An Ancient, Unified Mechanism for Metformin Growth Inhibition in C. elegans and Cancer.

Metformin has utility in cancer prevention and treatment, though the mechanisms for these effects remain elusive. Through genetic screening in C. elegans, we uncover two metformin response elements: the nuclear pore complex (NPC) and acyl-CoA dehydrogenase family member-10 (ACAD10). We demonstrate that biguanides inhibit growth by inhibiting mitochondrial respiratory capacity, which restrains transit of the RagA-RagC GTPase heterodimer through the NPC. Nuclear exclusion renders RagC incapable of gaining the GDP-bound state necessary to stimulate mTORC1. Biguanide-induced inactivation of mTORC1 subsequently inhibits growth through transcriptional induction of ACAD10. This ancient metformin response pathway is conserved from worms to humans. Both restricted nuclear pore transit and upregulation of ACAD10 are required for biguanides to reduce viability in melanoma and pancreatic cancer cells, and to extend C. elegans lifespan. This pathway provides a unified mechanism by which metformin kills cancer cells and extends lifespan, and illuminates potential cancer targets. PAPERCLIP.

Laser micro-machining and damage testing of rounded shadow cone blockers on silica glass for arresting laser damage growth by redirection of light.

Structured conical blockers manufactured on optical input surfaces are being used to shadow, and thereby, arrest growth of exit surface damage on large optics for applications in high-energy laser systems to extend their lifetime usage. However, as the size of the Shadow Cone Blocker (SCB) is increased, the deflected light must be carefully managed to prevent consequential damage from downstream intensification. Here, we design and fabricate a distinct input SCB geometry to alleviate this problem, enabling larger damage site mitigation. The demonstrated ∼1 mm diameter SCB was manufactured with a convergent approach using a CO2 pulsed laser ablative scanning sequence on a fused silica window. The SCB design was refined to maximize resistance to both input and exit surface damage initiations on 1 cm thick fused silica windows when exposed to 351 nm irradiation and validated with laser damage testing. The design showed to prevent damage onset to the exit surface for incident fluences on the SCB of 10.7 ± 1.3  J·cm-2 and is resistant to damage on the input surface exceeding 30 J·cm-2 input fluence.

Outcomes up to age 36 months after congenital Zika virus infection-U.S. states.

BACKGROUND: To characterize neurodevelopmental abnormalities in children up to 36 months of age with congenital Zika virus exposure. METHODS: From the U.S. Zika Pregnancy and Infant Registry, a national surveillance system to monitor pregnancies with laboratory evidence of Zika virus infection, pregnancy outcomes and presence of Zika associated birth defects (ZBD) were reported among infants with available information. Neurologic sequelae and developmental delay were reported among children with ≥1 follow-up exam after 14 days of age or with ≥1 visit with development reported, respectively. RESULTS: Among 2248 infants, 10.1% were born preterm, and 10.5% were small-for-gestational age. Overall, 122 (5.4%) had any ZBD; 91.8% of infants had brain abnormalities or microcephaly, 23.0% had eye abnormalities, and 14.8% had both. Of 1881 children ≥1 follow-up exam reported, neurologic sequelae were more common among children with ZBD (44.6%) vs. without ZBD (1.5%). Of children with ≥1 visit with development reported, 46.8% (51/109) of children with ZBD and 7.4% (129/1739) of children without ZBD had confirmed or possible developmental delay. CONCLUSION: Understanding the prevalence of developmental delays and healthcare needs of children with congenital Zika virus exposure can inform health systems and planning to ensure services are available for affected families. IMPACT: We characterize pregnancy and infant outcomes and describe neurodevelopmental abnormalities up to 36 months of age by presence of Zika associated birth defects (ZBD). Neurologic sequelae and developmental delays were common among children with ZBD. Children with ZBD had increased frequency of neurologic sequelae and developmental delay compared to children without ZBD. Longitudinal follow-up of infants with Zika virus exposure in utero is important to characterize neurodevelopmental delay not apparent in early infancy, but logistically challenging in surveillance models.

Wide-field probing of silica laser-induced damage precursors by photoluminescence photochemical quenching.

