Repeated origin and loss of adhesive toepads in geckos

Microhabitat and adhesive toepads shape gecko limb morphology

Different substrates pose varied biomechanical challenges that select specific morphologies, such as long limbs for faster running and short limbs for balanced posture while climbing narrow substrates. We tested how gecko locomotion is affected by the microhabitat they occupy and by a key adaptation-adhesive toepads-through analyzing how those are related to limb morphology. We collected microhabitat and toepads data for over 90% of limbed gecko species, and limb measurements for 403 species from 83 of the 121 limbed gecko genera, which we then used in phylogenetic comparative analyses. Our data highlight the association of adhesive toepads with arboreality, but a phylogenetic analysis shows that this relationship is not significant, suggesting that these traits are phylogenetically constrained. Comparative analyses reveal that pad-bearing species possess shorter hindlimbs and feet, more even limb lengths, and lower crus: thigh ratios, than padless geckos, across microhabitats. Saxicolous geckos have the longest limbs and limb segments. This is probably influenced by selection for long strides, increased takeoff velocity, and static stability on inclined surfaces. Terrestrial geckos have more even hind- and forelimbs than arboreal geckos, unlike patterns found in other lizards. Our findings underline the difficulty to infer on microhabitat-morphology relationships from one taxon to another, given their differing ecologies and evolutionary pathways. We emphasize the importance of key innovation traits, such as adhesive toepads, in shaping limb morphology in geckos and, accordingly, their locomotion within their immediate environment.

A new species of Namib Day Gecko (Gekkonidae: Rhoptropus Peters, 1869) from the Serra da Neve inselberg, southwestern Angola

The genus Rhoptropus comprises nine recognized species of diurnal geckos endemic to the arid regions of Angola and Namibia. Seven species occur in Angola, including the widespread R. boultoni and the poorly known Angolan endemics R. benguellensis and R. montanus, formerly recognized as subspecies of R. boultoni. While R. benguellensis is relatively widespread in the Angolan Escarpment highlands, R. montanus is geographically restricted to the Huíla Plateau. Recent fieldwork on the Serra da Neve inselberg, a herpetological diversity hotspot in southwestern Angola, revealed the presence of an undescribed species of Rhoptropus at an elevation of approximately 1600 m. An integrative taxonomic approach combining coloration, morphological and molecular data supports the recognition of this population as a distinct taxonomic unit with affinities to R. montanus, which we describe herein as Rhoptropus nivimontanus sp. nov. The discovery of a new species of Rhoptropus endemic to Serra da Neve is discussed in the biogeographic context of the region.

Frictional adhesion of geckos predicts maximum running performance in nature

Despite the myriad studies examining the diversity and mechanisms of gecko adhesion in the lab, we have a poor understanding of how this translates to locomotion in nature. It has long been assumed that greater adhesive strength should translate to superior performance in nature. Using 13 individuals of Bradfield's Namib day gecko (Rhoptropus bradfieldi) in Namibia, I tested the hypothesis that maximum running performance in nature (speed and acceleration) is driven by maximum frictional adhesive strength. Specifically, those individuals with greater frictional adhesion should escape with faster speed and acceleration because of increased contact with the surface from which to apply propulsive forces. I tested this prediction by quantifying laboratory adhesive performance and then releasing the geckos into the field while simultaneously recording the escape using high-speed videography. Additional measurements included how this species modulates maximum running speed (stride length and/or stride frequency) and how temperature influences field performance. I found that maximum acceleration was significantly correlated with maximum frictional adhesive strength, whereas maximum sprinting speed was only correlated with increases in stride frequency (not stride length) and temperature. Thus, different measures of performance (acceleration and speed) are limited by very different variables. Acceleration is key for rapidly escaping predation and, given their correlation, maximum frictional adhesion likely plays a key role in fitness.

Exploring the Influence of Neomorphic Gekkotan Paraphalanges on Limb Modularity and Integration

Digital specializations of geckos are widely associated with their climbing abilities. A recurring feature that has independently emerged within the sister families Gekkonidae and Phyllodactylidae is the presence of neomorphic paraphalanges (PPEs), usually paired, paraxial skeletal structures lying adjacent to interphalangeal and metapodial-phalangeal joints. The incorporation of PPEs into gekkotan autopodia has the potential to modify the modularity and integration of the ancestral limb pattern by affecting information flow among skeletal limb parts. Here we explore the influence of PPEs on limb organization using anatomical networks. We modeled the fore- and hindlimbs in species ancestrally devoid of PPEs (Iguana iguana and Gekko gecko) and paraphalanx-bearing species (Hemidactylus mabouia and Uroplatus fimbriatus). To further clarify the impact of PPEs we also expunged PPEs from paraphalanx-bearing network models. We found that PPEs significantly increase modularity, giving rise to tightly integrated sub-modules along the digits, suggesting functional specialization. Species-specific singularities also emerged, such as the trade-off between the presence of PPEs favoring modularity (along the proximodistal axis) and the interdigital webbing favoring integration (across the lateromedial axis) in the limbs of U. fimbriatus. The PPEs are characterized by low connectivity compared with other skeletal elements; nevertheless, this varies based on their specific location and seemingly reflects developmental constraints. Our results also highlight the importance of the fifth metatarsal in generating a shift in lepidosaurian hindlimb polarity that contrasts with the more symmetrical bauplan of tetrapods. Our findings support extensive modification of the autopodial system in association with the addition of the neomorphic and intriguing PPEs.

Adaptive or non-adaptive? Cranial evolution in a radiation of miniaturized day geckos

Lygodactylus geckos represent a well-documented radiation of miniaturized lizards with diverse life-history traits that are widely distributed in Africa, Madagascar, and South America. The group has diversified into numerous species with high levels of morphological similarity. The evolutionary processes underlying such diversification remain enigmatic, because species live in different ecological biomes, ecoregions and microhabitats, while suggesting strikingly high levels of homoplasy. To underscore this evolutionary pattern, here we explore the shape variation of skull elements (i.e., cranium, jaw and inner ear) using 3D geometric morphometrics and phylogenetic comparative methods on computed tomography scans (CT-scan) of a sample encompassing almost all recognized taxa within Lygodactylus. The results of this work show that skull and inner ear shape variation is low (i.e., there is high overlapping on the morphospace) across geographic regions, macrohabitats and lifestyles, implying extensive homoplasy. Furthermore, we also found a strong influence of allometry shaping cranial variation both at intra and interspecific levels, suggesting a major constraint underlying skull architecture, probably as a consequence of its miniaturization. The remaining variation that is not allometric is independent of phylogeny and ecological adaptation and can probably be interpreted as the result of intrinsic developmental plasticity. This, in turn, supports the interpretation that speciation in this group is largely concordant with a non-adaptive hypothesis, which results mainly from vicariant processes.

Bio-inspired designs: leveraging biological brilliance in mechanical engineering-an overview

Nature's evolutionary mastery has perfected design over the years, yielding organisms superbly adapted to their surroundings. This research delves into the promising domain of bio-inspired designs, poised to revolutionize mechanical engineering. Leveraging insights drawn from prior conversations, we categorize innovations influenced by life on land, in water, and through the air, emphasizing their pivotal contributions to mechanical properties. Our comprehensive review reveals a wealth of bio-inspired designs that have already made substantial inroads in mechanical engineering. From avian-inspired lightweight yet robust materials to hydrodynamically optimized forms borrowed from marine creatures, these innovations hold immense potential for enhancing mechanical systems. In conclusion, this study underscores the transformative potential of bio-inspired designs, offering improved mechanical characteristics and the promise of sustainability and efficiency across a broad spectrum of applications. This research envisions a future where bio-inspired designs shape the mechanical landscape, fostering a more harmonious coexistence between human technology and the natural world.

