Littérature scientifique sur le sujet « Lygosoma »

AbstractThe genera Lepidothyris, Lygosoma and Mochlus comprise the writhing or supple skinks, a group of semi-fossorial, elongate-bodied skinks distributed across the Old World Tropics. Due to their generalized morphology and lack of diagnostic characters, species- and clade-level relationships have long been debated. Recent molecular phylogenetic studies of the group have provided some clarification of species-level relationships, but a number of issues regarding higher level relationships among genera still remain. Here we present a phylogenetic estimate of relationships among species in Lygosoma, Mochlus and Lepidothyris generated by concatenated and species tree analyses of multilocus data using the most extensive taxonomic sampling of the group to date. We also use multivariate statistics to examine species and clade distributions in morpho space. Our results reject the monophyly of Lygosoma s.l., Lygosoma s.s. and Mochlus, which highlights the instability of the current taxonomic classification of the group. We, therefore, revise the taxonomy of the writhing skinks to better reflect the evolutionary history of Lygosoma s.l. by restricting Lygosoma for Southeast Asia, resurrecting the genus Riopa for a clade of Indian and Southeast Asian species, expanding the genus Mochlus to include all African species of writhing skinks and describing a new genus in Southeast Asia.

The type series of Lygosoma melanopogon Duméril and Bibron 1839, the type species of the scincid lizard genusSphenomorphus Fitzinger 1843, consists of four specimens representing three species, all of which have available juniorsynonyms. A lectotype is designated, and Lygosoma melanopogon becomes a senior synonym of Lygosoma florenseWeber 1891 (= Sphenomorphus florensis) and that species is redefined based on specimens from throughout itsdistribution for the first time. Based on a lack of consistent differences in morphology and coloration, previously namedsubspecies of Sphenomorphus florensis are placed in synonymy, leaving a single wide-ranging species S. melanopogon.Lygosoma Kühnei Roux 1910 is also placed in the synonymy of S. melanopogon, and the nomenclatural status of the nameScincus naevius Duméril and Bibron 1839 resolved. Lygosoma Meyeri Doria 1874 is raised from synonymy to becomethe name for the New Guinean Sphenomorphus species to which the name S. melanopogon has sometimes previously beenapplied, and Hinulia papuensis Macleay 1877 synonymised with it. Sphenomorphus melanopogon is identified as amember of a group of Sphenomorphus species which show an extension of the imbricate dorsal scalation onto the solar surface of the pes.

The genus Lygosoma Hardwicke & Gray, 1827 is a group of semi-fossorial supple skink from Southeast Asia, the members of which are still understudied in Indochina. Lysosoma quadrupes (Linnaeus, 1766) was once recorded from China based on historical literature; until recent its Indochina specimens were revised and placed into a newly described species, i.e., L. siamense Siler, Heitz, Davis, Freitas, Aowphol, Termprayoon & Grismer, 2018. However, Lygosoma quadrupes had long been unknown from China but the historical record had not been confirmed. Here we report a vouchered record for L. siamense from China for the first time based on four specimens collected in Sanya, Hainan, China. Furthermore, the taxonomic history of Lygosoma from China is also reviewed.

We collected two specimens of an undescribed species of Lygosoma from pitfall traps in an urban rainforest in Kuching and from the base of a forested hill in western Sarawak, East Malaysia. The new species is diagnosable from all south-east Asian congeners by morphological characters, and most closely resembles Lygosoma herberti from the Thai-Malay Peninsula. The new species shows substantial molecular divergence from its closest relatives in two protein-coding genes, one mitochondrial (ND1) and one nuclear (R35) that we sequenced for several south-east Asian congeners. We describe the new species on the basis of this distinct morphology and genetic divergence. It is the third species of Lygosoma known from Borneo, and highlights the continuing rise in lizard species diversity on the island. In addition, the discovery of this species from a small urban rainforest underscores the importance of preserving intact rainforest areas of any size in maintaining species diversity.