We describe a wide-field approach to probe transient changes in photoluminescence (PL) of defects on silica surfaces. This technique allows simultaneous capture of spatially resolved PL with spontaneous quenching behavior. We attribute the quenching of PL intensity to photochemical reactions of surface defects and/or subsurface fractures with ambient molecules. Such quenching curves can be accurately reproduced by our theoretical model using two quenchable defect populations with different reaction rates. The fitting parameters of our model are spatially correlated to fractures in silica where point defects and mechanical stresses are known to be present, potentially indicating regions prone to laser-induced damage growth. We believe that our approach allows rapid spatial resolved identification of damage prone morphology, providing a new pathway to fast, non-destructive predictions of laser-induced damage growth.

Enhanced laser-induced damage performance of all-glass metasurfaces for energetic pulsed laser applications.

To fabricate optical components with surface layers compatible with high-power laser applications that may operate as antireflective coatings, polarization rotators, or harness physical anisotropy for other uses, metasurfaces are becoming an appealing candidate. In this study, large-beam (1.05 cm diameter) 351-nm laser-induced damage testing was performed on an all-glass metasurface structure composed of cone-like features with a subwavelength spacing of adjacent features. These structures were fabricated on untreated fused silica glass and damage tested, as were structures that were fabricated on fused silica glass that experienced a preliminary etching process to remove the surface Beilby layer that is characteristic of polished fused silica. The laser-induced damage onset for structures on untreated fused silica glass was 19.3J⋅c m -2, while the sample that saw an initial pretreatment etch exhibited an improved damage onset of 20.4J⋅c m -2, only 6% short of the reference pretreated glass damage onset of 21.7J⋅c m -2. For perspective, the National Ignition Facility operational average fluence at this wavelength and pulse length is about 10J/c m 2. At a fluence of 25.5J⋅c m -2, the reference (pretreated) fused silica initiated 5.2 damage sites per m m 2, while the antireflective metasurface sample with a preliminary etching process treatment initiated 9.8 damage sites per m m 2. These findings demonstrate that substrate-engraved metasurfaces are compatible with high energy and power laser applications, further broadening their application space.

Competition between bridged dinucleotides and activated mononucleotides determines the error frequency of nonenzymatic RNA primer extension.

Nonenzymatic copying of RNA templates with activated nucleotides is a useful model for studying the emergence of heredity at the origin of life. Previous experiments with defined-sequence templates have pointed to the poor fidelity of primer extension as a major problem. Here we examine the origin of mismatches during primer extension on random templates in the simultaneous presence of all four 2-aminoimidazole-activated nucleotides. Using a deep sequencing approach that reports on millions of individual template-product pairs, we are able to examine correct and incorrect polymerization as a function of sequence context. We have previously shown that the predominant pathway for primer extension involves reaction with imidazolium-bridged dinucleotides, which form spontaneously by the reaction of two mononucleotides with each other. We now show that the sequences of correctly paired products reveal patterns that are expected from the bridged dinucleotide mechanism, whereas those associated with mismatches are consistent with direct reaction of the primer with activated mononucleotides. Increasing the ratio of bridged dinucleotides to activated mononucleotides, either by using purified components or by using isocyanide-based activation chemistry, reduces the error frequency. Our results point to testable strategies for the accurate nonenzymatic copying of arbitrary RNA sequences.

Interpersonal Discrimination, Neighborhood Inequities, and Children's Body Mass Index: A Descriptive, Cross-Sectional Analysis.

Psychosocial stressors have been implicated in childhood obesity, but the role of racism-related stressors is less clear. This study explored associations between neighborhood inequities, discrimination/harassment, and child body mass index (BMI). Parents of children aged 5-9 years from diverse racial/ethnic backgrounds (n = 1307), completed surveys of their child's exposure to discrimination/harassment. Census tract data derived from addresses were used to construct an index of concentration at the extremes, a measure of neighborhood social polarization. Child's height and weight were obtained from medical records. Multiple regression and hierarchical models examined child's BMI and racism at the individual and census tract levels. Children residing in the most Black-homogenous census tracts had 8.2 percentage units higher BMI percentile (95% confidence interval, 1.5-14.9) compared with white-homogenous tracts (P = .03). Household income and home values were lower, poverty rates higher, and single parent households more common among Black-homogeneous census tracts. Almost 30% of children experienced discrimination/harassment in the past year, which was associated with a 5.28-unit higher BMI percentile (95% confidence interval, 1.72-8.84; P = .004). Discrimination and racial/economic segregation were correlated with higher child BMI. Longitudinal studies are needed to understand whether these factors may be related to weight gain trajectories and future health.

