Expression of a hindlimb-determining factor Pitx1 in the forelimb of the lizard Pogona vitticeps during morphogenesis

Squamates as a model to understand key dental features of vertebrates

Thanks to their exceptional diversity, teeth are among the most distinctive features of vertebrates. Parameters such as tooth size, shape, number, identity, and implantation can have substantial implications for the ecology and certain social behaviors of toothed species. Despite decades of research primarily focused on mammalian dentition, particularly using the laboratory mouse model, squamate reptiles ("lizards" and snakes) offer a wide array of tooth types and dentition variations. This diversity, which includes differences in size, shape, function, and replacement capacity, provides invaluable opportunities for investigating these fundamental properties. The central bearded dragon (Pogona vitticeps), a popular pet species with well-established husbandry practices, is of particular interest. It features a broad spectrum of morphs and spontaneous mutants and exhibits a wide range of heterodont phenotypes, including variation in the size, shape, number, implantation, and renewal of teeth at both posterior and anterior positions. These characteristics position the species as a crucial model organism for developmental studies in tooth research and for gaining deeper insights into evolutionary patterns of vertebrate dentitions. In this article, we provide an overview of the current understanding of squamate dentition, its diversity, development, and replacement. Furthermore, we discuss the significant advantages offered by squamate species as model organisms for investigating the evolutionary and developmental aspects of vertebrate dentition.

Genome-wide parallelism underlies contemporary adaptation in urban lizards

Urbanization drastically transforms landscapes, resulting in fragmentation, degradation, and the loss of local biodiversity. Yet, urban environments also offer opportunities to observe rapid evolutionary change in wild populations that survive and even thrive in these novel habitats. In many ways, cities represent replicated "natural experiments" in which geographically separated populations adaptively respond to similar selection pressures over rapid evolutionary timescales. Little is known, however, about the genetic basis of adaptive phenotypic differentiation in urban populations nor the extent to which phenotypic parallelism is reflected at the genomic level with signatures of parallel selection. Here, we analyzed the genomic underpinnings of parallel urban-associated phenotypic change in Anolis cristatellus, a small-bodied neotropical lizard found abundantly in both urbanized and forested environments. We show that phenotypic parallelism in response to parallel urban environmental change is underlain by genomic parallelism and identify candidate loci across the Anolis genome associated with this adaptive morphological divergence. Our findings point to polygenic selection on standing genetic variation as a key process to effectuate rapid morphological adaptation. Identified candidate loci represent several functions associated with skeletomuscular development, morphology, and human disease. Taken together, these results shed light on the genomic basis of complex morphological adaptations, provide insight into the role of contingency and determinism in adaptation to novel environments, and underscore the value of urban environments to address fundamental evolutionary questions.

Reproductive phenotype predicts adult bite-force performance in sex-reversed dragons (Pogona vitticeps)

Sex-related differences in morphology and behavior are well documented, but the relative contributions of genes and environment to these traits are less well understood. Species that undergo sex reversal, such as the central bearded dragon (Pogona vitticeps), offer an opportunity to better understand sexually dimorphic traits because sexual phenotypes can exist on different chromosomal backgrounds. Reproductively female dragons with a discordant sex chromosome complement (sex reversed), at least as juveniles, exhibit traits in common with males (e.g., longer tails and greater boldness). However, the impact of sex reversal on sexually dimorphic traits in adult dragons is unknown. Here, we investigate the effect of sex reversal on bite-force performance, which may be important in resource acquisition (e.g., mates and/or food). We measured body size, head size, and bite force of the three sexual phenotypes in a colony of captive animals. Among adults, we found that males (ZZm) bite more forcefully than either chromosomally concordant females (ZWf) or sex-reversed females (ZZf), and this difference is associated with having relatively larger head dimensions. Therefore, adult sex-reversed females, despite apparently exhibiting male traits as juveniles, do not develop the larger head and enhanced bite force of adult male bearded dragons. This pattern is further illustrated in the full sample by a lack of positive allometry of bite force in sex-reversed females that is observed in males. The results reveal a close association between reproductive phenotype and bite force performance, regardless of sex chromosome complement.

Skull Development, Ossification Pattern, and Adult Shape in the Emerging Lizard Model Organism Pogona vitticeps: A Comparative Analysis With Other Squamates

The rise of the Evo-Devo field and the development of multidisciplinary research tools at various levels of biological organization have led to a growing interest in researching for new non-model organisms. Squamates (lizards and snakes) are particularly important for understanding fundamental questions about the evolution of vertebrates because of their high diversity and evolutionary innovations and adaptations that portrait a striking body plan change that reached its extreme in snakes. Yet, little is known about the intricate connection between phenotype and genotype in squamates, partly due to limited developmental knowledge and incomplete characterization of embryonic development. Surprisingly, squamate models have received limited attention in comparative developmental studies, and only a few species examined so far can be considered as representative and appropriate model organism for mechanistic Evo-Devo studies. Fortunately, the agamid lizard Pogona vitticeps (central bearded dragon) is one of the most popular, domesticated reptile species with both a well-established history in captivity and key advantages for research, thus forming an ideal laboratory model system and justifying his recent use in reptile biology research. We first report here the complete post-oviposition embryonic development for P. vitticeps based on standardized staging systems and external morphological characters previously defined for squamates. Whereas the overall morphological development follows the general trends observed in other squamates, our comparisons indicate major differences in the developmental sequence of several tissues, including early craniofacial characters. Detailed analysis of both embryonic skull development and adult skull shape, using a comparative approach integrating CT-scans and gene expression studies in P. vitticeps as well as comparative embryology and 3D geometric morphometrics in a large dataset of lizards and snakes, highlights the extreme adult skull shape of P. vitticeps and further indicates that heterochrony has played a key role in the early development and ossification of squamate skull bones. Such detailed studies of embryonic character development, craniofacial patterning, and bone formation are essential for the establishment of well-selected squamate species as Evo-Devo model organisms. We expect that P. vitticeps will continue to emerge as a new attractive model organism for understanding developmental and molecular processes underlying tissue formation, morphology, and evolution.

Interaction between physical activity, PITX1 rs647161 genetic polymorphism and colorectal cancer risk in a Korean population: a case-control study

This study assessed the interaction between physical activity and colorectal cancer (CRC) risk based on a polymorphism in the paired-like homeodomain 1 (PITX1) gene in Koreans. In total, 923 cases and 1,846 controls were enrolled at the National Cancer Center, Korea. Subjects who did regular exercise showed a significantly reduced risk of CRC than those did not exercise regularly (OR = 0.37, 95% CI = 0.30-0.45). Subjects in the highest tertile of metabolic equivalents of task (MET)-minutes per week showed a significantly lower risk of CRC (OR = 0.62, 95% CI = 0.48-0.79, p-trend < 0.001). In the dominant model, minor allele carriers showed a significantly higher risk of CRC than subjects homozygous for the major allele (OR = 1.46, 95% CI = 1.18-1.80). The PITX1 genetic variant showed significant interactions with regular exercise and CRC risk (p-interaction = 0.018) and colon cancer risk (p-interaction = 0.029) among all subjects. Subjects who carried at least one minor allele and did not regularly exercise showed a greater risk of CRC (OR = 1.81, 95% CI = 1.37-2.41). Subjects who were homozygous for the major allele with high physical activity showed a significantly reduced risk of CRC (OR = 0.56, 95% CI = 0.38-0.82). Thus, individuals with PITX1 genetic variants can have benefit from physical activity regarding prevention of CRC risk in a Korean population.