The molecular evolution of vertebrate growth hormones: A pattern of near-stasis interrupted by sustained bursts of rapid change

Abstract

It has been demonstrated previously that in mammals the evolution of pituitary growth hormone shows an unusual pattern, with an underlying slow rate and at least two sustained bursts of rapid evolution (in the artiodactyls and primates), during which the rate increased at least 25-fold. It is demonstrated here that a similar pattern applies for growth hormone evolution throughout the vertebrates, with a basal rate similar to that seen in mammals, but bursts of rapid evolution in the amphibia and the elasmobranchs, and several bursts in the teleosts. The placental growth-hormone-like proteins of primates show a similar pattern. It is argued that the bursts of evolution seen for growth hormone are a consequence of selection and that this may reflect changes in the functions of the hormone additional to its basic growth-promoting actions.

Ancient and continuing Darwinian selection on insulin-like growth factor II in placental fishes

“…However, this model calculates 2 ϭ 1 and generates a likelihood value identical to that of the neutral/purifying model M1a (P ϭ 1). This test suggests, therefore, that one IGF2 codon may be evolving under positive selection in teleosts, but that the strength of selection, as measured by 2 , is very weak (averaged out to 1). In the comparison of models M7 and M8, the model allowing positive selection at specific sites fits the data significantly better than the neutral/purifying selection model (P ϭ 0.0027).…”

“…T he parent-offspring conflict theory posits that in organisms where there is parental inequality in the allocation of resources to the production of offspring, genetic antagonism may be a potent selective force shaping modes of reproduction and development (1)(2)(3)(4). According to the kinship theory of genomic imprinting, parent-specific gene expression in placental mammals and seedbearing plants is an outcome of this conflict (5).…”

Placental Growth Hormone-Related Proteins and Prolactin-Related Proteins

“…Thus, GH has changed little in the lineage leading to bushbabies but has undergone dramatic change in the lineage leading to humans since these lineages diverged from a common ancestor. Strepsirrhine primates, such as bushbabies, have a single evolutionarily conservative GH gene [24,25] whereas anthropoid primates, such as humans, have multiple GH-related genes that have undergone rapid evolutionary change [26].…”

“…Both GH and PRL have undergone rapid evolution in the lineage leading to ruminants [26,45,46]. PRL is duplicated in all well-studied ruminants whereas most species have a single GH-like gene.…”

A growth hormone-based phylogenetic analysis of euteleostean fishes including a representative species of the Atheriniformes Order, Odontesthes argentinensis

“…A number of different forms of the GH gene are present in several vertebrate species and gene duplication and divergence or mutation and allelic variation are believed to be responsible for these, in an evolutionary scenario of near-stasis periods interrupted by sustained bursts of rapid change (Wallis, 1996). In order to understand the molecular phylogeny of the GH, many efforts have been concentrated on the characterisation of GHs in fishes.…”