Group Of Lizards Research Articles

Evolutionary Links Between Skull Shape and Body Size Suggest Allometric Forces and Selection at Work in a Generalist Group of Lizards

ABSTRACTThe vertebrate skull is a complex structure, and studies of skull shape have yielded considerable insight into the evolutionary forces shaping specialized phenotypes in organisms as diverse as bats, frogs, and fossorial animals. Here, we used phylogenetic comparative analyses of CT scans of male skulls from 57 species of Sceloporus lizards to explore patterns of skull evolution in a group of generalist taxa. We found that most interspecific variation is in terms of skull elongation such that some species have long, narrow skulls, whereas others exhibit more compact and robust skulls. We also found strong links to overall body size, with evolutionary shifts to larger bodies being associated with more compact skulls and slower evolutionary rates. This is the opposite of the pattern in most mammals in which larger bodied species have longer snouts, and more like the pattern in frogs in which function has played a more important evolutionary role. Also, unlike other vertebrates, the jaw, anterior, and posterior parts of the Sceloporus skull are largely integrated, having evolved independently of each other only to a limited, albeit significant, degree. Our results emphasize the importance of body size in the evolutionary shaping of the skull and suggest that additional studies of behavioral function in a generalist group are warranted.

Ecological and taxonomic dissimilarity in species and higher taxa of reptiles in western Mexico.

Reptiles are one of the most diverse groups of vertebrates in the world that are distributed in almost all ecosystems. Many of these studies have focused on exploring their diversity patterns across different environments; and recent studies on reptile alpha and beta diversity have incorporated a multifaceted approach into their analysis to have more comprehensive evaluations. This study presents an assessment of the taxonomic diversity of reptile patterns using methods that incorporate the assessment of higher taxa. Likewise, the taxonomic dissimilarities between reptile communities in the physiographic regions of the state of Jalisco were analyzed. Evaluations for the groups of snakes and lizards independently are presented. We use the taxonomic distinctiveness index that assesses the complexity of the taxonomic structure of communities through hierarchical classification above the species level to measure the relationships between taxa. The dissimilarity of the taxonomic structure in each community was also analyzed. Beta diversity partitions were performed to identify the contribution of turnover and the differences in richness. We determined that alpha diversity of species and higher taxa maintain different patterns, indicating that Jalisco presents regions with overrepresentation of reptile families and genera, as well as regions with an opposite trend. The representation of higher taxa is higher in the lizard group, although in terms of species richness snakes are the most prominent group. The turnover is the most important component at species and higher taxa, with similar values for lizards and snakes. The findings presented show that incorporating phylogenetic information about species through taxonomic relationships provides complementary information that species diversity per se, especially at the level of alpha diversity.

Coordinating limbs and spine: (Pareto-)optimal locomotion in theory, in vivo, and in robots

Among vertebrates, patterns of movement vary considerably, from the lateral spine-based movements of fish and salamanders to the predominantly limb-based movements of mammals. Yet, we know little about why these changes may have occurred in the course of evolution. Lizards form an interesting intermediate group where locomotion appears to be driven by both motion of their limbs and lateral spinal undulation. To understand the evolution and relative advantages of limb versus spine locomotion, we developed an empirically informed mathematical model as well as a robotic model and compared in silico predictions to in-vivo data from running and climbing lizards. Our mathematical model showed that, if limbs were allowed to grow to long lengths, movements of the spine did not enable longer strides, since spinal movements reduced the achievable range of motion of the limbs before collision. Yet, in-vivo data show lateral spine movement is widespread among a diverse group of lizards moving on level ground or climbing up and down surfaces. Our climbing robotic model was able to explain this disparity, showing that increased movement of the spine was energetically favourable, being associated with a reduced cost of transport. Our robot model also revealed that stability, as another performance criterion, decreased with increased spine and limb range of motion—detailing the trade-off between speed and stability. Overall, our robotic model found a Pareto-optimal set of strides—when considering speed, efficiency, and stability—requiring both spine and limb movement, which closely agreed with movement patterns among lizards. Thus we demonstrate how robotic models, in combination with theoretical considerations, can reveal fundamental insights into the evolution of movement strategies among a broad range of taxa.

