Changing epidemiology and age-specific incidence of cutaneous malignant melanoma in England: An analysis of the national cancer registration data by age, gender and anatomical site, 1981-2018.

BACKGROUND: The incidence of cutaneous malignant melanoma, which is mostly attributable (86%) to UV radiation exposure, has been steadily increasing over the past four decades in predominantly fair-skinned populations. Although public health campaigns are increasing sun-protective behaviour in England, their effect on melanoma incidence is largely unknown. We conducted a retrospective population-based cohort study to examine whether there have been changes in the epidemiology of melanoma in England during the past four decades. METHODS: Individual level data for patients diagnosed with melanoma in England during 1981-2018 were obtained from the Office for National Statistics/Public Health England. Average annual incidence rates were calculated by three age categories (0-34, 35-64, 65+ years), gender and anatomical site during the seven five-year time periods (1981-85 to 2011-15) and the recent three-year period (2016-18). The percentage change in incidence was calculated as change in the average incidence rate from the first (1981-85) to the last time period (2016-18). The Average Annual Percentage Change (AAPC) was estimated using the slope of the linear trend line fitted to the incidence rates by year of diagnosis. FINDINGS: During the 38-year period (1981-2018), a total of 265,302 cases of melanoma (45.7% males, 54.3% females) were registered in England. The average annual number of cases increased from 837/year in 1981-85 to 6963/year in 2016-18 in males (+732%), and from 1609/year in 1981-85 to 6952/year in 2016-18 in females (+332%). In the young age-group (0-34 years), the average annual incidence rates initially increased from 1981-85 to 2001-05 and then stabilised during the recent period (2006-18). In the middle age group (35-64 years), the rates increased by +332% (AAPC, 10.4%) in males (from 5.6/100,000 in 1981-85 to 24.2/100,000 in 2016-18) and +185% (AAPC, 5.7%) in females (from 10.2/100,000 in 1981-85 to 29.1/100,000 in 2016-18); and in the old age-group (65+ years) the rates increased by +842% (AAPC, 25.7%) in males (from 9.6/100,000 in 1981-85 to 90.4/100,000 in 2016-18) and +381% (AAPC, 11.2%) in females (from 12.5/100,000 in 1981-85 to 60.1/100,000 in 2016-18). The largest increase in incidence in both males and females was observed for melanoma of the trunk (+817%, AAPC, 24.8% in males and +613%, AAPC, 18.3% in females), followed by melanoma of upper limb (+750%, AAPC, 22.9% in males and 518%, AAPC, 15.5% in females). INTERPRETATION: It appears that the incidence of melanoma among young people in England has stabilised (or levelled off) in recent decades, whereas it continues to increase substantially in older population. These findings suggest that public health campaigns targeted at children/adolescents/parents may be favourably influencing melanoma incidence. The steeper increase in incidence in males is consistent with their relatively greater sun exposure and poor sun-protective behaviour. All the available evidence suggests that the enormous increase in the melanoma of the trunk and upper limb, since the 1980s, is most likely due to increasing trend in intermittent high intensity recreational UV radiation exposure (e.g. sunbathing, holidaying in places with strong sunlight, indoor tanning). FUNDING: This work was supported by Brighton and Sussex Medical School (BSMS).

Long Covid in adults discharged from UK hospitals after Covid-19: A prospective, multicentre cohort study using the ISARIC WHO Clinical Characterisation Protocol.

