Soft-tissue evidence for homeothermy and crypsis in a Jurassic ichthyosaur.

Ichthyosaurs are extinct marine reptiles that display a notable external similarity to modern toothed whales. Here we show that this resemblance is more than skin deep. We apply a multidisciplinary experimental approach to characterize the cellular and molecular composition of integumental tissues in an exceptionally preserved specimen of the Early Jurassic ichthyosaur Stenopterygius. Our analyses recovered still-flexible remnants of the original scaleless skin, which comprises morphologically distinct epidermal and dermal layers. These are underlain by insulating blubber that would have augmented streamlining, buoyancy and homeothermy. Additionally, we identify endogenous proteinaceous and lipid constituents, together with keratinocytes and branched melanophores that contain eumelanin pigment. Distributional variation of melanophores across the body suggests countershading, possibly enhanced by physiological adjustments of colour to enable photoprotection, concealment and/or thermoregulation. Convergence of ichthyosaurs with extant marine amniotes thus extends to the ultrastructural and molecular levels, reflecting the omnipresent constraints of their shared adaptation to pelagic life.

Predator presence and recent climatic warming raise body temperatures of island lizards.

In ectothermic predator-prey relationships, evasion of predation by prey depends on physiological and behavioural responses relating to the thermal biology of both predator and prey. On Japan's Izu Islands, we investigated a prey lizard's physiological and thermal responses to the presence of a snake predator over geologic time in addition to recent climatic warming. Foraging lizard body temperatures increased by 1.3 °C from 1981 to 2019 overall, yet were 2.9 °C warmer on snake islands relative to snake-free islands. We also detected snake predator-induced selection on hind leg length, which in turn is a major determinant for sprint speed only in lizard populations exposed to predation by snakes. Accordingly, we found that warmer prey body temperatures result in faster sprint speeds by the prey at temperatures suboptimal for the snake predator, and therefore contribute to escaping predation. Given recent climatic change, further warming could irrevocably alter this and other ectothermic predator-prey relationships.

Complex Historical Biogeography of the Eastern Japanese Skink, Plestiodon finitimus (Scincidae, Squamata), Revealed by Geographic Variation in Molecular and Morphological Characters.

We investigated the geographic diversification of Plestiodon finitimus, which occurs in the central to northern parts of the Japanese Islands, based on a time-calibrated mitochondrial DNA (mtDNA) phylogeny and external morphological characters. The mtDNA phylogeny suggests that P. finitimus diverged from its sister species Plestiodon japonicus in western Japan 2.82-4.63 million years ago (MYA), which can be explained by geographic isolation due to the spread of sedimentary basins in the Pliocene. The primary intraspecific divergence was that between P. finitimus lineages in central and northeastern Japan 1.58-2.76 MYA, which could have been caused by the upliftings of major mountain ranges. In the northeastern lineage, mtDNA and morphological characters suggest a geographic differentiation between sub-lineages of the northwestern Tohoku District (α) and other areas (ß). Although the sub-lineage ß occurs in a disjunct geographic range, consisting of Hokkaido and the central to south of Tohoku, these areas are bridged by populations with intermediate characteristics along the Pacific side of northern Tohoku. Overall, the geographic variation in P. finitimus in northern Japan can be explained by an initial allopatric divergence of the sub-lineages α and ß at 0.71-1.39 MYA, a recent northward expansion of the sub-lineage ß, and subsequent secondary introgressive hybridization between the sub-lineages.

Embryonic developmental process governing the conspicuousness of body stripes and blue tail coloration in the lizard Plestiodon latiscutatus.

The combination of body stripes and vivid blue tail color has independently evolved in different lizard families. To understand how and when lizards developed this coloration, we microscopically compared the embryonic development of pigment cells in two island populations of Plestiodon latiscutatus that exhibit either striped and blue tailed or inconspicuously striped and blue tailed juveniles, based on the newly determined 12 normal developmental stages of embryos from shortly after egg laying to just before hatching. We focus on the role of the melanophores in the body stripe and the role of iridophore morphotypes in the extent of blue tail coloration. The melanophore density in the black background region was higher in lizards with vivid stripes than in lizards with drab stripes. Iridophores started to fill the dermal space that was not yet occupied by melanophores, which resulted in a higher iridophore density in stripes than in the inter-stripe regions. We also discovered that iridophores with thin platelets reflecting blue structural coloration appeared at a specific region in the tail at stage 11. The position of the tail where iridophores emerged coincided with the boundary area separating anterior brown and green colored tail from posterior blue colored tail after hatching.