Initial orientation and homing performances in the lacertid lizard Podarcis siculus

Homing abilities of lizards after experimental dislocations have been found to be well developed in several species. Following our preliminary findings in Podarcis siculus, the present paper reports a new series of experiments on homing performances and initial orientation behaviour upon release. For this purpose, three series of releases were performed at increasing distances from the home areas in which the lizards were captured (range 85–245 m). In each series, two groups of lizards were released: the route-based visual cues during displacement were denied to one of them (NVIS), but allowed for the other (YVIS). The results of initial orientation showed that both are significantly homeward oriented at all three distances tested. Male and female YVIS and female NVIS are similarly homeward oriented, while the male NVIS are not. All 74 lizards successfully returned to their respective home areas. Eleven lizards homed on the same day they were released, while most of them homed during the 1st day after release (n = 51) and the rest on the 2nd day (n = 12). The different transport treatments did not influence homing success at the different distances tested. These results seem to support the use of a geocentric pilotage strategy to re-enter home from the release spot. Alternatively, the possibility that P. siculus use a sun compass and a mosaic map to find their way home is also discussed.

Dragons in the tropics – Phylogeography and speciation in Diporiphora lizards and common geographic breaks in co-distributed taxa

Co-distributed taxa can respond both similarly or differently to the same climatic and geological events, resulting in a range of phylogeographic patterns across the region. Using a nested approach on a taxonomically diverse yet morphologically conservative group of agamid lizards, we first aimed to evaluate more precisely the extent of phylogeographic structuring within the genus. Then, focusing on four lineages within the more widespread species, we assessed the impact of biogeographic barriers on phylogeographic structuring and demographic history of species, comparing to patterns previously observed in co-distributed taxa. These species occur in the Australian Monsoonal Tropics, a vast tropical savanna system with high richness and endemism associated with environmental heterogeneity and past climate fluctuations. The employment of genomic data helped to determine the relationships between specific taxa that were previously difficult to place. We found a local influence of biogeographic and climatic breaks on population dynamics, analogous to other species. We detected high levels of population structure in the West Kimberley and Arnhem Plateau, which are already known for high endemism. However, we also highlighted unique lineages in areas that have been overlooked until recently, in the South Kimberley and West Top End. Climatic and geographical features in the Arnhem Plateau act as a soft barrier between populations in the east and west regions of the Top End. These observations reflect patterns observed for other vertebrates across this rich biome, indicating how climatic variation, species’ ecology, and landscape features interact to shape regional diversity and endemism.

The role of environmental gradients and microclimates in structuring communities and functional groups of lizards in a rainforest-savanna transition area.

Environmental heterogeneity poses a significant influence on the functional characteristics of species and communities at local scales. Environmental transition zones, such as at the savanna-forest borders, can act as regions of ecological tension when subjected to sharp variations in the microclimate. For ectothermic organisms, such as lizards, environmental temperatures directly influence physiological capabilities, and some species use different thermoregulation strategies that produce varied responses to local climatic conditions, which in turn affect species occurrence and community dynamics. In the context of global warming, these various strategies confer different types of vulnerability as well as risks of extinction. To assess the vulnerability of a species and understand the relationships between environmental variations, thermal tolerance of a species and community structure, lizard communities in forest-savanna transition areas of two national parks in the southwestern Amazon were sampled and their thermal functional traits were characterized. Then, we investigated how community structure and functional thermal variation were shaped by two environmental predictors (i.e., microclimates estimated locally and vegetation structure estimated from remote sensing). It was found that the community structure was more strongly predicted by the canopy surface reflectance values obtained via remote sensing than by microclimate variables. Environmental temperatures were not the most important factor affecting the occurrence of species, and the variations in ecothermal traits demonstrated a pattern within the taxonomic hierarchy at the family level. This pattern may indicate a tendency for evolutionary history to indirectly influence these functional features. Considering the estimates of the thermal tolerance range and warming tolerance, thermoconformer lizards are likely to be more vulnerable and at greater risk of extinction due to global warming than thermoregulators. The latter, more associated with open environments, seem to take advantage of their lower vulnerability and occur in both habitat types across the transition, potentially out-competing and further increasing the risk of extinction and vulnerability of forest-adapted thermoconformer lizards in these transitional areas.

