From the Cover: Large variation in availability of Maya food plant sources during ancient droughts

Paleoclimatic evidence indicating a series of droughts in the Yucatan Peninsula during the Terminal Classic period suggests that climate change may have contributed to the disruption or collapse of Classic Maya polities. Although climate change cannot fully account for the multifaceted, political turmoil of the period, it is clear that droughts of strong magnitude could have limited food availability, potentially causing famine, migration, and societal decline. Maize was undoubtedly an important staple food of the ancient Maya, but a complete analysis of other food resources that would have been available during drought remains unresolved. Here, we assess drought resistance of all 497 indigenous food plant species documented in ethnographic, ethnobotanical, and botanical studies as having been used by the lowland Maya and classify the availability of these plant species and their edible components under various drought scenarios. Our analysis indicates availability of 83% of food plant species in short-term drought, but this percentage drops to 22% of food plant species available in moderate drought up to 1 y. During extreme drought, lasting several years, our analysis indicates availability of 11% of food plant species. Our results demonstrate a greater diversity of food sources beyond maize that would have been available to the Maya during climate disruption of the Terminal Classic period than has been previously acknowledged. While drought would have necessitated shifts in dietary patterns, the range of physiological drought responses for the available food plants would have allowed a continuing food supply under all but the most dire conditions.

It is widely accepted that something significantly disrupted ancient Maya social order during the Terminal Classic period (ca. 750 to 900/1000 CE). Population growth and the accompanying environmental impacts of deforestation have historically been suggested as causes of the social decline during this period (1). In recent years, evidence for extended droughts in the Maya Lowlands have gained prominence in both popular and academic circles as a likely cause for the Terminal Classic decline. Paleoclimatic records derived from lake and marine sediment cores and speleothems have been interpreted as indicating multiple, often closely spaced, droughts of varying intensity across the Maya Lowlands during the Terminal Classic (2–4), suggesting to some that climate impacts contributed to the disruption of Classic Maya polities and economic organization, and led to a decline in health and population levels (5). However, complex human–environmental interactions and sociopolitical factors have also been advanced as causes for what is sometimes considered more of a “reorganization” than “collapse,” in which droughts were potentially a contributing factor rather than a direct cause (6–13). We focus here on the events and processes of the Terminal Classic period, which have received the most attention regarding the possible impact of drought, while recognizing that severe droughts of both earlier and later periods would have necessitated responses by Maya groups. One of the keys for understanding the potential for drought to have destabilized ancient Maya society is whether the documented meteorological droughts led to agricultural drought and were severe enough to disrupt food production and cause food shortages. Meteorological drought refers to rainfall amounts, while agricultural drought is related to the availability of water for crops; specifically, water availability for a particular crop to grow at a particular time and place. Archaeologists have tended to equate agricultural drought directly with meteorological drought, with the assumption there is a direct causal/proportional relationship between rainfall deficit and agricultural drought. This relationship is, however, not a simple one, as we will explore in this study. Climatological publications on the Maya droughts often discuss links between droughts and the disruption of Classic Maya society, without specifically suggesting agricultural collapse (2, 14, 15), by briefly noting the potential impact on food production or agriculture (4, 16–18) or by discussing only maize in relation to drought impact on ancient agriculture (19, 20). Turning to the impact of droughts and associated famines suffered by the Maya during the Colonial period, Hoggarth and colleagues (21) use historic records to examine maize availability during droughts, while the only reference to other food plants used during droughts is a brief allusion to eating the bark of trees. Other approaches argue that droughts were a constant threat to Maya society, reaching the most disastrous levels of agricultural collapse and starvation during the Terminal Classic (22).Human populations can respond to droughts and other food stresses in a number of ways (23–25), including reliance on stored foodstuffs, crop diversification, and trading nonfood materials for food available in neighboring communities or regions. Contemporary Maya people enhance food security by planting crops in contrasting soil types (26–30) and diversifying agricultural varieties and landraces capable of production in differing microenvironments (28–32). Archaeological evidence for food storage by the ancient Maya is scant (33–35), and there is no evidence of large-scale food storage, such as storehouses, as found in several other ancient cultures of the New World (e.g., ref. 36). Ethnographic studies for the Maya document only small-scale storage facilities associated with households (37).While there is strong evidence that maize was important to the ancient Maya as both a staple food and symbolic touchstone, there has been growing evidence for and recognition of the contribution of many other crops for both their subsistence and symbolic values (38–44). Still, little attention has been given to the relative drought resistance of maize when compared to other crops. Maize is an annual herbaceous plant that gains some water conservation through the C₄ photosynthetic pathway (45) of which more drought tolerant landraces have been selected, but maize harvests can be significantly reduced during drought years (29, 46, 47). Ethnographic studies of food plant species used by contemporary Maya people during drought or food shortage indicate that many so-called famine foods are both cultivated and grow in a natural forest, representing a form of food storage through living plants. Until now, a broad analysis of the food resources that would have been available to Maya people during ancient droughts has not been undertaken. Here, we analyze the drought resistance of the 497 indigenous food plant species, documented ethnographically, as having been used by the lowland Maya (39) and estimate the range of crop and wildland plant food products that would have been available under varying levels of drought.In the Maya Lowlands, annual rainfall is divided into a wet season, generally from June to October, and a drier season, generally from November to May. Rainfall fluctuation between seasons can be significant, as can rainfall patterns within the wet season. Reduction in annual rainfall due to drought can manifest in various ways, and plants have a high diversity of responses to drought (48–50). A short-term drought could have a catastrophic impact on rain-fed herbaceous crops without any effect on woody tree crops with roots that reach the water table. Lengthening the dry season could have significant impact on agriculture and plant growth, while decreasing rainfall during a rainy season of normal length could have little or no impact on agriculture or plant growth, as long as the ground retained enough moisture for the plants to grow. It should be noted that an excess of wet season rainfall, usually a result of hurricanes or tropical storms, can also severely impact crops and livelihoods of Maya farmers (51, 52). Much of this interseasonal rainfall variation can be masked by annual precipitation records. Globally, only ∼33% of contemporary variation in crop production is explained by interannual climate variability (46). For the modern Maya, fine-scale daily rainfall variations within a growing season, rather than annual precipitation, are recognized as determining crop success or failure. Too much or too little rain within a growing season is the significant variable (53). Unfortunately, most paleoclimatological studies for the Maya region are not yet able to distinguish the seasonal distribution of rainfall reduction. One paleoclimatic study does suggest that rainfall reduction during the Terminal Classic period was likely due, primarily, to a decrease in frequency and intensity of summer season tropical rainstorms rather than a complete loss of summer tropical storm activity (15).A key to understanding the potential role of drought in ancient Maya social history is whether the droughts were intense enough to affect food production. Our evaluation of indigenous food plants is aimed at determining what would have been available under varying levels of drought during any period of ancient Maya history, based on well-established plant functional traits (54, 55) and knowledge of nutritional value for the plant parts eaten (56, 57). Our definitions for levels of drought severity used in this study are provided below in Materials and Methods. Our main questions are the following:

• 1)What is the range of growth forms and drought survival traits found among Maya food plants?
• 2)How would the availability of food plants vary during different drought intensities?
• 3)What types of plant-based foods would have been available during the most severe drought scenarios?

