Endolithic microbial colonization of limestone in a high-altitude arid environment.

The morphology of endolithic colonization in a limestone escarpment and surrounding rocky debris (termed float) at a high-altitude arid site in central Tibet was documented using scanning electron microscopy. Putative lichenized structures and extensive coccoid bacterial colonization were observed. Absolute and relative abundance of rRNA gene signatures using real-time quantitative polymerase chain reaction and phylogenetic analysis of environmental phylotypes were used to characterize community structure across all domains. Escarpment endoliths were dominated by eukaryotic phylotypes suggestive of lichenised associations (a Trebouxia lichen phycobiont and Leptodontidium lichen mycobiont), whereas float endoliths were dominated by bacterial phylotypes, including the cyanobacterium Chroococcidiopsis plus several unidentified beta proteobacteria and crenarchaea. Among a range of abiotic variables tested, ultraviolet (UV) transmittance by rock substrates was the factor best able to explain differences in community structure, with eukaryotic lichen phylotypes more abundant under conditions of greater UV-exposure compared to prokaryotes. Variously pigmented float rocks did not support significantly different communities. Estimates of in situ carbon fixation based upon (14)C radio-labelled bicarbonate uptake indicated endolithic productivity of approximately 2.01 g C/m(2)/year(-1), intermediate between estimates for Antarctic and temperate communities.

Bacterial community composition in thermophilic microbial mats from five hot springs in central Tibet.

Despite detailed study of selected thermophilic taxa, overall community diversity of bacteria in thermophilic mats remains relatively poorly understood. A sequence-based survey of bacterial communities from several hot spring locations in central Tibet was undertaken. Diversity and frequency of occurrence for 140 unique 16S rRNA gene phylotypes were identified in clone libraries constructed from environmental samples. A lineage-per-time plot revealed that individual locations have evolved to support relatively large numbers of phylogenetically closely related phylotypes. Application of the F ( ST ) statistic and P test to community data was used to demonstrate that phylogenetic divergence between locations was significant, thus emphasizing the status of hot springs as isolated habitats. Among phylotypes, only the Chlorobi were ubiquitous to all mats, other phototrophs (Cyanobacteria and Chloroflexi) occurred in most but not all samples and generally accounted for a large number of recovered phylotypes. Phylogenetic analyses of phototrophic phylotypes revealed support for location-specific lineages. The alpha, beta and gamma proteobacteria were also frequently recovered phyla, suggesting they may be abundant phylotypes in mats, a hitherto unappreciated aspect of thermophilic mat biodiversity. Samples from one location indicated that where phototrophic bacteria were rare or absent due to niche disturbance, the relative frequency of proteobacterial phylotypes increased.

Adding a new dimension to investigations of early radiolarian evolution.

Knowledge of the detailed architecture of the earliest radiolarian microfossils is key to resolving the evolution and systematics of this important group of marine protozoans. Non-destructive methods for observing the complexity within the internal structures of their siliceous skeletons have long eluded paleontologists. By developing methodologies that overcome some limitations of existing micro-computed tomography (micro-CT) we demonstrate a technique with potential to provide new insight into their evolution. Using 3D micro-CT data to generate models for six well-preserved siliceous radiolarian skeletons from the Middle Cambrian Inca Formation in far north Queensland, Australia and the Middle Ordovician Piccadilly Formation, in western Newfoundland, Canada, we can reconstruct phylogenetic relationships amongst some of the earliest radiolarians. Better knowledge of early radiolarian morphologies clarifies the vital function of internal structures and hierarchical diagnosis across a range of taxonomic affiliations.

Live birth in an archosauromorph reptile.

Live birth has evolved many times independently in vertebrates, such as mammals and diverse groups of lizards and snakes. However, live birth is unknown in the major clade Archosauromorpha, a group that first evolved some 260 million years ago and is represented today by birds and crocodilians. Here we report the discovery of a pregnant long-necked marine reptile (Dinocephalosaurus) from the Middle Triassic (∼245 million years ago) of southwest China showing live birth in archosauromorphs. Our discovery pushes back evidence of reproductive biology in the clade by roughly 50 million years, and shows that there is no fundamental reason that archosauromorphs could not achieve live birth. Our phylogenetic models indicate that Dinocephalosaurus determined the sex of their offspring by sex chromosomes rather than by environmental temperature like crocodilians. Our results provide crucial evidence for genotypic sex determination facilitating land-water transitions in amniotes.