Body size estimation from isolated fossil bones reveals deep time evolutionary trends in North American lizards.

Lizards play vital roles in extant ecosystems. However, their roles in extinct ecosystems are poorly understood because the fossil record of lizards consists mostly of isolated bones. This makes it difficult to document changes in lizard morphology and body size over time, which is essential for studies of lizard paleoecology and evolution. It is also difficult to compare available fossil lizard data with existing sources of extant lizard data because extant studies rarely measure individual bones. Furthermore, no previous study has regressed measurements of individual bones to body length across crown lizard groups, nor tested those regressions on fossil skeletons. An extensive dataset of individual bone measurements from extant lizards across crown taxonomic groups is here employed to develop novel methods for estimating lizard body size from isolated fossil elements. These methods were applied to a comparably large dataset of fossil lizard specimens from the robust Paleogene record (66-23 Ma) of the Western Interior of North America. This study tests the hypothesis that anatomical proportions have been conserved within higher-level crown lizard groups since the Paleogene and can therefore be used to reconstruct snout-vent length (SVL) and mass for fossil specimens referred to the same groups. Individual bones demonstrated strong correlation with SVL in extant as well as fossil lizard specimens (R2 ≥ 0.69). Equations for mass estimation from individual bones were derived from the SVL regressions using published equations for calculating lizard body mass from SVL. The resulting body size estimates from regression equations for the entire fossil dataset revealed that lizards reached greatest maximum body size in the middle Paleogene, with the largest size class dominated by anguid lizards that exceeded 1 meter in SVL and 1.5 kg in body mass. Maximum body size decreased to under 400 mm and below 1.5 kg in the late Paleogene. No association was found between changes in maximum lizard body size and marine isotope proxies of global temperature through the Paleogene. This is the first study to investigate body size evolution across lizard clades over a deep time interval and for a large geographic region. The proposed methods can be used to generate body size regressions and provide estimates of body size for isolated lizard bones referred to any crown group.

Built for success: Distribution, morphology, ecology and life history of the world's skinks.

In animals, the success of particular lineages can be measured in terms of their number of species, the extent of their geographic range, the breadth of their habitats and ecological niches, and the diversity of their morphological and life-history traits. Here, we review the distribution, ecology, morphology and life history of skinks, a diverse lineage of terrestrial vertebrates. We compared key traits between the three subfamilies of skinks, and between skinks and non-scincid lizards. There are currently 1743 described species of skink, which represent 24% of global lizard diversity. Since 2010, 16% of lizard descriptions have been of skinks. The centres of skink diversity are in Australia, New Guinea, southeast Asia, Oceania, Madagascar and central Africa. Compared with non-scincid lizards, skinks have larger distributional ranges, but smaller body sizes. Sexual size dimorphism is rare in skinks. Almost a quarter (23%) of skinks exhibit limb reduction or loss, compared with just 3% of non-scincid lizards. Skinks are more likely to be viviparous (34% of species) compared with non-scincids (13%), and have higher clutch/litter sizes than non-scincids. Although skinks mature later than non-scincids, their longevity is similar to that exhibited by other lizard groups. Most skinks (88%) are active foragers, and they are more likely to be carnivorous than non-scincids. Skinks are more likely to be diurnal or cathemeral than other lizard groups, but they generally have lower field body temperatures compared with non-scincids. The success of skinks appears to be both a result of them hitting upon a winning body plan and ecology, and their capacity to regularly deviate from this body plan and adapt their ecology and life history (e.g. repeated limb reduction and loss, transitions to viviparity) to prevailing conditions.