     

Kax and kol: collapse and resilience in lowland Maya civilization

Episodes of population loss and cultural change, including the famous Classic Collapse, punctuated the long course of Maya civilization. In many cases, these downturns in the fortunes of individual sites and entire regions included significant environmental components such as droughts or anthropogenic environmental degradation. Some afflicted areas remained depopulated for long periods, whereas others recovered more quickly. We examine the dynamics of growth and decline in several areas in the Maya Lowlands in terms of both environmental and cultural resilience and with a focus on downturns that occurred in the Terminal Preclassic (second century Common Era) and Terminal Classic (9th and 10th centuries CE) periods. This examination of available data indicates that the elevated interior areas of the Yucatán Peninsula were more susceptible to system collapse and less suitable for resilient recovery than adjacent lower-lying areas.     

Development of sedentary communities in the Maya lowlands: Coexisting mobile groups and public ceremonies at Ceibal,Guatemala

Our archaeological investigations at Ceibal, a lowland Maya site located in the Pasión region, documented that a formal ceremonial complex was built around 950 B.C. at the onset of the Middle Preclassic period, when ceramics began to be used in the Maya lowlands. Our refined chronology allowed us to trace the subsequent social changes in a resolution that had not been possible before. Many residents of Ceibal appear to have remained relatively mobile during the following centuries, living in ephemeral post-in-ground structures and frequently changing their residential localities. In other parts of the Pasión region, there may have existed more mobile populations who maintained the traditional lifestyle of the preceramic period. Although the emerging elite of Ceibal began to live in a substantial residential complex by 700 B.C., advanced sedentism with durable residences rebuilt in the same locations and burials placed under house floors was not adopted in most residential areas until 500 B.C., and did not become common until 300 B.C. or the Late Preclassic period. During the Middle Preclassic period, substantial formal ceremonial complexes appear to have been built only at a small number of important communities in the Maya lowlands, and groups with different levels of sedentism probably gathered for their constructions and for public rituals held in them. These collaborative activities likely played a central role in socially integrating diverse groups with different lifestyles and, eventually, in developing fully established sedentary communities.Recent archaeological investigations have shown that the development of agriculture and sedentism was more diverse than the simple model of agriculture leading to sedentism and then to social complexity. In Europe, for example, the farming lifestyle that originated in the Near East spread in complex ways, involving the coexistence of farmers and foragers in relatively small areas and differential adoptions of Neolithic cultural elements in different regions (1–3). Studies of early monuments, such as Göbekli Tepe in Turkey, Watson Brake in Louisiana, and Caral and earlier mounds in the Andes, show that large constructions involving significant collective labor could be built by preceramic people who were still foragers or were at the early stage of farming adaptation (4–7). These emerging understandings lead to important questions about how sedentary and mobile populations interacted and how their relations affected the process of social change. To address these questions, researchers need fine-grained chronological information and a broad spatial coverage, which are not easy to obtain in many cases. A uniquely rich dataset obtained from the Maya site of Ceibal (or Seibal) suggests the possibility that groups with different levels of mobility gathered and collaborated for constructions and public ceremonies, which contrasts with the common assumption that sedentary and mobile groups maintained separate communities.In the areas surrounding the Maya lowlands, including the southern Gulf Coast, the southern Pacific Coast, and northern Honduras, settlements with ceramic use emerged between 1900 and 1400 B.C. (8, 9). Some inhabitants of the Maya lowlands adopted maize and other domesticates possibly as early as 3400 B.C., but did not accept sedentary lifeways and ceramic use for many centuries (10). Once they began to establish villages with ceramic use around 1000 B.C., the subsequent social change was rapid. Within 1,000 y the lowland Maya developed numerous large centers with pyramids and centralized political organizations. Although a few scholars have suggested the possibility that early sedentary villages in the Maya lowlands coexisted with mobile groups (11), the specific social configurations and the process of transition have not been well understood, partly because of the rapidity of social change and partly because of difficulty in investigating early deposits deeply buried under later constructions.Since 2005 we have been conducting archaeological investigations at the site of Ceibal, Guatemala, located in the Pasión region of the southwestern Maya lowlands (Fig. 1). Previous explorations by Harvard University in the 1960s demonstrated that Ceibal was one of the earliest sedentary communities in the Maya lowlands and subsequently became a major center (12–14). Building on this pioneering work, our deep, intensive excavations targeted specific locations to reveal early constructions and deposits. With detailed stratigraphic information and ceramic data, as well as through the Bayesian analysis of radiocarbon dates, we developed a high-resolution chronology of Ceibal, which we correlated with the archaeological sequences in other parts of the Maya lowlands (SI Text, Figs. S1–S3, and Table S1). This refined chronology allowed us to reconstruct social processes on a fine temporal scale that was not possible before.Open in a separate windowFig. 1.Map of the Maya area with a close-up of the Pasión region.In addressing the development of sedentism, we need to examine its multiple dimensions as continuums rather than categorical divisions (15). In this regard, the lowland Maya of the Classic period (A.D. 250–950) possessed a particularly strong sense of attachment to fixed localities. Houses were repeatedly rebuilt over older ones in the same locations, and some of the dead were buried under house floors. In other words, kin-based groups, or at least their central members, were tied to fixed locations physically and symbolically through generations, although this practice did not preclude certain members from moving out to establish new residences. Temples and public plazas were also periodically rebuilt over previous ones, tethering entire communities to fixed locations. In examining the trajectory leading to this system, we need to analyze diverse levels of residential mobility and the possible coexistence of different modes, potentially including seasonal mobility without ceramic use, residential relocations every few years with ceramic use, and the use of durable houses without transgenerational continuity. These levels of mobility were most likely associated with different subsistence strategies and different notions of property and land ownership (16).     

