is the process of experimentally shifting the scaling relationships
of a population. More specifically, the process of experimentally breaking the tight covariance
In probability theory and statistics, covariance is a measure of how much two variables change together. Variance is a special case of the covariance when the two variables are identical.- Definition :...
evident among component traits of a complex phenotype
A phenotype is an organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior...
by altering the variance
In probability theory and statistics, the variance is a measure of how far a set of numbers is spread out. It is one of several descriptors of a probability distribution, describing how far the numbers lie from the mean . In particular, the variance is one of the moments of a distribution...
of one trait
Trait may refer to:* Trait, a characteristic or property of some object* Trait , which involve genes and characteristics of organisms* Trait theory, an approach to the psychological study of personality...
relative to another. Typically, body size is one of the two traits. The measurements of the two traits are plotted against each other and the scaling relationship can be represented as
Manipulations of this sort alter the scaling relationships either by shifting the intercept (b
), slope (m
) or both to create novel variants (see allometry
for more details). These novel variants can then be tested for differences in performance or fitness. Through careful testing, one could sequentially test each component of a trait suite to determine how each part contributes to the function of the entire complex phenotype, and ultimately the fitness of the organism. This technique allows for comparison within or among biological groups which differ in size by adjusting morphology to match one another and comparing their performances.
Allometric engineering has been used to test Lack
To lack something is not to have it.Lack may also refer to:* Andrew Lack , British botanist and biologist* David Lack , British ornithologist and biologist* Lack Township, Juniata County, Pennsylvania...
's hypothesis in the lizard Sceloporus occidentalis
. In this study, two populations were "engineered" to fit morphology of the other by manipulating egg yolk quantity, removing effect of size difference between groups. After manipulation, they found that speed was inversely proportional to body size.
Nature versus nurture
Maternal investment was "allometrically engineered" by surgically removing an ovary in cockroaches (Diploptera
Diploptera is a genus of cockroach, used particularly in molecular research into allatostatins. The species Diploptera punctata, the Pacific beetle cockroach, is the only known viviparous cockroach ....
). This effectively reduced number of progeny and increased resource allocation to each offspring. They coupled this manipulation with group effects (faster development in large groups), and found that maternal investment can overcome group effect.
The male Long-tailed Widowbird
The Long-tailed Widowbird is a species of bird in the Ploceidae family.It is found in Angola, Botswana, Democratic Republic of the Congo, Kenya, Lesotho, South Africa, Swaziland, and Zambia.-References:...
) has exceptionally long tail feathers roughly half a meter in length. Male tail feathers were cropped and glued and those with artificially enhanced tail lengths secured the most matings, demonstrating female preference.
The fly Zonosemata
Zonosemata is a genus of tephritid or fruit flies in the family Tephritidae, comprising six species from North America and one from South America...
has a banding pattern on its wings which was found to mimic movements of a jumping spider. Greene et al.
engineered novel phenotypes, breaking correlation between a behavior and morphology, by cutting and transplanting the wings of this fly with the common housefly
The housefly , Musca domestica, is a fly of the suborder Cyclorrhapha...
. This manipulation demonstrated that it was behavior coupled with the banding pattern deterred jumping spiders from attacking, though not other predators.
Current uses have involved truncation or cropping, yolk manipulation, hormonal treatments, maternal allocation, temperature manipulation, or altering nutritional states. Each method undoubtedly has its merits and pitfalls to consider before designing an experiment, but these techniques are opening new avenues of research in comparative and evolutionary biology.