Conserved ZZ/ZW Sex Chromosomes in Caribbean Croaking Geckos (\u3cem\u3eAristelliger\u3c/em\u3e: Sphaerodactylidae)

Current understanding of sex chromosome evolution is largely dependent on species with highly degenerated, heteromorphic sex chromosomes, but by studying species with recently evolved or morphologically indistinct sex chromosomes we can greatly increase our understanding of sex chromosome origins, degeneration and turnover. Here, we examine sex chromosome evolution and stability in the gecko genus Aristelliger. We used RADseq to identify sex‐specific markers and show that four Aristelliger species, spanning the phylogenetic breadth of the genus, share a conserved ZZ/ZW system syntenic with avian chromosome 2. These conserved sex chromosomes contrast with many other gecko sex chromosome systems by showing a degree of stability among a group known for its dynamic sex‐determining mechanisms. Cytogenetic data from A. expectatus revealed homomorphic sex chromosomes with an accumulation of repetitive elements on the W chromosome. Taken together, the large number of female‐specific A. praesignis RAD markers and the accumulation of repetitive DNA on the A. expectatus W karyotype suggest that the Z and W chromosomes are highly differentiated despite their overall morphological similarity. We discuss this paradoxical situation and suggest that it may, in fact, be common in many animal species

Embryonic Development of A Parthenogenetic Vertebrate, The Mourning Gecko (\u3cem\u3eLepidodactylus lugubris\u3c/em\u3e)

Background One goal of evolutionary developmental biology is to understand the role of development in the origin of phenotypic novelty and convergent evolution. Geckos are an ideal system to study this topic, as they are species‐rich and exhibit a suite of diverse morphologies—many of which have independently evolved multiple times within geckos. Results We characterized and discretized the embryonic development of Lepidodactylus lugubris—an all‐female, parthenogenetic gecko species. We also used soft‐tissue μCT to characterize the development of the brain and central nervous system, which is difficult to visualize using traditional microscopy techniques. Additionally, we sequenced and assembled a de novo transcriptome for a late‐stage embryo as a resource for generating future developmental tools. Herein, we describe the derived and conserved patterns of L. lugubris development in the context of squamate evolution and development. Conclusions This embryonic staging series, μCT data, and transcriptome together serve as critical enabling resources to study morphological evolution and development, the evolution and development of parthenogenesis, and other questions concerning vertebrate evolution and development in an emerging gecko model

Colour scales with climate in North American ratsnakes: a test of the thermal melanism hypothesis using community science images

Animal colour is a complex trait shaped by multiple selection pressures that can vary across geography. The thermal melanism hypothesis predicts that darker coloration is beneficial to animals in colder regions because it allows for more rapid solar absorption. Here, we use community science images of three closely related species of North American ratsnakes (genus Pantherophis) to examine if climate predicts colour variation across range-wide scales. We predicted that darker individuals are found in colder regions and higher elevations, in accordance with the thermal melanism hypothesis. Using an unprecedented dataset of over 8000 images, we found strong support for temperature as a key predictor of darker colour, supporting thermal melanism. We also found that elevation and precipitation are predictive of colour, but the direction and magnitude of these effects were more variable across species. Our study is the first to quantify colour variation in Pantherophis ratsnakes, highlighting the value of community science images for studying range-wide colour variation

Distinct patterns of pigment development underlie convergent hyperpigmentation between nocturnal and diurnal geckos (Squamata: Gekkota) / Aaron H. Griffing, Tony Gamble, Aaron M. Bauer.