Developmental Patterns Underlying Variation in Form and Function Exhibited by House Gecko Toe Pads

Adhesive toe pads have evolved numerous times over lizard evolutionary history, most notably in geckos. Despite significant variation in adult toe pad morphology across independent origins of toe pads, early developmental patterns of toe pad morphogenesis are similar among distantly related species. In these distant phylogenetic comparisons, toe pad variation is achieved during the later stages of development. We aimed to understand how toe pad variation is generated among species sharing a single evolutionary origin of toe pads (house geckos-Hemidactylus). We investigated toe pad functional variation and developmental patterns in three species of Hemidactylus, ranging from highly scansorial (H. platyurus), to less scansorial (H. turcicus), to fully terrestrial (H. imbricatus). We found that H. platyurus generated significantly greater frictional adhesive force and exhibited much larger toe pad area relative to the other two species. Furthermore, differences in the offset of toe pad extension phase during embryonic development results in the variable morphologies seen in adults. Taken together, we demonstrate how morphological variation is generated in a complex structure during development and how that variation relates in important functional outcomes.

Toe pad morphology and adhesion in the miniaturized gecko, Chatogekko amazonicus (Gekkota: Sphaerodactylidae)

Chatogekko amazonicus is a miniaturized gecko from northern South America and is among the smallest of toe pad bearing lizards. The toe pads of C. amazonicus are miniscule, between 18% and 27% of the plantar surface area. We aimed to investigate the relationship between adhesive toe pad morphology, body size, and adhesive capabilities. Using scanning electron microscopy, we determine that the adhesive pads of C. amazonicus exhibit branched setae similar to those of other geckos, but that are generally much smaller. When compared with other gecko taxa, we show that C. amazonicus setae occupy a similar range of seta length: snout-vent length ratio and aspect ratio as other gekkonoid species (i.e. Gekkonidae, Phyllodactylidae, and Sphaerodactylidae). We demonstrate that C. amazonicus-even with its relatively small toe pads-is capable of climbing a smooth glass surface at a nearly vertical angle. We suggest that sphaerodactylids like C. amazonicus offer an excellent system for studying toe pad morphology and function in relation to miniaturization.

Substrate specialisation drives an unexpectedly diverse radiation in barking geckos (Ptenopus: Gekkonidae)

Barking geckos (genus Ptenopus) are terrestrial, burrowing lizards endemic to southern Africa, currently with three recognised species. Two species are range-restricted (P. kochi and P. carpi) and display clear differences in substrate preference (soft sand vs. hard gravel). The third and most widespread species, P. garrulus, occurs on a variety of substrates of differing hardness, across potential geographic barriers, and over a steep climatic gradient. Variations in morphology and advertisement calls indicates that P. garrulus may be a species complex. Two subspecies of P. garrulus are currently recognised: P. g. maculatus and P. g. garrulus. To investigate species boundaries, we produced the first comprehensive phylogeny for the genus. We used a novel application of multiple regression on matrices models to assess multiple environmental drivers of diversification, as contrasted to isolation by distance. We show that P. kochi, P. carpi, and P. g. garrulus are valid species, but that P. g. maculatus is a paraphyletic complex of five previously unrecognised taxa. Specialisation onto different substrates was likely the main driver of divergence, with parapatric occurrence of two to four clades occurring at each of the three substrate transition zones identified a priori. The region encompasses diverse bioclimatic regions and potential geographic barriers, and these likely played a role in some divergence events.

Decoupled evolution of ventral and dorsal scales in agamid lizards: ventral keels are associated with arboreality

Arboreality has evolved in all major vertebrate lineages and is often associated with morphological adaptations and increased diversification concomitant with accessing novel niche space. In squamate reptiles, foot, claw, and tail morphology are well-studied adaptations shown to be associated with transitions to arboreality. Here, we examined a less well understood trait-the keeled scale-in relation to microhabitat, climate, and diversification dynamics across a diverse lizard radiation, Agamidae. We found that the ancestral agamid had keeled dorsal but not ventral scales; further, dorsal and ventral keels are evolutionarily decoupled. Ventral keeled scales evolved repeatedly in association with arboreality and may be advantageous in reducing wear or by promoting interlocking when climbing. We did not find an association between keeled scales and diversification, suggesting keels do not allow finer-scale microhabitat partitioning observed in other arboreal-associated traits. We additionally found a relationship between keeled ventral scales and precipitation in terrestrial species where we posit that the keels may function to reduce scale degradation. Our results suggest that keeled ventral scales facilitated transitions to arboreality across agamid lizards, and highlight a need for future studies that explore their biomechanical function in relation to microhabitat and climate.

Spatio-temporal expression patterns of glycine-rich beta proteins and cysteine-rich beta proteins in setae development of Gekko japonicus

BACKGROUND

Setae on the pad lamellae of the Japanese gecko Gekko japonicus (Schlegel, 1836), a vital epidermal derivative, are primarily composed of cornified beta-proteins (CBPs) and play a pivotal role in adhesion and climbing. The amino acid composition of CBPs might be a determining factor influencing their functional properties. However, the molecular mechanisms governed by CBP genes with diverse amino acid compositions in setae development remain unexplored.

RESULTS

Based on RNA-seq analyses, this study confirmed that all G. japonicus CBPs (GjCBPs) are involved in setae formation. Cysteine-rich CBPs encoding genes (ge-cprp-17 to ge-cprp-26) and glycine-rich CBPs encoding genes (ge-gprp-17 to ge-gprp-22) were haphazardly selected, with quantitative real-time PCR revealing their expression patterns in embryonic pad lamellae and dorsal epidermis. It is inferred that glycine-rich CBPs are integral to the formation of both dorsal scales and lamellar setae, cysteine-rich CBPs are primarily associated with setae development. Additionally, fluorescence in situ hybridization revealed spatiotemporal differences in the expression of a glycine-rich CBP encoding gene (ge-gprp-19) and a cysteine-rich CBP encoding gene (ge-cprp-17) during dorsal scales and/or lamellar development.

CONCLUSIONS

All 66 CBPs are involved in the formation of setae. Glycine-rich CBPs hold a significant role in the development of dorsal scales and lamellar setae, whereas most cysteine-rich CBPs appear to be essential components of G. japonicus setae. Even GjCBPs with similar amino acid compositions may play diverse functions. The clear spatio-temporal expression differences between the glycine-rich and cysteine-rich CBP encoding genes during epidermal scale and/or setae formation were observed. Embryonic developmental stages 39 to 42 emerged as crucial phases for setae development. These findings lay the groundwork for deeper investigation into the function of GjCBPs in the development of G. japonicus setae.

Ontogeny of the autopodial skeleton of the gecko Tarentola (Squamata: Phyllodactylidae)

Squamates exhibit evident diversity in their limb morphology. Gekkotans are a particularly diverse group in this respect. The appearance of toepads in gekkotans usually cooccurs with the reduction or loss of claws. The gecko Tarentola (Phyllodactylidae) shows a unique combination of features among geckos, with toepads, hyperphalangy, and dimorphism of claw expression (claws are retained on digits III and IV, but lost (manus) or strongly reduced (pes) on the remaining digits). Despite being a candidate model for studying embryonic skeletal development of the autopodium, no studies have investigated the autopodial development of the gecko Tarentola in detail. Here, we aim to follow up the development of the autopodial skeleton in T. annularis and T. mauritanica using acid-free double staining. The results indicate that the terminal phalanges of claw-bearing digits III and IV ossify earlier than in the remaining digits. This confirms the differential ossification as a result of claw regression in Tarentola. The strongly reduced second phalanges of digits IV in both the fore- and hindlimbs are the last ossifying phalanges. Such late ossification may precede the evolutionary loss of this phalanx. If this is correct, the autopodia of Tarentola would be an interesting example of both the hyperphalangy in digit I and the process of phalanx loss in digit IV. Delay in ossification of the miniaturised phalanx probably represents an example of paedomorphosis.

