Range-wide phylogeography of a temperate lizard, the five-lined skink (Eumeces fasciatus)

We used mitochondrial DNA and microsatellite loci to examine the phylogeographic patterns of the most broadly distributed lizard in eastern North America, the five-lined skink (Eumeces fasciatus). We infer that longitudinal phylogeographic patterns in E. fasciatus are consistent with fragmentation due to refugial and post-glacial dynamics, but that deep divergences within the species imply historical fragmentation that predates the Pleistocene. The effect of multiple refugia is implied from our nested clade analyses, including a northern refugium in Wisconsin. Analysis of population structure using nuclear microsatellite data within the species suggests the importance of glacial dynamics in shaping more recent genetic structuring within one widely distributed lineage that ranges from the Mississippi River to the Atlantic Ocean in longitude and from southern Ontario to the Gulf of Mexico in latitude. Results shed light on the historical processes that have influenced current population structure of a temperate lizard, support the striking similarity of longitudinal phylogeographic structure across many herpetofaunal species in eastern North America, and illustrate the utility of employing multiple markers in phylogeographic studies.     

Placentation in the lizard Gerrhonotus coeruleus with a comparison to the extraembryonic membranes of the oviparous Gerrhonotus multicarinatus (Sauria,Anguidae)

Paraffin sections of an ontogenetic series of embryos of the viviparous lizard Gerrhonotus coeruleus and the oviparous congener G. multicarinatus reveal that although general features of the development of the chorioallantoic and yolk sac membranes are similar, differences are evident in the distribution of the chorioallantoic membrane in late stage embryos. An acellular shell membrane surrounds the egg throughout gestation in both species although the thickness of this structure is much reduced in G. coeruleus over that of G. multicarinatus. The initial vascular membrane to contact the shell membrane in both species is a trilaminar omphalopleure (choriovitelline membrane) composed of ectoderm, mesoderm of the area vasculosa, and endoderm. This transitory membrane is replaced by the vascularized chorioallantois as the allantois expands to contact the inner surface of the chorion. Prior to the establishment of the chorioallantois at the embryonic pole, a membrane begins to form within the yolk ventral to the sinus terminalis. This membrane, which becomes vascularized, extends across the entire width of the abembryonic region and isolates a mass of yolk ventral to the yolk mass proper. The outer membrane of the yolk pole is a nonvascular bilaminar omphalopleure (chorionic ectoderm and yolk endoderm). In G. multicarinatus the bilaminar omphalopleure is supported internally by the vascularized allantoic membrane, whereas in G. coeruleus the allantois does not extend beyond the margin of the isolated yolk mass and the bilaminar omphalopleure is supported by the vascularized intravitelline membrane. Both the chorioallantoic placenta (uterine epithelium, chorionic ectoderm and mesoderm, and allantoic mesoderm and endoderm) and the yolk sac placenta at the abembryonic pole (uterine epithelium, chorionic ectoderm, and yolk sac endoderm) persist to the end of gestation in G. coeruleus.     

Morphogenesis of extraembryonic membranes and placentation in Mabuya mabouya (Squamata, Scincidae)

Topological and histological analyses of Mabuya mabouya embryos at different developmental stages showed an extraembryonic membrane sequence as follows: a bilaminar omphalopleure and progressive mesodermal expansion around the whole yolk sac at gastrula stages; mesodermal split and formation of an exocoelom in the entire embryonic chamber at neurula stages; beginning of the expansion of the allantois into the exocoelom to form a chorioallantoic membrane at pharyngula stages; complete extension of the allantois into the exocoelom between limb-bud to preparturition stages. Thus, a placental sequence could be enumerated: bilaminar yolk sac placenta; chorioplacenta; allantoplacenta. All placentas are highly specialized for nutrient absorption from early developmental stages. The bistratified extraembryonic ectoderm possesses an external layer with cuboidal cells and a microvillar surface around the whole yolk sac, which absorbs uterine secretions during development of the bilaminar yolk sac placenta and chorioplacenta. During gastrulation, with mesodermal expansion a dorsal absorptive plaque forms above the embryo and several smaller absorptive plaques develop antimesometrially. Both structures are similar histologically and are active in histotrophic transfer from gastrula stages until the end of development. The dorsal absorptive plaque will constitute the placentome and paraplacentome during allantoplacental development. At late gastrula-early neurula stages some absorptive plaques form chorionic concavities or chorionic bags that are penetrated by a long uterine fold and seem to have a specialized histotrophic and/or metabolic role. The extraembryonic mesoderm does not ingress into the yolk sac and neither an isolated yolk mass nor a yolk cleft are formed. This derived pattern of development may be related to the drastic reduction of the egg size and obligatory placentotrophy from early developmental stages. Our results show new specialized placentotrophic structures and a novel arrangement of extraembryonic membrane morphogenesis for Squamata.     