Meta-analysis and machine learning-augmented mixed effects cohort analysis of improved diets among 5847 medical trainees, providers and patients.

OBJECTIVE: We sought to produce the first meta-analysis (of medical trainee competency improvement in nutrition counseling) informing the first cohort study of patient diet improvement through medical trainees and providers counseling patients on nutrition. DESIGN: (Part A) A systematic review and meta-analysis informing (Part B) the intervention analysed in the world's largest prospective multi-centre cohort study on hands-on cooking and nutrition education for medical trainees, providers and patients. SETTINGS: (A) Medical educational institutions. (B) Teaching kitchens. PARTICIPANTS: (A) Medical trainees. (B) Trainees, providers and patients. RESULTS: (A) Of the 212 citations identified (n 1698 trainees), eleven studies met inclusion criteria. The overall effect size was 9·80 (95 % CI (7·15, 12·45) and 95 % CI (6·87, 13·85); P < 0·001), comparable with the machine learning (ML)-augmented results. The number needed to treat for the top performing high-quality study was 12. (B) The hands-on cooking and nutrition education curriculum from the top performing study were applied for medical trainees and providers who subsequently taught patients in the same curriculum (n 5847). The intervention compared with standard medical care and education alone significantly increased the odds of superior diets (high/medium v. low Mediterranean diet adherence) for residents/fellows most (OR 10·79, 95 % CI (4·94, 23·58); P < 0·001) followed by students (OR 9·62, 95 % CI (5·92, 15·63); P < 0·001), providers (OR 5·19, 95 % CI (3·23, 8·32), P < 0·001) and patients (OR 2·48, 95 % CI (1·38, 4·45); P = 0·002), results consistent with those from ML. CONCLUSIONS: The current study suggests that medical trainees and providers can improve patients' diets with nutrition counseling in a manner that is clinically and cost effective and may simultaneously advance societal equity.

Deep sequencing of non-enzymatic RNA primer extension.

Life emerging in an RNA world is expected to propagate RNA as hereditary information, requiring some form of primitive replication without enzymes. Non-enzymatic template-directed RNA primer extension is a model of the copying step in this posited form of replication. The sequence space accessed by primer extension dictates potential pathways to self-replication and, eventually, ribozymes. Which sequences can be accessed? What is the fidelity of the reaction? Does the recently illuminated mechanism of primer extension affect the distribution of sequences that can be copied? How do sequence features respond to experimental conditions and prebiotically relevant contexts? To help answer these and related questions, we here introduce a deep-sequencing methodology for studying RNA primer extension. We have designed and vetted special RNA constructs for this purpose, honed a protocol for sample preparation and developed custom software that analyzes sequencing data. We apply this new methodology to proof-of-concept controls, and demonstrate that it works as expected and reports on key features of the sequences accessed by primer extension.

Current state of athalassohaline deep-sea hypersaline anoxic basin research-recommendations for future work and relevance to astrobiology.

Deep-sea hypersaline anoxic basins (DHABs) are uniquely stratified polyextreme environments generally found in enclosed seas. These environments select for elusive and widely uncharacterized microbes that may be living below the currently recognized window of life on Earth. Still, there is strong evidence of highly specialized active microbial communities in the Kryos, Discovery, and Hephaestus basins located in the Eastern Mediterranean Sea; the only known athalassohaline DHABs. Life is further constrained in these DHABs as near-saturated concentrations of magnesium chloride significantly reduces water activity (aw ) and exerts extreme chaotropic stress, the tendency of a solution to disorder biomolecules. In this review, we provide an overview of microbial adaptations to polyextremes focusing primarily on chaotropicity, summarize current evidence of microbial life within athalassohaline DHABs and describe the difficulties of life detection approaches and sampling within these environments. We also reveal inconsistent measurements of chaotropic activity in the literature highlighting the need for a new methodology. Finally, we generate recommendations for future investigations and discuss the importance of athalassohaline DHAB research to help inform extraterrestrial life detection missions.

Microbial diversity and activity in Southern California salterns and bitterns: analogues for remnant ocean worlds.

