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When populations colonise new environments, they may be exposed to novel selection pressures but also suffer from extensive genetic drift due to founder effects, small population sizes and limited interpopulation gene flow. Genomic approaches enable us to study how these factors drive divergence, and disentangle neutral effects from differentiation at specific loci due to selection. Here, we investigate patterns of genetic diversity and divergence using whole‐genome resequencing (>22× coverage) in Berthelot's pipit (Anthus berthelotii), a passerine endemic to the islands of three north Atlantic archipelagos. Strong environmental gradients, including in pathogen pressure, across populations in the species range, make it an excellent system in which to explore traits important in adaptation and/or incipient speciation. First, we quantify how genomic divergence accumulates across the speciation continuum, that is, among Berthelot's pipit populations, between sub species across archipelagos, and between Berthelot's pipit and its mainland ancestor, the tawny pipit (Anthus campestris). Across these colonisation timeframes (2.1 million–ca. 8000 years ago), we identify highly differentiated loci within genomic islands of divergence and conclude that the observed distributions align with expectations for non‐neutral divergence. Characteristic signatures of selection are identified in loci associated with craniofacial/bone and eye development, metabolism and immune response between population comparisons. Interestingly, we find limited evidence for repeated divergence of the same loci across the colonisation range but do identify different loci putatively associated with the same biological traits in different populations, likely due to parallel adaptation. Incipient speciation across these island populations, in which founder effects and selective pressures are strong, may therefore be repeatedly associated with morphology, metabolism and immune defence. [ABSTRACT FROM AUTHOR]

Diverse clades of fishes adapted to feeding on the benthos repeatedly converge on steep craniofacial profiles and shorter, wider heads. But in an incipient radiation, to what extent is this morphological evolution measurable and can we distinguish the relative genetic vs. plastic effects? We use the Trinidadian guppy (Poecilia reticulata) to test the repeatability of adaptation and the alignment of genetic and environmental effects shaping poecilid craniofacial morphology. We compare wild-caught and common garden lab-reared fish to quantify the genetic and plastic components of craniofacial morphology across 4 populations from 2 river drainage systems (n  = 56 total). We first use micro-computed tomography to capture 3D morphology, then place both landmarks and semilandmarks to perform size-corrected 3D morphometrics and quantify shape space. We find a measurable, significant, and repeatable divergence in craniofacial shape between high-predation invertivore and low-predation detritivore populations. As predicted from previous examples of piscine adaptive trophic divergence, we find increases in head slope and craniofacial compression among the benthic detritivore foragers. Furthermore, the effects of environmental plasticity among benthic detritivores produce exaggerated craniofacial morphological change along a parallel axis to genetic morphological adaptation from invertivore ancestors. Overall, many of the major patterns of benthic-limnetic craniofacial evolution appear convergent among disparate groups of teleost fishes. [ABSTRACT FROM AUTHOR]

Mice are arguably the dominant model organisms for studies investigating the effect of genetic traits on the pathways to mammalian skull and teeth development, thus being integral in exploring craniofacial and dental evolution. The aim of this study is to analyse the functional significance of masticatory loads on the mouse mandible and identify critical stress accumulations that could trigger phenotypic and/or growth alterations in mandible-related structures. To achieve this, a 3D model of mouse skulls was reconstructed based on Micro Computed Tomography measurements. Upon segmenting the main hard tissue components of the mandible such as incisors, molars and alveolar bone, boundary conditions were assigned on the basis of the masticatory muscle architecture. The model was subjected to four loading scenarios simulating different feeding ecologies according to the hard or soft type of food and chewing or gnawing biting movement. Chewing and gnawing resulted in varying loading patterns, with biting type exerting a dominant effect on the stress variations experienced by the mandible and loading intensity correlating linearly to the stress increase. The simulation provided refined insight on the mechanobiology of the mouse mandible, indicating that food consistency could influence micro evolutionary divergence patterns in mandible shape of rodents.