Morphogenesis of placental membranes in the viviparous,placentotrophic lizard Chalcides chalcides (Squamata: Scincidae)

In the scincid lizard Chalcides chalcides, females ovulate small ova and supply most of the nutrients for development by placental means. The yolk is enveloped precocially by extraembryonic ectoderm and endoderm during the gastrula stage, establishing a simple bilaminar yolk sac placenta. The shell membrane begins to degenerate at this time, resulting in apposition of extraembryonic and maternal tissues. A true chorioplacenta has developed by the early pharyngula stage, as has a choriovitelline placenta and the first stages of an omphaloplacenta. Although the choriovitelline membrane disappears rapidly, the omphaloplacenta spreads to occupy the entire abembryonic pole. The yolk cleft is not confluent with the exocoelom, and no omphalallantoic placenta develops. By the limb-bud stage, an allantoplacenta has been established, with a mesometrial placentome composed of interdigitating ridges of chorioallantois and uterine mucosa. The discovery of five distinct placental arrangements in this species, three of which are transitory and two of which have not previously been recorded in reptiles, emphasizes the need for accounts that specify ontogenetic stages and the precise identity and composition of squamate placental membranes. Contrary to previous interpretations, the pattern of extraembryonic membrane development in C. chalcides is evolutionarily conservative, despite the presence of a reduced yolk mass and cytological specializations for nutrient transfer. Our observations indicate that substantial placentotrophy can evolve in squamates without major modifications of morphogenetic patterns. J Morphol 232:35–55, 1997. © 1997 Wiley-Liss, Inc.     

Ultrastructural studies of normal and alloxan-treated islet cells of the pancreas of the lizard, Eumeces fasciatus

Alpha and beta cells can be distinguished by differences in mitochondrial and secretion granule structure. Many mitochondria of alpha cells possess “tubular” or prismatic cristae oriented longitudinally and having triangular profiles in cross-section. The matrix is particulate, with the roughly spherical particles measuring about 100 A in diameter. Evidence is presented indicating that alpha and beta granules are sequestrated in association with Golgi elements. Fully-condensed beta granules, assumed to be insulin, appear homogeneously dense and crystalline. Recurrent profiles of crystalline beta granules suggest that they possess an octahedral configuration. Alpha cell granules also appear homogeneously dense but have round profiles. Many acinar cell nuclei in both normal and alloxan-treated pancreata display masses of moderately dense fibrils oriented roughly parallel to each other. These fibrils are about 200 A across and their terminal portions are rebranched and often appear to be continuous with the finely granular or filamentous component of the nucleoplasm. Not infrequently the fibrils show evidence of periodicity. Alloxan has a specific destructive effect on beta cells. An initial effect seems to be the disruption and coalescence of the bounding membranes of beta granules. Lysosome-like bodies are often seen in beta cell cytoplasm, which ultimately becomes degranulated and necrotic following prolonged administration of large doses of alloxan.     

