Search Results (6)

Understanding species distribution and environmental niches is crucial for conserving endangered taxa. The recent taxonomic split of the European freshwater mussels U. crassus and U. nanus into distinct species requires a reassessment of their distinct ecologies for conservation. This study uses species distribution models (SDMs) to define and compare the environmental niches and reconstruct the distributions across six past time periods, starting from the mid-Pliocene Warm Period (mPWP, ca. 3.205 Ma) to the present. Our results reveal significant environmental niche differentiation between the two species, with U. crassus occupying a broader environmental niche primarily influenced by annual mean temperature and precipitation in the warmest quarter. In contrast, U. nanus shows a narrower niche shaped by temperature seasonality, mean diurnal range, annual mean temperature, and precipitation seasonality. Paleodistribution models indicate that during the Last Glacial Maximum (LGM, ca. 21 ka), U. crassus persisted in multiple southern refugia, whereas U. nanus was restricted to a single western refugium. These contrasting glacial histories led to divergent post-glacial colonization routes, explaining their current genetic patterns and partially overlapping ranges. By identifying present environmental hotspots, this research provides an essential framework for developing targeted, species-specific conservation strategies for these freshwater mussels. Full article

Knowledge of dry–wet variations in arid Central Asia (ACA) during the mid-Pliocene warm period (mPWP; ~3.3–3.0 Ma) is instructive to understanding the future variations in this fragile ecosystem region. However, the dry–wet variations in ACA during the mPWP remain controversial. Here, we present high-resolution evaporite mineralogy records from the Gansen (GS) section of the western Qaidam Basin during 3.25–2.95 Ma. Based on the similar periodic variations between the calcite content and χ_fd/HIRM value-based precipitation records, we infer that the calcite content has the potential to reflect precipitation variations. The results suggest that the calcite content reveals dominant 20 kyr precessional cycles and strong 40 kyr non-obliquity cycles, consistent with the χ_fd/HIRM values from the GS section, further demonstrating that Qaidam precipitation was affected by the intensified East Asian summer monsoon during the mPWP. However, the occurrence of gypsum beds reveals that the Qaidam Basin still experienced relatively arid climatic conditions despite the increased precipitation during this warm interval. Furthermore, halite and gypsum records suggest that the degree of aridification was relatively moderate during 3.25–3.06 Ma but intensified during 3.06–2.95 Ma. For the intensified aridification, we infer that the further global cooling, which induced a relative decrease in water vapor, played an important role at ~3.06 Ma. Taking the mPWP as the reference, our findings indicate that under continued warming the East Asian summer monsoon will bring abundant water vapor to the inland basin and alleviate aridification in ACA. However, the increased precipitation will have difficulty reversing the aridification trend in the short term. This requires us to evaluate the warming and wetting trend in ACA from a dialectical perspective. Full article

The Mongolian racerunner, Eremias argus, is a small lizard endemic to Northeast Asia that can serve as an excellent model for investigating how geography and past climate change have jointly influenced the evolution of biodiversity in this region. To elucidate the processes underlying its diversification and demography, we reconstructed the range-wide phylogeographic pattern and evolutionary trajectory, using phylogenetic, population genetic, landscape genetic, Bayesian phylogeographic reconstruction and ecological niche modeling approaches. Phylogenetic analyses of the mtDNA cyt b gene revealed eight lineages that were unbounded by geographic region. The genetic structure of E. argus was mainly determined by geographic distance. Divergence dating indicated that E. argus and E. brenchleyi diverged during the Mid-Pliocene Warm Period. E. argus was estimated to have coalesced at~0.4351 Ma (Marine Isotope Stage 19). Bayesian phylogeographic diffusion analysis revealed out-of-Inner Mongolia and rapid colonization events from the end of the Last Interglacial to the Last Glacial Maximum, which is consistent with the expanded suitable range of the Last Glacial Maximum. Pre-Last Glacial Maximum growth of population is presented for most lineages of E. argus. The Glacial Maximum contraction model and the previous multiple glacial refugia hypotheses are rejected. This may be due to an increase in the amount of climatically favorable habitats in Northeast Asia. Furthermore, E. argus barbouri most likely represents an invalid taxon. The present study is the first to report a range-wide phylogeography of reptiles over such a large region in Northeast Asia. Our results make a significant contribution towards understanding the biogeography of the entire Northeast Asia. Full article

