Question

1. Many traits show an allometric relationship with body size, such that the log of the trait is linearly related to the log of body size. In some cases this is due to different growth rates of different body parts during development, while in other cases it is due to selection acting differently at different body sizes. Identify three examples of allometry such that your examples include:
   -- At least one example resulting from differential growth rates.
   -- At least one example resulting from different selection at different sizes.
   -- At least one case where the slope of the allometric line is greater than 1.
   -- At least one case where the slope is less than 1.

Answer 1

Allometry is the study of the relative change in proportion of an attribute compared to another one during organismal growth. These attributes may be morphological, physiological, or otherwise.

An example for the allotropy resulting from differential growth rates is Male fiddler crab.Male fiddler crabs have one normal claw for feeding and one giant claw, which can be up to one-third of the crab's total body weight. This giant claw is used for attracting female fiddler crabs and for fighting with other males.Claw was growing at a faster rate than the body of the crab.When we plot this using log-log scale using equation log y = α log x + log b where x is body size, y is organ size, log b is the intercept of the line on the y-axis and α is the slope of the line, also known as the allometric coefficient.When the organ has a higher growth rate than the body as whole,like, the claw of male fiddler crab, α > 1, which is called positive allometry or hyperallometry.

An example of allotropy resulting from different selection at different sizes is  the human head, which grows more slowly than the rest of the body after birth and so is proportionally smaller in adults than in children.In this example the allotropy coefficient is less than 1 and so is called  negative allometry.

Another example is when an organ grows at the same rate as the rest of the body, α = 1, a condition called isometry. Such an organ maintains a constant proportionate size throughout development.Many animals undergo isometric growth as they mature from new hatchling to adult. This means that all the body parts grow at approximately the same rate, and the adult proportions are not significantly different from those of the juvenile. For example, Batrachoseps, one of the few salamanders that has a terrestrial larva.