Gene networks, occlusal clocks, and functional patches: new understanding of pattern and process in the evolution of the dentition

Abstract

Our understanding of the evolution of the dentition has been transformed by advances in the developmental biology, genetics, and functional morphology of teeth, as well as the methods available for studying tooth form and function. The hierarchical complexity of dental developmental genetics combined with dynamic effects of cells and tissues during development allow for substantial, rapid, and potentially non-linear evolutionary changes. Studies of selection on tooth function in the wild and evolutionary functional comparisons both suggest that tooth function and adaptation to diets are the most important factors guiding the evolution of teeth, yet selection against random changes that produce malocclusions (selectional drift) may be an equally important factor in groups with tribosphenic dentitions. These advances are critically reviewed here.

Inferring diet from dental morphology in terrestrial mammals

“…Upper and lower dentitions need to evolve in parallel. Failing to do so leads to malocclusion and therefore to reduced fitness (Butler ; Kurtén , ; Polly, Le Comber & Burland ; Polly ). RowOPCR and avOPCR variables inform about the number of mechanical tools on the tooth surface.…”

“…Phylogenetic constraints could be the reason behind most of the misclassifications (Smith et al . ; Evans & Sanson ; Polly ). Some animals belong to a mammalian order that has extremely morphologically derived tooth shapes, so it becomes more difficult to change tooth shape to better deal with the new food.…”

“…The combination of upper and lower tooth rows provides the overall set of tools for processing the foods (Evans & Sanson ; Polly , ). Thus, we recorded 12 variables for each specimen, six for the upper tooth row and six for the lower for the MPDMA (multi‐proxy dental morphology analysis) test.…”

Quantitative genetic analyses of postcanine morphological crown variation

“…For this reason, and due to the comparative abundance of tooth crowns in the fossil and archaeological records, understanding the genetic signals manifest in patterns of dental variation is important for a number of fields including anthropology, paleontology, and comparative mammalogy. Researchers have used a combination of experimental, evolutionary‐developmental, and quantitative genetic analyses to identify the mechanisms involved in tooth crown differentiation and to reconstruct the developmental processes responsible for the observed range of variation in molar crowns (Gómez‐Roblez & Polly, ; Grieco, Rizk, & Hlusko, ; Hlusko & Mahaney, ; Hlusko, Maas, & Mahaney, ; Hlusko, Sage, & Mahaney, ; Jernvall, Åberg, Kettunen, Keränen, & Thesleff, ; Jernvall, Kettunen, Karavanova, Martin, & Thesleff, ; Koh et al, ; Polly, ; Polly & Mock, ; Salazar‐Ciudad & Jernvall, , ). Developmental origins of crown variants have also been discussed within a quantitative genetic framework, particularly in studies of single species datasets (e.g., Papio hamadryas —Hlukso, Do, & Mahaney, 2007; Hlusko et al, 2004; Cryptocoryne parva —Polly & Mock, ).…”

Morphometrics and evolution: the challenge of crossing rugged phenotypic landscapes with straight paths

“…In fact, incremental changes in the level of expression of activator and inhibitor molecules can produce not only non-linear trajectories in morphospace, but large jumps from one part of morphospace to another as cusps are gained and lost (Salazar-Ciudad, Jernvall, 2004;Harjunmaa et al, 2014). The phenotypic landscape of teeth would create non-linear maps between trajectories in morphospace and the space of the underlying molecular parameters much like in the shell example (Polly, 2008(Polly, , 2015. Indeed, the real developmental processes involved in shell coiling probably operate much like the signalling cascades that control cell proliferation and secretion in teeth and thus produce phenomena like the ones illustrated in the Raup shell coiling example above (Rice, 1998;Marin et al, 2012).…”