Concurrent osmotic and chaotropic stress make MgCl2 -rich brines extremely inhospitable environments. Understanding the limits of life in these brines is essential to the search for extraterrestrial life on contemporary and relict ocean worlds, like Mars, which could host similar environments. We sequenced environmental 16S rRNA genes and quantified microbial activity across a broad range of salinity and chaotropicity at a Mars-analogue salt harvesting facility in Southern California, where seawater is evaporated in a series of ponds ranging from kosmotropic NaCl brines to highly chaotropic MgCl2 brines. Within NaCl brines, we observed a proliferation of specialized halophilic Euryarchaeota, which corresponded closely with the dominant taxa found in salterns around the world. These communities were characterized by very slow growth rates and high biomass accumulation. As salinity and chaotropicity increased, we found that the MgCl2 -rich brines eventually exceeded the limits of microbial activity. We found evidence that exogenous genetic material is preserved in these chaotropic brines, producing an unexpected increase in diversity in the presumably sterile MgCl2 -saturated brines. Because of their high potential for biomarker preservation, chaotropic brines could therefore serve as repositories of genetic biomarkers from nearby environments (both on Earth and beyond) making them prime targets for future life-detection missions.

Fused silica optics damage from downstream intensification on laser-induced damage precursors.

Management and control of damage initiation and growth on high-value National Ignition Facility (NIF) optics are critical to its operation. Cone-shaped features are currently being used on the input surfaces to arrest growth of exit surface damage by creating "shadows." Light refracted from the walls of the cones interferes with the incident beam at the exit surface to create an intensified annulus. Significant exit surface damage was observed at the locations of these annuli. Analysis showed that this damage is consistent with a recently reported new mechanism that degrades damage resistance by dispersing damage precursors over the surface upon exposure to UV laser radiation. This has significant implications for the design and operation of high-energy and power laser systems such as the NIF.

Aneurysmal subarachnoid hemorrhage during pregnancy: a comprehensive and systematic review of the literature.

Aneurysmal subarachnoid hemorrhage (aSAH) is an emergent condition requiring rapid intervention and prolonged monitoring. There are few recommendations regarding the management of aSAH in pregnancy. We identified all available literature and compiled management decisions as well as reported outcomes through a systematic literature review without meta-analysis to provide recommendations for management of aSAH during pregnancy. We included a total of 23 articles containing 54 cases of pregnancy-related aSAH in our review. From these reports and other literature, we evaluated information on aSAH pathophysiology, diagnosis, and management with respect to pregnancy. Early transfer to an appropriate facility with neurocritical care, a high-risk obstetric service, and a neurosurgery team available is crucial for the management of aSAH in pregnancy. Intensive monitoring and a multidisciplinary approach remain fundamental to ensure maternal and fetal health.

Patient-reported outcomes in stroke clinical trials 2002-2016: a systematic review.

OBJECTIVE: Given the global and economic burden of stroke as a major cause of long-term disability, patient-reported outcomes (PRO) data from clinical trials can elucidate differential benefits/harms of interventions from patients' perspectives and influence clinical decision making in stroke care management. METHODS: This systematic review examines stroke-related randomized controlled trials (RCT) published in 12 high-impact journals between 2002 and 2016 for (1) associations between trial characteristics and the reporting of PRO measures; and (2) psychometric properties of PRO instruments used in these studies. The study combines clinical trials identified in a prior review with trials identified with an updated literature search. RESULTS: Only 34 of 159 stroke-related RCTs reported PRO measures. Among the 34 trials, most were published in rehabilitation and general medical journals, were conducted in the United States or Europe, were funded by government/non-industry sponsors, and focused on post-stroke care. Thirty-one PRO instruments were employed in these studies. Only 5 instruments were stroke-specific measures, whereas the remaining 26 instruments were generic measures. Eight instruments assessed functional status, 9 measured quality of life, and 14 assessed symptoms. The most common health domains measured were emotional status and physical function. CONCLUSIONS: This study highlights the paucity of information from patients' perspective in stroke-related RCTs. This trend may change over time as researchers increase adherence to reporting guidelines for clinical trial protocols.

CarrierSeq: a sequence analysis workflow for low-input nanopore sequencing.