Uterine morphology during the annual cycle in Chalcides ocellatus tiligugu (Gmelin) (Squamata: scincidae)

The uterus of the viviparous skink Chalcides ocellatus tiligugu was studied by SEM and LM during the annual cycle. Three functional phases were identified: preovulatory (spring), gestatory (summer), and quiescent (autumn-winter), characterized by changes in the uterine wall (mainly the endometrial layer). In the preovulatory phase, the uterine wall increases in thickness; its luminal epithelium has ciliated cells and two types of unciliated secretory cells. The first type secretes sulfated glycosaminoglycans (GAGs), which form the amorphous inner layer of the eggshell membrane; the second type secretes acidic glycoproteins that form the intrafibrillar matrix of the outer layer of the eggshell membrane. The lamina propria contains simple alveolar glands that secrete the collagen fibers of the eggshell membrane. During the gestatory phase, the glycoproteins produced by secretory cells of the second type have histotrophic activity for the developing embryo. The uterus widens to form incubation chambers with two hemispheres, one embryonic and the other abembryonic. Both a chorioallantoic placenta and an omphaloplacenta with histotrophic activity are present in late gestation. The chorioallantoic placenta, with aspects of a Weekes (1935) Type III placenta, develops in the embryonic hemisphere. The omphaloplacenta forms at the vegetative pole of the egg and shows cellular hypertrophy of the bilaminar omphalopleure and uterus. During the quiescent phase, the uterus gradually decreases in thickness and activity; its luminal epithelium does not show secretory activity. The annual variations in the myometrial layer involved the inner circular and the outer longitudinal muscle layers.     

Genetic variation and differentiation in the Japanese five-lined skink,Eumeces latiscutatus (Reptilia: Squamata)

The genetic variation in Eumeces latiscutatus from the main islands of Japan and the northern Ryukyus was investigated and compared with that of its close relatives (E. okadae and E. marginatus) using allozyme data. All three samples from the northern Tokara Island Group, currently identified as E. latiscutatus, were shown to belong to E. marginatus and not to E. latiscutatus. The non-monophyly of the northern Tokara samples and the great genetic differences within these samples may have resulted from colonization from more than one source population by northeastward overseas dispersal. The samples from the Izu Peninsula were genetically much closer to E. okadae than the other conspecific ones. This indicates that the samples from the Izu Peninsula and the other samples of E. latiscutatus should be treated as distinct species, and that E. latiscutatus from the Izu Peninsula and E. okadae from the Izu Island Group may be treated as conspecific. Samples from western Japan were genetically well differentiated from those of eastern Japan. Within the western group, the samples from the Osumi Island Group was genetically distinct from those from the other regions, by possessing unique alleles. Our phenograms also reveal a distant affinity between samples from the Danjo Island Group and the main islands of Japan. This may be the result of long geographic isolation of the Osumi and Danjo Island Groups from Kyushu. By contrast, samples from Sapporo and Aomori were poorly differentiated genetically in spite of the long separation of these two localities by the Tsugaru Strait. This suggests that overseas dispersal of E. latiscutatus occurred across this strait after its formation.     

Interspecific odour discrimination by a lizard (Eumeces laticeps)

When presented with odours on cotton swabs, adult borad-headed skinks (Eumeces laticeps) of both sexes flicked their tongues at much higher rates to conspecific odour stimuli than to those of their most closely related congeners, E. fasciatus and E. inexpectatus, during 60-s exposures to cloacal odours from lizards of the opposite sex. A successive discrimination design was used in which each lizard responded to five different odour treatments in a random sequence. In addition to the three lizard odours, water was used as a measure of baseline tongue protrusion rates and a cologne was used as a pungency control. There were no significant differences among the four non-conspecific odour treatments in numbers of tongue flicks elicited, but the skinks emitted significantly greater numbers of tongue flicks to conspecific cloacal odours than to any of the other stimuli. It is hypothesized that E. laticeps produces a pheromone which may function for species identification. Although it is tempting to speculate that the pheromone may serve as a pre-mating mechanism for maintaining reproductive isolation from syntopic congeners, insufficient information is avialable to draw firm conclusions regarding such a function.     