An evolutionary innovation for mating facilitates ecological niche expansion and buffers species against climate change

One of the drivers of life's diversification has been the emergence of "evolutionary innovations": The evolution of traits that grant access to underused ecological niches. Since ecological interactions can occur separately from mating, mating-related traits have not traditionally been considered factors in niche evolution. However, in order to persist in their environment, animals need to successfully mate just as much as they need to survive. Innovations that facilitate mating activity may therefore be an overlooked determinant of species' ecological limits. Here, we show that species' historical niches and responses to contemporary climate change are shaped by an innovation involved in mating-a waxy, ultra-violet-reflective pruinescence produced by male dragonflies. Physiological experiments in two species demonstrate that pruinescence reduces heating and water loss. Phylogenetic analyses show that pruinescence is gained after taxa begin adopting a thermohydrically stressful mating behavior. Further comparative analyses reveal that pruinose species are more likely to breed in exposed, open-canopy microhabitats. Biogeographic analyses uncover that pruinose species occupy warmer and drier regions in North America. Citizen-science observations of Pachydiplax longipennis suggest that the extent of pruinescence can be optimized to match the local conditions. Finally, temporal analyses indicate that pruinose species have been buffered against contemporary climate change. Overall, these historical and contemporary patterns show that successful mating can shape species' niche limits in the same way as growth and survival.

Embryonic development of the skull in a parthenogenetic lizard, the mourning gecko (Lepidodactylus lugubris)

Gekkotans are one of the major clades of squamate reptiles. As one of the earliest-diverging lineages, they are crucial in studying deep-level squamate phylogeny and evolution. Developmental studies can shed light on the origin of many important morphological characters, yet our knowledge of cranial development in gekkotans is very incomplete. Here, we describe the embryonic development of the skull in a parthenogenetic gekkonid, the mourning gecko (Lepidodactylus lugubris), studied using non-acidic double staining and histological sectioning. Our analysis indicates that the pterygoid is the first ossifying bone in the skull, as in almost all other studied squamates, followed closely by the surangular and prearticular. The next to appear are the dentary, frontal, parietal and squamosal. The tooth-bearing upper jaw bones, the premaxilla and maxilla, develop relatively late. In contrast to previous reports, the premaxilla starts ossifying from two distinct centres, reminiscent of the condition observed in diplodactylids and eublepharids. Only a single ossification centre of the postorbitofrontal is observed. Some of the endochondral bones of the braincase (prootic, opisthotic, supraoccipital) and the dermal parasphenoid are the last bones to appear. The skull roof is relatively poorly ossified near the time of hatching, with a large frontoparietal fontanelle still present. Many bones begin ossifying relatively later in L. lugubris than in the phyllodactylid Tarentola annularis, which suggests that its ossification sequence is heterochronic with respect to T. annularis.

The revised reference genome of the leopard gecko (Eublepharis macularius) provides insight into the considerations of genome phasing and assembly

Genomic resources across squamate reptiles (lizards and snakes) have lagged behind other vertebrate systems and high-quality reference genomes remain scarce. Of the 23 chromosome-scale reference genomes across the order, only 12 of the ~60 squamate families are represented. Within geckos (infraorder Gekkota), a species-rich clade of lizards, chromosome-level genomes are exceptionally sparse representing only two of the seven extant families. Using the latest advances in genome sequencing and assembly methods, we generated one of the highest-quality squamate genomes to date for the leopard gecko, Eublepharis macularius (Eublepharidae). We compared this assembly to the previous, short-read only, E. macularius reference genome published in 2016 and examined potential factors within the assembly influencing contiguity of genome assemblies using PacBio HiFi data. Briefly, the read N50 of the PacBio HiFi reads generated for this study was equal to the contig N50 of the previous E. macularius reference genome at 20.4 kilobases. The HiFi reads were assembled into a total of 132 contigs, which was further scaffolded using HiC data into 75 total sequences representing all 19 chromosomes. We identified 9 of the 19 chromosomal scaffolds were assembled as a near-single contig, whereas the other 10 chromosomes were each scaffolded together from multiple contigs. We qualitatively identified that the percent repeat content within a chromosome broadly affects its assembly contiguity prior to scaffolding. This genome assembly signifies a new age for squamate genomics where high-quality reference genomes rivaling some of the best vertebrate genome assemblies can be generated for a fraction of previous cost estimates. This new E. macularius reference assembly is available on NCBI at JAOPLA010000000.

A lizard is never late: Squamate genomics as a recent catalyst for understanding sex chromosome and microchromosome evolution

In 2011, the first high-quality genome assembly of a squamate reptile (lizard or snake) was published for the green anole. Dozens of genome assemblies were subsequently published over the next decade, yet these assemblies were largely inadequate for answering fundamental questions regarding genome evolution in squamates due to their lack of contiguity or annotation. As the "genomics age" was beginning to hit its stride in many organismal study systems, progress in squamates was largely stagnant following the publication of the green anole genome. In fact, zero high-quality (chromosome-level) squamate genomes were published between the years 2012 and 2017. However, since 2018, an exponential increase in high-quality genome assemblies has materialized with 24 additional high-quality genomes published for species across the squamate tree of life. As the field of squamate genomics is rapidly evolving, we provide a systematic review from an evolutionary genomics perspective. We collated a near-complete list of publicly available squamate genome assemblies from more than half-a-dozen international and third-party repositories and systematically evaluated them with regard to their overall quality, phylogenetic breadth, and usefulness for continuing to provide accurate and efficient insights into genome evolution across squamate reptiles. This review both highlights and catalogs the currently available genomic resources in squamates and their ability to address broader questions in vertebrates, specifically sex chromosome and microchromosome evolution, while addressing why squamates may have received less historical focus and has caused their progress in genomics to lag behind peer taxa.

Reappraising the evolutionary history of the largest known gecko, the presumably extinct Hoplodactylus delcourti, via high-throughput sequencing of archival DNA

Hoplodactylus delcourti is a presumably extinct species of diplodactylid gecko known only from a single specimen of unknown provenance. It is by far the largest known gekkotan, approximately 50% longer than the next largest-known species. It has been considered a member of the New Zealand endemic genus Hoplodactylus based on external morphological features including shared toe pad structure. We obtained DNA from a bone sample of the only known specimen to generate high-throughput sequence data suitable for phylogenetic analysis of its evolutionary history. Complementary sequence data were obtained from a broad sample of diplodactylid geckos. Our results indicate that the species is not most closely related to extant Hoplodactylus or any other New Zealand gecko. Instead, it is a member of a clade whose living species are endemic to New Caledonia. Phylogenetic comparative analyses indicate that the New Caledonian diplodactylid clade has evolved significantly more disparate body sizes than either the Australian or New Zealand clades. Toe pad structure has changed repeatedly across diplodactylids, including multiple times in the New Caledonia clade, partially explaining the convergence in form between H. delcourti and New Zealand Hoplodactylus. Based on the phylogenetic results, we place H. delcourti in a new genus.

Bristles formation in adhesive pads and sensilli of the gecko Tarentola mauritanica derive from a massive accumulation of corneous material in Oberhautchen cells of the epidermis

Among lizards, geckos possess special digital scales modified as hairy-like lamellae that allow attachment to vertical substrates for the movement using adhesive nanoscale filaments called setae. The present study shows new ultrastructural details on setae formation in the gecko Tarentula mauritanica. Setae derive from the special differentiation of an epidermal layer termed Oberhauchen and can reach 30-60 µm in length. Oberhautchen cells in the adhesive pad lamellae becomes hypertrophic and rest upon 2 layers of non-corneous and pale cells instead of beta-cells like in the other scales. Only 1-2 beta-layers are formed underneath the pale layer. Setae derive from the accumulation of numerous roundish and heterogenous beta-packets with variable electron-density in Oberhautchen cells, possibly indicating a mixed protein composition. Immunofluorescence and immunogold labeling for CBPs show that beta-packets merge at the base of the growing setae forming long corneous bundles. Pale cells formed underneath the Oberhautchen layer contain small vesicles or tubules with a likely lipid content, sparse keratin filaments and ribosomes. In mature lamellae these cells merge with Oberhautchen and beta-cells forming a thin electron-paler layer located between the Oberhautchen and the thin beta-layer, a variation of the typical sequence of epidermal layers present in other scales. The formation of a softer pale layer and of a thin beta-layer likely determines a flexible corneous support for the adhesive setae. The specific molecular mechanism that stimulates the cellular changes observed during Oberhautchen hypertrophy and the alteration of the typical epidermal stratification in the pad epidermis remains unknown.