During its expansion across the globe, Homo sapiens successfully survived to major adaptive challenges as a species, inviting scientific research to plunge into the particularities of continental settlement dynamics. A recurrent paleoanthropological concern is about the understanding of the great deal of craniofacial diversity that evolved into the Americas, which includes a vector of continuum variation between a generalized morphology observed among humans groups leading the Out-of-Africa dispersion, and a derived set of craniofacial traits classically labeled as "mongoloid" and that would have arise in Asia during the Holocene. Here, we use geometric morphometric techniques and multivariate statistics along with quantitative genetic approaches to look more closely into the human craniofacial evolutionary history during the Late Pleistocene-Early Holocene from Asia and the New World. We detected significant signals of deviation of the neutral evolutionary expectations, suggesting an important action of non-stochastic evolution (e.g. natural selection, phenotypic plasticity) in the Americas. We also found further support to the Recurrent Gene Flow model that refers to an ancestral, founder population experiencing a standstill in Beringia, and exhibiting high within-group craniofacial variation. This original, internally variable stock would have been the ancestral source of variation that fuelled the subsequent local micro evolution of other derived phenotypic patterns, giving origin to the craniofacial diversity observed among Holocene Native American samples. [ABSTRACT FROM AUTHOR]

Patterns of genetic variation and covariation impact the evolution of the craniofacial complex and contribute to clinically significant malocclusions in modern human populations. Previous quantitative genetic studies have estimated the heritabilities and genetic correlations of skeletal and dental traits in humans and nonhuman primates, but none have estimated these quantitative genetic parameters across the dentognathic complex. A large and powerful pedigree from the Jirel population of Nepal was leveraged to estimate heritabilities and genetic correlations in 62 maxillary and mandibular arch dimensions, incisor and canine lengths, and post-canine tooth crown areas (N ≥ 739). Quantitative genetic parameter estimation was performed using maximum likelihood-based variance decomposition. Residual heritability estimates were significant for all traits, ranging from 0.269 to 0.898. Genetic correlations were positive for all trait pairs. Principal components analyses of the phenotypic and genetic correlation matrices indicate an overall size effect across all measurements on the first principal component. Additional principal components demonstrate positive relationships between post-canine tooth crown areas and arch lengths and negative relationships between post-canine tooth crown areas and arch widths, and between arch lengths and arch widths. Based on these findings, morphological variation in the human dentognathic complex may be constrained by genetic relationships between dental dimensions and arch lengths, with weaker genetic correlations between these traits and arch widths allowing for variation in arch shape. The patterns identified are expected to have impacted the evolution of the dentognathic complex and its genetic architecture as well as the prevalence of dental crowding in modern human populations., (© 2022 American Association for Anatomy.)

Bird beaks display tremendous variation in shape and size, which is closely associated with the exploitation of multiple ecological niches and likely played a key role in the diversification of thousands of avian species. Previous studies have demonstrated some of the molecular mechanisms that regulate morphogenesis of the prenasal cartilage, which forms the initial beak skeleton. However, much of the beak diversity in birds depends on variation in the premaxillary bone. It forms later in development and becomes the most prominent functional and structural component of the adult upper beak/jaw, yet its regulation is unknown. Here, we studied a group of Darwin's finch species with different beak shapes. We found that TGFβIIr, β-catenin, and Dickkopf-3, the top candidate genes from a cDNA microarray screen, are differentially expressed in the developing premaxillary bone of embryos of species with different beak shapes. Furthermore, our functional experiments demonstrate that these molecules form a regulatory network governing the morphology of the premaxillary bone, which differs from the network controlling the prenasal cartilage, but has the same species-specific domains of expression. These results offer potential mechanisms that may explain how the tightly coupled depth and width dimensions can evolve independently. The two-module program of development involving independent regulating molecules offers unique insights into how different developmental pathways may be modified and combined to induce multidimensional shifts in beak morphology. Similar modularity in development may characterize complex traits in other organisms to a greater extent than is currently appreciated. [ABSTRACT FROM AUTHOR]

Abstract: Understanding variation in the basicranium is of central importance to paleoanthropology because of its fundamental structural role in skull development and evolution. Among primates, encephalisation is well known to be associated with flexion between midline basicranial elements, although it has been proposed that the size or shape of the face influences basicranial flexion. In particular, brain size and facial size are hypothesized to act as antagonists on basicranial flexion. One important and unresolved problem in hominin skull evolution is that large-brained Neanderthals and some Mid-Pleistocene humans have slightly less flexed basicrania than equally large-brained modern humans. To determine whether or not this is a consequence of differences in facial size, geometric morphometric methods were applied to a large comparative data set of non-human primates, hominin fossils, and humans (N=142; 29 species). Multiple multivariate regression and thin plate spline analyses suggest that basicranial evolution is highly significantly influenced by both brain size and facial size. Increasing facial size rotates the basicranium away from the face and slightly increases the basicranial angle, whereas increasing brain size reduces the angles between the spheno-occipital clivus and the presphenoid plane, as well as between the latter and the cribriform plate. These interactions can explain why Neanderthals and some Mid-Pleistocene humans have less flexed cranial bases than modern humans, despite their relatively similar brain sizes. We highlight that, in addition to brain size (the prime factor implicated in basicranial evolution in Homo), facial size is an important influence on basicranial morphology and orientation. To better address the multifactorial nature of basicranial flexion, future studies should focus on the underlying factors influencing facial size evolution in hominins. [Copyright &y& Elsevier]