BACKGROUND: This study sought to establish the long-term effects of Covid-19 following hospitalisation. METHODS: 327 hospitalised participants, with SARS-CoV-2 infection were recruited into a prospective multicentre cohort study at least 3 months post-discharge. The primary outcome was self-reported recovery at least ninety days after initial Covid-19 symptom onset. Secondary outcomes included new symptoms, disability (Washington group short scale), breathlessness (MRC Dyspnoea scale) and quality of life (EQ5D-5L). FINDINGS: 55% of participants reported not feeling fully recovered. 93% reported persistent symptoms, with fatigue the most common (83%), followed by breathlessness (54%). 47% reported an increase in MRC dyspnoea scale of at least one grade. New or worse disability was reported by 24% of participants. The EQ5D-5L summary index was significantly worse following acute illness (median difference 0.1 points on a scale of 0 to 1, IQR: -0.2 to 0.0). Females under the age of 50 years were five times less likely to report feeling recovered (adjusted OR 5.09, 95% CI 1.64 to 15.74), were more likely to have greater disability (adjusted OR 4.22, 95% CI 1.12 to 15.94), twice as likely to report worse fatigue (adjusted OR 2.06, 95% CI 0.81 to 3.31) and seven times more likely to become more breathless (adjusted OR 7.15, 95% CI 2.24 to 22.83) than men of the same age. INTERPRETATION: Survivors of Covid-19 experienced long-term symptoms, new disability, increased breathlessness, and reduced quality of life. These findings were present in young, previously healthy working age adults, and were most common in younger females. FUNDING: National Institute for Health Research, UK Medical Research Council, Wellcome Trust, Department for International Development and the Bill and Melinda Gates Foundation.

Evaluating clinical characteristics studies produced early in the Covid-19 pandemic: A systematic review.

OBJECTIVES: Clinical characterisation studies have been essential in helping inform research, diagnosis and clinical management efforts, particularly early in a pandemic. This systematic review summarises the early literature on clinical characteristics of patients admitted to hospital, and evaluates the quality of evidence produced during the initial stages of the pandemic. METHODS: MEDLINE, EMBASE and Global Health databases were searched for studies published from January 1st 2020 to April 28th 2020. Studies which reported on at least 100 hospitalised patients with Covid-19 of any age were included. Data on clinical characteristics were independently extracted by two review authors. Study design specific critical appraisal tools were used to evaluate included studies: the Newcastle Ottawa scale for cohort and cross sectional studies, Joanna Briggs Institute checklist for case series and the Cochrane collaboration tool for assessing risk of bias in randomised trials. RESULTS: The search yielded 78 studies presenting data on 77,443 people. Most studies (82%) were conducted in China. No studies included patients from low- and middle-income countries. The overall quality of included studies was low to moderate, and the majority of studies did not include a control group. Fever and cough were the most commonly reported symptoms early in the pandemic. Laboratory and imaging findings were diverse with lymphocytopenia and ground glass opacities the most common findings respectively. Clinical data in children and vulnerable populations were limited. CONCLUSIONS: The early Covid-19 literature had moderate to high risk of bias and presented several methodological issues. Early clinical characterisation studies should aim to include different at-risk populations, including patients in non-hospital settings. Pandemic preparedness requires collection tools to ensure observational studies are methodologically robust and will help produce high-quality data early on in the pandemic to guide clinical practice and public health policy. REVIEW REGISTRATION: Available at https://osf.io/mpafn.

Online Information of Vaccines: Information Quality, Not Only Privacy, Is an Ethical Responsibility of Search Engines.

The fact that Internet companies may record our personal data and track our online behavior for commercial or political purpose has emphasized aspects related to online privacy. This has also led to the development of search engines that promise no tracking and privacy. Search engines also have a major role in spreading low-quality health information such as that of anti-vaccine websites. This study investigates the relationship between search engines' approach to privacy and the scientific quality of the information they return. We analyzed the first 30 webpages returned searching "vaccines autism" in English, Spanish, Italian, and French. The results show that not only "alternative" search engines (Duckduckgo, Ecosia, Qwant, Swisscows, and Mojeek) but also other commercial engines (Bing, Yahoo) often return more anti-vaccine pages (10-53%) than Google.com (0%). Some localized versions of Google, however, returned more anti-vaccine webpages (up to 10%) than Google.com. Health information returned by search engines has an impact on public health and, specifically, in the acceptance of vaccines. The issue of information quality when seeking information for making health-related decisions also impact the ethical aspect represented by the right to an informed consent. Our study suggests that designing a search engine that is privacy savvy and avoids issues with filter bubbles that can result from user-tracking is necessary but insufficient; instead, mechanisms should be developed to test search engines from the perspective of information quality (particularly for health-related webpages) before they can be deemed trustworthy providers of public health information.

Addressing challenges for clinical research responses to emerging epidemics and pandemics: a scoping review.