The species Lygosoma (Keneuxia) dubium was described by Franz Werner (1909) based on a single specimen from the Royal Natural History Cabinet (Königliches Naturalienkabinett) in Stuttgart, collection number 3651. According to the original description the specimen was collected by “Direktor Mayer” in Yokohama, Japan in 1897. Much later Nakamura & Ueno (1963) transferred the species to the Genus Dasia Gray, 1839, without further comments. Recently Uetz et al. (2018) questioned the type locality given by Werner (1909) and suggested that the name Lygosoma dubium is likely to be a synonym of Dasia grisea (Gray, 1845) referring to a personal comment of T. Hikida in 2014. However the actual taxonomic status of the species still remains unresolved.

We describe a new species of the genus Lygosoma from northeastern Cambodia based on a single voucher specimen col-lected from Veun Sai Proposed Protected Forest, Veun Sai District, Ratanakiri Province. Lygosoma veunsaiensis sp. nov.is differentiated from all congeners occurring in mainland Southeast Asia by the combination of the following characters:outer ear opening absent; supranasals distinct and separated from each other by frontonasal; supranasals not fused withnasals; midbody scales in 22 rows; fontoparietals paired; five supralabials; a light stripe present on outer edge of the dor-sum; and a dark dorsolateral stripe present, from behind the eye to the tail. A key to the Southeast Asian mainland species of Lygoma is provided.

Three newly recorded localities for Lygosoma haroldyoungi (Taylor, 1962) in Thailand are presented, which represent first sightings for Khon Kaen, Sakhon Nakhon and Mukdaharn provinces. An updated compilation of the known geographical distribution of L. haroldyoungi is provided.

Lankascincus dorsicatenatus is an endemic species of litter-skink distributed throughout the wet zone of Sri Lanka (elevations from 15 to 800 m a.s.l.). The recent resurrection of Lygosoma megalops by the recent description of its neotype designated by Batuwita (2019), presently lost, destabilized the taxonomic status of Lankascincus dorsicatenatus. Amarasinghe et al. (2022) synonymized Lygosoma megalops with Lankascincus fallax, and accepted Lankascincus dorsicatenatus as a valid taxon. Deraniyagala (1953) described Sphenomorphus dorsicatenatus based on a holotype and three paratypes. All the types are lost except one paratype at the National Museum of Sri Lanka, Colombo, Sri Lanka (NMSL), but it is in bad condition. Therefore, with a comparative discussion on the status of ‘Lankascincus megalops‘, here we designate a neotype for Lankascincus dorsicatenatus for clarification of the taxonomic status and stabilize the nomen. A discussion on the distribution and conservation of Lankascincus dorsicatenatus is also provided.

The White-spotted Skink Lygosoma albopunctatum, a rarely recorded lizard, has been re-sighted from its type locality: Madras in the Coromandel Coastal Plains. Morphological details and field notes on the findings are elaborated. Since many past surveys in and around Madras, and in southern India generally, did not record this species, lack of consensus about its existence in southern India had developed, leading to published misconceptions about its distribution. These are highlighted and corrected herein. The species is also illustrated in life based on topotypical examples.

