Evolution and development of the primate limb skeleton

Abstract

Recognition that the transformation of one form into another is caused by both internal and external factors is the foundation and driving philosophy underlying all research in the field of biology. 10,11 In practice, however, studies of the internal (proximate) causes of biological transformation within the lifetime of an organism and of the external (ultimate) causes of transformation from one generation to the next (evolutionary transformation) have been pursued independently in two sub-disciplines, developmental and evolutionary biology, respectively. This situation has changed with the emergence of evolutionary developmental biology or "evo-devo," which seeks, by means of a comparative approach, to explain the evolution and development of morphological characters as well as the evolution of their underlying genetic and developmental mechanisms. 12 Essential to this approach is a well-defined and strongly supported phylogeny from which homology and the direction of morphological transformations can be accurately assessed. [13][14][15] Exciting and significant findings have been made in evo-devo. One is that the metazoan body plan is established by a surprisingly small set of highly conserved patterning genes. These homeobox (Hox) genes (Fig. 2), which originated early in metazoan evolution, are distributed throughout the animal kingdom. 16 -18 Another important finding is that homology at the genetic level is not necessarily correlated with homology at the morphological level. For example, the compound eyes of insects and the camera eyes of vertebrates evolved independently, but in both the initiation of eye formation requires expression of the same gene, Pax-6. 19 It also has been demonstrated that morphological novelties such as butterfly eye spots 20 or limbless tetrapods (snakes 21 ) result from alterations in the molecular mechanisms that control the development of major anatomical structures. Moreover, the evolution of developmental systems, which mediate morphological evolution, can occur by slight changes in the regulation of otherwise conserved patterning genes (Fig. 3). [22][23][24] While evo-devo research has focused primarily on broad taxonomic comparisons and major morphological transitions such as that from fish fins to tetrapod limbs, its potential for explaining phenotypic differences between and among closely related taxa is clearly recognized. [25][26][27] In this context, understanding how molecular evolution shapes genetic variation of patterning and growth genes in different primate lineages can be a powerful method for linking genetic and developmental variation to phenotypic (morphological) variation at both the microevolutionary and macroevolutionary scales. 28 -31 Indeed, the focus of evo- The order Primates is composed of many closely related lineages, each having a relatively well established phylogeny supported by both the fossil record and molecular data. 1 Primate evolution is characterized by a series of adaptive radiations beginning early in the Cenozoic era. Studies of th...

Molecular evolution of the HoxA cluster in the three major gnathostome lineages

“…1) coincide with an 11.1-kb genomic fragment of mouse hoxa5 (from Ϫ3.8 kb to ϩ 7.3 kb) that reproduces, to a large extent, the endogenous expression of hoxa5 in transgenic mouse embryos (25). Our findings are consistent with the observations that for vertebrate taxa, (i) functional cis sequences in one species are evolutionarily conserved (26,27) and (ii) cis sequences identified using evolution-based methods are functional when tested (16,20,28,29). It will be important to determine whether the additional PFCs identified in this study are functional.…”

The anthropoid postcranial axial skeleton: Comments on development, variation, and evolution

“…Levine and Tjian note (2003, p. 150), ''Increasingly powerful methods of comparative genomics should identify many of the changes in cis-regulatory DNAs and general transcription complexes underlying animal diversity.'' As key regulatory sequences are increasingly elucidated in the mouse, and as complete or partial genome sequences become available in primates such as chimp, gorilla, and baboon, in addition to humans, it will be possible to locate homologous regulatory elements in these (and other) primates (see, for example, Chiu and Hamrick, 2002;Nobrega et al, 2003). Hox genes and their regulatory elements to target would include Hoxc-8, Hoxa-9, and Hoxc-9, expressed in the thoracic region and at the thoracic-lumbar boundary, and Hoxa-10, Hoxd-10, and Hoxd-11, expressed around the lumbarsacral boundary.…”

Understanding Entheses: Bridging the Gap Between Clinical and Anthropological Perspectives

“…Frost (2003) suggests that genetics predetermine the baseline conditions in bone in utero. These baseline conditions are predominately driven by Hox gene expression, which current research postulates is responsible for canalized limb patterning, basic neuromuscular and physiologic anatomy, and the biologic machinery necessary for increasing bone strength following birth (Shubin et al, 1997;Capdevila and Belmonte, 2001;Chiu and Hamrick, 2002). Lovejoy (2002) also suggests that genetic precursors play a more significant role than environmental factors in the primary development of morphological indicators on bone.…”