Skeletal development in the fossorial gymnophthalmids Calyptommatus sinebrachiatus and Nothobachia ablephara

The development of the cartilaginous and bony elements that form the skull and axial and appendicular skeleton is described in detail for the post-ovipositional embryonic development of the fossorial gymnophthalmid species Calyptommatus sinebrachiatus and Nothobachia ablephara. Both species have a snake-like morphology, showing an elongated body and reduced or absent limbs, as well as modifications in skull bones for burrowing, such as complex articulation surfaces and development of bony extensions that enclose and protect the brain. Similar morphological changes have originated independently in several squamate groups, including the one that led to the snake radiation. This study characterizes the patterns of chondrogenesis and osteogenesis, with special emphasis on the features associated with the burrowing habit, and may be used for future comparative analyses of the developmental patterns involved in the origin of the convergent serpentiform morphologies.     

Rates and patterns in the evolution of snake-like body form in squamate reptiles: evidence for repeated re-evolution of lost digits and long-term persistence of intermediate body forms

An important challenge in evolutionary biology is to understand how major changes in body form arise. The dramatic transition from a lizard-like to snake-like body form in squamate reptiles offers an exciting system for such research because this change is replicated dozens of times. Here, we use morphometric data for 258 species and a time-calibrated phylogeny to explore rates and patterns of body-form evolution across squamates. We also demonstrate how time-calibrated phylogenies may be used to make inferences about the time frame over which major morphological transitions occur. Using the morphometric data, we find that the transition from lizard-like to snake-like body form involves concerted evolution of limb reduction, digit loss, and body elongation. These correlations are similar across squamate clades, despite very different ecologies and >180 million years (My) of divergence. Using the time-calibrated phylogeny and ancestral reconstructions, we find that the dramatic transition between these body forms can occur in 20 My or less, but that seemingly intermediate morphologies can also persist for tens of millions of years. Finally, although loss of digits is common, we find statistically significant support for at least six examples of the re-evolution of lost digits in the forelimb and hind limb.     

Locomotion and palaeoclimate explain the re-evolution of quadrupedal body form in Brachymeles lizards

Evolutionary reversals, including re-evolution of lost structures, are commonly found in phylogenetic studies. However, we lack an understanding of how these reversals happen mechanistically. A snake-like body form has evolved many times in vertebrates, and occasionally a quadrupedal form has re-evolved, including in Brachymeles lizards. We use body form and locomotion data for species ranging from snake-like to quadrupedal to address how a quadrupedal form could re-evolve. We show that large, quadrupedal species are faster at burying and surface locomotion than snake-like species, indicating a lack of expected performance trade-off between these modes of locomotion. Species with limbs use them while burying, suggesting that limbs are useful for burying in wet, packed substrates. Palaeoclimatological data suggest that Brachymeles originally evolved a snake-like form under a drier climate probably with looser soil in which it was easier to dig. The quadrupedal clade evolved as the climate became humid, where limbs and large size facilitated fossorial locomotion in packed soils.     

A developmental staging series for the lizard genus Anolis: a new system for the integration of evolution, development, and ecology

Vertebrate developmental biologists typically rely on a limited number of model organisms to understand the evolutionary bases of morphological change. Unfortunately, a typical model system for squamates (lizards and snakes) has not yet been developed leaving many fundamental questions about morphological evolution unaddressed. New model systems would ideally include clades, rather than single species, that are amenable to both laboratory studies of development and field-based analyses of ecology and evolution. Combining an understanding of development with an understanding of ecology and evolution within and between closely related species has the potential to create a seamless understanding of how genetic variation underlies ecologically and evolutionarily relevant variation within populations and between species. Here we briefly introduce a new model system for the integration of development, evolution, and ecology, the lizard genus Anolis, a diverse group of lizards whose ecology and evolution is well understood, and whose genome has recently been sequenced. We present a developmental staging series for Anolis lizards that can act as a baseline for later comparative and experimental studies within this genus.     