Harmful algal blooms and cyanotoxins in Lake Amatitlán,Guatemala, coincided with ancient Maya occupation in the watershed

Human-induced deforestation and soil erosion were environmental stressors for the ancient Maya of Mesoamerica. Furthermore, intense, periodic droughts during the Terminal Classic Period, ca. Common Era 830 to 950, have been documented from lake sediment cores and speleothems. Today, lakes worldwide that are surrounded by dense human settlement and intense riparian land use often develop algae/cyanobacteria blooms that can compromise water quality by depleting oxygen and producing toxins. Such environmental impacts have rarely been explored in the context of ancient Maya settlement. We measured nutrients, biomarkers for cyanobacteria, and the cyanotoxin microcystin in a sediment core from Lake Amatitlán, highland Guatemala, which spans the last ∼2,100 y. The lake is currently hypereutrophic and characterized by high cyanotoxin concentrations from persistent blooms of the cyanobacterium Microcystis aeruginosa. Our paleolimnological data show that harmful cyanobacteria blooms and cyanotoxin production occurred during periods of ancient Maya occupation. Highest prehistoric concentrations of cyanotoxins in the sediment coincided with alterations of the water system in the Maya city of Kaminaljuyú, and changes in nutrient stoichiometry and maximum cyanobacteria abundance were coeval with times of greatest ancient human populations in the watershed. These prehistoric episodes of cyanobacteria proliferation and cyanotoxin production rivaled modern conditions in the lake, with respect to both bloom magnitude and toxicity. This suggests that pre-Columbian Maya occupation of the Lake Amatitlán watershed negatively impacted water potability. Prehistoric cultural eutrophication indicates that human-driven nutrient enrichment of water bodies is not an exclusively modern phenomenon and may well have been a stressor for the ancient Maya.

Dense populations of algae and cyanobacteria, called harmful algal blooms (HABs), are global environmental phenomena that are increasing in frequency and magnitude (1, 2). HABs negatively impact ecosystem processes and can lead to water column hypoxia/anoxia, alter aquatic communities, and reduce biodiversity (3, 4). Furthermore, some cyanobacteria release toxins into the environment. Cyanotoxins are metabolites that are capable of affecting the health of humans and other animals through poisoning, oxidative stress, and bioaccumulation (5, 6). Ecological drivers of HABs and cyanotoxin production include climate change [i.e., warmer temperatures (4, 7)] and cultural eutrophication [i.e., excessive urban or agricultural nutrient inputs (1, 2, 8)]. Prevention and mitigation of HABs and cyanotoxin production are of tremendous concern and are receiving considerable attention (9–11). Few studies, however, have investigated whether ancient human populations caused or were affected by toxic algal blooms (12, 13). One ancient society, known to have achieved high population densities and caused profound land cover changes, was the Maya of Mesoamerica.Maya culture first arose >3,000 y ago and experienced a florescence during the Classic Period, from ca. Common Era (CE) 250 to 900 (14). Classic Maya cities of the Mesoamerican lowlands were densely populated, and urban centers relied on intensive agricultural practices, which were associated with environmental impacts such as deforestation (15) and soil erosion (16–18). In the past few decades, evidence of profound climate changes during the period of Maya occupation has emerged, and ancient droughts in the Maya region were shown to have been temporally correlated with times of sociopolitical disintegration (19–24). Whereas these multiple environmental stressors probably affected ancient Maya society, individually and/or in concert, far less attention has been directed at exploring ancient, human-mediated changes in water quality. A few studies, however, have shown the importance of water characteristics to the ancient Maya (25) and documented water quality changes in Yucatán and Belize during the Classic Period (26, 27). A recent study that conducted 16S ribosomal rRNA amplicon sequencing on sediments from reservoirs at the ancient Maya city of Tikal (Guatemala) showed that two cyanobacteria genera capable of producing toxins, Planktothrix and Microcystis, were present at the site (28). Cyanotoxin measurements, however, were not undertaken. Concentrations of photosynthetic pigments (29, 30) and cyanotoxins (31, 32) can, however, be measured in lake sediments, making it possible to infer the magnitude of past HABs and their toxin production through time.The Lake Amatitlán watershed in highland Guatemala (Fig. 1) hosted the pre-Columbian Maya city of Kaminaljuyú, a major urban center during the Preclassic and Classic Periods, with ancient population numbers that rivaled urban centers in the Maya Lowlands (33). Whereas highland Maya areas have received less attention than lowland sites, with respect to past human demography, environmental degradation, and the Terminal Classic “collapse,” the Valley of Guatemala was home to dense Maya populations and subject to land use intensification, extensive agriculture, and changes in water quantity, similar to the lowlands (34–36). Today, Lake Amatitlán is hypereutrophic, with persistent, dense HABs, low water clarity (Secchi depths 0.1 to 0.8 m) (37), and high concentrations of the cyanotoxin microcystin, with mean values of 90 µg ⋅ L⁻¹ (extracellular) and 1,931 µg ⋅ L⁻¹ (intracellular) (38), the latter prone to settling out of the water column and accumulating in the lake sediments. The World Health Organization provisional guideline value for microcystin-LR concentration in inland waters is 1 µg ⋅ L⁻¹ (39). Lake Amatitlán hydrology is largely dominated by inputs from the Villalobos River, which drains a substantial portion of the Valley of Guatemala watershed (Fig. 1). Water is also delivered to the lake by direct rainfall, overland drilling, and discharge from small streams, but these hydrologic inputs are small compared with inflow from the Villalobos River.Open in a separate windowFig. 1.Map of the Valley of Guatemala, showing the location of Lake Amatitlán. The blue area is the lake watershed, and the pink area is the modern metropolitan area of Guatemala City. The brown box shows the location of the ancient Maya site of Kaminaljuyú, and the red dot in the lake indicates the sediment coring site. Insert A shows the location of the Guatemala highlands in Central America. Inserts B, C, and D show cyanobacteria blooms in the lake. Photographs used with permission from the National Geographic Society.We conducted a paleolimnological study, using a sediment core from Lake Amatitlán, to address two research questions: 1) did Lake Amatitlán experience HABs and cyanotoxin production during the period of ancient Maya occupation? and 2) if so, how closely did water quality degradation track documented human occupation in the catchment? We collected a 550-cm sediment core in 2019 from a site in the lake where cores for previous paleolimnological studies have been obtained (36, 40). Core chronology was established using 10 accelerator mass spectrometry radiocarbon (AMS ¹⁴C) dates and Bayesian statistics, which showed that we had retrieved a ∼2,100-y record of continuous sediment accumulation that extends from the Maya Late Preclassic Period to present. We measured concentrations of nutrients (organic carbon, total nitrogen, total phosphorus, and total sulfur), photosynthetic pigments, and cyanotoxins (total microcystins) in samples throughout the core.     