Histology of the extraembryonic membranes of an oviparous snake: towards a reconstruction of basal squamate patterns

An understanding of the evolutionary morphology of extraembryonic membranes in reptiles requires information about oviparous as well as viviparous species. We are studying histology and ultrastructure of the extraembryonic membranes of snakes to clarify the evolutionary history of reptilian fetal membranes, including determination of basal (ancestral) ophidian and squamate patterns. Microscopic anatomy of the membranes of oviparous corn snakes (Elaphe guttata) was examined using light and electron microscopy. At mid-development the inner surface of the eggshell is lined by two extraembryonic membranes, the chorioallantois and the omphalallantoic membrane. The chorioallantois consists of a bilayered cuboidal epithelium that overlies the allantoic blood vessels. During development, allantoic capillaries become more abundant, and the chorionic epithelium thins, decreasing the diffusion distance for respiratory gas exchange. The abembryonic pole of the egg is delimited by a bilaminar omphalopleure and isolated yolk mass, the latter of which is lined on its inner face by the allantois. The isolated yolk mass regresses developmentally, and patches of yolk droplets become isolated and surrounded by allantoic blood vessels. By late development, the abembryonic hemisphere has been fully vascularized by allantoic vessels, forming a "secondary chorioallantois." With regard to its extraembryonic membranes, Elaphe gutatta is similar to viviparous snakes. However, this species exhibits features that have not previously been reported among squamates, perhaps reflecting its oviparous reproductive habits. Morphological evidence for the uptake of eggshell material by epithelia of the chorion and omphalopleure suggests that the potential for absorption by extraembryonic membranes predates the origin of viviparity.     

Placental ontogeny of the Tasmanian scincid lizard, Niveoscincus ocellatus (Reptilia: Squamata)

A prominent scenario for the evolution of reptilian placentation infers that placentotrophy arose by gradual modification of a simple vascular chorioallantoic placenta to a complex structure with a specialized region for nutrient transfer. The structure of the chorioallantoic placenta of Niveoscincus ocellatus, apparently described originally from a single embryonic stage, was interpreted as a transitional evolutionary type that provided support for the model. Recently, N. ocellatus has been found to be as placentotrophic as species with complex chorioallantoic placentae containing a specialized region called a placentome. We studied placental development in N. ocellatus and confirmed that the chorioallantoic placenta lacks specializations found in species with a placentome. We also found that this species has a specialized omphaloplacenta. The chorioallantoic placenta is confined to the region adjacent to the embryo by a membrane, similar to that found in some other viviparous skinks, that divides the egg into embryonic and abembryonic hemispheres. We term this structure the "inter-omphalopleuric" membrane. The position of this membrane in N. ocellatus is closer to the embryonic pole of the egg than to the abembryonic pole and thus the surface area of the omphaloplacenta is greater than that of the chorioallantoic placenta. In addition, the omphaloplacenta is regionally diversified and more complex histologically than the chorioallantoic placenta. An impressive and unusual feature of the omphaloplacenta of N. ocellatus is the development of extensive overlapping folds in the embryonic component of mid-gestation embryos. The histological complexity and extensive folding of the omphaloplacenta make this a likely site of placental transfer of nutrients in this species.     

Microsatellite loci from the five‐lined skink (Eumeces fasciatus)

The geographical range of the five‐lined skink is the most expansive of any eastern North American lizard, ranging from previously glaciated southern Canada southward to the Gulf of Mexico and from the Atlantic seaboard west to Texas and Minnesota. The most northerly populations occur in southern Ontario and are of conservation concern. We developed six polymorphic dinucleotide microsatellite loci to examine the genetic structure within and among Ontario's populations and to examine the intrapopulation levels of genetic diversity relative to more southern populations.     