A new fossil Squamata from the Quiricó Formation (Lower Cretaceous), Sanfranciscana Basin, Minas Gerais, Brazil

The Borioteiioidea (Polyglyphanodontia) is a group of lizards commonly found in Cretaceous Laurasian deposits and is considered as the sister group of Teiidae. While the Asian record comprises several well-preserved skulls and skeletons, other Laurasian occurrences are generally known from disarticulated skull material and isolated teeth. Additionally, the Gondwanan record is rare, with only one species described so far, Bicuspidon hogreli, from the Ifezouane Formation, Kem Kem Beds of Morocco. Given their wide geographic distribution, several biogeographic hypotheses were suggested to explain the temporal and spatial distribution of borioteiioids. In this study, we report the first record of a borioteiioid from the Lower Cretaceous of South America. The specimen was unearthed from Aptian deposits of the Quiricó Formation (Sanfranciscana Basin), Brazil, and consists of both anterior portions of dentaries. Among other characteristics, the material has transversally wide mid-posterior teeth with two distinct cusps (labial and lingual), as typically seen in species of the genus Bicuspidon. It also exhibits additional features, such first mental foramen facing anteriorly and the remaining ones forming a line in the lateral portion of the dentary, anterior symphyseal process extending from the anterior margin of the symphysis, and symphysis bearing an oval-shaped and thick process. These characteristics allowed us to erect a new species of Borioteiioidea, Cryptobicuspidon pachysymphysealis gen. et sp. nov. Cryptobicuspidon pachysymphysealis is one of the oldest records of Borioteiioidea known so far and suggests that Polyglyphanodontini borioteiioids originated in Gondwana with a posterior dispersal to North America and Europe during the Late Cretaceous.

Phylogenomic data reveal cryptic diversity and deep phylogeographical structure within the common chuckwalla, Sauromalus ater (Squamata: Iguanidae)

Abstract Understanding how historical geological processes drive diversification and shape the contemporary distribution of species is fundamental to phylogeography. We take a genomic approach in order to elucidate the deep phylogeographical history and species limits of chuckwallas (Sauromalus), a conspicuous group of lizards of the arid lands of south-western North America. Phylogenetic and population genomic analyses of double digest restriction site-associated DNA sequencing data confirm the presence of at least two major lineages, peninsular and continental groups, within the widespread and morphologically variable common chuckwalla (Sauromalus ater). These lineages diversified in the vicinity of the head of the Gulf of California in north-eastern Baja California in the early Pliocene to late Miocene, during the formation of the northern gulf. The peninsular lineage of S. ater subsequently gave rise to the four insular endemic species of Sauromalus associated with the Baja California peninsula. Genomic analyses strongly support the continued recognition of the insular gigantics Sauromalus varius and Sauromalus hispidus as distinct species, although their relationship as sister species remains unresolved. Weaker phylogenetic signal for the insular species Sauromalus slevini and Sauromalus klauberi is provided by the genomic data; thus, it is advocated to continue recognizing these species until additional data can be analysed to evaluate their distinctiveness.

Ecomorphological correlates of inner ear shape in Australian limb-reduced skinks (Scincidae: Sphenomorphini)

Abstract The inner ear labyrinth is an organ able to perceive balance and spatial orientation, but the drivers of its morphological variation across and within vertebrate lineages are unclear. We assess two competing hypotheses whether this organ, and specifically the semicircular canals, modifies its shape as a functional adaptation to ecology and locomotion, or according to the constraints of skull morphology. We test these using 52 species of Australian sphenomorphines, a group of scincid lizards that evolved changes in body shape and locomotory adaptations to fossoriality multiple times independently, by reducing their limbs. We find a correlation between semicircular canal shape and degree of limb reduction in these lizards, supporting a functional hypothesis. The interaction between body shape and substrate ecology is also a significant predictor. The wider and more eccentric semicircular canals of limb-reduced skinks indicate higher balance sensitivity and manoeuvrability compared with fully limbed skinks, probably as an adaptation to navigating cluttered environments. Conversely, our results show only a minimal influence of skull constraints on semicircular canal shape, having instead significant effects on size. This supports the hypothesis that in these skinks inner ear shape evolution is driven by specific locomotory strategies more than it is constrained by cranial anatomy.

Fixed Allele Differences Associated With the Centromere Reveal Chromosome Morphology and Rearrangements in a Reptile (Varanus acanthurus BOULENGER).