Declining vulnerability to river floods and the global benefits of adaptation

The global impacts of river floods are substantial and rising. Effective adaptation to the increasing risks requires an in-depth understanding of the physical and socioeconomic drivers of risk. Whereas the modeling of flood hazard and exposure has improved greatly, compelling evidence on spatiotemporal patterns in vulnerability of societies around the world is still lacking. Due to this knowledge gap, the effects of vulnerability on global flood risk are not fully understood, and future projections of fatalities and losses available today are based on simplistic assumptions or do not include vulnerability. We show for the first time (to our knowledge) that trends and fluctuations in vulnerability to river floods around the world can be estimated by dynamic high-resolution modeling of flood hazard and exposure. We find that rising per-capita income coincided with a global decline in vulnerability between 1980 and 2010, which is reflected in decreasing mortality and losses as a share of the people and gross domestic product exposed to inundation. The results also demonstrate that vulnerability levels in low- and high-income countries have been converging, due to a relatively strong trend of vulnerability reduction in developing countries. Finally, we present projections of flood losses and fatalities under 100 individual scenario and model combinations, and three possible global vulnerability scenarios. The projections emphasize that materialized flood risk largely results from human behavior and that future risk increases can be largely contained using effective disaster risk reduction strategies.Flooding is one of the most frequent and damaging natural hazards affecting societies across the globe, with average annual reported losses and fatalities between 1980 and 2012 exceeding $23 billion (bn) (in 2010 prices) and 5,900 people, respectively (1). These risks have been shown to negatively affect economic growth on a country level (2). Global trends and regional differences in flood risk result from the dynamics of hazard (i.e., the natural frequency and intensity of floods, without human interference), exposure (i.e., the population and economic assets located in flood hazard-prone areas), and vulnerability (i.e., the susceptibility of the exposed elements to the hazard) (3, 4). Each of these contributing factors can be expected to change over time.Trends in global flood losses have been increasing over the past decades and have been attributed mainly to increasing exposure due to high population growth and economic development in flood-prone areas (4–9). At the same time, rainfall patterns and intensities may shift under climate change (10, 11), which could influence the flood hazard (12–15). In addition, interannual variations in peak discharge, caused by climatic oscillations such as El Niño Southern Oscillation, may lead to strong spatiotemporal fluctuations in the occurrence of floods (16, 17). These hazard and exposure elements can only partly explain spatiotemporal patterns in flood risk, because of the importance of vulnerability (8, 18). There are many different and competing definitions of vulnerability in literature (see ref. 4, chap. 2, for a discussion on these). Vulnerability is considered in this study to include all man-made efforts to reduce the impact of the natural flood hazard on the exposed elements, including structural flood defenses, building quality early-warning systems, and available health care and communication facilities (19–21). Vulnerability is dynamic and varying across temporal and spatial scales, and may depend on economic, social, geographic, demographic, cultural, institutional, governance, and environmental factors (ref. 4, chap. 2). The level of vulnerability is therefore affected by socioeconomic development (ref. 4, chap. 2; see also ref. 22) and can specifically be influenced by deliberate disaster risk reduction efforts (19, 23). The reduction of vulnerability over time makes countries less prone to the adverse effects of the current and future flood hazard and is therefore considered as a display of adaptation.For example, two similar tropical cyclones made landfall in eastern India, one in 2013 (Phailin) and one in 1999 (Cyclone 05B). Exposed population was greater in 2013 due to population growth and development in cyclone-prone areas. However, the vulnerability in the region had drastically decreased with the implementation of a disaster management authority; cyclone shelters and early-warning systems ensured that only a small fraction of the population was vulnerable to this event. Because of this, the total reported impacts for the similar event in 2013 were much lower; fewer than 50 lives were lost in 2013, whereas the cyclone in 1999 was responsible for more than 10,000 lives lost (24). A similar study examined the effect of mangrove forests in the 1999 event; controlling for distance from the coast and storm surge (exposure and hazard, respectively), they found a differential vulnerability in the number of deaths as a percentage of the potentially exposed population (25).The level of vulnerability of a community is therefore reflected in the actual losses and fatalities as a share of the people and assets exposed to the flood hazard (26). In vulnerable communities, these mortality and loss rates can be expected to be higher than in less vulnerable communities for the same hazard event.Understanding the complexity of the risk chain and the resulting past and future trends in flood risk is increasingly important for international decisions on risk financing (13, 27), for the allocation of disaster risk reduction (DRR)-related development aid (28, 29), and for designing effective climate change adaptation policies (4, 30, 31). Recently, disentangling the contribution of hazard, exposure, and vulnerability has once again been emphasized explicitly in the climate change debate, as the acceptance of the Warsaw International Mechanism for Loss and Damage Associated with Climate Change Impacts in December 2013 (32) raises questions of causality, responsibility, and equity (33).The understanding of climatic and socioeconomic drivers of risk has improved considerably over the past years, and a range of studies have demonstrated that feasible estimates can be made of current and future flood hazard (34, 35) and exposure (19, 36) at a global scale. These scientific advances have recently been combined in first global-scale risk assessments under current and future climate conditions (37–39). However, the understanding of vulnerability remains one of the biggest hurdles in existing continental to global-scale flood risk assessments (33, 37). To disentangle the risk chain and identify the contribution of vulnerability on historical flood losses, it is critical to have consistent information on global flood hazard, exposure, and reported impacts. Previous recent studies (6–9) have tried to unravel reported flood loss patterns from various disaster databases by normalizing the trends using data on gross domestic product (GDP) and population growth (exposure) and, at best, simplistic climate proxies (hazard). Whereas increases in the proxies for hazard and exposure have been statistically linked to rising long-term global trends in losses, they do not represent interannual variability in flood occurrence and offer limited explanatory power for year-to-year global loss patterns. Finding evidence for changes in vulnerability in these long-term trends has therefore been very difficult (8). No previous study has yet been able to quantify the contribution of the individual risk drivers and convincingly disentangle the dynamics of hazard, exposure, and vulnerability on a global scale.Consequently, little quantitative evidence is yet available about regional differences in human and economic vulnerability to flooding; changes in this vulnerability over time under socioeconomic growth, adaptation, and DRR efforts; and how this relates to observed trends in global disaster risk (8). As a result, past trends in losses and fatalities are not fully understood; the potential effect of climate change-induced increases in flood hazard remains unclear; the global effects of adaptation measures are unquantified; and future projections of fatalities and losses available today are based on simplistic assumptions or do not include vulnerability (8, 13, 40).Here, we focus on analyzing this missing link in the risk chain. We show that variation and trends in vulnerability can be derived by modeling flood hazard and exposure at a high level of detail and paralleling these to reported impacts over the past decades. We investigate the relationship between GDP per capita and vulnerability, whereby we consider vulnerability to be represented by mortality rates (reported fatalities as a percentage of modeled exposed population) and loss rates (reported losses as a percentage of modeled exposed GDP). We also show how the vulnerability of different world regions has changed over time. Finally, we demonstrate how reducing vulnerability by improved adaptation efforts may strongly lower the magnitude of human and economic flood losses in the future.     

