Variability in vertebral numbers does not contribute to sexual size dimorphism, interspecific variability, or phenotypic plasticity in body size in geckos (Squamata: Gekkota:Paroedura)

A juvenile pleurosaurid (Lepidosauria: Rhynchocephalia) from the Tithonian of the Mörnsheim Formation, Germany

Late Jurassic rhynchocephalians from the Solnhofen Archipelago have been known for almost two centuries. The number of specimens and taxa is constantly increasing, but little is known about the ontogeny of these animals. The well-documented marine taxon Pleurosaurus is one of such cases. With over 15 described (and many more undescribed) specimens, there were no unambiguous juveniles so far. Some authors have argued that Acrosaurus, another common component of the Solnhofen Archipelago herpetofauna, might represent an early ontogenetic stage of Pleurosaurus, but the lack of proper descriptions for this taxon makes this assignment tentative, at best. Here, we describe the first unambiguous post-hatchling juvenile of Pleurosaurus and tentatively attribute it to Pleurosaurus cf. P. ginsburgi. The new specimen comes from the Lower Tithonian of the Mörnsheim Formation, Germany. This specimen is small, disarticulated, and incomplete, but preserves several of its craniomandibular bones and presacral vertebrae. It shares with Pleurosaurus a set of diagnostic features, such as an elongated and triangular skull, a low anterior flange in its dentition, and an elongated axial skeleton. It can be identified as a juvenile due to the presence of an unworn dentition, well-spaced posteriormost dentary teeth, a large gap between the last teeth and the coronoid process of the dentary, and poorly ossified vertebrae with unfused neural arches. Acrosaurus shares many anatomical features with both this specimen and Pleurosaurus, which could indicate that the two genera are indeed synonyms. The early ontogenetic stage inferred for the new Pleurosaurus specimen argues for an even earlier ontogenetic placement for specimens referred to Acrosaurus, the latter possibly pertaining to hatchlings.

The macroevolutionary singularity of snakes

Snakes and lizards (Squamata) represent a third of terrestrial vertebrates and exhibit spectacular innovations in locomotion, feeding, and sensory processing. However, the evolutionary drivers of this radiation remain poorly known. We infer potential causes and ultimate consequences of squamate macroevolution by combining individual-based natural history observations (>60,000 animals) with a comprehensive time-calibrated phylogeny that we anchored with genomic data (5400 loci) from 1018 species. Due to shifts in the dynamics of speciation and phenotypic evolution, snakes have transformed the trophic structure of animal communities through the recurrent origin and diversification of specialized predatory strategies. Squamate biodiversity reflects a legacy of singular events that occurred during the early history of snakes and reveals the impact of historical contingency on vertebrate biodiversity.

Evolutionary rates of body-size-related genes and ecological factors involved in driving body size evolution of squamates

Body size is one of the most important traits of an organism. Among reptiles, both lizards and snakes show body size differences that span a similar six orders of magnitude variation. However, the molecular mechanisms underlying body size variation in squamates remain obscure. Here, we performed comparative genomic analyses of 101 body-size-related genes from 28 reptilian genomes. Phylogenetic analysis by maximum likelihood (PAML) revealed that snakes showed higher evolutionary rates in body-size-related genes, and had an almost two-fold increase in the number of positively selected genes (∼20.3%) compared with lizards (∼8.9%). The high similarities in dN/dS values were obtained between the branches of large-bodied lizards and large-bodied snakes by Spearman correlation analysis. Combining the results from site model, branch-site model and clade model analyses, we found some key genes regulating the evolution of body size in squamates, such as COL10A1, GHR, NPC1, GALNS, CDKN2C, FBN1, and LCORL. Phylogenetic generalized least squares (PGLS) indicated that AKT1, BMP1, IGF1, SOX5, SOX7 in lizards and BMP5, BMP7, GPC6, SH2B3, SOX17 in snakes were significantly correlated with body length and body mass. Furthermore, ecological factors had varying degrees of impact on body size and the evolutionary rate of body-size-related genes in squamates. Intriguingly, climate had little effect on body size of lizards and snakes, but the contribution of climate-related factors to the variation in evolutionary rate of body-size-related genes were relatively higher. Our study lays a foundation for a comprehensive understanding of genetic mechanisms of body size evolution in squamates during the process of adapting to terrestrial life.

Individual and age-related variation of cellular brain composition in a squamate reptile

Within-species variation in the number of neurons, other brain cells and their allocation to different brain parts is poorly studied. Here, we assess these numbers in a squamate reptile, the Madagascar ground gecko (Paroedura picta). We examined adults from two captive populations and three age groups within one population. Even though reptiles exhibit extensive adult neurogenesis, intrapopulation variation in the number of neurons is similar to that in mice. However, the two populations differed significantly in most measures, highlighting the fact that using only one population can underestimate within-species variation. There is a substantial increase in the number of neurons and decrease in neuronal density in adult geckos relative to hatchlings and an increase in the number of neurons in the telencephalon in fully grown adults relative to sexually mature young adults. This finding implies that adult neurogenesis does not only replace worn out but also adds new telencephalic neurons in reptiles during adulthood. This markedly contrasts with the situation in mammals, where the number of cortical neurons declines with age.

Introduction to the special issue-Developmental plasticity in reptiles: Physiological mechanisms and ecological consequences

Scientific interest in developmental plasticity spans many disciplines, and research on reptiles has provided many insights into this field. We highlight these contributions, review the field's history, and introduce the special issue on this topic .