Effects of COVID-19 Infection and Vaccination on the Female Reproductive System: A Narrative Review

Several studies and research papers have been published to elucidate and understand the mechanism of the coronavirus disease 2019 (COVID-19) pandemic and its long-term effects on the human body. COVID-19 affects a number of organs, including the female reproductive system. However, less attention has been given to the effects of COVID-19 on the female reproductive system due to their low morbidity. The results of studies investigating the relationship between COVID-19 infection and ovarian function in women of reproductive age have shown the harmless involvement of COVID-19 infection. Several studies have reported the involvement of COVID-19 infection in oocyte quality, ovarian function, and dysfunctions in the uterine endometrium and the menstrual cycle. The findings of these studies indicate that COVID-19 infection negatively affects the follicular microenvironment and dysregulate ovarian function. Although the COVID-19 pandemic and female reproductive health have been studied in humans and animals, very few studies have examined how COVID-19 affects the female reproductive system. The objective of this review is to summarize the current literature and categorize the effects of COVID-19 on the female reproductive system, including the ovaries, uterus, and hormonal profiles. The effects on oocyte maturation, oxidative stress, which causes chromosomal instability and apoptosis in ovaries, in vitro fertilization cycle, high-quality embryos, premature ovarian insufficiency, ovarian vein thrombosis, hypercoagulable state, women’s menstrual cycle, the hypothalamus-pituitary-ovary axis, and sex hormones, including estrogen, progesterone, and the anti-Müllerian hormone, are discussed in particular.

A lizard is never late: squamate genomics as a recent catalyst for understanding sex chromosome and microchromosome evolution

In 2011, the first high-quality genome assembly of a squamate reptile (lizard or snake) was published for the green anole. Dozens of genome assemblies were subsequently published over the next decade, yet these assemblies were largely inadequate for answering fundamental questions regarding genome evolution in squamates due to their lack of contiguity or annotation. As the "genomics age" was beginning to hit its stride in many organismal study systems, progress in squamates was largely stagnant following the publication of the green anole genome. In fact, zero high-quality (chromosome-level) squamate genomes were published between the years 2012-2017. However, since 2018, an exponential increase in high-quality genome assemblies has materialized with 24 additional high-quality genomes published for species across the squamate tree of life. As the field of squamate genomics is rapidly evolving, we provide a systematic review from an evolutionary genomics perspective. We collated a near-complete list of publicly available squamate genome assemblies from more than half-a-dozen international and third-party repositories and systematically evaluated them with regard to their overall quality, phylogenetic breadth, and usefulness for continuing to provide accurate and efficient insights into genome evolution across squamate reptiles. This review both highlights and catalogs the currently available genomic resources in squamates and their ability to address broader questions in vertebrates, specifically sex chromosome and microchromosome evolution, while addressing why squamates may have received less historical focus and has caused their progress in genomics to lag behind peer taxa.

Diversity and Endemism of Southern African Gekkonids Linked with the Escarpment Has Implications for Conservation Priorities

South Africa is recognised for its high reptile diversity and endemism, specifically among lizards. Phylogenetic diversity, endemism, and richness can have clear implications or raise important questions in a range of fields, and most urgently in conservation. Among squamate reptiles, these indices are very commonly associated with high temperatures and topographic heterogeneity. Indeed, mountainous biogeography has been a critical driver in the radiation of the family Gekkonidae within the subregion. Here, we assess the species richness, diversity, and endemism of Gekkonidae species inhabiting South Africa, Lesotho, and Eswatini, accounting for phylogenetic relationships. We also employ the CANAPE method to identify regions that have neo- and/or paleoendemics. Southern African gekkonids appear to be most diverse and show high levels of endemism in three regions of Southern Africa: the northwestern Richtersveld, the escarpment running west to southeast, and the northeastern escarpment in the Limpopo province. Implications for conservation priorities are discussed.

The revised reference genome of the leopard gecko ( Eublepharis macularius ) provides insight into the considerations of genome phasing and assembly

Genomic resources across squamate reptiles (lizards and snakes) have lagged behind other vertebrate systems and high-quality reference genomes remain scarce. Of the 23 chromosome-scale reference genomes across the order, only 12 of the ~60 squamate families are represented. Within geckos (infraorder Gekkota), a species-rich clade of lizards, chromosome-level genomes are exceptionally sparse representing only two of the seven extant families. Using the latest advances in genome sequencing and assembly methods, we generated one of the highest quality squamate genomes to date for the leopard gecko, Eublepharis macularius (Eublepharidae). We compared this assembly to the previous, short-read only, E. macularius reference genome published in 2016 and examined potential factors within the assembly influencing contiguity of genome assemblies using PacBio HiFi data. Briefly, the read N50 of the PacBio HiFi reads generated for this study was equal to the contig N50 of the previous E. macularius reference genome at 20.4 kilobases. The HiFi reads were assembled into a total of 132 contigs, which was further scaffolded using HiC data into 75 total sequences representing all 19 chromosomes. We identified that 9 of the 19 chromosomes were assembled as single contigs, while the other 10 chromosomes were each scaffolded together from two or more contigs. We qualitatively identified that percent repeat content within a chromosome broadly affects its assembly contiguity prior to scaffolding. This genome assembly signifies a new age for squamate genomics where high-quality reference genomes rivaling some of the best vertebrate genome assemblies can be generated for a fraction previous cost estimates. This new E. macularius reference assembly is available on NCBI at JAOPLA010000000. The genome version and its associated annotations are also available via this Figshare repository https://doi.org/10.6084/m9.figshare.20069273 .

The Periodic Replacement of Adhesive Setae in Pad Lamellae of Climbing Lizards Is Driven by Patterns of Corneous Layer Growth

The adhesive digital pads in some gecko and anoline lizards are continuously utilized for movements on vertical surfaces that may determine wear and a decrease of adhesion efficiency. The pads are formed by lamellae bearing adhesive setae that are worn out following frequent usage and are replaced by new inner setae that maintain an efficient adhesion. Whether the extensive usage of adhesive setae determines a higher shedding frequency in the digital pads with respect to other body regions remains unknown. Setae replacement has been analyzed in embryos and adult lizards using autoradiography and 5BrdU-immunohistochemistry. The observation strongly suggests that during development and epidermal renewal in adult lamellae, there is a shifting of the outer setae toward the apex of the lamella. This movement is likely derived from the continuous addition of proteins in the beta- and alpha-layers sustaining the outer setae while the inner setae are forming. Ultrastructural and in situ hybridization studies indicate that the thin outer beta- and alpha-layers still contain mRNAs and ribosomes that may contribute to the continuous production of corneous beta proteins (CBPs) and keratins for the growth of the free margin at the apex of the lamella. This process determines the apical shifting and release of the old setae, while the new inner setae formed underneath becomes the new outer setae.

Growing up in a rough world: scaling of frictional adhesion and morphology of the Tokay gecko (Gekko gecko)

Many geckos have the remarkable ability to reversibly adhere to surfaces using a hierarchical system that includes both internal and external elements. The vast majority of studies have examined the performance of the adhesive system using adults and engineered materials and substrates (e.g., acrylic glass). Almost nothing is known about how the system changes with body size, nor how these changes would influence the ability to adhere to surfaces in nature. Using Tokay geckos (Gekko gecko), we examined the post-hatching scaling of morphology and frictional adhesive performance in animals ranging from 5 to 125 grams in body mass. We quantified setal density, setal length, and toepad area using SEM. This was then used to estimate the theoretical maximum adhesive force. We tested performance with 14 live geckos on eight surfaces ranging from extremely smooth (acrylic glass) to relatively rough (100-grit sandpaper). Surfaces were attached to a force transducer, and multiple trials were conducted for each individual. We found that setal length scaled with negatively allometry, but toepad area scaled with isometry. Setal density remained constant across the wide range in body size. The relationship between body mass and adhesive performance was generally similar across all surfaces, but rough surfaces had much lower values than smooth surfaces. The safety factor went down with body mass and with surface roughness, suggesting that smaller animals may be more likely to occupy rough substrates in their natural habitat.