Warming of the Indian Ocean threatens eastern and southern African food security but could be mitigated by agricultural development

Since 1980, the number of undernourished people in eastern and southern Africa has more than doubled. Rural development stalled and rural poverty expanded during the 1990s. Population growth remains very high, and declining per-capita agricultural capacity retards progress toward Millennium Development goals. Analyses of in situ station data and satellite observations of precipitation have identified another problematic trend: main growing-season rainfall receipts have diminished by ≈15% in food-insecure countries clustered along the western rim of the Indian Ocean. Occurring during the main growing seasons in poor countries dependent on rain-fed agriculture, these declines are societally dangerous. Will they persist or intensify? Tracing moisture deficits upstream to an anthropogenically warming Indian Ocean leads us to conclude that further rainfall declines are likely. We present analyses suggesting that warming in the central Indian Ocean disrupts onshore moisture transports, reducing continental rainfall. Thus, late 20th-century anthropogenic Indian Ocean warming has probably already produced societally dangerous climate change by creating drought and social disruption in some of the world''s most fragile food economies. We quantify the potential impacts of the observed precipitation and agricultural capacity trends by modeling “millions of undernourished people” as a function of rainfall, population, cultivated area, seed, and fertilizer use. Persistence of current tendencies may result in a 50% increase in undernourished people by 2030. On the other hand, modest increases in per-capita agricultural productivity could more than offset the observed precipitation declines. Investing in agricultural development can help mitigate climate change while decreasing rural poverty and vulnerability.     

Climate,vocal folds,and tonal languages: Connecting the physiological and geographic dots

We summarize a number of findings in laryngology demonstrating that perturbations of phonation, including increased jitter and shimmer, are associated with desiccated ambient air. We predict that, given the relative imprecision of vocal fold vibration in desiccated versus humid contexts, arid and cold ecologies should be less amenable, when contrasted to warm and humid ecologies, to the development of languages with phonemic tone, especially complex tone. This prediction is supported by data from two large independently coded databases representing 3,700+ languages. Languages with complex tonality have generally not developed in very cold or otherwise desiccated climates, in accordance with the physiologically based predictions. The predicted global geographic–linguistic association is shown to operate within continents, within major language families, and across language isolates. Our results offer evidence that human sound systems are influenced by environmental factors.A standard assumption in linguistics is that sound systems are immune to ecological effects (1). This presumption has been called into question by several recent studies providing evidence for a correlation between aspects of phonology (such as sonority) and climatic and geographic factors (such as temperature, plant cover, or terrain), as well as behaviors associated with such factors (2–9). Most recently, a correlation was uncovered between ejective sounds and regions of high elevation in a sample of nearly 600 languages (10). Although two plausible physiological motivations are offered in ref. 10 for the correlation between ejective use and reduced ambient air pressure, those explanations have yet to be supported by experimental evidence. The uncovered patterns could be epiphenomenal, and in general, the cross-linguistic statistical studies in question have not been buttressed by experimental support (11).In this study, we offer evidence for a negative correlation between linguistic tone and characteristic rates of desiccation in ambient air. In contradistinction to the aforementioned studies offering geographic/phonetic correlations, however, we suggest this correlation is predicted by extensive experimental research on the properties of the human larynx. This research, which has been conducted by numerous laryngologists over the last decade and a half, has not been previously tied to the distribution of the world’s tonal languages. We submit that the research predicts that the relatively precise manipulation of the vocal folds associated with tone, especially complex tone, should be more difficult to achieve in arid climates—particularly very cold ones—when contrasted to warmer and more humid climates. We offer global, continental, and intralinguistic-family data consistent with the expected geographic/tonemic association. Our results cannot facilely be ascribed to well-known phylogenetic and areal relatedness. We conclude by suggesting that the most reasonable interpretation of the data is that the articulation of linguistic sounds is ecologically adaptive, just like other forms of human behavior.     

Coping strategies and adaptation for the disabled elderly in Taiwan

Aim: This study explored the relationship between coping strategies and adaptation difficulties for the disabled elderly. Methods: Data were collected during face‐to‐face interviews with the physically disabled elderly in long‐term care institutions and in rehabilitation departments in middle Taiwan. Totally, 505 persons were analyzed. The adaptation to disability was evaluated by health care, domestic environment, family relationships, social life and psychological distress as the dependent variables. Factor analysis and multiple regression models were applied for the analysis. Results: Three types of coping strategies were identified: (i) acceptance and action reduced the difficulty in adapting to disability in the health‐care and social life dimensions; (ii) venting and avoidance increased the difficulty in adapting in the health‐care, domestic environment and psychological distress dimensions; and (iii) seeking support was related to greater adapting to difficulty in terms of family relationships. Conclusion: More effective coping strategies should be offered to the disabled elderly to help them adapt to their disability. Geriatr Gerontol Int 2011; 11: 488–495.     

Substantial increase in concurrent droughts and heatwaves in the United States

A combination of climate events (e.g., low precipitation and high temperatures) may cause a significant impact on the ecosystem and society, although individual events involved may not be severe extremes themselves. Analyzing historical changes in concurrent climate extremes is critical to preparing for and mitigating the negative effects of climatic change and variability. This study focuses on the changes in concurrences of heatwaves and meteorological droughts from 1960 to 2010. Despite an apparent hiatus in rising temperature and no significant trend in droughts, we show a substantial increase in concurrent droughts and heatwaves across most parts of the United States, and a statistically significant shift in the distribution of concurrent extremes. Although commonly used trend analysis methods do not show any trend in concurrent droughts and heatwaves, a unique statistical approach discussed in this study exhibits a statistically significant change in the distribution of the data.Heatwaves cause severe damage to society and the environment (1), with impacts on human health, air quality, and vegetation (2, 3). In 2003, for example, European countries faced an unprecedented heatwave, which in turn caused unusually high ozone concentrations (3) and severe health problems, particularly in France, where 15,000 extra deaths occurred (3–5). United Nations Environment Programme considers the European heatwave the world’s most costly weather-related disaster in 2003. Impacts were exacerbated because the region was in a drought (6).Heatwaves have a variety of direct, indirect, immediate, and delayed impacts, including higher water loss via evapotranspiration, lower yields of grains and other agricultural products (7), increased energy consumption, a decrease in efficiency of power plants (8), air pollution, and adverse effects on human health (3, 6). Heatwaves have also contributed to an increase in the duration, size, and intensity of wildfires, causing economic losses and catastrophic environmental impacts (8).Droughts also have pronounced impacts on society and the environment, such as significant reductions in gross primary productivity, leading to shortages in food production and increases in global food prices (2). The annual economic damage caused by droughts is estimated to be approximately $7 billion globally (9), with potential impacts on livestock, transportation by river, hydropower production, bioenergy, and energy consumption (8, 10–12).Extreme climatic events can occur simultaneously, exacerbating environmental and societal impacts. Environmental hazards often result from a combination of climatic events (13, 14) over a range of spatial and temporal scales (15, 16). A wildfire, for example, may occur on a hot, dry, and windy day, although each of these individual conditions may not necessarily be extreme by themselves (16). In the Intergovernmental Panel on Climate Change special report on managing the risks of extreme events and disasters, the combination of multiple climate extreme events is termed a compound event (14, 16). Most analyses of climate and weather extremes typically tend to focus on a single climatic condition; however, this univariate approach may underestimate the effects of concurrent and compound extremes (16).Sustained precipitation deficit in summer can be a contributory factor to hot summer days (17). Heatwaves reduce the total energy transfer to the atmosphere, resulting in a decrease in convective precipitation (7). This in turn causes a soil−precipitation feedback loop that tends to extend or intensify drought conditions (7). The interaction between precipitation and temperature has been widely recognized in numerous studies (18, 19). Heatwaves concurrent with droughts can intensify individual impacts of heatwaves or drought on society, the environment, and the global economy (19, 20). Studies suggest that changes in the relationship between precipitation and temperature may be more important than the changes in each of the variables individually (16, 21). This study investigates changes in concurrent droughts and heatwaves in the United States using several different statistical techniques.A heatwave is typically defined as a period of consecutive extremely hot days (22, 23), such as five consecutive days with temperature above the 90th percentile. Here, we use the 85th, 90th, and 95th percentiles of the warm season (May–October) temperature as extreme thresholds, and three heatwave durations (3 d, 5 d, and 7 d). A 5-d heatwave with a 90th percentile threshold is defined as five consecutive days with the maximum temperature exceeding the 90th percentile of the long-term climatology for that month. In this study, meteorological droughts are defined as precipitation deficits relative to the climatology using the Standardized Precipitation Index (SPI) (24). Throughout this study, a drought is defined as an event that leads to SPI < −0.8 (approximately the 20th percentile precipitation). We use daily temperature and monthly precipitation information to identify historical droughts and heatwaves in the United States (see Data).     