The upland lakes (ULs) in Carajás, southeastern Amazonia, have been extensively studied with respect to their high-resolution structural geology, geomorphology, stratigraphy, multielement and isotope geochemistry, palynology and limnology. These studies have generated large multiproxy datasets, which were integrated in this review to explain the formation and evolution of the ULs. These ULs evolved during the Pliocene–Pleistocene periods through several episodes of a subsidence of the lateritic crust (canga) promoted by fault reactivation. The resulting ULs were filled under wet/dry and warm/cool paleoclimatic conditions during the Pleistocene period. The multielement geochemical signature indicates that the detrital sediments of these ULs were predominantly derived from weathered canga and ferruginous soils, while the sedimentary organic matter came from autochthonous (siliceous sponge spicules, algae, macrophytes) and allochthonous (C3/C4 canga and forest plants and freshwater dissolved organic carbon) sources. Modern pollen rain suggests that even small ULs can record both the influence of canga vegetation and forest signals; thus, they can serve as reliable sites to provide a record of vegetation history. The integrated data from the sedimentary cores indicate that the active ULs have never dried up during the last 50 ka cal BP. However, subaerial exposure occurred in filled ULs, such as the Tarzan mountain range during the Last Glacial Maximum (LGM) and the Bocaína and S11 mountain ranges in the mid-Holocene period, due to the drier conditions. Considering the organic proxies, the expansion of C4 plants has been observed in the S11 and Tarzan ULs during dry events. Extensive precipitation of siderite in UL deposits during the LGM indicated drier paleoenvironmental conditions, interrupting the predominantly wet conditions. However, there is no evidence of widespread forest replacement by savanna in the Carajás plateau of southeastern Amazonia during the late Pleistocene and Holocene. Full article

The Yorktown Formation records paleoclimate conditions along the mid-Atlantic Coastal Plain during the mid-Piacenzian Warm Period (3.264 to 3.025 Ma), a climate interval of the Pliocene in some ways analogous to near future climate projections. To gain insight into potential near future changes, we investigated Yorktown Formation outcrops and cores in southeastern Virginia, refining the stratigraphic framework. We analyzed 485 samples for alkenone-based sea surface temperature (SST) and productivity estimates from the Holland and Dory cores, an outcrop at Morgarts Beach, Virginia, and the lectostratotype of the Yorktown Formation at Rushmere, Virginia, and analyzed planktonic foraminferal assemblage data from the type section. Using the structure of the SST record, we improved the chronology of the Yorktown Formation by establishing the maximum age ranges of the Rushmere (3.3–3.2 Ma) and Morgarts Beach (3.2–3.15 Ma) Members. SST values for these members average ~26 °C, corroborating existing sclerochronological data. Increasing planktonic foraminifer abundance, productivity, and species diversity parallel increasing SST over the MIS M2/M1 transition. These records constitute the greatest temporal concentration of paleoecological estimates within the Yorktown Formation, aiding our understanding of western North Atlantic temperature patterns, seasonality and ocean circulation during this interval. We provide a chronologic framework for future studies analyzing ecological responses to profound climate change. Full article

How variations in Earth’s orbit pace the glacial-interglacial cycles of the Quaternary are probably one of the greatest mysteries of modern climate science. These changes in the forcing are too small to explain the observed climate variations as simple linear responses. Consequently, to strictly apply the Milankovitch’s theory, a mediator involving positive feedbacks must be found, endowing the climate response with a resonant feature. This mediation should help explain the Mid-Pleistocene Transition (MPT) by involving orbital variations as the only external forcing, contrary to the current theory that supposes the coevolution of climate, ice sheets, and carbon cycle over the past 3 million years. Supported by both observational and theoretical considerations, recent work shows that long-period Rossby waves winding around subtropical ocean gyres meet the requirements of the sought mediator. Propagating cyclonically around the subtropical gyres, the so-called Gyral Rossby waves (GRWs) owe their origin to the gradient β of the Coriolis parameter relative to the mean radius of the gyres. The resulting modulated western boundary current, whose velocity is added to that of the steady anticyclonic wind-driven current, accelerates/decelerates according to the phase of GRWs. This amplifies the oscillation of the thermocline because of a positive feedback loop ensuing from the temperature gradient between the high and low latitudes of the gyres. Multi-frequency GRWs overlap, behaving as coupled oscillators with inertia resonantly forced by solar and orbital cycles in subharmonic modes. So, the efficiency of forcing increases considerably as the forcing period approaches a natural period of the GRWs. Taking advantage of (1) the alkenone paleothermometer in sediment cores sampled in the Tasman Sea floor, we show that, in the same way as during the MPT, but with periods 10 times longer, a transition occurred at the hinge of Pliocene-Pleistocene. Both transitions as well as the observed adjustment of the South Pacific gyre to the resonance conditions during the MPT are explained from orbital forcing alone—(2) data set of individual Globigerinoides ruber$\delta \mathrm{O}_{ }^{18}$ spanning the Holocene and the Last Glacial Maximum from sediment core in the eastern equatorial Pacific, we show how the El Niño–Southern Oscillation (ENSO) activity is modulated according to subharmonic modes. Periods of warming induce a decrease in ENSO activity while periods of cooling induce an increase. Full article