Divergence of craniofacial developmental trajectories among avian embryos

Abstract

Background Morphological divergence among related species involves changes to developmental processes. When such variation arises in development has garnered considerable theoretical interest relating to the broader issue of how development may constrain evolutionary change. The hourglass model holds that while early developmental events may be highly evolvable, there is a phylotypic stage when key developmental events are conserved. Thus, evolutionary divergence among related species should tend to arise after such a stage of reduced evolvability and, consequently, reduced variation among species. We test this prediction by comparing developmental trajectories among three avian species of varying relatedness (chick, quail, and duck) to locate their putative point of divergence. Three-dimensional geometric morphometrics and trajectory analyses were used to measure the significance of the facial shape variation observed among these species. Results Duck embryos, being more distantly related, differed from the more closely-related chick and quail embryos in the enlargement of their frontonasal prominences. Phenotypic trajectory analyses demonstrated divergence of the three species, most notably, duck. Conclusions The results demonstrate that the two more closely related species share similar facial morphologies for a longer time during development, while ducks diverge. This suggests a surprising lability of craniofacial development during early face formation.

Quantifying three‐dimensional morphology and RNA from individual embryos

“…This method allows pooling of embryos that are approximately the same age (e.g., within 1 day for E11.5 mouse embryos). Previous results have shown that the combination of age and size generates a more linear regression than either variable alone, possibly due to the occasional difficulty of counting tail somites (Smith et al, ). Once age and size have been corrected for, the shape differences between the two lines represent the majority of the remaining variation (Fig.…”

Testing the evolutionary constraints of metamorphosis: The ontogeny of head shape inTriturusnewts

“…; Adams and Collyer ; Collyer and Adams ; Smith et al. ). Trajectories can diverge from each other at different points in space and time.…”

Morphometrics, 3D Imaging, and Craniofacial Development

“…For these reasons, quantification of both ontogenetic and static allometry is a critical component of the phenotypic analysis of any mutant. A useful tool in such analyses is to do a combined analysis of shape and size, or form space, by adding centroid size back into a morphometric analysis (Mitteroecker and Bookstein 2008; Smith et al 2015). …”

“…Recent studies have used morphometrics and 3D imaging to quantify variation in craniofacial morphogenesis (Billington et al 2015; Green et al 2015; Hu et al 2015a; Hu et al 2015c; Smith et al 2015; Young et al 2014). These studies have shown that morphometric analyses can significantly add to mechanistic studies of development and thus that morphometrics and 3D imaging of embryos have significant potential for developmental biology.…”