A new species of feather-tailed leaf-toed gecko, Kolekanos Heinicke, Daza, Greenbaum, Jackman, Bauer, 2014 (Squamata, Gekkonidae) from the poorly explored savannah of western Angola

We here describe a new species of feather-tailed leaf-toed gecko, Kolekanos, from southern Benguela Province, Angola, based on morphological and osteological evidence, supported by phylogenetic analysis of mitochondrial data. The new species adds to the rapidly growing and newly-recognised endemic biodiversity of Angola, doubling the number of Kolekanos species, breaking the pattern observed within other closely-related African members of a clade of circum-Indian Ocean leaf-toed geckos - Ramigekko, Cryptactites and Afrogecko - all of which are presently monotypic. The new species is easily distinguished from K.plumicaudus, based on spine-like (as opposed to feather-like) scales on the margins of the original tail. Phylogenetic analyses also recovered the new taxon as monophyletic, with a well-supported sister relationship to K.plumicaudus, from which it differs by a substantial 24.1% NADH-dehydrogenase subunit 2 mitochondrial gene uncorrected p-distance.

Hidden diversity of rock geckos within the Cnemaspissiamensis species group (Gekkonidae, Squamata): genetic and morphological data from southern Thailand reveal two new insular species and verify the phylogenetic affinities of C.chanardi and C.kamolnorranathi

Two new insular rock geckos in the genus Cnemaspis are described from Ko Samui in Surat Thani Province and Ko Similan in Phang-nga Province, southern Thailand, based on a combination of morphological and mitochondrial NADH dehydrogenase subunit 2 (ND2) data. Both new species represent divergent lineages within the Cnemaspissiamensis species group. Cnemaspissamui sp. nov. is distinguished from other species in the group by having eight or nine supralabial and infralabial scales; 5-8 pore-bearing precloacal scales in males, pores rounded; 25-27 paravertebral tubercles, arranged randomly; 22-25 subdigital lamellae under 4^th toe; enlarged median subcaudal scale row present; gular region, abdomen, limbs and subcaudal region yellowish only in males, and uncorrected pairwise divergences of 8.86-26.83% from all other species in the C.siamensis species group. Cnemaspissimilan sp. nov. is distinguished from other species in the group by having eight or nine supralabial and seven or eight infralabial scales; one pore-bearing precloacal scale in males, pore rounded; 24 or 25 paravertebral tubercles, arranged randomly; 23 or 24 subdigital lamellae under 4^th toe; no enlarged median subcaudal scale row; pale yellow reticulum on head, neck, flanks, belly and limbs in male only, and uncorrected pairwise divergences of 9.34-27.11% from all other species in the C.siamensis species group. Cnemaspissamui sp. nov. is found along granitic rocky stream outcrops of Hin Lad Waterfall, Ko Samui, Gulf of Thailand, while Cnemaspissimilan sp. nov. occurs in granitic rocky outcrops near Ao Nguang Chang Bay, Ko Similan, Andaman Sea. The phylogenetic analyses confirmed that C.chanardi and C.kamolnorranathi are also nested within the C.siamensis species group, as previously hypothesized from morphology and color pattern characters.

Ontogeny of the paraphalanges and derived phalanges of Hemidactylus turcicus (Squamata: Gekkonidae)

Gekkotan lizards of the genus Hemidactylus exhibit derived digital morphologies. These include heavily reduced antepenultimate phalanges of digits III and IV of the manus and digits III-V of the pes, as well as enigmatic cartilaginous structures called paraphalanges. Despite this well-known morphological derivation, no studies have investigated the development of these structures. We aimed to determine if heterochrony underlies the derived antepenultimate phalanges of Hemidactylus. Furthermore, we aimed to determine if convergently evolved paraphalanges exhibit similar or divergent developmental patterns. Herein we describe embryonic skeletal development in the hands and feet of four gekkonid species, exhibiting a range of digital morphologies. We determined that the derived antepenultimate phalanges of Hemidactylus are the products of paedomorphosis. Furthermore, we found divergent developmental patterns between convergently evolved paraphalanges.

The Comparative approach to bio-inspired design: integrating biodiversity and biologists into the design process

Biodiversity provides a massive library of ideas for bio-inspired design, but the sheer number of species to consider can be daunting. Current approaches for sifting through biodiversity to identify relevant biological models include searching for champion adapters that are particularly adept at solving a particular design challenge. While the champion adapter approach has benefits, it tends to focus on a narrow set of popular models while neglecting the majority of species. An alternative approach to bio-inspired design is the comparative method, which leverages biodiversity by drawing inspiration across a broad range of species. This approach uses methods in phylogenetics to map traits across evolutionary trees and compare trait variation to infer structure-function relationships. Although comparative methods have not been widely used in bio-inspired design, they have led to breakthroughs in studies on gecko-inspired adhesives and multifunctionality of butterfly wing scales. Here we outline how comparative methods can be used to complement existing approaches to bioinspired design, and we provide an example focused on bio-inspired lattices, including honeycomb and glass sponges. We demonstrate how comparative methods can lead to breakthroughs in bio-inspired applications as well as answer major questions in biology, which can strengthen collaborations with biologists and produce deeper insights into biological function.

Systematic revision of Afrogecko ansorgii (Boulenger, 1907) (Sauria: Gekkonidae) from western Angola

Here we provide the first phylogenetic analysis that include Afrogecko ansorgii and a detailed morphological comparison with other species of leaf-toed geckos. For this purpose, we used two mitochondrial (16S, ND2) and four nuclear (RAG1, RAG2, CMOS, PDC) genes to produce a robust phylogenetic reconstruction. This allowed us to show that A. ansorgii is not related as previously believed to circum-Indian Ocean leaf-toed geckos and is rather more closely related to other Malagasy leaf-toed geckos. Additionally, we explore and compare osteological variation in A. ansorgii skulls through High Resolution X-ray Computed Tomography with previously published material. This allowed us to describe herein a new genus, Bauerius gen. nov., and additionally provide a detailed redescription of the species (including the first description of male material), supplementing the limited original description and type series, which consisted of only two females.

The biogeography of bent-toed geckos, Cyrtodactylus (Squamata: Gekkonidae)

The gekkonid genus Cyrtodactylus is the third largest vertebrate genus on the planet with well over 300 species that range across at least eight biogeographic regions from South Asia to Melanesia. The ecological and morphological plasticity within the genus, has contributed to its ability to disperse across ephemeral seaways, river systems, basins, land bridges, and mountain ranges-followed by in situ diversification within specific geographic areas. Ancestral ranges were reconstructed on a mitochondrial phylogeny with 346 described and undescribed species from which it was inferred that Cyrtodactylus evolved in a proto-Himalaya region during the early Eocene. From there, it dispersed to what is currently Indoburma and Indochina during the mid-Eocene-the latter becoming the first major center of origin for the remainder of the genus that seeded dispersals to the Indian subcontinent, Papua, and Sundaland. Sundaland became a second major center of radiation during the Oligocene and gave rise to a large number of species that radiated further within Sundaland and dispersed to Wallacea, the Philippines, and back to Indochina. One Papuan lineage dispersed west to recolonize and radiate in Sundaland. Currently, Indochina and Sundaland still harbor the vast majority of species of Cyrtodactylus.

Variation in density, but not morphology, of cutaneous sensilla among body regions in nine species of Australian geckos

Skin sense organs, i.e., cutaneous sensilla, are a well-known feature of the integument of squamate reptiles, and particularly geckos. They vary widely in morphology among species, and are thought to be mechanosensitive, associated with prey capture and handling, tail autotomy, and placement of the adhesive toepads in pad-bearing species. Some authors suggest that they may also sense abiotic environmental features, such as temperature, or humidity. Here, we describe the morphology and distribution of cutaneous sensilla among body regions of nine Australian gecko species, in four genera. We hypothesised that if sensilla morphology was distinct, or sensilla density high, around the mouth, on the tail, and on extremities, sensilla were likely used for these direct tactile functions. We found that sensilla morphology was uniform among body regions within species, but varied among species, while sensilla densities varied among species and body regions. In gecko species studied, sensilla density was highest on the labials and the dorsal tail scales, and low on the feet, head and body, providing strong support for the hypothesis that sensilla serve tactile mechanoreceptive functions for prey capture and handling and for predator avoidance, but not for toepad placement. We suggest sensilla density may be explained by mechanoreception, whereas structure may be influenced by other factors.