Drought,drying and climate change: Emerging health issues for ageing Australians in rural areas

Older Australians living in rural areas have long faced significant challenges in maintaining health. Their circumstances are shaped by the occupations, lifestyles, environments and remoteness which characterise the diversity of rural communities. Many rural regions face threats to future sustainability and greater proportions of the aged reside in these areas. The emerging changes in Australia's climate over the past decade may be considered indicative of future trends, and herald amplification of these familiar challenges for rural communities. Such climate changes are likely to exacerbate existing health risks and compromise community infrastructure in some instances. This paper discusses climate change‐related health risks facing older people in rural areas, with an emphasis on the impact of heat, drought and drying on rural and remote regions. Adaptive health sector responses are identified to promote mitigation of this substantial emerging need as individuals and their communities experience the projected impact of climate change.     

Alpha-MSH, the melanocortin-1 receptor and background adaptation in the Mozambique tilapia, Oreochromis mossambicus

The regulation of skin darkness in vertebrates is mediated by alpha-melanophore-stimulating-hormone (alphaMSH). For this action, alphaMSH binds to the melanocortin (MC)-1 receptor, a 7-transmembrane receptor located in melanophore cell membranes. The Mozambique tilapia, Oreochromis mossambicus, can change the hue of its body in response to a change in background, a process that may involve alphaMSH and the MC1R. Scale melanophores were isolated from tilapia that were acclimatised for 25 days to a black, control grey or white background and then tested for their sensitivity to des-, mono-, and di-acetylated alphaMSH. On all backgrounds, mono-acetylated alphaMSH was the dominant isoform present in pituitary homogenates. Mono-acetylated alphaMSH also had the highest potency to disperse melanosomes. Black background adapted fish showed the highest dispersing response to alphaMSH, independent of the isoform applied. We elucidated the nucleotide and amino acid sequence of the tilapia MC1R. We show that its expression in skin does not change when tilapia are acclimatised for 25 days to a black, grey or white background, while a clear change in hue is visible. This finding, combined with the absence of differential MC1R gene expression following background acclimation indicates that the increased sensitivity to alphaMSH is most likely a result of changes in the intracellular signalling system in melanophores of black background adapted fish, rather than up-regulation of the MC1R.     

Climate change in the Fertile Crescent and implications of the recent Syrian drought

Before the Syrian uprising that began in 2011, the greater Fertile Crescent experienced the most severe drought in the instrumental record. For Syria, a country marked by poor governance and unsustainable agricultural and environmental policies, the drought had a catalytic effect, contributing to political unrest. We show that the recent decrease in Syrian precipitation is a combination of natural variability and a long-term drying trend, and the unusual severity of the observed drought is here shown to be highly unlikely without this trend. Precipitation changes in Syria are linked to rising mean sea-level pressure in the Eastern Mediterranean, which also shows a long-term trend. There has been also a long-term warming trend in the Eastern Mediterranean, adding to the drawdown of soil moisture. No natural cause is apparent for these trends, whereas the observed drying and warming are consistent with model studies of the response to increases in greenhouse gases. Furthermore, model studies show an increasingly drier and hotter future mean climate for the Eastern Mediterranean. Analyses of observations and model simulations indicate that a drought of the severity and duration of the recent Syrian drought, which is implicated in the current conflict, has become more than twice as likely as a consequence of human interference in the climate system.Beginning in the winter of 2006/2007, Syria and the greater Fertile Crescent (FC), where agriculture and animal herding began some 12,000 years ago (1), experienced the worst 3-year drought in the instrumental record (2). The drought exacerbated existing water and agricultural insecurity and caused massive agricultural failures and livestock mortality. The most significant consequence was the migration of as many as 1.5 million people from rural farming areas to the peripheries of urban centers (3, 4). Characterizing risk as the product of vulnerability and hazard severity, we first analyze Syria’s vulnerability to drought and the social impacts of the recent drought leading to the onset of the Syrian civil war. We then use observations and climate models to assess how unusual the drought was within the observed record and the reasons it was so severe. We also show that climate models simulate a long-term drying trend for the region as a consequence of human-induced climate change. If correct, this has increased the severity and frequency of occurrence of extreme multiyear droughts such as the recent one. We also present evidence that the circulation anomalies associated with the recent drought are consistent with model projections of human-induced climate change and aridification in the region and are less consistent with patterns of natural variability.     

Cortical brightness adaptation when darkness and brightness produce different dynamical states in the visual cortex