Chromosome rearrangements are often implicated with genomic divergence and are proposed to be associated with species evolution. Rearrangements alter the genomic structure and interfere with homologous recombination by isolating a portion of the genome. Integration of multiplatform next-generation DNA sequencing technologies has enabled putative identification of chromosome rearrangements in many taxa; however, integrating these data sets with cytogenetics is still uncommon beyond model genetic organisms. Therefore, to achieve the ultimate goal for the genomic classification of eukaryotic organisms, physical chromosome mapping remains critical. The ridge-tailed goannas (Varanus acanthurus BOULENGER) are a group of dwarf monitor lizards comprised of several species found throughout northern Australia. These lizards exhibit extreme divergence at both the genic and chromosomal levels. The chromosome polymorphisms are widespread extending across much of their distribution, raising the question if these polymorphisms are homologous within the V. acanthurus complex. We used a combined genomic and cytogenetic approach to test for homology across divergent populations with morphologically similar chromosome rearrangements. We showed that more than one chromosome pair was involved with the widespread rearrangements. This finding provides evidence to support de novo chromosome rearrangements have occurred within populations. These chromosome rearrangements are characterized by fixed allele differences originating in the vicinity of the centromeric region. We then compared this region with several other assembled genomes of reptiles, chicken, and the platypus. We demonstrated that the synteny of genes in Reptilia remains conserved despite centromere repositioning across these taxa.

A Contribution to the Systematics of Sunda Shelf Angle-Headed Dragons (Agamidae: Gonocephalus) with the Description of New Taxa from Sumatra

We review morphology of Sunda Shelf Gonocephalus with an emphasis on Sumatran and Javan species. At least 15 species and subspecies inhabit Peninsular Malaysia, Sumatra, Java, Borneo, and adjacent smaller continental islands. Following analysis of external morphology, we provide a dichotomous key to Sunda Shelf Gonocephalus and resolve two taxonomic problems with this group of lizards. Three populations of Gonocephalus doriae on Borneo, Peninsular Malaysia, and Sumatra are recognized as subspecies, because they lack concordance of multiple morphological differences and have low genetic divergence in a 556 base-pair fragment of the 16S rRNA gene. Described as new herein, G. doriae brevis from Aceh and North Sumatra differs from G. d. abbotti and G. d. doriae in usually having more scales around midbody and a relatively shorter tail with fewer dark bands. Though previously reported as lost, a syntype of G. d. doriae (MSNG 29152) is designated as lectotype, illustrated, and described. Also described as new, G. inauris from high elevations of the Bukit Barisan Range of Bengkulu, Sumatra, is a species of the G. megalepis Group differing from all congeners in having 7/6 (vs. 8–19) loreals separating the last canthal and supralabials, 8/8 (11–27) infraorbitals, and 58 (73–153) scales around midbody. In this new species, distinctly enlarged suboculars broadly contact its supralabials, whereas 1–4 lorilabials separate the suboculars and supralabials in congeners. High genetic divergence in the new species mirrors its high level of morphological divergence.

Revealing anole diversity in the highlands of the Northern Andes: New and resurrected species of the Anolis heterodermus species group

The Anolis heterodermus group comprises eight big-headed and short-legged lizard species from the highlands of the northernmost South American Andes. Recent studies revealed unknown lineages within this group that had previously been categorized as a species complex. By widely sampling and applying an integrative taxonomic framework, we (1) assessed the species diversity of the group using a molecular dataset (two mitochondrial and one nuclear markers) along with an inclusive morphological study (scalation, scale configuration and ornamentation, morphometrics, and dewlap and body colour patterns); and (2) we inferred the evolutionary relationships within this species group. Our analyses confirmed the formerly reported differentiation between populations of those high-altitude lizards, and we identified several unknown evolutionary lineages. Our results provided evidence for the existence of nine distinct, independently evolving evolutionary lineages in the heterodermus group. As a result, we described two morphologically and genetically highly distinct lineages as species new to science (A. quimbayasp. nov. and A. tequendamasp. nov.). We redescribed A. heterodermus and erected as a valid species Anolis richteri, a previously described synonym of A. heterodermus. A taxonomic key for the identification of species of the Phenacosaurus clade was presented. The identification of two additional poorly-known lineages suggested that the diversity of this group of lizards is still unknown; therefore, it is necessary to establish measurements for the group´s conservation, as well as to perform fieldwork and revision of herpetological collections to identify possible hidden diversity within the group.

