was a British naturalist, explorer, geographer, anthropologist, biologist and illustrator. He is best known for independently conceiving the theory of evolution through natural se ...
wrote this in a letter to
E. B. Poulton in 1865.
[see Finch, C. 1990 ''Longevity, senescence, and the genome'' Univ Chicago Press Appendix 3] The surface area that is of importance is the part that is involved in substrate uptake (e.g. the gut surface), which is typically a fixed fraction of the total surface area in an isomorph. The DEB theory explains why isomorphs grow according to the
von Bertalanffy curve if food availability is constant.
Organisms can also change in shape during growth, which affects the growth curve and the ultimate size, see for instance
V0-morph A V0-morph is an organism whose surface area remains constant as the organism grows.
The reason why the concept is important in the context of the Dynamic Energy Budget theory is that food (substrate) uptake is proportional to surface area, and mai ...
s and
V1-morph
An V1-morph is an organism that changes in shape during growth such that its surface area is proportional to its volume. In most cases both volume and surface area are proportional to length
The reason the concept is important in the context of th ...
s. Isomorphs can also be called V2/3-morphs.
Most animals approximate isomorphy, but plants in a vegetation typically start as
V1-morph
An V1-morph is an organism that changes in shape during growth such that its surface area is proportional to its volume. In most cases both volume and surface area are proportional to length
The reason the concept is important in the context of th ...
s, then convert to isomorphs, and end up as
V0-morph A V0-morph is an organism whose surface area remains constant as the organism grows.
The reason why the concept is important in the context of the Dynamic Energy Budget theory is that food (substrate) uptake is proportional to surface area, and mai ...
s (if neighbouring plants affect their uptake).
See also
*
Dynamic energy budget
The dynamic energy budget (DEB) theory is a formal metabolic theory which provides a single quantitative framework to dynamically describe the aspects of metabolism (energy and mass budgets) of all living organisms at the individual level, based o ...
*
V0-morph A V0-morph is an organism whose surface area remains constant as the organism grows.
The reason why the concept is important in the context of the Dynamic Energy Budget theory is that food (substrate) uptake is proportional to surface area, and mai ...
*
V1-morph
An V1-morph is an organism that changes in shape during growth such that its surface area is proportional to its volume. In most cases both volume and surface area are proportional to length
The reason the concept is important in the context of th ...
*
shape correction function The shape correction function is a ratio of the surface area of a growing organism and that of an isomorph as function of the volume. The shape of the isomorph is taken to be equal to that of the organism for a given reference volume, so for that pa ...
References
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Developmental biology