Darkness and brightness are very different perceptually. To understand the neural basis for the visual difference, we studied the dynamical states of populations of neurons in macaque primary visual cortex when a spatially uniform area (8° × 8°) of the visual field alternated between black and white. Darkness evoked sustained nerve-impulse spiking in primary visual cortex neurons, but bright stimuli evoked only a transient response. A peak in the local field potential (LFP) γ band (30–80 Hz) occurred during darkness; white-induced LFP fluctuations were of lower amplitude, peaking at 25 Hz. However, the sustained response to white in the evoked LFP was larger than for black. Together with the results on spiking, the LFP results imply that, throughout the stimulus period, bright fields evoked strong net sustained inhibition. Such cortical brightness adaptation can explain many perceptual phenomena: interocular speeding up of dark adaptation, tonic interocular suppression, and interocular masking.Light adaptation is a vitally important visual function for enabling a stable perception of the visual world when background luminance levels can be as different as night and day. Previous psychophysical studies suggested that light adaptation was caused mainly by gain control mechanisms in the retina (1–3) that have been well studied (4). However, some psychophysical results suggested that there might be also a cortical contribution to light adaptation (5), but the nature of the cortical contribution is much less well understood. Here, we report our studies of cortical adaptation to brightness and darkness in macaque primary visual cortex (V1) and the implications for visual perception.We asked the following question: how does macaque V1 cortex respond to large dark and bright regions like those that would comprise the background of a visual scene during the night or the day, respectively? The experiments reported here focused on two cortical layers, 4C and 2/3. The layers of V1 are distinct stages of processing of visual signals (6, 7). The input layer 4C is the first cortical stage where the cortex could distinguish between blackness and whiteness (8). Layer 2/3 comprise one of the main visual outputs of V1 to extrastriate visual cortex (9). To obtain a comprehensive view of the response to black and white in cortical layers 4C and 2/3, we used measurements of population activity: multiunit spike rate, termed multiunit activity (MUA), and local field potential (LFP) (10–12).Cortical brightness adaptation was evident in the qualitatively different dynamics of neural population activity in layers 4C and 2/3 when the monkeys viewed black and white regions. Both black and white large-area stimuli evoked transient excitatory responses in MUA, but in response to a white region, there was a slowly developing but much stronger inhibition of spike activity. Such suppression of sustained spiking in cortical neurons by white backgrounds would increase the signal/noise ratio of targets on white backgrounds. Such cortical brightness adaptation is likely the explanation for many previously observed perceptual phenomena such as tonic interocular suppression, dichoptic effects in light and dark adaptation, and interocular masking (5, 13–16).     

From the Cover: Genomic structural variants constrain and facilitate adaptation in natural populations of Theobroma cacao,the chocolate tree

Genomic structural variants (SVs) can play important roles in adaptation and speciation. Yet the overall fitness effects of SVs are poorly understood, partly because accurate population-level identification of SVs requires multiple high-quality genome assemblies. Here, we use 31 chromosome-scale, haplotype-resolved genome assemblies of Theobroma cacao—an outcrossing, long-lived tree species that is the source of chocolate—to investigate the fitness consequences of SVs in natural populations. Among the 31 accessions, we find over 160,000 SVs, which together cover eight times more of the genome than single-nucleotide polymorphisms and short indels (125 versus 15 Mb). Our results indicate that a vast majority of these SVs are deleterious: they segregate at low frequencies and are depleted from functional regions of the genome. We show that SVs influence gene expression, which likely impairs gene function and contributes to the detrimental effects of SVs. We also provide empirical support for a theoretical prediction that SVs, particularly inversions, increase genetic load through the accumulation of deleterious nucleotide variants as a result of suppressed recombination. Despite the overall detrimental effects, we identify individual SVs bearing signatures of local adaptation, several of which are associated with genes differentially expressed between populations. Genes involved in pathogen resistance are strongly enriched among these candidates, highlighting the contribution of SVs to this important local adaptation trait. Beyond revealing empirical evidence for the evolutionary importance of SVs, these 31 de novo assemblies provide a valuable resource for genetic and breeding studies in T. cacao.

For more than a century, genomic structural variants (SVs) have been recognized as an important source of functional variation (1–3). Such variants influence the presence, quantity, position, and/or direction of nucleotide sequence, commonly affecting a larger proportion of the genome than single-nucleotide polymorphisms (SNPs) (4–8). SVs also can have large phenotypic effects (9–12) and contribute to adaptation and speciation (13, 14). However, genome-scale analyses have revealed that SVs usually segregate at low frequencies and are depleted from functional regions of the genome, indicating strong purifying selection (4, 7, 15, 16). Despite this general observation, processes responsible for the fitness effects are poorly understood. The fitness consequences of SVs could be due to direct effects on gene function, through disruption of coding regions or regulatory elements (17–19), or the effects may be indirect, arising from suppression of recombination (20, 21).The suppression of recombination by SVs might play an important role in local adaptation, as theory predicts that SVs can shelter locally beneficial alleles from gene flow by preventing or reducing the formation of viable crossovers within chromosomal heterozygotes (22, 23). Consistent with this expectation, SVs—particularly inversions—have been associated with locally beneficial phenotypes in multiple species, including Mimulus guttatus (24), Zea mays (25), Boechera stricta (26), and Helianthus annuus (27). However, the suppression of recombination also has a downside, as it reduces the effective population size (N_e) of the arrangements. The lower N_e can, in turn, weaken the efficacy of purifying selection and thus increase the accumulation of deleterious mutations within the SVs (28, 29).To examine the fitness consequences of SVs, we constructed chromosome-scale, haplotype-resolved de novo assemblies for 31 wild-collected accessions of Theobroma cacao (hereafter cacao). Most previous work on the evolutionary role of SVs has been conducted on short-lived, selfing, and/or domesticated species. By contrast, cacao is a predominantly outcrossing and long-lived perennial with diverse accessions originating from undomesticated populations (30, 31). The combination of wild-collected accessions and SV detection based on diploid assemblies—the gold standard of SV detection (32)—makes our dataset uniquely suited for studying the evolutionary impact of SVs in natural populations. We ask the following questions: What are the overall fitness effects of SVs? Do SVs influence gene expression, suggestive of impaired gene function? Do SVs accumulate deleterious nucleotide variants as a result of suppressed recombination? What proportion of SVs are likely contributors to local adaptation?     

Glucocorticoid receptor upregulation during seawater adaptation in a euryhaline teleost,the tilapia (Oreochromis mossambicus)

Cortisol is an important seawater (SW) osmoregulatory hormone in the Mozambique tilapia (Oreochromis mossambicus), a highly euryhaline cichlid able to live in environments ranging from fresh water (FW) to salinities well in excess of full-strength seawater. Previous studies indicate that cortisol may promote SW adaptation by increasing gill chloride cell differentiation, Na(+)/K(+)-ATPase activity and subsequent excretion of excess salt following seawater acclimation. Despite cortisol's widely accepted role as a SW-adapting hormone, cortisol receptor regulation during SW acclimation is not well understood. The purpose of these studies was to determine whether the intracellular glucocorticoid receptor (GR) might be regulated in a manner consistent with cortisol's actions in SW adaptation. Saturation radioligand binding assays were conducted on gill cytoplasm preparations from fish sampled 4 and 24h and 4 and 14 days after transfer from FW to 2/3 SW or FW (control). Affinity (K(d)) of the gill GR remained constant over the timecourse, while numbers of receptors (B(max)) in SW fish were significantly elevated compared with controls at 24h and 4 days after transfer. Plasma osmolality was higher in fish transferred to SW for 24h, 4 days, and 14 days compared with those animals moved to FW. Plasma cortisol levels and hepatic cortisol binding remained constant between SW and FW fish throughout the timecourse of the salinity challenge. These studies indicate that seawater acclimation is accompanied by a specific upregulation of intracellular GR numbers in gill tissue. The lack of increase in circulating cortisol following SW adaptation may reflect enhancement of clearance of the steroid. It appears that an increase in cortisol receptors, which is closely associated with the rise in blood osmotic pressure that accompanies SW exposure, is an important component of cortisol's ability to promote SW adaptation in the tilapia.     