Characterizing the Annual Reproductive Cycles of Captive Male Veiled Chameleons (Chamaeleo calyptratus) and Panther Chameleons (Furcifer pardalis)

Chameleons represent one of the most endangered groups of lizards, with most being characterized as threatened or near-threatened. Anthropogenic impacts on their native habitat are responsible for their declines. To protect these animals, we must develop functional assisted reproductive programs. However, a full understanding of their basic reproductive biology is required to develop such a program. This study represents the first attempt at characterizing the reproductive cycles of male chameleons. Sixteen veiled chameleons (Chamaeleo calyptratus) and 16 panther chameleons (Furcifer pardalis) being housed in captivity under static conditions were used for this study. Chameleons were anesthetized twice monthly for semen collection via electroejaculation, blood sampling to measure plasma testosterone concentrations, and ultrasonographic testicular measurements. Plasma testosterone concentrations were found to be significantly different between species (P = 0.02) and the interaction of species and month (P = 0.04). In veiled chameleons, plasma testosterone concentrations were significantly elevated during October through December, while for panther chameleons, plasma testosterone concentrations were elevated in July through September, and December. Electroejaculation success was found to be seasonal in both species. In veiled chameleons, semen collection was highest in April, May, and June, while in panther chameleons semen collection success was highest in March, April, May, and June. Median spermatozoa concentrations for veiled and panther chameleons were 6.66 and 7.52 x 107 million sperm/mL, respectively. Motility was lower than expected for both veiled chameleon (median 23%) and panther chameleons (median 25%). Spermatozoa clumping was a common finding. The majority of the spermatozoa (mean 51%) were...

Signal detection shapes ornament allometry in functionally convergent Caribbean Anolis and Southeast Asian Draco lizards.

Visual ornaments have long been assumed to evolve hyper-allometry as an outcome of sexual selection. Yet growing evidence suggests many sexually selected morphologies can exhibit other scaling patterns with body size, including hypo-allometry. The large conspicuous throat fan, or dewlap, of arboreal Caribbean Anolis lizards was one ornament previously thought to conform to the classical expectation of hyper-allometry. We re-evaluated this classic example alongside a second arboreal group of lizards that has also independently evolved a functionally equivalent dewlap, the Southeast Asian Draco lizards. Across multiple closely related species in both genera, the Anolis and Draco dewlaps were either isometric or had hypo-allometric scaling patterns. In the case of the Anolis dewlap, variation in dewlap allometry was predicted by the distance of conspecifics and the light environment in which the dewlap was typically viewed. Signal efficacy, therefore, appears to have driven the evolution of hypo-allometry in what was originally thought to be a sexually selected ornament with hyper-allometry. Our findings suggest that other elaborate morphological structures used in social communication might similarly exhibit isometric or hypo-allometric scaling patterns because of environmental constraints on signal detection.

Environmental temperature predicts resting metabolic rates in tropidurinae lizards.

Interspecific variation in metabolic rates may be associated with climate, habitat structure, and resource availability. Despite a strong link between ecology and physiology, there is a dearth in the understanding of how the costs of body maintenance change during ecological transitions. We focused on an ecologically diverse group of neotropical lizards (Tropidurinae) to investigate whether and how resting metabolic rate (RMR) evolved under divergent micro- and macrohabitat conditions. Using a phylogenetic framework, we tested whether species from hot and dry habitats had lower RMRs in relation to those from cooler and mesic habitats, and investigated whether microhabitat usage had an effect over body mass-adjusted RMRs. Our results suggest that RMRs are not phylogenetically structured in Tropidurinae. We found no correlation between metabolism, precipitation, and microhabitat usage. Species from warmer habitats had lower RMR compared to those from cooler habitats, supporting a mechanism of negative compensation in metabolic responses to temperature. Ectotherms from warmer habitats can limit energetic demand and expenditure through reduced RMR, whereas those from cooler habitats may sustain activity despite thermal constraints via increased RMR. Our work highlights the role of temperature in shaping metabolic responses in lizards, giving additional support to the notion that physiology and ecological contexts are intertwined.

