Late quaternary extinction of a tree species in eastern North America

Widespread species- and genus-level extinctions of mammals in North America and Europe occurred during the last deglaciation [16,000-9,000 yr B.P. (by (14)C)], a period of rapid and often abrupt climatic and vegetational change. These extinctions are variously ascribed to environmental change and overkill by human hunters. By contrast, plant extinctions since the Middle Pleistocene are undocumented, suggesting that plant species have been able to respond to environmental changes of the past several glacial/interglacial cycles by migration. We provide evidence from morphological studies of fossil cones and anatomical studies of fossil needles that a now-extinct species of spruce (Picea critchfieldii sp. nov.) was widespread in eastern North America during the Last Glacial Maximum. P. critchfieldii was dominant in vegetation of the Lower Mississippi Valley, and extended at least as far east as western Georgia. P. critchfieldii disappeared during the last deglaciation, and its extinction is not directly attributable to human activities. Similarly widespread plant species may be at risk of extinction in the face of future climate change.     

Sunflower domestication alleles support single domestication center in eastern North America

Phylogenetic analyses of genes with demonstrated involvement in evolutionary transitions can be an important means of resolving conflicting hypotheses about evolutionary history or process. In sunflower, two genes have previously been shown to have experienced selective sweeps during its early domestication. In the present study, we identified a third candidate early domestication gene and conducted haplotype analyses of all three genes to address a recent, controversial hypothesis about the origin of cultivated sunflower. Although the scientific consensus had long been that sunflower was domesticated once in eastern North America, the discovery of pre-Columbian sunflower remains at archaeological sites in Mexico led to the proposal of a second domestication center in southern Mexico. Previous molecular studies with neutral markers were consistent with the former hypothesis. However, only two indigenous Mexican cultivars were included in these studies, and their provenance and genetic purity have been questioned. Therefore, we sequenced regions of the three candidate domestication genes containing SNPs diagnostic for domestication from large, newly collected samples of Mexican sunflower landraces and Mexican wild populations from a broad geographic range. The new germplasm also was genotyped for 12 microsatellite loci. Our evidence from multiple evolutionarily important loci and from neutral markers supports a single domestication event for extant cultivated sunflower in eastern North America.     

Distribution of the Ixodes ricinus-like ticks of eastern North America.

We analyzed the geographic distribution of the Ixodes ricinus-like ticks in eastern North America by comparing the mitochondrial 16S rDNA sequences of specimens sampled directly from the field during the 1990s. Two distinct lineages are evident. The southern clade includes ticks from the southeastern and middle-eastern regions of the United States. The range of the northern clade, which appears to have been restricted to the northeastern region until the mid-1900s, now extends throughout the northeastern and middle-eastern regions. These phyletic units correspond to northern and southern taxa that have previously been assigned specific status as Ixodes dammini and Ixodes scapularis, respectively. The expanding range of I. dammini appears to drive the present outbreaks of zoonotic disease in eastern North America that include Lyme disease and human babesiosis.     

Applying a regional community concept to forest birds of eastern North America

The regional community concept embraces the idea that species interactions across large areas shape both the geographic/ecological distributions and the local abundances of populations. Within this framework, I analyzed the distribution and abundance of 79 species of land birds across 142 ca. 10-ha census plots from standardized breeding bird censuses in deciduous and mixed forests of eastern North America. To characterize the regional ecological space, plots were ordinated on the basis of species abundances. Within the regional community defined by these synthetic axes, the distribution and abundance of individual species did not appear to be shaped by competition or to reflect the adaptations of individuals: (i) local abundance and population extent across the ordination axes were unrelated, (ii) pairwise correlation coefficients of species abundances were centered on 0, (iii) average species distribution and abundance were independent of the number of close relatives, and (iv) distribution and abundance exhibited no evolutionary (phylogenetic) conservatism. To explain these seemingly random patterns, I speculate that species are approximately evenly matched competitors over much of the region and that their distributions and relative abundances are determined by the labile coevolutionary outcomes of interactions with specialized pathogens. Thus, despite the appearance that random processes determine patterns in the distribution and abundance of populations in the regional community, it is plausible that species-specific deterministic interactions are responsible. Although competition is a dominant force in ecological communities, variation in the distribution and abundance of individual species might instead reflect the outcome of interactions with specialized antagonists, including pathogens.     