In this thesis, I investigate the phylogeny and evolution of Lerista, a clade of more than 75 species of scincid lizards, distributed in arid, semi-arid, and seasonally dry habitats throughout Australia. Among extant tetrapods, Lerista is exceptional in comprising a large number of closely-related species displaying prodigious variability of body form; several species possessing well-developed, pentadactyl limbs resemble typical non-fossorial scincids in body proportions, while many other species exhibit varying degrees of limb reduction and body elongation, including two that are highly elongate and entirely limbless. The extensive variation in limb morphology observed among species, incorporating at least 20 distinct phalangeal configurations, has prompted some authors to identify Lerista as the best available model for studying limb reduction in squamates. Nonetheless, lack of a well-resolved phylogeny has impeded investigation of the pattern and mode of limb reduction and loss within the clade. The primary goal of my research was to furnish a comprehensive phylogenetic hypothesis for Lerista, enabling more sophisticated study of the evolution of limb morphology and body form in this clade than has previously been possible. A recent phylogenetic analysis of mitochondrial DNA sequences for a series of Australian Sphenomorphus group scincids (including two species of Lerista) recovered several well-supported, major clades, although these were generally separated by relatively short branches associated with low support values. Applying a recently described methodology for inferring lineage-level polytomies, I use ATP synthetase-β subunit intron sequences and the existing mitochondrial DNA data set (with sequences for additional taxa) to assess the hypothesis that the poorly resolved basal relationships within the Australian Sphenomorphus group are a consequence of the major clades having originated essentially simultaneously. Phylogenetic analyses of the separate mitochondrial DNA and intron sequence data reveal a number of congruent clades, however, the relationships among these clades indicated by the two data sets are generally incongruent. Although this may be partly ascribed in to error in estimating phylogenetic relationships due to insufficient data, some incongruence is evident when uncertainty in inferred relationships is allowed for. Moreover, the congruent clades are typically separated by very short branches, several having a length insignificantly different from zero. These results suggest that initial diversification of Australian Sphenomorphus group scincids was rapid relative to the substitution rates of the mitochondrial DNA and intron fragments considered, if not essentially simultaneous. The pattern and rate of limb reduction in Lerista are investigated, employing a nearly complete phylogeny inferred from nucleotide sequences for a nuclear intron and six mitochondrial genes. Ancestral digit configurations reconstructed assuming this phylogeny indicate at least ten independent reductions in the number of digits from a pentadactyl condition, including four independent losses of all digits, three from pentadactyl or tetradactyl conditions. At the highest rate, complete loss of digits from a pentadactyl condition is estimated to have occurred within no more than 3.6 million years. Patterns of digit loss for the manus and pes are consistent with selection for preserving hindlimb utility as the limbs are reduced, and suggest that intermediate digit configurations exhibited by extant species do not represent transitory stages in a continuing process of limb reduction. An increase in the relative length of the body is demonstrated to precede digit loss in lineages experiencing substantial reduction of the limbs, supporting the hypothesis that limb reduction and loss is a consequence of the adoption of lateral undulation as a significant locomotory mode. However, less extensive limb reduction may proceed in the absence of body elongation, perhaps due to a decrease in absolute body size. The exceptionally high frequency and rate of limb reduction in Lerista emphasise the potential for rapid and dramatic evolutionary transformation of body form in squamates. The substantial divergence of relative limb and body length evident within Lerista is more readily explained by the correlated progression model of phenotypic transformation than the independent blocks model. At each step in the attainment of a limb-reduced, elongate body form, alterations to the relative length of the limbs are accompanied by changes in relative snout-vent length (or vice versa) enabling the maintenance of locomotory ability. Nonetheless, some dissociation of hindlimb reduction and body elongation is possible, emphasising the potentially variable intensity of functional constraints and, accordingly, that the independent blocks model and correlated progression are extremes of a continuum of models (each invoking a different degree of functional integration) and do not describe discrete categories of phenotypic change. An increase in the extent of seasonally dry and arid habitats coincident with the origination of Lerista would have facilitated limb reduction and body elongation by furnishing an environment conducive to the adoption of fossorial habits, however, trends toward a limbless, highly elongate body form may be attributed primarily to the very low probability of re-elaborating reduced limbs. Such asymmetry in the probabilities of possible phenotypic changes may be a significant cause of evolutionary trends resulting in the emergence of higher taxa.
Thesis (Ph.D.) -- University of Adelaide, School of Earth and Environmental Sciences, 2008