Evolution of morphology and locomotor performance in anurans: relationships with microhabitat diversification

The relationships between morphology, performance, behavior and ecology provide evidence for multiple and complex phenotypic adaptations. The anuran body plan, for example, is evolutionarily conserved and shows clear specializations to jumping performance back at least to the early Jurassic. However, there are instances of more recent adaptation to habit diversity in the post‐cranial skeleton, including relative limb length. The present study tested adaptive models of morphological evolution in anurans associated with the diversity of microhabitat use (semi‐aquatic arboreal, fossorial, torrent, and terrestrial) in species of anuran amphibians from Brazil and Australia. We use phylogenetic comparative methods to determine which evolutionary models, including Brownian motion (BM) and Ornstein‐Uhlenbeck (OU) are consistent with morphological variation observed across anuran species. Furthermore, this study investigated the relationship of maximum distance jumped as a function of components of morphological variables and microhabitat use. We found there are multiple optima of limb lengths associated to different microhabitats with a trend of increasing hindlimbs in torrent, arboreal, semi‐aquatic whereas fossorial and terrestrial species evolve toward optima with shorter hindlimbs. Moreover, arboreal, semi‐aquatic and torrent anurans have higher jumping performance and longer hindlimbs, when compared to terrestrial and fossorial species. We corroborate the hypothesis that evolutionary modifications of overall limb morphology have been important in the diversification of locomotor performance along the anuran phylogeny. Such evolutionary changes converged in different phylogenetic groups adapted to similar microhabitat use in two different zoogeographical regions.     

Phylogenetic taxonomy of the Cercosaurini (Squamata: Gymnophthalmidae), with new genera for species of Neusticurus and Proctoporus

The tribe Cercosaurini is one of the most poorly studied groups of the lizard family Gymnophthalmidae. Recent studies have suggested that two cercosauriine genera, Neusticurus and Proctoporus , are polyphyletic. The aim of the current study was to rectify the polyphyletic relationships and construct a phylogenetic taxonomy of the Cercosaurini that is congruent with evolutionary history. Neusticurus is divided into two genera, one of them new ( Potamites ), based on the clades recovered by molecular studies and previously discussed morphological data. Proctoporus is divided into three genera, one of which is new ( Petracola ), while an older name ( Riama ) is resurrected for another. All five genera are described and defined and taxonomic keys are presented. This study represents an important advance in rectifying the taxonomy of the Cercosaurini. Many other para- and polyphyletic genera remain in the Gymnophthalmidae and much future work on this group is warranted.  © 2005 The Linnean Society of London, Zoological Journal of the Linnean Society , 2005, 143 , 405–416.     

Developmental mechanisms of longitudinal stripes in the Japanese four‐lined snake

The developmental mechanisms of color patterns formation and its evolution remain unclear in reptilian sauropsids. We, therefore, studied the pigment cell mechanisms of stripe pattern formation during embryonic development of the snake Elaphe quadrivirgata. We identified 10 post‐ovipositional embryonic developmental stages based on external morphological characteristics. Examination for the temporal changes in differentiation, distribution, and density of pigment cells during embryonic development revealed that melanophores first appeared in myotome and body cavity but not in skin surface at Stage 5. Epidermal melanophores were first recognized at Stage 7, and dermal melanophores and iridophores appeared in Stage 9. Stripe pattern first appeared to establish at Stage 8 as a spatial density gradient of epidermal melanophores between the regions of future dark brown longitudinal stripes and light colored background. Our study, thus, provides a comprehensive pigment‐cell‐based understanding of stripe pattern formation during embryonic development. We briefly discuss the importance of the gene expression studies by considering the biologically relevant theoretical models with standard developmental staging for understanding reptilian color pattern evolution.     

多疣壁虎胚胎发育分期的形态学特征

脊椎动物发育生物学的研究通常依赖于数量有限的模式生物的形态变化,胚胎发育分期表的建立为物种胚胎发育的一系列过程确立了一个统一的标准,成为研究形态演化的重要工具。本研究对多疣壁虎(Gekko japonicus)28℃孵化条件下的胚胎发育过程进行显微观察,并记录了整个胚胎发育历程。基于多疣壁虎胚胎发育过程中头部、咽、四肢等形态变化及皮肤色素沉积和被鳞的情况,将多疣壁虎胚胎发育分为42个时期。刚排出体外的受精卵,其胚胎发育一般已经发生至28期,该期胚胎头部和躯干分化明显,眼泡、咽弓、心和体节可见;29期前、后肢芽均可见;30期肢芽延长并开始出现分区,31期可见明显肢身,32期四肢均出现肢柱和肢杆的分区;33期咽裂消失,指和趾开始显现;35期指和趾间带退化,指和趾完全形成;36期出现爪;37期爪完全形成;38期皮肤色素沉积明显;39期指、趾底部膨大,形成单行攀瓣;40期身体背部和四肢色素沉积且被鳞明显;41期腹部出现色素沉积且被覆鳞片。42期鼻孔开放,体背整体呈灰棕色。对多疣壁虎卵产出后胚胎28~42期发育期形态学变化进行了详细描述,旨在为蜥蜴类胚胎发育研究提供参考。     