Novel approach for detecting classical swine fever virus from swabs of wild boar cut tails using nested real-time PCR.

We devised a method to detect the classical swine fever virus (CSFV) in tail-wiped swabs from wild boars. The CSFV gene in swabs was detected with high sensitivity using nested real-time polymerase chain reaction (PCR), which is a combination of reverse transcription-PCR (RT-PCR) and real-time PCR. We compared CSFV gene detection from boar tissue using the conventional and our tail-wiped swab method. The tail-wiped swab method showed sensitivity and specificity of 100% (26/26) and 98.8% (172/174), respectively compared to the conventional method. Thus, the swab-based CSFV detection method was considered to have detection sensitivity comparable to that of conventional methods. Additionally, we conducted surveillance for CSFV in wild boars on Awaji Island. CSFV was detected in 10.7% (45/420) of samples.

Small-scale variation in ecosystem CO2 fluxes in an alpine meadow depends on plant biomass and species richness.

Characterizing the spatial variation in the CO2 flux at both large and small scales is essential for precise estimation of an ecosystem's CO2 sink strength. However, little is known about small-scale CO2 flux variations in an ecosystem. We explored these variations in a Kobresia meadow ecosystem on the Qinghai-Tibetan plateau in relation to spatial variability in species composition and biomass. We established 14 points and measured net ecosystem production (NEP), gross primary production (GPP), and ecosystem respiration (Re) in relation to vegetation biomass, species richness, and environmental variables at each point, using an automated chamber system during the 2005 growing season. Mean light-saturated NEP and GPP were 30.3 and 40.5 micromol CO2 m(-2) s(-1) [coefficient of variation (CV), 42.7 and 29.4], respectively. Mean Re at 20 degrees C soil temperature, Re(20), was -10.9 micromol CO2 m(-2) s(-1) (CV, 27.3). Re(20) was positively correlated with vegetation biomass. GPP(max) was positively correlated with species richness, but 2 of the 14 points were outliers. Vegetation biomass was the main determinant of spatial variation of Re, whereas species richness mainly affected that of GPP, probably reflecting the complexity of canopy structure and light partitioning in this small grassland patch.

Estimating range expansion of wildlife in heterogeneous landscapes: A spatially explicit state-space matrix model coupled with an improved numerical integration technique.

Dispersal as well as population growth is a key demographic process that determines population dynamics. However, determining the effects of environmental covariates on dispersal from spatial-temporal abundance proxy data is challenging owing to the complexity of model specification for directional dispersal permeability and the extremely high computational loads for numerical integration. In this paper, we present a case study estimating how environmental covariates affect the dispersal of Japanese sika deer by developing a spatially explicit state-space matrix model coupled with an improved numerical integration technique (Markov chain Monte Carlo with particle filters). In particular, we explored the environmental drivers of inhomogeneous range expansion, characteristic of animals with short dispersal. Our model framework successfully reproduced the complex population dynamics of sika deer, including rapid changes in densely populated areas and distribution fronts within a decade. Furthermore, our results revealed that the inhomogeneous range expansion of sika deer seemed to be primarily caused by the dispersal process (i.e., movement barriers in fragmented forests) rather than population growth. Our state-space matrix model enables the inference of population dynamics for a broad range of organisms, even those with low dispersal ability, in heterogeneous landscapes, and could address many pressing issues in conservation biology and ecosystem management.

Developmental mechanisms of longitudinal stripes in the Japanese four-lined snake.