The evolutionary history of an accidental model organism, the leopard gecko Eublepharis macularius (Squamata: Eublepharidae)

The leopard gecko, Eublepharis macularius, is a widely used model organism in laboratory and experimental studies. The high phenotypic diversity in the pet trade, the fact that the provenance of different breeding lines is unknown, and that distinct Eublepharis species are known to hybridize, implies that the continued use of E. macularius as a model requires clarity on the origin of the lineages in the pet trade. We combine multi-locus sequence data and the first range-wide sampling of the genus Eublepharis to reconstruct the evolutionary history of the Eublepharidae and Eublepharis, with an updated time-tree for the Eublepharidae. Our sampling includes five of the six recognized species and additional nominal taxa of uncertain status comprising 43 samples from 34 localities plus 48 pet-trade samples. The Eublepharidae began diversifying in the Cretaceous. Eublepharis split from its sister genera in Africa in the Palaeocene-Eocene, and began diversifying in the Oligocene-Miocene, with late Miocene-Pliocene cladogenesis giving rise to extant species. The current species diversity within this group is moderately underestimated. Our species delimitation suggests 10 species with four potentially unnamed divergent lineages in Iran, India and Pakistan. All 30 individuals of E. macularius that we sampled from the pet trade, which include diverse morphotypes, come from a few shallow E. macularius clades, confirming that lab and pet trade strains are part of a single taxon. One of the wild-caught haplotypes of E. macularius, from near Karachi, Pakistan, is identical to (10) pet-trade samples and all other captive populations are closely related to wild-caught animals from central/southern Pakistan (0.1-0.5 % minimum pairwise uncorrected ND2 sequence divergence).

Development and function explain the modular evolution of phalanges in gecko lizards

Selective regimes favouring the evolution of functional specialization probably affect covariation among phenotypic traits. Phalanges of most tetrapods develop from a conserved module that constrains their relative proportions. In geckos, however, biomechanical specializations associated with adhesive toepads involve morphological variation in the autopodium and might reorganize such modular structures. We tested two hypotheses to explain the modular architecture of hand bones in geckos, one based on developmental interactions and another incorporating functional associations related to locomotion, and compared the empirical support for each hypothetical module between padded and padless lineages. We found strong evidence for developmental modules in most species, which probably reflects embryological constraints during phalangeal formation. Although padded geckos exhibit a functional specialization involving the hyperextension of the distal phalanges that is absent in padless species, the padless species are the ones that show a distal functional module with high integration. Some ancestrally padless geckos apparently deviate from developmental predictions and present a relatively weak developmental module of phalanges and a strongly integrated distal module, which may reflect selective regimes involving incipient frictional adhesion in digit morphology. Modularity of digit elements seems dynamic along the evolutionary history of geckos, being associated with the presence/absence of adhesive toepads.

Convergent developmental patterns underlie the repeated evolution of adhesive toe pads among lizards

How developmental modifications produce key innovations, which subsequently allow for rapid diversification of a clade into new adaptive zones, has received much attention. However, few studies have used a robust comparative framework to investigate the influence of evolutionary and developmental constraints on the origin of key innovations, such as the adhesive toe pad of lizards. Adhesive toe pads evolved independently at least 16 times in lizards, allowing us to examine whether the patterns observed are general evolutionary phenomena or unique, lineage-specific events. We performed a high-resolution comparison of plantar scale development in 14 lizard species in Anolis and geckos, encompassing five independent origins of toe pads (one in Anolis, four in geckos). Despite substantial evolutionary divergence between Anolis and geckos, we find that these clades have undergone similar developmental modifications to generate their adhesive toe pads. Relative to the ancestral plantar scale development, in which scale ridges form synchronously along the digit, both padded geckos and Anolis exhibit scansor formation in a distal-to-proximal direction. Both clades have undergone developmental repatterning and, following their origin, modifications in toe pad morphology occurred through relatively minor developmental modifications, suggesting that developmental constraints governed the diversification of the adhesive toe pad in lizards.

Ankle structure of the Tokay gecko (Gekko gecko) and its role in the deployment of the subdigital adhesive system

The remarkable ability of geckos to adhere to smooth surfaces is often thought of in terms of external structures, including the branching setae that make contact with the surface producing van der Waals forces. Some geckos also exhibit unique movements of the distal segments of the limbs during locomotion and static clinging, including active digital hyperextension and considerable pedal rotation. During static clinging, geckos can exhibit considerable adduction/abduction of the pes while the crus and thigh remain firmly adpressed to the substratum. This decoupling of pedal adduction/abduction from ankle flexion/extension and pedal long-axis rotation is a significant departure from pedal displacements of a typical lizard lacking adhesive ability. The structure of the ankle is likely key to this decoupling, although no detailed comparison of this complex joint between pad-bearing geckos and other lizards is available. Here we compare the configuration of the mesotarsal joint of nongekkotan lizards (Iguana and Pristidactylus) with that of the Tokay gecko (Gekko gecko) using prepared skeletons, scanning electron microscopy, and micro-computed tomographic (µCT) scans. We focus on the structure of the astragalocalcaneum and the fourth distal tarsal. The mesotarsal joint exhibits a suite of modifications that are likely associated with the secondarily symmetrical pes of pad-bearing geckos. For example, the lateral process of the astragalocalcaneum is much more extensive in G. gecko compared with other lizards. The mesotarsal joint exhibits several other differences permitting dissociation of long-axis rotation of the pes from flexion-extension movement, including a reduced ventral peg on the fourth distal tarsal, an articulatory pattern dominated by a well-defined, expansive distomesial notch of the astragalocalcaneum, and an associated broad proximodorsal articulatory facet of the fourth distal tarsal. Pad-bearing geckos are capable of effectively deploying their intricate adhesive system across a broad array of body angles because of this highly modified ankle. Future research should determine whether the differences encountered in G. gecko (and their extent) apply to the Gekkota as a whole and should examine how the elements of the ankle move dynamically during locomotion across a range of taxa.

Complete mitochondrial genome of Teratoscincus przewalskii (Reptilia, Squamata, Sphaerodactylidae) and phylogenetic analysis

The complete mitochondrial genome of the lizard, Teratoscincus przewalskii, which belongs to the family Sphaerodactylidae was determined based on Illumina data in this study. The result showed that the closed double-stranded circular mitogenome was 16,779 bp in total length (GenBank accession number: MW491837) with 44.07% GC. The complete mitochondrial genome consisted of 13 protein-coding genes, 22 transfer RNA genes, two ribosomal genes, and one noncoding control region. Phylogenetic analysis using mitochondrial genomes suggested that T. przewalskii was most closely related to its congener T. keyserlingii. This work provides valuable molecular information for further research on species identification and molecular evolution.

Between sand, rocks and branches: an integrative taxonomic revision of Angolan Hemidactylus Goldfuss, 1820, with description of four new species

Abstract

The taxonomy of Angolan Hemidactylus has recently been revised. However, the lack of fresh material for some groups and regions, has led to the misidentification of some taxa and an underestimation of actual diversity in others. To shed light on the evolutionary history and systematics of Angolan Hemidactylus, we generated a new phylogenetic hypothesis for the group, and updated the taxonomy following an integrative approach. This resulted in the description of four new species (H. pfindaensissp. nov., H. faustussp. nov., H. carivoensissp. nov. and H. cinganjisp. nov.), the reevaluation of two recently described species (H. vernayi and H. paivae) and the synonymization of a recently described species (H. hannahsabinnae). We estimate divergence times for these lineages, providing a preliminary interpretation of their speciation process. Moreover, we suggest and outline 13 Angolan Main Biogeographic Units (AMBUs) in the area, defining a new biogeographic context for future works on Angolan herpetofauna. We now recognize eleven Hemidactylus species in Angola, and we provide here a new morphological key for Angolan Hemidactylus to help with identifications and species assignments in this group.