Recent studies have supported the hypothesis that there is a tendency to evolution in the occlusal relationships of urban populations. Due to its role in the stomatognathic system and the hypothesis of the role of deep overbite in the appearance and development of TMD, particular interest is given to the incisal relationship and its evolution in urban populations. Incisal situation and relationship can be studied with anthropometric and cephalomatric determinants. This study compares the incisal relationship of two groups of young Caucasian adults born in 1870 and 1970, respectively. Twenty-four anthropometric and cephalometric points were analyzed for 30 subjects from each group. A statistically significant difference between the 1870/1970 samples was found for the following criteria ( p<0.001): overbite: 1.17/3.81, position of the free edge of the mandibular incisor, sagittal values (orthodontic norm PAO) 78.75 mm/82.88 mm, position of the free edge of the mandibular incisor, vertical values 54.74 mm/58.87 mm, FMIA angle: 65.97°/58.4° and Angle classes: difference in distribution of the skeletal classes (Classes I, II and III) between the two populations (increase in Class II, 1970). Within the limits of this study results show a remarkable increase in overbite, a tendency towards a reduced prevalence of class III malocclusions and an increased prevalence of Class II malocclusions with vestibular position of the mandibular incisors. [ABSTRACT FROM AUTHOR]

Abstract: Evolution of facial morphology arises from variation in the activity of developmental regulatory networks that guide the formation of specific craniofacial elements. Importantly, the acquisition of novel morphology must be integrated with a phylogenetically inherited developmental program. We have identified a unique region of the secondary palate associated with the periodic formation of rugae during the rostral outgrowth of the face. Rugae function as SHH signaling centers to pattern the elongating palatal shelves. We have found that a network of signaling genes and transcription factors is spatially organized relative to palatal rugae. Additionally, the first formed ruga is strategically positioned at the presumptive junction of the future hard and soft palate that defines anterior–posterior differences in regional growth, mesenchymal gene expression, and cell fate. We propose a molecular circuit integrating FGF and BMP signaling to control proliferation and differentiation during the sequential formation of rugae and inter-rugae domains in the palatal epithelium. The loss of p63 and Sostdc1 expression and failed rugae differentiation highlight that coordinated epithelial–mesenchymal signaling is lost in the Fgf10 mutant palate. Our results establish a genetic program that reiteratively organizes signaling domains to coordinate the growth of the secondary palate with the elongating midfacial complex. [Copyright &y& Elsevier]

Abstract: Unlike most primates, extant cercopithecoids lack maxillary sinuses, which are pneumatic spaces in the facial skeleton lateral of the nasal cavity proper. Character state analysis of living cercopithecoids across well-supported topologies suggests that the sinus was lost at the origin of the superfamily, only to have evolved again convergently in extant macaques. Recent work has shown that a) the ‘early loss’ hypothesis is supported by the lack of any pneumatization in Victoriapithecus, a stem cercopithecoid, b) like extant macaques, the fossil cercopithecine Paradolichopithecus shows evidence of presence of the maxillary sinus (MS), and c) unlike extant colobines, the fossil colobine Libypithecus also possesses a maxillary sinus. To more fully assess the pattern of cercopithecoid sinus evolution, fossil taxa from both subfamilies (Colobinae, Cercopithecinae) were examined both visually and by computed tomography (CT). The observations were evaluated according to standard anatomical criteria for defining sinus spaces, and compared with data from all extant Old World monkey genera. Most taxa examined conformed to the pattern already discerned from extant cercopithecoids. Maxillary sinus absence in Theropithecus oswaldi, Mesopithecus, and Rhinocolobus is typical for all extant cercopithecids except Macaca. The fossil macaque Macaca majori possesses a well-developed maxillary sinus, as do all living species of the genus. Cercopithecoides, on the other hand, differs from all extant colobines in possessing a maxillary sinus. Thus, paranasal pneumatization has reemerged a minimum of two and possibly three times in cercopithecoids. The results suggest that maxillary sinus absence in cercopithecoids is due to suppression, rather than complete loss. [Copyright &y& Elsevier]