Temperature dependence, spatial scale, and tree species diversity in eastern Asia and North America

The increase of biodiversity from poles to equator is one of the most pervasive features of nature. For 2 centuries since von Humboldt, Wallace, and Darwin, biogeographers and ecologists have investigated the environmental and historical factors that determine the latitudinal gradient of species diversity, but the underlying mechanisms remain poorly understood. The recently proposed metabolic theory of ecology (MTE) aims to explain ecological patterns and processes, including geographical patterns of species richness, in terms of the effects of temperature and body size on the metabolism of organisms. Here we use 2 comparable databases of tree distributions in eastern Asia and North America to investigate the roles of environmental temperature and spatial scale in shaping geographical patterns of species diversity. We find that number of species increases exponentially with environmental temperature as predicted by the MTE, and so does the rate of spatial turnover in species composition (slope of the species-area relationship). The magnitude of temperature dependence of species richness increases with spatial scale. Moreover, the relationship between species richness and temperature is much steeper in eastern Asia than in North America: in cold climates at high latitudes there are more tree species in North America, but the reverse is true in warmer climates at lower latitudes. These patterns provide evidence that the kinetics of ecological and evolutionary processes play a major role in the latitudinal pattern of biodiversity.     

Heart Failure in North America

Heart failure is a major health problem that affects patients and healthcare systems worldwide. Within the continent of North America, differences in economic development, genetic susceptibility, cultural practices, and trends in risk factors and treatment all contribute to both inter-continental and within-continent differences in heart failure. The United States and Canada represent industrialized countries with similar culture, geography, and advanced economies and infrastructure. During the epidemiologic transition from rural to industrial in countries such as the United States and Canada, nutritional deficiencies and infectious diseases made way for degenerative diseases such as cardiovascular diseases, cancer, overweight/obesity, and diabetes. This in turn has resulted in an increase in heart failure incidence in these countries, especially as overall life expectancy increases. Mexico, on the other hand, has a less developed economy and infrastructure, and has a wide distribution in the level of urbanization as it becomes more industrialized. Mexico is under a period of epidemiologic transition and the etiology and incidence of heart failure is rapidly changing. Ethnic differences within the populations of the United States and Canada highlight the changing demographics of each country as well as potential disparities in heart failure care. Heart failure with preserved ejection fraction makes up approximately half of all hospital admissions throughout North America; however, important differences in demographics and etiology exist between countries. Similarly, acute heart failure etiology, severity, and management differ between countries in North America. The overall economic burden of heart failure continues to be large and growing worldwide, with each country managing this burden differently. Understanding the inter-and within-continental differences may help improve understanding of the heart failure epidemic, and may aid healthcare systems in delivering better heart failure prevention and treatment.     

Clinical trials in North America

Abstract:  Majority of patients with Hodgkin lymphoma are cured with current therapy. The short and long-term toxicity of therapy is a current issue, most especially the radiation-induced second tumors and cardiac abnormalities. Optimal therapy of advanced disease is being compared to ABVD (doxorubicin, bleomycin, vinblastine, dacarbazine). More intensive chemotherapy may result in higher response but greater toxicity. Regimens requiring radiotherapy are also at risk of long-term toxicity. New targeted biologic therapy is under current investigation.     

Newborn screening in North America

Summary Newborn screening in North America dates to the early work of Bob Guthrie in the USA. Screening programmes in both the USA and Canada began in the early 1960s, with documented programmes in both countries as early as 1962. Throughout the 1960s and 1970s, many of the screening tests that later became part of routine screening around the world were developed in US and Canadian laboratories, including tests for phenylketonuria, other inborn errors of metabolism, congenital hypothyroidism, congenital adrenal hyperplasia, and haemoglobinopathies. An automated punching machine developed in the USA facilitated screening expansion by significantly reducing sample preparation time and effort. US and Canadian programmes were leaders in applying computerized data management to newborn screening in the 1980s. In the 1990s, DNA and tandem mass spectrometry testing protocols were developed in the USA and applied to newborn screening. US programmes have continually expanded over time, while most Canadian programmes have not. With impetus from private laboratories and professional and consumer groups, many US programmes now screen for more than 50 conditions and there is increased expansion activity in Canada. NBS research in the USA is focused on improving system efficiency and translating other genetic testing to NBS, particularly where new technologies and treatment therapies exist. Although national newborn screening policies do not exist in either Canada or the USA, there are intense efforts to provide uniform access to screening nationwide in both countries. New partnerships between health professionals, consumers and politicians are benefiting the overall screening systems in both countries. Competing interests: None declared References to electronic databases: ; ; .     