Cryptic extinction risk in a western Pacific lizard radiation

Cryptic ecologies, the Wallacean Shortfall of undocumented species’ geographical ranges and the Linnaean Shortfall of undescribed diversity, are all major barriers to conservation assessment. When these factors overlap with drivers of extinction risk, such as insular distributions, the number of threatened species in a region or clade may be underestimated, a situation we term ‘cryptic extinction risk’. The genus Lepidodactylus is a diverse radiation of insular and arboreal geckos that occurs across the western Pacific. Previous work on Lepidodactylus showed evidence of evolutionary displacement around continental fringes, suggesting an inherent vulnerability to extinction from factors such as competition and predation. We sought to (1) comprehensively review status and threats, (2) estimate the number of undescribed species, and (3) estimate extinction risk in data deficient and candidate species, in Lepidodactylus. From our updated IUCN Red List assessment, 60% of the 58 recognized species are threatened (n = 15) or Data Deficient (n = 21), which is higher than reported for most other lizard groups. Species from the smaller and isolated Pacific islands are of greatest conservation concern, with most either threatened or Data Deficient, and all particularly vulnerable to invasive species. We estimated 32 undescribed candidate species and linear modelling predicted that an additional 18 species, among these and the data deficient species, are threatened with extinction. Focusing efforts to resolve the taxonomy and conservation status of key taxa, especially on small islands in the Pacific, is a high priority for conserving this remarkably diverse, yet poorly understood, lizard fauna. Our data highlight how cryptic ecologies and cryptic diversity combine and lead to significant underestimation of extinction risk.

Sexual Selection in San Cristóbal Lava Lizards (Microlophus bivittatus): A Test of Male Body Size Using Lizard Robots

Intrasexual selection through male competition favoring larger male body size is the preferred explanation for the evolution and maintenance of male-biased sexual size dimorphism among polygynous species. Although sexual selection has been well studied in some groups of lizards, sexual selection in the nine species of lava lizards (Microlophus spp.) of the Galápagos has received little attention. The purpose of this research was to test the importance of male body size in the context of sexual selection by both sexes. Using three different sizes of robotic models capable of emulating the appearance and display patterns of male San Cristóbal Lava Lizards (M. bivittatus), we analyzed the responses that the models elicited among free-ranging lizards of the same sex (confrontation) and opposite sex (courtship). Results showed that body size of both male lizards and robotic antagonists influenced the number of displays performed by males. Male body size positively influenced the number of aggressive responses, scaling with the size of the opponent. The model representing larger lizards received higher display counts from males. Body size of robotic models, but not female lizards, influenced the number of displays performed by females. Females responded the most to the small and large models. Display intensity was not affected by any of the variables considered for either sex. Results from this study support the hypothesis that male-biased sexual size dimorphism in M. bivittatus is driven at least in part by both intrasexual and intersexual selection favoring larger male body size.

Between a rock and a dry place: phylogenomics, biogeography, and systematics of ridge-tailed monitors (Squamata: Varanidae: Varanus acanthurus complex)

Genomic data are a powerful tool for the elucidation of evolutionary patterns at the population level and above. The combined analysis of genomic and morphological data can result in species delimitation hypotheses that reflect evolutionary history better than traditional taxonomy or any individual source of evidence. Here, we used thousands of single nucleotide polymorphisms, mitochondrial sequences, and comprehensive morphological data to characterize the evolutionary history of the ridge-tailed monitors in the Varanus acanthurus complex (V. acanthurus, V. baritji, and V. storri), a group of saxicolous lizards with a wide distribution in Australia, the driest vegetated continent. We found substantial genetic structure in the group and identify nine geographically clustered populations. Based on admixture patterns and species delimitation analyses we propose a taxonomic scheme that differs from current taxonomy. We consider V. acanthurus as monotypic, synonymize V. baritji with V. a. insulanicus (as a redefined V. insulanicus), elevate the subspecies of V. storri to full species (V. storri and V. ocreatus), and describe a new species from a previously identified center of endemism. The relationships among the species remain unresolved, likely as a result of fast speciation. Our study highlights the capability of large datasets to illuminate admixture patterns, biogeographic history, and species limits, even when phylogeny is not completely resolved. Furthermore, our results highlight the impact that the Cenozoic aridification of Australia had on saxicolous taxa and the role of mesic rocky escarpments as refugia. These habitats apparently allowed the persistence of lineages that became sources of colonization for arid environments.