Heterochrony: the Evolution of Development

Abstract

Heterochrony can be defined as change to the timing or rate of development relative to the ancestor. Because organisms generally change in shape as well as increase in size during their development, any variation to the duration of growth or to the rate of growth of different parts of the organism can cause morphological changes in the descendant form. Heterochrony takes the form of both increased and decreased degrees of development, known as "peramorphosis" and "paedomorphosis," respectively. These are the morphological consequences of the operation of processes that change the duration of the period of an individual's growth, either starting or stopping it earlier or later than in the ancestor, or by extending or contracting the period of growth. Heterochrony operates both intra-and interspecifically and is the source of much intraspecific variation. It is often also the cause of sexual dimorphism. Selection of a sequence of species with a specific heterochronic trait can produce evolutionary trends in the form of pera-or paedomorphoclines. Many different life history traits arise from the operation of heterochronic processes, and these may sometimes be the targets of selection rather than morphological features themselves. It has been suggested that some significant steps in evolution, such as the evolution of vertebrates, were engendered by heterochrony. Human evolution was fuelled by heterochrony, with some traits, such as a large brain, being peramorphic, whereas others, such as reduced jaw size, are paedomorphic.

Cranial ontogenetic variation in Mapusaurus roseae (Dinosauria: Theropoda) and the probable role of heterochrony in carcharodontosaurid evolution

“…Although peramorphosis probably predominated in the evolution of Allosauroidea, at least one possible paedomorphic character is present in this group: the reduction of arms (especially the modules of forearm and hand) in proportion to body size, as seen in Acrocanthosaurus in comparison with Allosaurus (Currie and Carpenter 2000). The combination of both processes is called ''dissociated heterochrony'' and is also recorded in Diplodocimorpha (Salgado 1999) and Tyrannosauridae (Long and McNamara 1997b;McNamara 2012). Despite the similarities between Tyrannosauridae and Carcharodontosauridae regarding peramorphosis as the dominant process in the evolution of both groups, it is interesting to note that in the case of Tyrannosaurinae, characters related to craniofacial pneumaticity, such as the size of the maxillary fenestra, are strongly developed during later stages of ontogeny (Carr 1999), whereas in Carcharodontosauridae (and Allosauroidea in general) they are significantly reduced.…”

“…1). Gigantism is a feature widely cited for clades where peramorphic changes predominate over paedomorphosis (McNamara 2012;McNamara and Long 2012), such as in tyrannosauroid coelurosaurs McNamara 1995, 1997a, b), or diplodocine sauropods (Salgado 1999). This peramorphic gigantism usually occurs by hypermorphosis, acceleration, or a combination of both (Long and McNamara 1997b;Salgado 1999;McNamara and Long 2012).…”

Three-dimensional cranial ontogeny in pantherines (Panthera leo,P. onca,P. pardus,P. tigris; Carnivora:, Felidae)

“…Accordingly, paedomorphosis could be produced by a post-displacement (delayed onset of growth) or by neoteny or deceleration (reduced rate of growth) (Reilly, Wiley & Meinhardt, 1997;Klingenberg, 1998;McNamara, 2012). However, it is also possible that the evolutionary tendency in P. leo and P. tigris was an increase in size and, in this case, they could be considered peramorphic.…”

“…However, it is also possible that the evolutionary tendency in P. leo and P. tigris was an increase in size and, in this case, they could be considered peramorphic. Peramorphosis could be produced by a pre-displacement (earlier onset of growth) or by acceleration (increased rate of growth) (Reilly et al, 1997;Klingenberg, 1998;McNamara, 2012) (Fig. 10).…”

Anatomia e morfogênese da margem do manto da vieira Nodipecten nodosus (L. 1758) (Bivalvia: Pectinidae)

“…Despite common pallial features in those bivalves, the timing of emergence of cilia and mantle folds seems to vary. This could be explained by different rates of differentiation during ontogeny, leading to heterochronical alterations across Bivalvia groups (Smith, 2001;McNamara, 2012). Heterochrony has been argued as the reason for modifications in developmental time of bivalve larvae, and for significant anatomical and evolutionary changes (Yonge, 1962;.…”