Human impacts on the rates of recent, present, and future bird extinctions

Unqualified, the statement that approximately 1.3% of the approximately 10,000 presently known bird species have become extinct since A.D. 1500 yields an estimate of approximately 26 extinctions per million species per year (or 26 E/MSY). This is higher than the benchmark rate of approximately 1 E/MSY before human impacts, but is a serious underestimate. First, Polynesian expansion across the Pacific also exterminated many species well before European explorations. Second, three factors increase the rate: (i) The number of known extinctions before 1800 is increasing as taxonomists describe new species from skeletal remains. (ii) One should calculate extinction rates over the years since taxonomists described the species. Most bird species were described only after 1850. (iii) Some species are probably extinct; there is reluctance to declare them so prematurely. Thus corrected, recent extinction rates are approximately 100 E/MSY. In the last decades, the rate is <50 E/MSY, but would be 150 E/MSY were it not for conservation efforts. Increasing numbers of extinctions are on continents, whereas previously most were on islands. We predict a 21st century rate of approximately 1,000 E/MSY. Extinction threatens 12% of bird species; another 12% have small geographical ranges and live where human actions rapidly destroy their habitats. If present forest losses continue, extinction rates will reach 1,500 E/MSY by the century's end. Invasive species, expanding human technologies, and global change will harm additional species. Birds are poor models for predicting extinction rates for other taxa. Human actions threaten higher fractions of other well known taxa than they do birds. Moreover, people take special efforts to protect birds.     

Injection drug use in North America

Injection drug use of psychotropic agents for nontherapeutic purposes is associated with some of the most pernicious infectious diseases seen in the United States. There is an inextricable link between infection, injection drug use (IDU) and other risk behaviors, especially those related to sexual activity. A number of national surveys now provide excellent databases to track the breadth, scope and impact of IDU across the United States. The prevalence of heroin use has increased over the past decade with larger numbers of users presenting for treatment of drug use disorders. A host of serious infections can result from IDU. Prevention and early intervention with evidence-based harm-reduction strategies are crucial to reducing and eliminating these odious consequences.     

Epidemiology of spondyloarthritis in North America

Many challenges have made it difficult to determine the prevalence of spondyloarthritis (SpA) in North America. They include the ethnic heterogeneity of the population, the lack of feasibility of applying current criteria (such as requirements for human leukocyte antigen-B27 testing and imaging studies such as pelvic radiographs and magnetic resonance imaging scanning) and the transient nature of some SpA symptoms (ie, peripheral arthritis and enthesitis). Current estimates of the prevalence of SpA in the United States range between 0.2% and 0.5% for ankylosing spondylitis, 0.1% for psoriatic arthritis, 0.065% for enteropathic peripheral arthritis, between 0.05% and 0.25% for enteropathic axial arthritis and an overall prevalence of SpA as high as >1%. With newer population-based instruments becoming available, the availability of the widely validated European Spondyloarthropathy Study Group criteria and the lower cost and greater feasibility of genetic testing, opportunities for true population-based studies of SpA are possible and will likely soon ensue.     

From the Cover: Late Pleistocene shrub expansion preceded megafauna turnover and extinctions in eastern Beringia

The collapse of the steppe-tundra biome (mammoth steppe) at the end of the Pleistocene is used as an important example of top-down ecosystem cascades, where human hunting of keystone species led to profound changes in vegetation across high latitudes in the Northern Hemisphere. Alternatively, it is argued that this biome transformation occurred through a bottom-up process, where climate-driven expansion of shrub tundra (Betula, Salix spp.) replaced the steppe-tundra vegetation that grazing megafauna taxa relied on. In eastern Beringia, these differing hypotheses remain largely untested, in part because the precise timing and spatial pattern of Late Pleistocene shrub expansion remains poorly resolved. This uncertainty is caused by chronological ambiguity in many lake sediment records, which typically rely on radiocarbon (¹⁴C) dates from bulk sediment or aquatic macrofossils—materials that are known to overestimate the age of sediment layers. Here, we reexamine Late Pleistocene pollen records for which ¹⁴C dating of terrestrial macrofossils is available and augment these data with ¹⁴C dates from arctic ground-squirrel middens and plant macrofossils. Comparing these paleovegetation data with a database of published ¹⁴C dates from megafauna remains, we find the postglacial expansion of shrub tundra preceded the regional extinctions of horse (Equus spp.) and mammoth (Mammuthus primigenius) and began during a period when the frequency of ¹⁴C dates indicates large grazers were abundant. These results are not consistent with a model of top-down ecosystem cascades and support the hypothesis that climate-driven habitat loss preceded and contributed to turnover in mammal communities.