Population genomic structure and adaptation in the zoonotic malaria parasite Plasmodium knowlesi

Malaria cases caused by the zoonotic parasite Plasmodium knowlesi are being increasingly reported throughout Southeast Asia and in travelers returning from the region. To test for evidence of signatures of selection or unusual population structure in this parasite, we surveyed genome sequence diversity in 48 clinical isolates recently sampled from Malaysian Borneo and in five lines maintained in laboratory rhesus macaques after isolation in the 1960s from Peninsular Malaysia and the Philippines. Overall genomewide nucleotide diversity (π = 6.03 × 10⁻³) was much higher than has been seen in worldwide samples of either of the major endemic malaria parasite species Plasmodium falciparum and Plasmodium vivax. A remarkable substructure is revealed within P. knowlesi, consisting of two major sympatric clusters of the clinical isolates and a third cluster comprising the laboratory isolates. There was deep differentiation between the two clusters of clinical isolates [mean genomewide fixation index (F_ST) = 0.21, with 9,293 SNPs having fixed differences of F_ST = 1.0]. This differentiation showed marked heterogeneity across the genome, with mean F_ST values of different chromosomes ranging from 0.08 to 0.34 and with further significant variation across regions within several chromosomes. Analysis of the largest cluster (cluster 1, 38 isolates) indicated long-term population growth, with negatively skewed allele frequency distributions (genomewide average Tajima’s D = −1.35). Against this background there was evidence of balancing selection on particular genes, including the circumsporozoite protein (csp) gene, which had the top Tajima’s D value (1.57), and scans of haplotype homozygosity implicate several genomic regions as being under recent positive selection.The zoonotic malaria parasite Plasmodium knowlesi is a significant cause of human malaria, with a wide spectrum of clinical outcomes including high parasitemia and death (1–4). Long known as a malaria parasite of long-tailed and pig-tailed macaques (5), the first large focus of human cases was described only in 2004 in the Kapit Division of Sarawak in Malaysian Borneo (6). Since then infections have been described from almost all countries in Southeast Asia (2, 7). Travelers to the region from Europe, North America, and Australasia also have recently acquired P. knowlesi malaria (7, 8). Until the application of molecular assays for specific detection, human P. knowlesi malaria was largely misdiagnosed as Plasmodium malariae, a morphologically similar but distantly related species (1, 6, 9, 10). Studies in the Kapit Division of Sarawak in Malaysian Borneo have indicated that P. knowlesi malaria is primarily a zoonosis with macaques as reservoir hosts (11) and that the forest-dwelling mosquito species Anopheles latens is the local vector for P. knowlesi (12). Other members of the Anopheles leucosphyrus group are vectors in different parts of Southeast Asia and may determine the geographical distribution of transmission (13, 14).Although P. knowlesi malaria is regarded as an emerging infection, there clearly have been increased efforts in detection made since its existence as a significant zoonosis was discovered, and specific detection has been enhanced by the declining numbers of human cases caused by other malaria parasites in Southeast Asia (15). Aside from the first two human cases described several decades ago (5), there is direct evidence of human P. knowlesi infections from ∼20 y ago in Malaysian Borneo and Thailand obtained by retrospective molecular analysis of material from archived blood spots and slides (10, 16), and molecular population genetic evidence indicates the zoonosis has been in existence for a much longer time (11). The genetic diversity of P. knowlesi is high within humans as well as macaques, with sequence data on three loci [the circumsporozoite protein (csp) gene, 18S rRNA, and mtDNA genome] indicating extensive shared polymorphism and no fixed differences between P. knowlesi parasites from humans and monkeys sampled in the same area in Sarawak, Malaysian Borneo (6, 11). Analysis of samples from a smaller number of humans and monkeys in Thailand showed alleles of the P. knowlesi merozoite surface protein 1 (msp1) gene to be similarly diverse in both hosts (16), and there were shared polymorphisms of the csp gene in parasites from a few infections examined in humans and macaques in Singapore (17). Recent multilocus microsatellite analysis has indicated a deep population subdivision in P. knowlesi associated with long-tailed and pig-tailed macaques; both major types infect humans and occur sympatrically at most sites in Malaysia, but the two types show some additional geographical differentiation across sites (18).Human populations have grown very rapidly in the Southeast Asian region and encroach on most of the wild macaque habitats, so it is vital to know if P. knowlesi parasites are adapting to human hosts or to anthropophilic mosquito vector species, either of which could cause human–mosquito–human transmission. Initial analysis of the P. knowlesi reference genome sequence (strain H) highlighted some unique features of the genome of this species (19), namely, schizont infected cell agglutination variant (SICAvar) and knowlesi interspersed repeat (KIR) variant antigen genes, which were widely dispersed instead of being predominantly localized in subtelomeric regions as seen in large gene families in Plasmodium falciparum and Plasmodium vivax (20). Here, we analyzed genomewide diversity in P. knowlesi and conducted scans for signatures of balancing and directional selection, revealing extremely high genetic diversity and significant structuring of this species into subpopulation clusters that appear to be reproductively isolated as well as loci that show evidence of recent strong selection.     

Forest responses to increasing aridity and warmth in the southwestern United States

In recent decades, intense droughts, insect outbreaks, and wildfires have led to decreasing tree growth and increasing mortality in many temperate forests. We compared annual tree-ring width data from 1,097 populations in the coterminous United States to climate data and evaluated site-specific tree responses to climate variations throughout the 20th century. For each population, we developed a climate-driven growth equation by using climate records to predict annual ring widths. Forests within the southwestern United States appear particularly sensitive to drought and warmth. We input 21st century climate projections to the equations to predict growth responses. Our results suggest that if temperature and aridity rise as they are projected to, southwestern trees will experience substantially reduced growth during this century. As tree growth declines, mortality rates may increase at many sites. Increases in wildfires and bark-beetle outbreaks in the most recent decade are likely related to extreme drought and high temperatures during this period. Using satellite imagery and aerial survey data, we conservatively calculate that ≈ 2.7% of southwestern forest and woodland area experienced substantial mortality due to wildfires from 1984 to 2006, and ≈ 7.6% experienced mortality associated with bark beetles from 1997 to 2008. We estimate that up to ≈ 18% of southwestern forest area (excluding woodlands) experienced mortality due to bark beetles or wildfire during this period. Expected climatic changes will alter future forest productivity, disturbance regimes, and species ranges throughout the Southwest. Emerging knowledge of these impending transitions informs efforts to adaptively manage southwestern forests.