Question

If two allometrically related traits show a strong correlation both within and among species, what kinds of experiments would you use to test whether these correlations are due to natural selection or to developmental genetic constraints? (Assume the organisms of interest are easily amenable to laboratory study.) What can we infer about the underlying genetic architecture of traits whose allometric relationships do not vary? What about those that do vary?

Answer 1

? = growth coefficient of the organ, and b = a constantAllometric growth is defined as a regular and systematic pattern of growth such that the mass or size of any organ or part of a body can be expressed in relation to the total mass or size of the entire organism.

The allometric equation is Y=bx^?

where Y is the mass of the organ

x is the mass of the organism

? = growth coefficient of the organ, and

b = a constant.

Julian Huxley was one of the first people to notice these trends, in 1936. These studies were made in Fiddler crabs which belong to the Genus Uca and they were best known for their giant claws.

Female fiddler crabs have two normally-sized claws for feeding. Male 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.

Huxley noticed that the claw grew disproportionately relative to the rest of the crab's body. That is, a young, small male fiddler crab would have a fairly small display claw, while a larger, older fiddler crab would have a huge display claw, this made him realize that the claw was growing at a faster rate than the body of the crab.

The tests that can be used for natural selection theory would definitely include the study of the life cycles of the organism involved right from its developmental stages to the senescence.

While in case of genetic constraints simple genetic testing at various stages of life can be used to identify the underlying architecture of the traits involved and if they vary or not.