In northern high latitudes, the widespread extinction of Quaternary megafauna (animals weighing >44 kg) and disappearance of the steppe-tundra biome they inhabited is used as an important example of top-down ecosystem cascades, where human hunting of keystone species led to profound changes in vegetation structure at the end of the Pleistocene (15 thousand years before 1950 [15 ka] to 11.7 ka) (1–5). This hypothesis, however, is not well tested, and it is unclear whether the relative timing of megafauna extinctions and vegetation change is consistent with a top-down model. Resolving this question is an important part of understanding how past ecosystems functioned and may help predict how modern high-latitude ecosystems will respond to climate-driven vegetation change, current declines in large mammal species, or their deliberate reintroduction.In eastern Beringia (modern-day Alaska and the Yukon interior) (Fig. 1), Late Pleistocene megafauna extinctions broadly coincided with an expansion of shrub tundra vegetation including dwarf and tall-shrub species of birch (Betula nana and Betula glandulosa) and willow (Salix spp.) (6). Prior to these events, herds of grazing megafauna occupied a biome termed the mammoth steppe (7–9) or steppe-tundra (10, 11), which has no widespread modern analog. This novel, dry environment supported diverse plant communities, dominated by grasses, sedges, Artemisia spp., and a range of other forbs (8, 12–16). Sometime between 16 ka and 13 ka, woody shrub species began to expand across eastern Beringia, coupled with the development of peatlands and organic soil horizons (14, 17, 18). Lake sediment records show that the expansion of shrubs was rapid in many cases, and, although pollen influx data suggest herbaceous plant taxa continued to form an important part of the vegetation community, the abundance of Betula and Salix pollen (often >50% of the pollen sum) indicates that eastern Beringia became increasingly dominated by woody vegetation during this period (19–22).Open in a separate windowFig. 1.Eastern Beringia during the Late Pleistocene. Ice limits (14.2 and 15.5 ka) are redrawn from Dalton et al. (80). Lake sediment records reanalyzed in this study are numbered and include the following: 1, Burial Lake (81); 2, Tukuto Lake (82); 3, Lake of the Pleistocene (18); 4, Okpilak Lake (44); 5, Trout Lake (55); 6, Hanging Lake (54); 7, Ruppert Lake (83); 8, Xindi Lake (84); 9, Harding Lake (45); 10, Birch Lake (19); 11, Lost Lake (21); 12, Jan Lake (47); 13, Idavain Lake (20); 14, Beaver Lake (46); and 15, Discovery Pond (85).During the same time period, mammal communities in eastern Beringia underwent some of the most profound changes to occur in the region since at least the end of the last interglacial (Marine Isotope Stage 5e), 115 ka. Of the 13 megafauna taxa present in eastern Beringia immediately prior to 15 ka, only seven survived in situ beyond the Pleistocene (steppe bison, Bison priscus; caribou, Rangifer tarandus; wapiti, Cervus canadensis; muskox, Ovibos moschatus; wolf, Canis lupus; grizzly bear, Ursus arctos; and sheep, Ovis). The remaining taxa (caballine/stout-legged horses, Equus; stilt-legged horses, Haringtonhippus; woolly mammoth, Mammuthus primigenius; saiga antelope, Saiga tatarica; lion, Panthera spelaea; and short-faced bear, Arctodus simus), along with smaller mammals such as the arctic ground squirrel (Urocitellus parryii), became regionally extinct throughout large areas between 15.0 ka and 11.7 ka, leaving behind a comparatively impoverished mammal community (6, 23). The arrival of moose (Alces alces), an obligate browser, in eastern Beringia shortly after 15 ka (24) marks the beginning of a shift from the grazer community of the steppe-tundra toward a community of mixed-feeding megafauna species better adapted to a shrub tundra environment.The broad chronological overlap between the timing of shrub expansion and turnover in mammal populations has led numerous authors to hypothesize that habitat loss was a key driver of Late Pleistocene extinctions in eastern Beringia (8, 25–27). These authors argue that the Betula- and Salix-dominated shrub tundra was inhospitable to grazing megafauna because low-growing shrubs develop strong antiherbivory compounds, making them inedible or toxic to many mammals that lack a rumen to aid digestion (28). Other researchers have suggested that the decline in populations of grazing megafauna preceded shrub expansion, and that the spread of shrub tundra was caused by the resulting reduction in browsing pressure, vegetation trampling, and snow clearance (2, 29). These studies argue that grazers, and particularly megaherbivores (mammals of >1,000 kg), such as mammoth, acted as keystone species and were essential to the continuation of the steppe-tundra (1). In this case, human-caused “overkill” (30) or the compounded impacts of humans (e.g., burning, hunting, or simply their