Ontogeny, anatomy and attachment of the dentition in mosasaurs (Mosasauridae: Squamata)

Aspects of mosasaur dental ontogeny are well preserved in many fossils of these giant marine squamates. Replacement teeth on the tooth-bearing elements (TBEs) first appear as small enamel crowns positioned posterolingual to the attached tooth (posterolabial for the pterygoid). Several developing crowns, of progressively larger size, are aligned in rows relating to a specific tooth position. The crowns rest in a dental groove that varies in width and depth depending on the TBE. The crown closest to the attached tooth is always the largest and is found in a small resorption pit. As resorption proceeds, the pit expands in volume (cementum and alveolar bone), and the crown increases in size and settles into the pit. Once mature crown size is achieved, the dentine root and cementum portion of the root develop rapidly, the attached tooth is lost and the replacement tooth erupts out of the alveolus. Mosasaurid teeth develop along a 'zig-zag'-shaped movement path: horizontally along the dental groove, down into the alveolus, and up and out of the alveolus prior to attachment to the alveolar wall. At no point in mosasaurid tooth development are the crowns observed in a horizontal position. The mosasaurid dental lamina appears to have been a continuous strip of dental epithelium as it is in other squamates. Mosasaurid tooth attachment is thecodont (histologically and geometrically) not subpleurodont. Most aspects of mosasaurid tooth attachment and ontogeny are autapomorphic for the group.  © 2007 The Linnean Society of London, Zoological Journal of the Linnean Society , 2007, 149 , 687–700.     

Placentation in the Mexican lizard Sceloporus mucronatus (Squamata: Phrynosomatidae)

We used light microscopy to study placental structure of the lizard Sceloporus mucronatus throughout 6 months of embryonic development. Three stages of placental development could be assigned to embryos based on the arrangement of the extraembryonic membranes. A highly vascular choriovitelline placenta was present in the embryonic hemisphere and a nonvascular bilaminar omphalopleure covered most of the abembryonic hemisphere of the egg during embryonic Stages 10-28. A chorioallantoic placenta replaced the choriovitelline placenta by embryonic Stage 29 and an omphaloplacenta covered the abembryonic hemisphere at this stage. The combination of these two placental types occurred in Stage 29-36 embryos. The final stage of placentation, embryonic Stages 37-40, was characterized by an omphalallantoic placenta in the abembryonic hemisphere and a chorioallantoic placenta in the embryonic hemisphere of the egg. The choriovitelline and chorioallantoic placentae are well vascularized, with closely apposed maternal and embryonic blood vessels. These structures are the most likely sites of respiratory exchange. In contrast, the omphaloplacenta and omphalallantoic placentae contain cuboidal or columnar epithelia and these structures may function in histotrophic exchange. Placentation of S. mucronatus is similar to that of predominantly lecithotrophic species in other squamate lineages suggesting that the evolution of this placental morphology is a response to similar factors and is independent of phylogeny.     

Karyotype of the lizard Eumeces taeniolatus]

Using bone marrow cell preparations, the karyotype of Eumeces taeniolatus Blyth was examined. The diploid chromosome set of E. taeniolatus is found equal to 28 (24 meta- and 4 submetacentrics), NF=56. Sex chromosomes do not differ morphologically.     

Polymorphic microsatellite markers for the lizard Psammodromus algirus (Squamata: Lacertidae)

Eight microsatellite loci are described for the lizard Psammodromus algirus, a species widely used as a model in behavioural and ecological studies. All loci were highly polymorphic (six alleles or more per locus) in a sample of 24 individuals from a single site near Navacerrada (central Spain). Observed heterozygosity ranged from 0.29 to 0.96. These markers will be used to study mating strategies and determinants of reproductive success in this species.     

A tiny lizard (Lepidosauria,Squamata) from the Lower Cretaceous of Spain

Abstract: The smallest living amniotes are all lizards, but the fossil history of this size trait in Squamata is difficult to follow because small skeletons have low preservation potential and are often hard to detect in the field. A new squamate taxon, Jucaraseps grandipes gen. et sp. nov., is here described on the basis of an articulated skeleton from the Early Cretaceous Spanish lagerstätten of Las Hoyas. It differs from other known Mesozoic lizards in combining very small body size with a short rostrum, low maxillary tooth count, a relatively slender and elongated body, and short limbs with large hind feet. Phylogenetic analysis using TNT places it on the stem of a clade encompassing scincomorphs, gekkotans, snakes, amphisbaenians and anguimorphs. Comparison with modern lizards suggests it was probably a cryptic surface or subsurface ground dweller but not a burrower.