BACKGROUND: Long-read nanopore sequencing technology is of particular significance for taxonomic identification at or below the species level. For many environmental samples, the total extractable DNA is far below the current input requirements of nanopore sequencing, preventing "sample to sequence" metagenomics from low-biomass or recalcitrant samples. RESULTS: Here we address this problem by employing carrier sequencing, a method to sequence low-input DNA by preparing the target DNA with a genomic carrier to achieve ideal library preparation and sequencing stoichiometry without amplification. We then use CarrierSeq, a sequence analysis workflow to identify the low-input target reads from the genomic carrier. We tested CarrierSeq experimentally by sequencing from a combination of 0.2 ng Bacillus subtilis ATCC 6633 DNA in a background of 1000 ng Enterobacteria phage λ DNA. After filtering of carrier, low quality, and low complexity reads, we detected target reads (B. subtilis), contamination reads, and "high quality noise reads" (HQNRs) not mapping to the carrier, target or known lab contaminants. These reads appear to be artifacts of the nanopore sequencing process as they are associated with specific channels (pores). CONCLUSION: By treating sequencing as a Poisson arrival process, we implement a statistical test to reject data from channels dominated by HQNRs while retaining low-input target reads.

The shifting burden of neurosurgical disease: Vietnam and the middle-income nations.

OBJECTIVE: The Global Burden of Disease (GBD) is an international collaboration and the largest comprehensive investigation of global health disease burden ever conducted. It has been particularly insightful for understanding disease demographics in middle-income nations undergoing rapid development, such as Vietnam, where 6 of the top 10 causes of death are relevant to the neurosurgeon. The burden of stroke-the number one cause of death in Vietnam-is particularly impressive. Likewise, road injuries, with a disproportionate rate of traumatic brain injury, continue to increase in Vietnam following economic development. Low-back and neck pain is the number one cause of disability. Simultaneously, more patients have access to care, and healthcare spending is increased. METHODS: It is imperative that neurosurgical capital and infrastructure keep pace with Vietnam's growth. The authors searched the existing literature for assessments of neurosurgical infrastructure or initiatives to address neurosurgical disease burden. Using GBD data, the authors also abstracted data for death by cause and prevalence of years of life lost due to disability (YLD) for common neurosurgical pathologies for Vietnam and comparison nations. RESULTS: Interventions aimed at primary prevention of risk factors for neurosurgical disease and focused on the transference of self-sustainable technical skills were found to be analogous to those that have been successful in other regions. Efforts toward stroke prevention have been focused on causal risk factors. Multiple investigators have found that interventions aimed at increasing helmet use were successful in preventing traumatic brain injury. Government-led reforms and equipment donation programs have improved technical capacity. Nevertheless, Vietnam lags behind other nations in neurosurgeons per capita; cause-attributable death and YLD attributable to neurosurgical disease are considerably higher in Vietnam and middle-income nations compared to both lower-income nations and upper-income nations. CONCLUSIONS: More than two-thirds of deaths attributable to neurosurgical pathologies in Vietnam and other middle-income nations were due to stroke, and one-fifth of both cause-attributable death and YLD was associated with neurosurgical pathologies. Vietnam and other middle-income nations continue to assume a global burden of disease profile that ever more closely resembles that of developed nations, with particular cerebrovascular, neurotrauma, and spinal disease burdens, leading to exponentially increased demand for neurosurgeons that threatens to outpace the training of neurosurgeons.

Decompressive Medial Cuneiform Exostectomy for Resistant Tibialis Anterior Insertional Tendinopathy.

Distal tibialis anterior tendinopathy, as a clinical entity, has only recently been documented in foot and ankle studies. We report our experience with medial cuneiform decompressive exostectomy and superficial tendon debridement in 14 cases of recalcitrant tibilalis anterior insertional pain. We reviewed 13 patients (14 feet; 12 females, 1 male; mean age 67.9 ± 7.5; range 55 to 80 years) in whom conservative treatment had failed who had undergone debridement of the insertional tibialis anterior tendon and decompressive exostectomy of the medial cuneiform. Pre- and postoperative American Orthopaedic Foot and Ankle Society (AOFAS) midfoot scale and visual analog scale (VAS) pain scores, local clinical findings, and dorsiflexion power at an average follow-up period of 28 ± 17.9 (range 6 to 55) months were assessed. All patients had experienced burning, nocturnal, medial midfoot pain and disability. The symptom longevity preoperatively was 8.5 ± 3.1 (range 6 to 17) months. Peritendinous or intrasubstance signal changes were noted on magnetic resonance imaging in 10 feet (71%). The mean preoperative VAS pain score was 8.7 ± 1.3 (range 5 to10), whereas postoperative it was 0.4 ± 0.5 (range 0 to1) (p = .001). The mean preoperative and postoperative AOFAS midfoot scale score was 54 ± 14.5 (range 20 to 70) and 91 ± 6.8 (range 79 to 100), respectively (p = .001). Postoperative ankle dorsiflexion power was normal and local tenderness had resolved in all patients. One patient (7.1%) stumbled at 2 weeks, resulting in avulsion of the tibialis anterior tendon, requiring transosseous fixation and gastrocnemius recession. All patients reported satisfaction with the surgical outcome and willingness to undergo the surgery again if necessary. A combination of medial cuneiform mechanical decompression and insertional tendon debridement can offer successful outcomes in resistant insertional tibialis anterior tendinopathy.