Background Evolutionary transitions in temporal niche necessitates specialized morphology, physiology, and behaviors. Diurnal, heliothermic squamates (lizards and snakes) that bask require protection from ultraviolet radiation (UV) that can damage internal organs such as the brain, viscera, and gonads. Many smaller squamates have accomplished this protection by hyperpigmentation of the peritoneum and subcutaneous dorsum. Typically, nocturnal species do not require these protections from ultraviolet light. However, some nocturnal species that exhibit extreme crypsis may be exposed to sunlight and UV and require some means of mediating that damage. One such species is Gekko (Ptychozoon) kuhli, a nocturnal, arboreal gecko that uses extreme crypsis to blend in with tree bark. Hiding motionless on tree trunks leaves geckos exposed to sunlight during the day. Thus, we predict that G. kuhli will have independently evolved a hyperpigmented phenotype. To investigate this hypothesized association between temporal niche, behavior, and morphology, we characterized adult subcutaneous pigment for eight gecko species and embryonic pigment accumulation for a subset of four of these species, exhibiting diverse temporal niche and thermoregulatory behaviors. We predicted that nocturnal/potentially-heliothermic G. kuhli would exhibit hyperpigmentation of internal structures like that of diurnal/heliothermic geckos. We further predicted that embryonic pigment accumulation of G. kuhli would resemble that of diurnal/heliothermic as opposed to nocturnal/thigmothermic geckos. Results We found that temporal niche and thermoregulatory behavior predicted the degree of subcutaneous pigment in the eight gecko species examined. We demonstrate that G. kuhli accumulates pigment extremely early in embryonic development, unlike a diurnal/heliothermic gecko species, despite having a similar adult phenotype. Conclusions The evolution of hyperpigmentation in G. kuhli is likely an adaptation to limit damage from occasional daytime UV exposure caused by crypsis-associated basking behavior. Gekko kuhli achieves its hyperpigmented phenotype through a derived developmental pattern, not seen in any other lizard species investigated to date, suggesting novel temporal differences in the migration and/or differentiation of reptilian neural crest derivatives. Background Temporal niche, also known as diel activity niche, is an important aspect of the biology of an organism, necessitating the evolution of specialized morphology, physiology, ecology, and behavior (e.g. [19, 41, 56, 72]). For example, many diurnal ectotherms thermoregulate through basking behavior (i.e. heliothermy), whereas nocturnal ectotherms thermoregulate through contact with surfaces of different temperatures (i.e. thigmothermy; [1, 16, 51]). Temporal niche appears to be phylogenetically conserved across major tetrapod clades [2] and thus many adaptations to specific temporal niches (diurnal, nocturnal, crepuscular, or cathemeral) are shared among closely related species. Despite its conservation in tetrapod evolutionary history [2], several squamate clades do exhibit temporal niche turnover. The crown group of geckos (Infraorder Gekkota) are hypothesized to be ancestrally nocturnal, with reversals to diurnality occurring in at least 10 lineages [2, 24, 76]. Many of these lineages exhibit an array of diurnal-specialized adaptations, most notably eye morphologies, with oil droplets which aid in light filtering and spectral tuning [9, 55, 70, 76], concaviclivate temporal fovea to aid in binocular vision [57, 71], and ovoid retinal pigmented epithelia (RPE) to aid in light filtering and absorption [31, 65]

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

Atypical Tuning and Amplification Mechanisms in Gecko Auditory Hair Cells

The auditory papilla of geckos contains two zones of sensory hair cells, one covered by a continuous tectorial membrane affixed to the hair bundles and the other by discrete tectorial sallets each surmounting a transverse row of bundles. Gecko papillae are thought to encode sound frequencies up to 5 kHz, but little is known about the hair cell electrical properties or their role in frequency tuning. We recorded from hair cells in the isolated auditory papilla of the crested gecko, Correlophus ciliatus, and found that in both the nonsalletal region and part of the salletal region, the cells displayed electrical tuning organized tonotopically. Along the salletal zone, occupying the apical two-thirds of the papilla, hair bundle length decreased threefold and stereociliary complement increased 1.5-fold. The two morphological variations predict a 13-fold gradient in bundle stiffness, confirmed experimentally, which, when coupled with salletal mass, could provide passive mechanical resonances from 1 to 6 kHz. Sinusoidal electrical currents injected across the papilla evoked hair bundle oscillations at twice the stimulation frequency, consistent with fast electromechanical responses from hair bundles of two opposing orientations across the papilla. Evoked bundle oscillations were diminished by reducing Ca2+ influx, but not by blocking the mechanotransduction channels or inhibiting prestin action, thereby distinguishing them from known electromechanical mechanisms in hair cells. We suggest the phenomenon may be a manifestation of an electromechanical amplification that augments the passive mechanical tuning of the sallets over the high-frequency region

Sheddable armour: identification of osteoderms in the integument of <i>Geckolepis maculata</i> (Gekkota)

<p>Osteoderms are bony deposits that form within the dermal layer of skin in vertebrates. Within geckos, osteoderms are uncommon, only described in <i>Gekko gecko</i> and the genus <i>Tarentola</i>. A previous report of osteoderms in the Afro-Malagasy gekkonid genus <i>Geckolepis</i> has been questioned due to the extreme skin fragility and regional integumentary loss within the group. We re-evaluated the integument anatomy of <i>Geckolepis maculata</i> using µCT scanning, histology, and clearing and staining to verify the presence or absence of osteoderms and, if present, to characterise and compare their morphology to the osteoderms of <i>Gekko gecko</i> and <i>Tarentola</i>, as well as osteoderm diversity within squamates. Osteoderms were confirmed present in <i>Geckolepis maculata</i>; however, these osteoderms are compound, imbricating, squamous elements that are morphologically similar to the dermal ossifications observed in scincids and gerrhosaurids, while <i>G. gecko</i> and <i>Tarentola</i> possess plate-like and granular osteoderms. Our results suggest that osteoderms have independently evolved at least three times within the Gekkota and that epidermal anatomy may be a better predictor of osteoderm morphology than ancestral history. Further research is required to investigate the regenerative capability of <i>Geckolepis</i> osteoderms following skin autotomy.</p

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