BACKGROUND: Major infectious disease outbreaks are a constant threat to human health. Clinical research responses to outbreaks generate evidence to improve outcomes and outbreak control. Experiences from previous epidemics have identified multiple challenges to undertaking timely clinical research responses. This scoping review is a systematic appraisal of political, economic, administrative, regulatory, logistical, ethical and social (PEARLES) challenges to clinical research responses to emergency epidemics and solutions identified to address these. METHODS: A scoping review. We searched six databases (MEDLINE, Embase, Global Health, PsycINFO, Scopus and Epistemonikos) for articles published from 2008 to July 2018. We included publications reporting PEARLES challenges to clinical research responses to emerging epidemics and pandemics and solutions identified to address these. Two reviewers screened articles for inclusion, extracted and analysed the data. RESULTS: Of 2678 articles screened, 76 were included. Most presented data relating to the 2014-2016 Ebola virus outbreak or the H1N1 outbreak in 2009. The articles related to clinical research responses in Africa (n = 37), Europe (n = 8), North America (n = 5), Latin America and the Caribbean (n = 3) and Asia (n = 1) and/or globally (n = 22). A wide range of solutions to PEARLES challenges was presented, including a need to strengthen global collaborations and coordination at all levels and develop pre-approved protocols and equitable frameworks, protocols and standards for emergencies. Clinical trial networks and expedited funding and approvals were some solutions implemented. National ownership and community engagement from the outset were a key enabler for delivery. Despite the wide range of recommended solutions, none had been formally evaluated. CONCLUSIONS: To strengthen global preparedness and response to the COVID-19 pandemic and future epidemics, identified solutions for rapid clinical research deployment, delivery, and dissemination must be implemented. Improvements are urgently needed to strengthen collaborations, funding mechanisms, global and national research capacity and capability, targeting regions vulnerable to epidemics and pandemics. Solutions need to be flexible to allow timely adaptations to context, and research led by governments of affected regions. Research communities globally need to evaluate their activities and incorporate lessons learnt to refine and rehearse collaborative outbreak response plans in between epidemics.

Scope, quality, and inclusivity of clinical guidelines produced early in the covid-19 pandemic: rapid review.

OBJECTIVE: To appraise the availability, quality, and inclusivity of clinical guidelines produced in the early stage of the coronavirus disease 2019 (covid-19) pandemic. DESIGN: Rapid review. DATA SOURCES: Ovid Medline, Ovid Embase, Ovid Global Health, Scopus, Web of Science Core Collection, and WHO Global Index Medicus, searched from inception to 14 Mar 2020. Search strategies applied the CADTH database guidelines search filter, with no limits applied to search results. Further studies were identified through searches of grey literature using the ISARIC network. INCLUSION CRITERIA: Clinical guidelines for the management of covid-19, Middle East respiratory syndrome (MERS), and severe acute respiratory syndrome (SARS) produced by international and national scientific organisations and government and non-governmental organisations relating to global health were included, with no exclusions for language. Regional/hospital guidelines were excluded. Only the earliest version of any guideline was included. QUALITY ASSESSMENT: Quality was assessed using the Appraisal of Guidelines for Research and Evaluation (AGREE) II tool. The quality and contents of early covid-19 guidelines were also compared with recent clinical guidelines for MERS and SARS. RESULTS: 2836 studies were identified, of which 2794 were excluded after screening. Forty two guidelines were considered eligible for inclusion, with 18 being specific to covid-19. Overall, the clinical guidelines lacked detail and covered a narrow range of topics. Recommendations varied in relation to, for example, the use of antiviral drugs. The overall quality was poor, particularly in the domains of stakeholder involvement, applicability, and editorial independence. Links between evidence and recommendations were limited. Minimal provision was made for vulnerable groups such as pregnant women, children, and older people. CONCLUSIONS: Guidelines available early in the covid-19 pandemic had methodological weaknesses and neglected vulnerable groups such as older people. A framework for development of clinical guidelines during public health emergencies is needed to ensure rigorous methods and the inclusion of vulnerable populations. SYSTEMATIC REVIEW REGISTRATION: PROSPERO CRD42020167361.

Diagnostic performance of prehospital ultrasound diagnosis for traumatic pneumothorax by a UK Helicopter Emergency Medical Service.