Prey-handling and the evolutionary ecology of sand-swimming lizards (Lerista : Scincidae)

Fossorial lizards differ in morphology from their surface-dwelling relatives. The Australian sphenomorphine skink genus Ctenotus consists of surface-dwelling species, and is closely related to the genus Lerista, which includes both surface-dwelling and fossorial species. Sand-swimming represents the derived condition and has evolved independently in several lineages of Lerista. The heads of lizards in the two genera differ in shape (blunt snout for Ctenotus versus wedge-shaped for Lerista) and in length relative to the body (approximately 20% of snout-vent length for Ctenotus versus 12% for sand-swimming Lerista). Do these specializations affect the sizes or types of prey that can be consumed by Lerista? We compared prey-handling by Ctenotus and Lerista to correlate morphological differences with differences in prey-handling ability, and to distinguish the effects of snout shape and head length. Feeding trials included three categories of insect prey that the lizards normally eat: soft-bodied larvae (Lepidoptera), hard-bodied larvae (Coleoptera), and roaches (Blatoidea). In comparisons based on the mass of a prey item relative to the mass of a lizard, Lerista had longer handling times for all prey categories and were limited to smaller prey than were Ctenotus. However, when comparisons were based on the length of prey relative to the length of a lizard's head, Lerista ate some elongate prey as fast or faster than did Ctenotus, and both genera successfully swallowed prey more than twice the length of their own head. Thus, the differences in prey-handling performance of Ctenotus and Lerista probably result from the fact that Lerista have a relatively shorter head than Ctenotus. All Lerista species, surface-dwelling and fossorial, have short heads compared to primitive sphenomorphine lizards. Fossorial species of Lerista have elongate trunks, and consequently their heads are shorter in proportion to trunk length than those of surface-dwelling Lerista. However, most fossorial species of Lerista are longer and heavier than any of their surface-dwelling congeners, and the heads of these fossorial species are large relative to the prey they encounter. As a consequence, the diets of large fossorial species of Lerista do not appear to be limited by their morphological specialization for sand-swimming.     

"Alien" wasps and evolution of development

A comparative analysis of early developmental programs in a group of parasitic wasps reveals that closely related species can undergo dramatic evolutionary shifts in their patterns of embryogenesis. Developmental changes detected include alterations in early cleavage divisions, the establishment of embryonic anteroposterior polarity and modifications of the segmentation gene hierarchy described from Drosophila. These changes appear to be adaptations to parasitic development, taking place within the body of the host. Wasps illustrate a surprising plasticity in their early development and embryogenesis. The alterations associated with different parasitic strategies suggest that ecological adaptations may have profound influences on developmental processes in animals.     

Diversity of functional microornamentation in slithering geckos Lialis (Pygopodidae)

The skin of geckos is covered with countless microscopic protuberances (spines). This surface structure causes low wettability to water. During evolution, representatives of the recent gekkotan clade Pygopodidae started slithering on the ground. This manner of locomotion affected limb reduction resulting in a snake-like body. Regarding abrasion and frictional properties, a surface covered with gekkotan spines is a topography that hampers the snake-like locomotion mode. Using scanning electron microscopy, we investigated the shed skins of two pygopodid lizards, Lialis jicari (Papua snake lizard) and Lialis burtonis (Burton''s legless lizard), in order to show epidermal adaptations to limbless locomotion. Our data showed that Pygopodidae differ from their relatives not only anatomically, but also in their epidermal microstructure. Scales of L. jicari have five different structural patterns on various body regions. Ventral scales have nanoridges, similar to those found on the ventralia of snakes. Surfaces of scales covering the jaw bones, have flattened spine-like microstructures that might be an adaptation to reduce abrasion. Dorsal scales have oblong microscopic bulges covered with nanoridges. Spines cover the undersides and the interstices of scales over the entire body of both species and in L. jicari also the top of dorsal head scales. Our measurements of surface wettability (surface free energy) show superhydrophobic properties of the spiny surfaces in comparison with the other microstructural patterns of other body parts.     

Moringua edwardsi (Moringuidae: Anguilliformes): Cranial specialization for head‐first burrowing?

