The concept of developmental reprogramming and the quest for an inclusive theory of evolutionary mechanisms

Abstract

Evolutionary developmental biology has already made a major contribution to our understanding of evolutionary patterns, notably homology. However, while it has the potential to make an equally important contribution to our understanding of evolutionary mechanisms, and indeed to the integration of mechanism and pattern, it has not yet done so. This paper explores how this potential may be realized. In particular, I focus on the limitations of present-day neo-Darwinian theory, and indicate how a combination of the neo-Darwinian and "evo-devo" approaches provides a more inclusive view of evolutionary mechanisms with greater explanatory power. There is a particular focus on developmental reprogramming, which lies logically between mutation and selection, yet has been neglected in mainstream evolutionary theory. The inclusion of developmental reprogramming in the list of evolutionary mechanisms leads to a view that the direction of evolutionary change is determined by a combination of internal and external factors, rather than being controlled entirely by the environment.

21st Century neontology and the comparative development of the vertebrate skull

“…With regard to the head development, loss of RA-mediated signaling has been experimentally studied in several systems, including in vitamin A-deficient quail, and murine gene knockouts of RA receptors (RARs and RXRs), and converting enzymes (Raldh1/2/3). Notably, these studies demonstrate a pronounced, selective sensitivity to the loss of RA by the caudal pharyngeal endoderm, in particular the pouches and those structures that require their development (Niederreither et al, 1999;2000Wendling et al, 2000;Begemann and Meyer, 2001;Quinlan et al, 2002;Vermot et al, 2003). In such experiments, however, the buccopharyngeal membrane and the first pouch, cleft, and arch form.…”

“…Vertebrate Pitx2 is expressed in the surface ectoderm that will cover the stomodeum, including associated hypophyseal and dental placodes and the peri-oral ectoderm (Mucchielli et al, 1997;St. Amand et al, 1998, 2000Campione et al, 1999;Lin et al, 1999;Lu et al, 1999;Schweickert et al, 2001a,b;Boorman and Shimeld, 2002;Liu et al, 2003;Jackman et al, 2004). Whereas the skeletal defects have not been extensively reported, murine mutants lacking Pitx2, much like the Fgf8 Nes-CreϪ/Ϫ mice, maintain the dis- tal rostral process of MC but lack most of the body of MC (Liu et al, 2003).…”

“…Although extensive effort has been made to understand ectodermal subdivisions within the neural plate, there has been a much less of an effort to understand early regional pattern within the cephalic surface ectoderm outside of those investigations examining the origination of the neural crest, the cranial placodes, and some perhaps generally underappreciated work involving the cement gland in amphibians (Gammill and Sive, 1997, 2000Fang and Elinson, 1999;Baker and Bronner-Fraser, 2001;Schweickert et al, 2001;Sauka-Spengler et al, 2002;Wardle and Sive, 2003;Streit, 2004;Nokhbatolfoghahai and Downie, 2005). Analyses of the development of the early vertebrate epiblast have typically been concerned either with (1) when and how the distinction between neural and non-neural ectoderm is established or (2) how is positional information, i.e., anterior (head) and posterior (trunk), within the neural plate established Stern, 2002Stern, , 2005Wilson and Houart, 2004), and have lead to several questions, including: Is the epiblast ubiquitously competent to become either neurectodermal or surface ectodermal, and if so, is the specification and eventual commitment to neural and surface ectodermal achieved simultaneously, or does one precede the other?…”

“…Lastly, phenotypic alteration due to change in developmental processes have traditionally been attributed to heterochronic (change in the timing of an event) or heterotopic (change in the topology of an event) shifts, although change due to heterofacience (change in the active capacetence, or the elaboration of capacity, of a developmental event) is also recognized. Two terms introduced by Arthur (2000), heterotypy (change in the type of an event) and heterometry (change in amount), are forms of heterofacience. A change in the affinity of a morphogen receptor or the level of transcription and translation of a morphogen inhibitor leading to differential induction and response are examples of heterofacience, as would be the isochronic, isotopic utilization of related but not directly orthologous genes during a developmental process.…”

The interaction between developmental bias and natural selection: from centipede segments to a general hypothesis

“…From a genetic perspective, this is 'mutation bias' (the term they use). However, from a phenotypic perspective -ie the ways in which the mutations concerned reprogram development (Arthur, 2000) -it is related to developmental bias.…”