In this thesis, I investigate the phylogeny and evolution of Lerista, a clade of more than 75 species of scincid lizards, distributed in arid, semi-arid, and seasonally dry habitats throughout Australia. Among extant tetrapods, Lerista is exceptional in comprising a large number of closely-related species displaying prodigious variability of body form; several species possessing well-developed, pentadactyl limbs resemble typical non-fossorial scincids in body proportions, while many other species exhibit varying degrees of limb reduction and body elongation, including two that are highly elongate and entirely limbless. The extensive variation in limb morphology observed among species, incorporating at least 20 distinct phalangeal configurations, has prompted some authors to identify Lerista as the best available model for studying limb reduction in squamates. Nonetheless, lack of a well-resolved phylogeny has impeded investigation of the pattern and mode of limb reduction and loss within the clade. The primary goal of my research was to furnish a comprehensive phylogenetic hypothesis for Lerista, enabling more sophisticated study of the evolution of limb morphology and body form in this clade than has previously been possible. A recent phylogenetic analysis of mitochondrial DNA sequences for a series of Australian Sphenomorphus group scincids (including two species of Lerista) recovered several well-supported, major clades, although these were generally separated by relatively short branches associated with low support values. Applying a recently described methodology for inferring lineage-level polytomies, I use ATP synthetase-β subunit intron sequences and the existing mitochondrial DNA data set (with sequences for additional taxa) to assess the hypothesis that the poorly resolved basal relationships within the Australian Sphenomorphus group are a consequence of the major clades having originated essentially simultaneously. Phylogenetic analyses of the separate mitochondrial DNA and intron sequence data reveal a number of congruent clades, however, the relationships among these clades indicated by the two data sets are generally incongruent. Although this may be partly ascribed in to error in estimating phylogenetic relationships due to insufficient data, some incongruence is evident when uncertainty in inferred relationships is allowed for. Moreover, the congruent clades are typically separated by very short branches, several having a length insignificantly different from zero. These results suggest that initial diversification of Australian Sphenomorphus group scincids was rapid relative to the substitution rates of the mitochondrial DNA and intron fragments considered, if not essentially simultaneous. The pattern and rate of limb reduction in Lerista are investigated, employing a nearly complete phylogeny inferred from nucleotide sequences for a nuclear intron and six mitochondrial genes. Ancestral digit configurations reconstructed assuming this phylogeny indicate at least ten independent reductions in the number of digits from a pentadactyl condition, including four independent losses of all digits, three from pentadactyl or tetradactyl conditions. At the highest rate, complete loss of digits from a pentadactyl condition is estimated to have occurred within no more than 3.6 million years. Patterns of digit loss for the manus and pes are consistent with selection for preserving hindlimb utility as the limbs are reduced, and suggest that intermediate digit configurations exhibited by extant species do not represent transitory stages in a continuing process of limb reduction. An increase in the relative length of the body is demonstrated to precede digit loss in lineages experiencing substantial reduction of the limbs, supporting the hypothesis that limb reduction and loss is a consequence of the adoption of lateral undulation as a significant locomotory mode. However, less extensive limb reduction may proceed in the absence of body elongation, perhaps due to a decrease in absolute body size. The exceptionally high frequency and rate of limb reduction in Lerista emphasise the potential for rapid and dramatic evolutionary transformation of body form in squamates. The substantial divergence of relative limb and body length evident within Lerista is more readily explained by the correlated progression model of phenotypic transformation than the independent blocks model. At each step in the attainment of a limb-reduced, elongate body form, alterations to the relative length of the limbs are accompanied by changes in relative snout-vent length (or vice versa) enabling the maintenance of locomotory ability. Nonetheless, some dissociation of hindlimb reduction and body elongation is possible, emphasising the potentially variable intensity of functional constraints and, accordingly, that the independent blocks model and correlated progression are extremes of a continuum of models (each invoking a different degree of functional integration) and do not describe discrete categories of phenotypic change. An increase in the extent of seasonally dry and arid habitats coincident with the origination of Lerista would have facilitated limb reduction and body elongation by furnishing an environment conducive to the adoption of fossorial habits, however, trends toward a limbless, highly elongate body form may be attributed primarily to the very low probability of re-elaborating reduced limbs. Such asymmetry in the probabilities of possible phenotypic changes may be a significant cause of evolutionary trends resulting in the emergence of higher taxa.
Thesis (Ph.D.) -- University of Adelaide, School of Earth and Environmental Sciences, 2008