And thereby hangs a tail: morphology, developmental patterns and biomechanics of the adhesive tails of crested geckos (Correlophus ciliatus)

Among the most specialized integumentary outgrowths in amniotes are the adhesive, scale-like scansors and lamellae on the digits of anoles and geckos. Less well-known are adhesive tail pads exhibited by 21 gecko genera. While described over 120 years ago, no studies have quantified their possible adhesive function or described their embryonic development. Here, we characterize adult and embryonic morphology and adhesive performance of crested gecko (Correlophus ciliatus) tail pads. Additionally, we use embryonic data to test whether tail pads are serial homologues to toe pads. External morphology and histology of C. ciliatus tail pads are largely similar to tail pads of closely related geckos. Functionally, C. ciliatus tail pads exhibit impressive adhesive ability, hypothetically capable of holding up to five times their own mass. Tail pads develop at approximately the same time during embryogenesis as toe pads. Further, tail pads exhibit similar developmental patterns to toe pads, which are markedly different from non-adhesive gecko toes and tails. Our data provide support for the serial homology of adhesive tail pads with toe pads.

Specialist versus Generalist at the Intraspecific Level: Functional Morphology and Substrate Preference of Mediodactylus kotschyi Geckos

Populations of the same species occupying different microhabitats can either exhibit generalized traits across them or display intraspecific variability, adapting to each microhabitat in order to maximize performance. Intraspecific variability contributes to the generation of diversity, following selection and adaptation, and understanding such variability is important for comprehending how individuals choose their microhabitats. Compared with interspecific variability, however, intraspecific variability in functional morphology and its relationship with microhabitat preference and use have been relatively little studied. Here we examined whether populations of the gecko Mediodactylus kotschyi that differ in the substrates they occupy display habitat-specific behaviors and differing morphologies associated with functional adaptation to their microhabitats. We collected 207 geckos from under or on rocks or on trees from seven populations in Greece. On large islands individuals occupy both substrates; whereas small islets are devoid of trees and the geckos are restricted to rocks, while on the mainland they are only found on trees. We determined gecko substrate preferences in the laboratory, together with their clinging abilities to the different substrates. We measured their limbs, digits, and claws and assessed how these measurements relate to clinging ability. Geckos from all populations preferred the tree made available to them, but this preference was not statistically significant. Geckos from both large and small islands clung better to the tree than to the rock in the laboratory, while those from the mainland clung similarly to both substrates. Geckos collected from trees had longer manual digits and hind limbs. Geckos collected from large and small islands had taller (longer on the dorso-ventral axis; henceforth "deeper") claws. Longer digits and deeper but shorter claws were associated with a better ability to cling to rocks. Our findings suggest that while M. kotschyi is potentially preferentially arboreal, due to the great variation and plasticity it possesses, it can successfully also exploit the habitats available on the smallest, treeless islets in the Aegean Sea. Our study suggests that the dichotomous use of generalist versus specialist in describing species' habitat use is oversimplified, and we suggest the use of a generalist-specialist gradient instead.

Underestimated diversity of Cnemaspis Strauch, 1887 (Sauria: Gekkonidae) on karst landscapes in Sarawak, East Malaysia, Borneo

The paraphyletic group of Old World rock gecko genus Cnemaspis, currently comprises ~180 described species from Africa and Asia.  The south-east Asian clade with 63 described species, is most diverse on the Thai-Malay Peninsula, with just five species known from Borneo, an island biodiversity hotspot.  Karst regions are known as centres for species endemism, and vast areas of caves and karst exist across northern Borneo.  Fieldwork from 2017 to 2020 recovered additional undescribed species of Cnemaspis from areas of karst forests in western and northern Sarawak.  These discoveries emphasize the importance of preserving areas of limestone karst within rainforest areas for maintaining species diversity, as well as accelerating research on documenting the biota.

Novel Tests of the Key Innovation Hypothesis: Adhesive Toepads in Arboreal Lizards

The evolution of key innovations-unique features that enable a lineage to interact with the environment in a novel way-may drive broad patterns of adaptive diversity. However, traditional tests of the key innovation hypothesis, those which attempt to identify the evolutionary effect of a purported key innovation by comparing patterns of diversity between lineages with and without the key trait, have been challenged on both conceptual and statistical grounds. Here, we explore alternative, untested hypotheses of the key innovation framework. In lizards, adhesive toepad structures increase grip strength on vertical and smooth surfaces such as tree trunks and leaves and have independently evolved multiple times. As such, toepads have been posited as a key innovation for the evolution of arboreality. Leveraging a habitat use dataset applied to a global phylogeny of 2692 lizard species, we estimated multiple origins of toepads in three major clades and more than 100 origins of arboreality widely across the phylogeny. Our results suggest that toepads arise adaptively in arboreal lineages and are subsequently rarely lost while maintaining arboreal ecologies. Padless lineages transition away from arboreality at a higher rate than those with toepads, and high rates of invasion of arboreal niches by non-arboreal padbearing lineages provides further evidence that toepads may be a key to unlocking evolutionary access to the arboreal zone. Our results and analytical framework provide novel insights to understand and evaluate the ecological and evolutionary consequences of key innovations.

Adaptive variation in the development of extraembryonic membranes of gekkotan embryos: A meta-analytical approach

Highly mineralized rigid-shelled eggs characterize one lineage of gekkotans. In contrast, poorly mineralized flexible-shelled eggs characterize basal lineages of gekkotans and all other squamates. Low oxygen permeability of rigid-shelled eggs is associated with small eggs and hatchlings, and long incubation lengths compared to flexible-shelled gekkotan eggs. These features represent a demographic cost for species with rigid-shelled eggs. This cost is offset, at least in part, because mortality due to desiccation and predation is reduced for rigid-shelled eggs relative to flexible-shelled eggs. Developmental traits may also compensate for the low oxygen permeability of rigid-shelled eggs. Oviposition, for example, occurs at earlier developmental stages for gekkotans with rigid- versus flexible-shelled eggs. Such early oviposition facilitates development because eggs move from the relatively hypoxic oviduct to the much better oxygenated nest environment. In this study, I tested the hypothesis that the growth of the yolk sac (YS) and chorioallantoic membrane (CAM) of gekkotans with rigid-shelled eggs is initiated and completed earlier than those of gekkotans with flexible-shelled eggs. I measured the surface area of eggs covered by the YS and CAM from oviposition to hatching and determined which of four nonlinear models provide the best fit for growth curves. I also compiled a data set on embryonic metabolism of gekkotans and other lizards in order to place growth of the YS and CAM in the context of energy utilization of lizard embryos overall. Growth of the YS and CAM of gekkotans with rigid-shelled eggs is accelerated relative to that of gekkotans with flexible-shelled eggs and may serve to separate the cost of YS and CAM development from that of the embryo itself. Adaptive variation in YS and CAM development may extend to birds, crocodilians, and turtles as they also exhibit life history variation that affects oxygen availability to embryos during development.

Molecular phylogenetics of sub-Saharan African natricine snakes, and the biogeographic origins of the Seychelles endemic Lycognathophis seychellensis

Phylogenetic relationships of sub-Saharan African natricine snakes are understudied and poorly understood, which in turn has precluded analyses of the historical biogeography of the Seychelles endemic Lycognathophis seychellensis. We inferred the phylogenetic relationships of Seychelles and mainland sub-Saharan natricines by analysing a multilocus DNA sequence dataset for three mitochondrial (mt) and four nuclear (nu) genes. The mainland sub-Saharan natricines and L. seychellensis comprise a well-supported clade. Two maximally supported sets of relationships within this clade are (Limnophis,Natriciteres) and (Afronatrix,(Hydraethiops,Helophis)). The relationships of L. seychellensis with respect to these two lineages are not clearly resolved by analysing concatenated mt and nu data. Analysed separately, nu data best support a sister relationship of L. seychellensis with (Afronatrix,(Hydraethiops,Helophis)) and mt data best support a sister relationship with all mainland sub-Saharan natricines. Methods designed to cope with incomplete lineage sorting strongly favour the former hypothesis. Genetic variation among up to 33 L. seychellensis from five Seychelles islands is low. Fossil calibrated divergence time estimates support an overseas dispersal of the L. seychellensis lineage to the Seychelles from mainland Africa ca. 43-25 million years before present (Ma), rather than this taxon being a Gondwanan relic.