presence) in a dynamic ecosystem are advanced as the causes of megafauna extinctions. Finally, it is also possible that both of these processes reinforced one another, and the disappearance of the steppe-tundra was caused by both bottom-up and top-down pressures, or even that there was no causal relationship between the megafauna declines and shrub expansion. All of these hypotheses remain largely untested and continue to be controversial, in part because human arrival patterns, hunting preferences, and population size are largely unknown (31).In eastern Beringia, it is difficult to distinguish between these alternative hypotheses because the regional timing and spatial pattern of Late Pleistocene shrub expansion is poorly resolved, despite more than 50 y of detailed paleoecological study (14, 32–35). This uncertainty is principally due to the difficulty in accurately dating lake sediments from high latitudes (36–38). Terrestrial plant macrofossil remains are often rare in these depositional environments, and many pioneering paleoenvironmental studies are founded on chronologies based on radiocarbon (¹⁴C) dates derived from bulk sediment or aquatic macrofossils. This is particularly common for lake records obtained before the routine availability of accelerator mass spectrometer radiocarbon (AMS ¹⁴C) dating, when larger samples were required. Radiocarbon dates from bulk sediment or aquatic macrofossils are often imprecise or contaminated by old carbon (SI Appendix, Text), and, as a result, chronologies developed in this way are unreliable.To assess the chronology of shrub expansion and megafauna community turnover in eastern Beringia, we reanalyzed 15 lake sediment records for which AMS ¹⁴C dating of terrestrial macrofossils is available (SI Appendix, Figs. S1 and S6–S9). We developed Bayesian age–depth models for each study site, and compared the results with a new database of published ¹⁴C dates from plant macrofossils, megafauna remains, and arctic ground squirrel middens (Materials and Methods and SI Appendix, Text). In each pollen record, we define the beginning of shrub tundra expansion as the first sustained increase (replicated in three or more consecutive pollen samples) in Betula pollen above pre-15-ka background values, which are typically <5% of the pollen sum (SI Appendix, Fig. S2 and Text). In most cases, this expansion represents an increase to >20% of the pollen sum, and, where they are available, we use pollen influx data to support this timing (SI Appendix, Fig. S3). In some records, Salix pollen increases in abundance before Betula by as much as 1,200 y, and, in these cases, we consider the taxa separately (Fig. 2 and SI Appendix, Figs. S2 and S3). We define the timing of Salix expansion as the first sustained increase in Salix pollen above background values (see above). In most cases, this expansion represents an increase to >15% of the pollen sum. This approach is conservative. It provides minimum ages for the beginning of shrub expansion, as the true increase in shrub pollen above these thresholds is likely to lie between sampling points (i.e., would have an older assigned age). In records with high-resolution sampling [e.g., Birch Lake (19)], this difference is small; however, in most records, sampling resolution is ≤1 pollen spectrum every 10 cm, which may represent >500 y of sediment accumulation (SI Appendix, Table S1). With this approach, we aim to establish whether shrub expansion began prior to turnover in megafauna communities, as predicted by Guthrie (6, 8), or after populations of keystone species collapsed, as suggested by Zimov et al. (2, 29). As these hypotheses predict events in the opposite order, it allows us to assess whether the Late Pleistocene extinction of grazing megafauna species was a response to, or the cause of, steppe-tundra decline.Open in a separate windowFig. 2.(A) North Greenland ice core project (NGRIP) δ¹⁸O record (86). (B) Modeled, calibrated age ranges (shown as probability density functions) for the beginning of Salix (shown in blue when clearly defined) and Betula (shown in gray) expansion from lake sediment records reanalyzed in this study. The medians of calibrated modeled dates are indicated by black crosses. (C) The median of calibrated ¹⁴C age ranges from shrub macrofossils in eastern Beringia. (D) Kernel Density Estimation modeled distributions (mean and 1σ uncertainty) for calibrated ¹⁴C dates from moose in eastern Beringia (sum probability distributions shown in SI Appendix, Fig. S3). (E) Kernel Density Estimation modeled distributions (mean and 1σ uncertainty) for calibrated ¹⁴C dates from horse, bison, and mammoth in eastern Beringia (sum probability distributions shown in SI Appendix, Fig. S3). (F) The median of calibrated ¹⁴C age ranges from arctic ground squirrel middens in eastern Beringia. (G) Periods of human occupation at archaeological sites in the Tanana River Valley, Alaska (70).