The developmental mechanisms of color patterns formation and its evolution remain unclear in reptilian sauropsids. We, therefore, studied the pigment cell mechanisms of stripe pattern formation during embryonic development of the snake Elaphe quadrivirgata. We identified 10 post-ovipositional embryonic developmental stages based on external morphological characteristics. Examination for the temporal changes in differentiation, distribution, and density of pigment cells during embryonic development revealed that melanophores first appeared in myotome and body cavity but not in skin surface at Stage 5. Epidermal melanophores were first recognized at Stage 7, and dermal melanophores and iridophores appeared in Stage 9. Stripe pattern first appeared to establish at Stage 8 as a spatial density gradient of epidermal melanophores between the regions of future dark brown longitudinal stripes and light colored background. Our study, thus, provides a comprehensive pigment-cell-based understanding of stripe pattern formation during embryonic development. We briefly discuss the importance of the gene expression studies by considering the biologically relevant theoretical models with standard developmental staging for understanding reptilian color pattern evolution.

Light reflection from crystal platelets in iridophores determines green or brown skin coloration in Takydromus lizards.

Brown and green are the most commonly imitated colors in prey animals because both colors occur in a range of habitats. Many researchers have evaluated survival with respect to background color matching, but the pigment cell mechanisms underlying such coloration are not known. Dorsal coloration of East Asian Takydromus lizards has shifted from green to brown or from brown to green on multiple occasions during the diversification of the genus, thus giving us an opportunity to examine the cellular mechanisms of background color matching. Brown and green skin were found to differ with respect to the morphological characteristics of iridophores, with different thicknesses of the reflecting platelets and the cytoplasmic spacing between platelets, despite a shared vertical arrangement of pigment cells, i.e., xanthophores in the upper layer, iridophores in the middle layer, and melanophores at the bottom of the dermal layer, among the different Takydromus lizards. Iridophores of brown skin reflected longer wavelengths of light than those of green skin, which may be attributed to the thicker platelets and longer distances between platelets in brown skin. We discuss the potential role of genetic and intracellular mechanisms explaining the thickness and orientation of the light-reflecting platelets of iridophores in Takydromus lizards.

Biochemistry and adaptive colouration of an exceptionally preserved juvenile fossil sea turtle.

The holotype (MHM-K2) of the Eocene cheloniine Tasbacka danica is arguably one of the best preserved juvenile fossil sea turtles on record. Notwithstanding compactional flattening, the specimen is virtually intact, comprising a fully articulated skeleton exposed in dorsal view. MHM-K2 also preserves, with great fidelity, soft tissue traces visible as a sharply delineated carbon film around the bones and marginal scutes along the edge of the carapace. Here we show that the extraordinary preservation of the type of T. danica goes beyond gross morphology to include ultrastructural details and labile molecular components of the once-living animal. Haemoglobin-derived compounds, eumelanic pigments and proteinaceous materials retaining the immunological characteristics of sauropsid-specific ß-keratin and tropomyosin were detected in tissues containing remnant melanosomes and decayed keratin plates. The preserved organics represent condensed remains of the cornified epidermis and, likely also, deeper anatomical features, and provide direct chemical evidence that adaptive melanism - a biological means used by extant sea turtle hatchlings to elevate metabolic and growth rates - had evolved 54 million years ago.

Ultrastructure of the dermal chromatophores in a lizard (Scincidae: Plestiodon latiscutatus) with conspicuous body and tail coloration.

Microscopic observation of the skin of Plestiodon lizards, which have body stripes and blue tail coloration, identified epidermal melanophores and three types of dermal chromatophores: xanthophores, iridophores, and melanophores. There was a vertical combination of these pigment cells, with xanthophores in the uppermost layer, iridophores in the intermediate layer, and melanophores in the basal layer, which varied according to the skin coloration. Skin with yellowish-white or brown coloration had an identical vertical order of xanthophores, iridophores, and melanophores, but yellowish-white skin had a thicker layer of iridophores and a thinner layer of melanophores than did brown skin. The thickness of the iridophore layer was proportional to the number of reflecting platelets within each iridophore. Skin showing green coloration also had three layers of dermal chromatophores, but the vertical order of xanthophores and iridophores was frequently reversed. Skin showing blue color had iridophores above the melanophores. In addition, the thickness of reflecting platelets in the blue tail was less than in yellowish-white or brown areas of the body. Skin with black coloration had only melanophores.