Highly diverse community structure in a remote central Tibetan geothermal spring does not display monotonic variation to thermal stress.

We report an assessment of whole-community diversity for an extremely isolated geothermal location with considerable phylogenetic and phylogeographic novelty. We further demonstrate, using multiple statistical analyses of sequence data, that the response of community diversity is not monotonic to thermal stress along a gradient of 52-83 degrees C. A combination of domain- and division-specific PCR was used to obtain a broad spectrum of community phylotypes, which were resolved by denaturing gradient gel electrophoresis. Among 58 sequences obtained from microbial mats and streamers, some 95% suggest novel archaeal and bacterial diversity at the species level or higher. Moreover, new phylogeographic and thermally defined lineages among the Cyanobacteria, Chloroflexi, Eubacterium and Thermus are identified. Shannon-Wiener diversity estimates suggest that mats at 63 degrees C supported highest diversity, but when alternate models were applied [Average Taxonomic Distinctness (AvTD) and Variation in Taxonomic Distinctness (VarTD)] that also take into account the phylogenetic relationships between phylotypes, it is evident that greatest taxonomic diversity (AvTD) occurred in streamers at 65-70 degrees C, whereas greatest phylogenetic distance between taxa (VarTD) occurred in streamers of 83 degrees C. All models demonstrated that diversity is not related to thermal stress in a linear fashion.

A gigantic nothosaur (Reptilia: Sauropterygia) from the Middle Triassic of SW China and its implication for the Triassic biotic recovery.

The presence of gigantic apex predators in the eastern Panthalassic and western Tethyan oceans suggests that complex ecosystems in the sea had become re-established in these regions at least by the early Middle Triassic, after the Permian-Triassic mass extinction (PTME). However, it is not clear whether oceanic ecosystem recovery from the PTME was globally synchronous because of the apparent lack of such predators in the eastern Tethyan/western Panthalassic region prior to the Late Triassic. Here we report a gigantic nothosaur from the lower Middle Triassic of Luoping in southwest China (eastern Tethyan ocean), which possesses the largest known lower jaw among Triassic sauropterygians. Phylogenetic analysis suggests parallel evolution of gigantism in Triassic sauropterygians. Discovery of this gigantic apex predator, together with associated diverse marine reptiles and the complex food web, indicates global recovery of shallow marine ecosystems from PTME by the early Middle Triassic.

Community phylogenetic analysis of moderately thermophilic cyanobacterial mats from China, the Philippines and Thailand.

Most community molecular studies of thermophilic cyanobacterial mats to date have focused on Synechococcus occurring at temperatures of approximately 50-65 degrees C. These reveal that molecular diversity exceeds that indicated by morphology, and that phylogeographic lineages exist. The moderately thermophilic and generally filamentous cyanobacterial mat communities occurring at lower temperatures have not previously been investigated at the community molecular level. Here we report community diversity in mats of 42-53 degrees C recovered from previously unstudied geothermal locations. Separation of 16S rRNA gene-defined genotypes from community DNA was achieved by DGGE. Genotypic diversity was greater than morphotype diversity in all mats sampled, although genotypes generally corresponded to observed morphotypes. Thirty-six sequences were recovered from DGGE bands. Phylogenetic analyses revealed these to form novel thermophilic lineages distinct from their mesophilic counterparts, within Calothrix, Cyanothece, Fischerella, Phormidium, Pleurocapsa, Oscillatoria and Synechococcus. Where filamentous cyanobacterial sequences belonging to the same genus were recovered from the same site, these were generally closely affiliated. Location-specific sequences were observed for some genotypes recovered from geochemically similar yet spatially separated sites, thus providing evidence for phylogeographic lineages that evolve in isolation. Other genotypes were more closely affiliated to geographically remote counterparts from similar habitats suggesting that adaptation to certain niches is also important.