heterochrony


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Related to heterochrony: Hypermorphosis

Heterochrony

An evolutionary phenomenon that involves changes in the rate and timing of development. As animals and plants grow from their earliest embryonic stages to the adult, they undergo changes in shape and size. This life history of an individual organism is known as its ontogeny. The amount of growth that an organism experiences during its ontogeny can be more or less than its ancestor. This can apply to the organism as a whole or to specific parts.

Evolution can be viewed as a branching tree of modified ontogenies. Heterochrony that produces these changes in size and shape may be the link between genetics at one extreme and natural selection at the other.

If a character of one species in an evolutionary sequence undergoes less growth than its ancestor, the process is known as pedomorphosis. If it undergoes more growth, the process is known as peramorphosis. Each state can be achieved by varying the timing of onset, offset, or rate of development.

If development is stopped at an earlier growth stage in the descendant than in the ancestor (for example, by earlier onset of sexual maturity), ancestral juvenile features will be retained by the descendant adult (progenesis). If the onset of development of a particular structure is delayed in a descendant, the structure will develop less than in the ancestor (postdisplacement). The third process that produces pedomorphosis is neoteny, whereby the rate of growth is reduced.

For peramorphosis, development can start earlier in the descendant than in the ancestor (predisplacement); or the rate of development can be increased, thus increasing the allometric coefficient (acceleration); or development can be extended by a delay in the onset of sexual maturity (hypermorphosis).

As an organism grows, the number of cells that it produces increases. Ultimately, changes to rate and timing of growth are reflections of changes to the timing of onset and rate of cell development, and the balance between cell growth and cell death. Morphogens and growth hormones play a major role in controlling development in terms of initiation, rate of division, and migration. Therefore, changes to the timing of their expression affect the shape and size of the final adult structure. Inception of hormonal activity is under the control of genes that regulate the timing of its production.

heterochrony

[‚hed·ə′rä·krə·nē]
(evolution)
An evolutionary phenomenon that involves changes in the rate and timing of species development.
References in periodicals archive ?
While James's "cross-cuts" mirror the dissociations of heterochrony, their results (creative genius, divine inspiration) mirror de Beer's theory of clandestine evolution.
The ontogeny of Pseudis platensis (Anura, Hylidae): Heterochrony and the effect of larval development on postmetamorphic life.
Analyses of ontogeny restricted to a single species are not enough to explain the direction of evolutionary change in certain structures within taxonomic groups; these analyses also cannot define the growth of a structure as paedomorphic or peramorphic, leaving the realm of heterochrony. However, this allometric approach allows us to associate the change in size or shape of a given structure with the variation in the total size of the organism (Vassallo and Mora, 2007).
Intraspecific heterochrony and life history evolution: decoupling somatic and sexual development in a facultatively paedomorphic salamander.
(2013): Ontogeny in the tube-crested dinosaur Parasaurolophus (Hadrosauridae) and heterochrony in hadrosaurids.
High levels of diversity in frogs have been attributed to two general mechanisms: (1) the evolution of a dramatic metamorphosis between larval and adult stages which potentially frees each stage to evolve relatively independently (Haas, 2001: Svensson and Haas, 2005), (2) heterochrony where features shift in their relative timing of development with respect to other features (Fabrezi and Quinzio, 2008; Fabrezi and Lobo, 2009; Vera-Candioti et al., 2011; Ziermann et al., 2011).
"Modernity, Heterochrony of Gender Construct and Libidinal Economy: A Dialogic Reading".
Duboule, Denis (1994), "Temporal colinearity and the phylotypic progression: A basis for the stability of a vertebrate Bauplan and the evolution of morphologies through heterochrony", Development, suplemento, pp.
Kovac V (2002) Synchrony and heterochrony in ontogeny (offish).
"This phenomenon, where a change in the developmental timing of a creature produces morphological changes is called heterochrony, and paedomorphosis is one example of it," Abzhanov explained.