Aquatic export of young dissolved and gaseous carbon from a pristine boreal fen: Implications for peat carbon stock stability

The stability of northern peatland's carbon (C) store under changing climate is of major concern for the global C cycle. The aquatic export of C from boreal peatlands is recognized as both a critical pathway for the remobilization of peat C stocks as well as a major component of the net ecosystem C balance (NECB). Here, we present a full year characterization of radiocarbon content (¹⁴C) of dissolved organic carbon (DOC), carbon dioxide (CO₂), and methane (CH₄) exported from a boreal peatland catchment coupled with ¹⁴C characterization of the catchment's peat profile of the same C species. The age of aquatic C in runoff varied little throughout the year and appeared to be sustained by recently fixed C from the atmosphere (<60 years), despite stream DOC, CO₂, and CH₄ primarily being sourced from deep peat horizons (2–4 m) near the mire's outlet. In fact, the ¹⁴C content of DOC, CO₂, and CH₄ across the entire peat profile was considerably enriched with postbomb C compared with the solid peat material. Overall, our results demonstrate little to no mobilization of ancient C stocks from this boreal peatland and a relatively large resilience of the source of aquatic C export to forecasted hydroclimatic changes.     

Newly discovered fossil- and artifact-bearing deposits, uranium-series ages, and Plio-Pleistocene hominids at Swartkrans Cave, South Africa

We report on new research at Swartkrans Cave, South Africa, that provides evidence of two previously unrealized artifact- and fossil-bearing deposits. These deposits underlie a speleothem dated by the uranium-thorium disequilibrium technique to 110,000 ± 1,980 years old, the first tightly constrained, geochronological date available for the site. Recovered fauna from the two underlying deposits—including, prominently, the dental remains of Paranthropus (Australopithecus) robustus from the uppermost layer (Talus Cone Deposit)—indicate a significantly older, late Pliocene or early Pleistocene age for these units. The lowest unit (LB East Extension) is inferred to be an eastward extension of the well-known Lower Bank of Member 1, the earliest surviving infill represented at the site. The date acquired from the speleothem also sets the maximum age of a rich Middle Stone Age lithic assemblage.     

Sapwood characteristics of Quercus robur species from the south-western part of the Pannonian Basin

We analysed sapwood characteristics in 344 pedunculate oak (Quercus robur L.) samples from the south-western part of the Pannonian Basin. The samples came from 13 sites, located in Slovenia, Croatia and Serbia. The trees had an average of 13.3 sapwood rings, with a minimum of 5 and maximum of 32. Fifteen log-log linear regression models were employed to assess the statistical relationship between sapwood and heartwood variables. The number of sapwood rings (N_SW), which is usually needed in dendroarchaeological dating, is significantly related to the number of heartwood rings (N_HW), heartwood width (W_HW) and heartwood growth rate (G_HW). Older and more slowly growing trees had a higher average number of sapwood rings. Using N_HW and W_HW, we employed an additional multiple regression model and calculated coefficients for N_SW predictions for real-world dendroarchaeological dating from the south-western part of the Pannonian Basin.     

Molecular dating and diversification of the South American lizard genus Liolaemus (subgenus Eulaemus) based on nuclear and mitochondrial DNA sequences

The temperate South American lizard genus Liolaemus is the one of the most widely distributed and species‐rich genera of lizards on earth. The genus is divided into two subgenera, Liolaemus sensu stricto (the ‘Chilean group’) and Eulaemus (the ‘Argentino group’), a division that is supported by recent molecular and morphological data. Owing to a lack of reliable fossil data, previous studies have been forced to use either global molecular clocks, a standardized mutation rate adopted from previous studies, or the use of geological events as calibration points. However, simulations indicate that these types of assumptions may result in less accurate estimates of divergence times when clock‐like models or mutation rates are violated. We used a multilocus data set combined with a newly described fossil to provide the first calibrated phylogeny for the crown groups of the clade Eulaemus, and derive new fossil‐calibrated substitution rates (with error) of both nuclear and mtDNA gene regions for Eulaemus specifically. Divergence date estimates for each of the crown groups and appropriate rate estimates will provide the foundation for understanding rates of speciation, historical biogeography, and phylogeographical history for various clades in one of the most diverse lizard genera in the poorly studied Patagonian region. © 2012 The Linnean Society of London, Zoological Journal of the Linnean Society, 2012, 164 , 825–835.     

Sudden expansion of a single brown bear maternal lineage across northern continental Eurasia after the last ice age: a general demographic model for mammals?

The brown bear has proved a useful model for studying Late Quaternary mammalian phylogeography. However, information is lacking from northern continental Eurasia, which constitutes a large part of the species' current distribution. We analysed mitochondrial DNA sequences (totalling 1943 bp) from 205 bears from northeast Europe and Russia in order to characterize the maternal phylogeography of bears in this region. We also estimated the formation times of the sampled brown bear lineages and those of its extinct relative, the cave bear.
Four closely related haplogroups belonging to a single mitochondrial subclade were identified in northern continental Eurasia. Several haplotypes were found throughout the whole study area, while one haplogroup was restricted to Kamchatka. The haplotype network, estimated divergence times and various statistical tests indicated that bears in northern continental Eurasia recently underwent a sudden expansion, preceded by a severe bottleneck. This brown bear population was therefore most likely founded by a small number of bears that were restricted to a single refuge area during the last glacial maximum. This pattern has been described previously for other mammal species and as such may represent one general model for the phylogeography of Eurasian mammals. Bayesian divergence time estimates are presented for different brown and cave bear clades. Moreover, our results demonstrate the extent of substitution rate variation occurring throughout the phylogenetic tree, highlighting the need for appropriate calibration when estimating divergence times.     