PL, Poyarkov NA, Le MD, Kraus F, Agarwal I, Oliver PM, Nguyen SN, Nguyen TQ, Karunarathna S, Welton LJ, Stuart BL, Luu VQ, Bauer AM, O’Connell KA, Quah ESH, Chan KO, Ziegler T, Ngo H, Nazarov RA, Aowphol A, Chomdej S, Suwannapoom C, Siler CD, Anuar S, Tri NV, Grismer JL. Phylogenetic partitioning of the third-largest vertebrate genus in the world, Cyrtodactylus Gray, 1827 (Reptilia; Squamata; Gekkonidae) and its relevance to taxonomy and conservation

The gekkonid genus Cyrtodactylus is the third most speciose vertebrate genus in the world, containing well over 300 species that collectively range from South Asia to Melanesia across some of the most diverse landscapes and imperiled habitats on the planet. A genus-wide phylogeny of the group has never been presented because researchers working on different groups were using different genetic markers to construct phylogenies that could not be integrated. We present here Maximum likelihood and Bayesian inference mitochondrial and mito-nuclear phylogenies incorporating of 310 species that include dozens of species that had never been included in a genus-wide analysis. Based on the mitochondrial phylogeny, we partition Cyrtodactylus into 31 well-supported monophyletic species groups which, if used as recommended herein, will increase the information content of future integrative taxonomic analyses that continue to add new species to this genus at an ever-increasing annual rate. Data presented here reiterate the outcome of several previous studies indicating that Cyrtodactylus comprises an unprecedented number of narrow-range endemics restricted to single mountain tops, small islands, or karst formations that still remain unprotected. This phylogeny can provide a platform for various comparative ecological studies that can be integrated with conservation management programs across the broad diversity of landscapes and habitats occupied by this genus. Additionally, these data indicate that the true number of Cyrtodactylus remains substantially underrepresented.

PL, Poyarkov NA, Le MD, Kraus F, Agarwal I, Oliver PM, Nguyen SN, Nguyen TQ, Karunarathna S, Welton LJ, Stuart BL, Luu VQ, Bauer AM, O’Connell KA, Quah ESH, Chan KO, Ziegler T, Ngo H, Nazarov RA, Aowphol A, Chomdej S, Suwannapoom C, Siler CD, Anuar S, Tri NV, Grismer JL. Phylogenetic partitioning of the third-largest vertebrate genus in the world, Cyrtodactylus Gray, 1827 (Reptilia; Squamata; Gekkonidae) and its relevance to taxonomy and conservation

The gekkonid genus Cyrtodactylus is the third most speciose vertebrate genus in the world, containing well over 300 species that collectively range from South Asia to Melanesia across some of the most diverse landscapes and imperiled habitats on the planet. A genus-wide phylogeny of the group has never been presented because researchers working on different groups were using different genetic markers to construct phylogenies that could not be integrated. We present here Maximum likelihood and Bayesian inference mitochondrial and mito-nuclear phylogenies incorporating of 310 species that include dozens of species that had never been included in a genus-wide analysis. Based on the mitochondrial phylogeny, we partition Cyrtodactylus into 31 well-supported monophyletic species groups which, if used as recommended herein, will increase the information content of future integrative taxonomic analyses that continue to add new species to this genus at an ever-increasing annual rate. Data presented here reiterate the outcome of several previous studies indicating that Cyrtodactylus comprises an unprecedented number of narrow-range endemics restricted to single mountain tops, small islands, or karst formations that still remain unprotected. This phylogeny can provide a platform for various comparative ecological studies that can be integrated with conservation management programs across the broad diversity of landscapes and habitats occupied by this genus. Additionally, these data indicate that the true number of Cyrtodactylus remains substantially underrepresented.

Sex Chromosome Turnover in Bent-Toed Geckos (Cyrtodactylus)

Lizards and snakes (squamates) are known for their varied sex determining systems, and gecko lizards are especially diverse, having evolved sex chromosomes independently multiple times. While sex chromosomes frequently turnover among gecko genera, intrageneric turnovers are known only from Gekko and Hemidactylus. Here, we used RADseq to identify sex-specific markers in two species of Burmese bent-toed geckos. We uncovered XX/XY sex chromosomes in Cyrtodactylus chaunghanakwaensis and ZZ/ZW sex chromosomes in Cyrtodactylus pharbaungensis. This is the third instance of intrageneric turnover of sex chromosomes in geckos. Additionally, Cyrtodactylus are closely related to another genus with intrageneric turnover, Hemidactylus. Together, these data suggest that sex chromosome turnover may be common in this clade, setting them apart as exceptionally diverse in a group already known for diverse sex determination systems.

Parallel evolution of toepads in rock-dwelling lineages of a terrestrial gecko (Gekkota: Gekkonidae: Heteronotia binoei)

Selection for effective locomotion can lead to specialized morphological structures. Adhesive toepads, which have arisen independently in different lizard clades, facilitate the use of vertical and inverted substrates. Their evolution is poorly understood because functionally intermediate morphological configurations between padless and pad-bearing forms are rare. To shed light on toepad evolution, we assessed the subdigital morphology of phylogenetically distinct lineages of the Bynoe’s gecko species complex (Heteronotia binoei). Most populations of H. binoei are terrestrial, but two relatively distantly related saxicoline (rock-dwelling) lineages have enlarged terminal subdigital scales resembling toepads. We reconstructed the ancestral terminal subdigital scale size of nine lineages of H. binoei in eastern Australia, including these two saxicoline lineages. Additionally, we compared the subdigital microstructures of four lineages: the two saxicoline lineages and their respective terrestrial sister-lineages. Surprisingly, all four lineages had fully developed setae, but the setae of the two saxicoline lineages were significantly longer, branched more often and were more widely spaced than the terrestrial sister-lineages. We conclude that the saxicoline lineages represent examples of parallel evolution of enlarged adhesive structures in response to vertical substrate use, and their morphology represents a useful model as an intermediate state in toepad evolution.

Evolution of habitat preference in 243 species of Bent-toed geckos (Genus Cyrtodactylus Gray, 1827) with a discussion of karst habitat conservation

Understanding the processes that underpin adaptive evolutionary shifts within major taxonomic groups has long been a research directive among many evolutionary biologists. Such phenomena are best studied in large monophyletic groups that occupy a broad range of habitats where repeated exposure to novel ecological opportunities has happened independently over time in different lineages. The gekkonid genus Cyrtodactylus is just such a lineage with approximately 300 species that range from South Asia to Melanesia and occupy a vast array of habitats. Ancestral state reconstructions using a stochastic character mapping analysis of nine different habitat preferences were employed across a phylogeny composed of 76% of the known species of Cyrtodactylus. This was done in order to ascertain which habitat preference is the ancestral condition and from that condition, the transition frequency to more derived habitat preferences. The results indicate that a general habitat preference is the ancestral condition for Cyrtodactylus and the frequency of transitioning from a general habitat preference to anything more specialized occurs approximately four times more often than the reverse. Species showing extreme morphological and/or ecological specializations generally do not give rise to species bearing other habitat preferences. The evolution of different habitat preferences is generally restricted to clades that tend to occur in specific geographic regions. The largest radiations in the genus occur in rocky habitats (granite and karst), indicating that the transition from a general habitat preference to a granite or karst-dwelling life style may be ecologically uncomplicated. Two large, unrelated clades of karst-associated species are centered in northern Indochina and the largest clade of granite-associated species occurs on the Thai-Malay Peninsula. Smaller, independent radiations of clades bearing other habitat preferences occur throughout the tree and across the broad distribution of the genus. With the exception of a general habitat preference, the data show that karst-associated species far out-number all others (29.6% vs. 0.4%-10.2%, respectively) and the common reference to karstic regions as "imperiled arcs of biodiversity" is not only misleading but potentially dangerous. Karstic regions are not simply refugia harboring the remnants of local biodiversity but are foci of speciation that continue to generate the most speciose, independent, radiations across the genus. Unfortunately, karstic landscapes are some of the most imperiled and least protected habitats on the planet and these data continue to underscore the urgent need for their conservation.