The order Anguilliformes forms a natural group of eel-like species. Moringua edwardsi (Moringuidae) is of special interest because of its peculiar fossorial lifestyle: this species burrows head-first. Externally pronounced morphological specializations for a fossorial lifestyle include: reduced eyes, lack of color, low or absent paired vertical fins, elongated, cylindrical body, reduced head pores of the lateral line system, etc. Many fossorial amphibians, reptiles, and even mammals have evolved similar external specializations related to burrowing. The present study focuses on osteological and myological features of M. edwardsi in order to evaluate the structural modifications that may have evolved as adaptations to burrowing. Convergent evolutionary structures and possible relations with head-first burrowing, miniaturization, feeding habits, etc., were investigated. Body elongation, reduction of the eyes, modified cranial lateral line system, and modified skull shape (pointed though firm) can be considered specializations for head-first burrowing. Hyperossification can probably be regarded more as a specialization to both head-first burrowing and feeding, even though an impact of miniaturization cannot be excluded. Hypertrophied adductor mandibulae muscles and the enlarged coronoid process can be associated with both feeding requirements (it enhances bite forces necessary for their predatory behavior) and with a burrowing lifestyle, as well as miniaturization.     

Analyzing evolutionary patterns in amniote embryonic development

Heterochrony (differences in developmental timing between species) is a major mechanism of evolutionary change. However, the dynamic nature of development and the lack of a universal time frame makes heterochrony difficult to analyze. This has important repercussions in any developmental study that compares patterns of morphogenesis and gene expression across species. We describe a method that makes it possible to quantify timing shifts in embryonic development and to map their evolutionary history. By removing a direct dependence on traditional staging series, through the use of a relative time frame, it allows the analysis of developmental sequences across species boundaries. Applying our method to published data on vertebrate development, we identified clear patterns of heterochrony. For example, an early onset of various heart characters occurs throughout amniote evolution. This suggests that advanced (precocious) heart development arose in evolutionary history before endothermy. Our approach can be adapted to analyze other forms of comparative dynamic data, including patterns of developmental gene expression.     

Head shape evolution in Gymnophthalmidae: does habitat use constrain the evolution of cranial design in fossorial lizards?

Habitat usage comprises interactions between ecological parameters and organismal capacities, and the selective pressures that ultimately determine the outcome of such processes in an evolutionary scale may be conflicting when the same morphological structure is recruited for different activities. Here, we investigate the roles of diet and locomotion in the evolution of cranial design in gymnophthalmid lizards and test the hypothesis that microhabitat use drives head shape evolution, particularly in head-first burrowers. Morphological factors were analysed in relation to continuous ecological indexes (prey hardness and substrate compactness) using conventional and phylogenetic approaches. Results suggest that the evolution of head morphology in Gymnophthalmidae was shaped under the influence of microhabitat use rather than diet: burrowers have shorter heads with lower rostral angulation, independently of the prey consumed. Food preferences appear to be relatively conserved throughout the phylogeny of the group, which may have permitted the extensive radiation of gymnophthalmids into fossorial microhabitats.     

A developmental staging series for the African house snake, Boaedon (Lamprophis) fuliginosus

Embryonic staging series are important tools in the study of morphological evolution as they establish a common standard for future studies. In this study, we describe the in ovo embryological development of the African house snake (Boaedon fuliginosus), a non-venomous, egg-laying species within the superfamily Elapoidea. We develop our staging series based on external morphology of the embryo including the head, eye, facial prominences, pharyngeal slits, heart, scales, and endolymphatic ducts. An analysis of embryonic growth in length and mass is presented, as well as preliminary data on craniofacial skeletal development. Our results indicate that B. fuliginosus embryos are well into organogenesis but lack well-defined facial prominences at the time of oviposition. Mandibular and maxillary processes extend rostrally within 8 days (stage 3), corresponding to the first appearance of Meckel's cartilages. Overall, the development of the craniofacial skeleton in B. fuliginosus appears similar to that of other snake species with intramembraneous bones (e.g., dentary and compound bones) ossifying before most of the endochondral bones, the first of which to ossify are the quadrate and the otic capsule. Our staging series is the first to describe the post-ovipositional development of a non-venomous elapoid based on external morphology. This species is an extremely tractable captive that can produce large clutches of eggs every 45 days throughout the year. As such, B. fuliginosus should be a good model for evolutionary developmental biologists focusing on the craniofacial skeleton, loss of limbs, generational teeth, and venom delivery systems.