Alternatives to the Wright-Fisher model: The robustness of mitochondrial Eve dating

Methods of calculating the distributions of the time to coalescence depend on the underlying model of population demography. In particular, the models assuming deterministic evolution of population size may not be applicable to populations evolving stochastically. Therefore the study of coalescence models involving stochastic demography is important for applications. One interesting approach which includes stochasticity is the O’Connell limit theory of genealogy in branching processes. Our paper explores how many generations are needed for the limiting distributions of O’Connell to become adequate approximations of exact distributions. We perform extensive simulations of slightly supercritical branching processes and compare the results to the O’Connell limits. Coalescent computations under the Wright-Fisher model are compared with limiting O’Connell results and with full genealogy-based predictions. These results are used to estimate the age of the so-called mitochondrial Eve, i.e., the root of the mitochondrial polymorphisms of the modern humans based on the DNA from humans and Neanderthal fossils.     

Reconstruction of the former charophyte community out of the fructifications identified in Albufera de València lagoon sediments

Several decades ago, due to eutrophication, Albufera de València lagoon lost the charophyte meadows that covered the bottom in the past but had never been studied in detail. An area close to the lagoon will be restored now to improve water quality and to recover submerged vegetation. To have information on the background of the charophytes from this area, four 80-87 cm long sediment cores were extracted from the lagoon. The subfossil charophyte fructifications (oospores and gyrogonites) were isolated and identified in two of the four cores. Moreover, sediment core fractions from the third and fourth cores were allowed to germinate under several conditions. The study of the lagoon sediments has revealed that at least 11 morphologies of charophyte fructifications existed in the past. Ten of these were determined at species level: Chara vulgaris, Chara hispida, Chara aspera, Chara baltica, Chara tomentosa, Chara globularis, Lamprothamnium papulosum, Nitella hyalina, Tolypella glomerata and Tolypella hispanica. However, one form of Chara gyrogonite did not fit in any known species. L. papulosum oospores and gyrogonites were the most abundant and concentrated in the deepest sediment layers when the lagoon held brackish water. Large changes in salinity due to freshwater input drove charophyte species substitution (disappearance of L. papulosum). During the oligohaline period C. vulgaris sexual propagules were the most abundant. The last charophyte community before its disappearance due to eutrophication was composed mainly of C. hispida, C. tomentosa and N. hyalina (the two latter with small numbers of oospores in the sediment). To characterize the morphology of the unidentified gyrogonite species, 100 specimens were studied. This type could be a local variety of a more common species, probably C. vulgaris, grown under particular ecological conditions. Old collected oospores (more than 45 years old) germinated and could be identified as C. vulgaris and C. hispida.     

Unravelling evolutionary relationships between epifoliar Meliolaceae and angiosperms

Epifoliar fungi are a group of poorly studied fungal symbionts that coinhabit the surface of living plants. Meliolaceae is the largest group of epifoliar fungi and has been considered as obligate parasites. We investigated the taxonomy of Meliolaceae and the coevolutionary events with their host plants using time-calibrated cophylogeny based on large subunit, small subunit, and internal transcribed spacer (ITS) sequence data obtained from 17 different fungal taxa and rbcL, ITS, and trnH-psbA sequence data from their corresponding hosts. Nine new fungal species are introduced in this paper and Appendiculella is synonymized under Asteridiella. The dominant coevolutionary events during the Cretaceous and Cenozoic are cospeciation and host shift, respectively. We hypothesize that the evolutionary history of epifoliar fungi can be divided into three major periods: origins of families, formations of genera, and diversification of species. The rise of angiosperms prompted the evolution of modern epifoliar fungi and the diversification of orders of Angiospermae fostered the formation of epifoliar fungal genera. Phylogenetically, epifoliar fungal genera can be delimited according to their coevolutionary patterns and divergent periods.     

Grasses through space and time: An overview of the biogeographical and macroevolutionary history of Poaceae

Grasses are widespread on every continent and are found in all terrestrial biomes. The dominance and spread of grasses and grassland ecosystems have led to significant changes in Earth′s climate, geochemistry, and biodiversity. The abundance of DNA sequence data, particularly chloroplast sequences, and advances in placing grass fossils within the family allows for a reappraisal of the family′s origins, timing, and geographic spread and the factors that have promoted diversification. We reconstructed a time-calibrated grass phylogeny and inferred ancestral areas using chloroplast DNA sequences from nearly 90% of extant grass genera. With a few notable exceptions, the phylogeny is well resolved to the subtribal level. The family began to diversify in the Early–Late Cretaceous (crown age of 98.54 Ma) on West Gondwana before the complete split between Africa and South America. Vicariance from the splitting of Gondwana may be responsible for the initial divergence in the family. However, Africa clearly served as the center of origin for much of the early diversification of the family. With this phylogenetic, temporal, and spatial framework, we review the evolution and biogeography of the family with the aim to facilitate the testing of biogeographical hypotheses about its origins, evolutionary tempo, and diversification. The current classification of the family is discussed with an extensive review of the extant diversity and distribution of species, molecular and morphological evidence supporting the current classification scheme, and the evidence informing our understanding of the biogeographical history of the family.