Pigment cell mechanism of postembryonic stripe pattern formation in the Japanese four-lined snake.

Postembryonic changes in the dermal and epidermal pigment cell architecture of the striped and nonstriped morph of the Japanese four-lined snake Elaphe quadrivirgata were examined to reveal stripe pattern formation after hatching. The striped and nonstriped morphs were distinguishable at the hatching, suggesting that the basis of stripe pattern was formed during embryonic development. In the striped morph, the color of stripes changed from red-brown in juveniles to vivid dark-brown in adults, and density of dermal melanophore increased much more in the stripe than background dorsal scales with growth. This increase in density of dermal melanophore was accompanied not only by the increased epidermal melanophore density but also by the change in vertical structures of dermal melanophore. By contrast, the density of epidermal and dermal melanophore evenly increased over the dorsal scales in the nonstriped morph. Thus, the increased vividness of the stripe pattern after hatching is achieved through localized increase of melanophore density particularly in the stripe region but not over the whole dorsal scales.

Snake and bird predation drive the repeated convergent evolution of correlated life history traits and phenotype in the Izu Island Scincid lizard (Plestiodon latiscutatus).

Predation may create strong natural selection pressure on the phenotype and life history characteristics of prey species. The Izu scincid lizards (Plestiodon latiscutatus) that inhabit the four Japanese Izu Islands with only bird predators are drab brown, mature later, lay small clutches of large eggs, and hatch large neonates. In contrast, skinks on seven islands with both snake and bird predators are conspicuously colored, mature early, lay large clutches of small eggs, and hatch small neonates. We test the hypothesis that these suites of traits have evolved independently on each island via natural selection pressures from one of two predator regimes--birds-only and birds + snakes. Using two mtDNA genes and a nuclear locus, we infer a time-calibrated phylogeny of P. latiscutatus that reveals a basal split between Mikura and all islands south, and Miyake, all islands north, and the Izu Peninsula. Populations inhabiting Miyake, Niijima, Shikine, and Toshima are not monophyletic, suggesting either multiple colonizations or an artifact of incomplete lineage sorting (ILS). We therefore developed novel phylogenetic comparative analyses that assume either a multiple colonization or more restrictive single colonization ILS scenario and found 1) statistically significant support for the of different suites of phenotypic and life history characteristics with the presence of bird-only or bird + snake predator assemblages, and 2) strong phylogenetic support for at least two independent derivations of either the "bird-only" or "snakes + birds" phenotypes regardless of colonization scenario. Finally, our time-calibrated phylogeographic analysis supports the conclusion that the ancestor to modern Izu Island P. latiscutatus dispersed from the mainland to the Izu proto-islands between 3-7.6 million years ago (Ma). These lineages remained present in the area during successive formation of the islands, with one lineage re-colonizing the mainland 0.24-0.7 Ma.

Pigment cell mechanisms underlying dorsal color-pattern polymorphism in the Japanese four-lined snake.

To provide histological foundation for studying the genetic mechanisms of color-pattern polymorphisms, we examined light reflectance profiles and cellular architectures of pigment cells that produced striped, nonstriped, and melanistic color patterns in the snake Elaphe quadrivirgata. Both, striped and nonstriped morphs, possessed the same set of epidermal melanophores and three types of dermal pigment cells (yellow xanthophores, iridescent iridophores, and black melanophores), but spatial variations in the densities of epidermal and dermal melanophores produced individual variations in stripe vividness. The densities of epidermal and dermal melanophores were two or three times higher in the dark-brown-stripe region than in the yellow background in the striped morph. However, the densities of epidermal and dermal melanophores between the striped and background regions were similar in the nonstriped morph. The melanistic morph had only epidermal and dermal melanophores and neither xanthophores nor iridophores were detected. Ghost stripes in the shed skin of some melanistic morphs suggested that stripe pattern formation and melanism were controlled independently. We proposed complete- and incomplete-dominance heredity models for the stripe-melanistic variation and striped, pale-striped, and nonstriped polymorphisms, respectively, according to the differences in pigment-cell composition and its spatial architecture.