Enabling the Next-Generation Radiology Report: Description of Two New System Standards.

Currently, most radiology reports are highly variable and consist of unconstrained narrative text. This variability limits the ability to extract information from the report to guide clinical care, populate a data registry, or support quality improvement. This article introduces two newly available standards that pertain to radiology reports. Management of Radiology Reporting Templates (MRRT) is an integration profile that defines the format and exchange mechanisms for radiology report templates. Digital Imaging and Communications in Medicine Part 20 defines how reports built using MRRT-based templates can be transmitted into an electronic health record (EHR). Together, these two standards enable new ways to improve report consistency and completeness, ensure proper clinical action, and improve the quality of patient care. Commercial and open-source developers are beginning to incorporate these standards into clinical systems. The authors use an example of a patient with an incidentally detected lung nodule to illustrate how these standards improve the exchange of information. The clinical scenario follows the use of the appropriate template through the completion of the radiology report, with the incidental finding structured and coded to enable automated follow-up in the EHR. ©RSNA, 2017.

Gene pathways that delay Caenorhabditis elegans reproductive senescence.

Reproductive senescence is a hallmark of aging. The molecular mechanisms regulating reproductive senescence and its association with the aging of somatic cells remain poorly understood. From a full genome RNA interference (RNAi) screen, we identified 32 Caenorhabditis elegans gene inactivations that delay reproductive senescence and extend reproductive lifespan. We found that many of these gene inactivations interact with insulin/IGF-1 and/or TGF-ß endocrine signaling pathways to regulate reproductive senescence, except nhx-2 and sgk-1 that modulate sodium reabsorption. Of these 32 gene inactivations, we also found that 19 increase reproductive lifespan through their effects on oocyte activities, 8 of them coordinate oocyte and sperm functions to extend reproductive lifespan, and 5 of them can induce sperm humoral response to promote reproductive longevity. Furthermore, we examined the effects of these reproductive aging regulators on somatic aging. We found that 5 of these gene inactivations prolong organismal lifespan, and 20 of them increase healthy life expectancy of an organism without altering total life span. These studies provide a systemic view on the genetic regulation of reproductive senescence and its intersection with organism longevity. The majority of these newly identified genes are conserved, and may provide new insights into age-associated reproductive senescence during human aging.

Forests, fields, and the edge of sustainability at the ancient Maya city of Tikal.

Tikal has long been viewed as one of the leading polities of the ancient Maya realm, yet how the city was able to maintain its substantial population in the midst of a tropical forest environment has been a topic of unresolved debate among researchers for decades. We present ecological, paleoethnobotanical, hydraulic, remote sensing, edaphic, and isotopic evidence that reveals how the Late Classic Maya at Tikal practiced intensive forms of agriculture (including irrigation, terrace construction, arboriculture, household gardens, and short fallow swidden) coupled with carefully controlled agroforestry and a complex system of water retention and redistribution. Empirical evidence is presented to demonstrate that this assiduously managed anthropogenic ecosystem of the Classic period Maya was a landscape optimized in a way that provided sustenance to a relatively large population in a preindustrial, low-density urban community. This landscape productivity optimization, however, came with a heavy cost of reduced environmental resiliency and a complete reliance on consistent annual rainfall. Recent speleothem data collected from regional caves showed that persistent episodes of unusually low rainfall were prevalent in the mid-9th century A.D., a time period that coincides strikingly with the abandonment of Tikal and the erection of its last dated monument in A.D. 869. The intensified resource management strategy used at Tikal-already operating at the landscape's carrying capacity-ceased to provide adequate food, fuel, and drinking water for the Late Classic populace in the face of extended periods of drought. As a result, social disorder and abandonment ensued.