OBJECTIVE: Up to 20% of major trauma patients may sustain a pneumothorax. Traumatic pneumothoraces can be difficult to diagnose on scene. Although the use of handheld ultrasound (HHUS) is becoming increasingly widespread, there remains uncertainty about its efficacy as a diagnostic tool in the prehospital setting. The aim of this study was to determine the diagnostic performance of prehospital chest HHUS in trauma patients. METHOD: Retrospective review of trauma patients who received a prehospital chest HHUS and subsequently conveyed to the Royal Sussex County Hospital (RSCH) between 1 July 2013 and 24 September 2018. Data including patient age, sex, mechanism of injury and clinical interventions were obtained. Prehospital ultrasound findings were compared with the computer tomography (CT) scan performed on arrival at the hospital. RESULTS: Four hundred eleven patients were conveyed to RSCH, the single largest group being following road traffic collisions. The majority of HHUS (66%) were performed by doctors. Three hundred sixty-one patients (88%) subsequently had a CT scan. Of these, 98 patients (27%) were found to have pneumothoraces. For pneumothorax diagnosis, prehospital HHUS had a sensitivity of 28% [95% confidence interval (CI): 19-37%] and specificity of 98% [95% CI: 97-99%]. CONCLUSION: In this retrospective study, sensitivity of prehospital HHUS for diagnosing a pneumothorax was lower than is often reported in in-hospital studies. This suggests that caution should be exercised in using HHUS for the exclusion of pneumothorax in the prehospital setting.

Transpiration, CO2 assimilation, WUE, and stomatal aperture in leaves of Viscum album (L.): Effect of abscisic acid (ABA) in the xylem sap of its host (Populus x euamericana).

Leaves of the mistletoe Viscum album (L.) show a high rate of transpiration, even when the host is under severe drought stress. The hypothesis that a strong control of ABA influx from the xylem sap of the host into the mistletoe prevents stomatal closure in mistletoe leaves was tested under the following conditions: sections of poplar twigs carrying a mistletoe were perfused with artificial xylem sap that contained different ABA concentrations and both transpiration and ABA levels were analysed in mistletoe leaves. Despite variation by a factor of 10(4), the ABA content of the host xylem did not affect ABA levels, leaf transpiration, CO(2) assimilation, WUE, or the degree of stomatal aperture in mistletoe leaves. These observations support the hypothesis of a strong control of ABA influx from the host of the xylem into the mistletoe, although degradation of ABA before it enters the mistletoe leaves cannot be excluded. This mechanism may ensure a water and nutritional status favourable for the mistletoe, even if the water status of the host is impaired. Despite the lack of short-term sensitivity of ABA levels in mistletoe leaves to even strong changes of ABA levels in the xylem sap of the host, ABA levels in mistletoe leaves were relatively high compared to ABA levels in the leaves of several tree species including poplar. Since significant transpiration of the mistletoe leaves was observed despite high ABA levels, a diminished sensitivity of the stomata of mistletoe leaves to ABA has to be concluded. The stomatal density of adaxial Viscum leaves of 89+/-23 stomata per mm is lower than those reported in a study performed at the end of the 19th century.

Sustained endogenous glucose production, diminished lipolysis and non-esterified fatty acid appearance and oxidation in non-obese women at high risk of type 2 diabetes.

OBJECTIVE: To evaluate early defects in glucose production, lipolysis and fatty acid oxidation in non-obese, normally glucose tolerant women, who are nevertheless at risk of type 2 diabetes. METHODS: Ten women with previous gestational diabetes (pGDM) and ten controls were studied in two 4 h infusions of stable isotopes 6,6-(2)H(2)-glucose, 1-(13)C-palmitate, and 1,1,2,3,3-(2)H(5)-glycerol with and without infusion of adrenaline. Fatty acid oxidation was quantified using indirect calorimetry and (13)CO(2) measurements. Insulin sensitivity was evaluated using the short insulin tolerance test. RESULTS: The pGDM and control women were non-obese and carefully matched for body mass index and fat mass. Whole body insulin sensitivity and basal insulin concentrations did not differ significantly but basal glucose concentrations were increased in women with pGDM. During a 0.9% saline infusion, glucose appearance was not significantly different at the first (90-120 min) and second (210-240 min) steady states. However, glucose appearance decreased in controls but was maintained in the pGDM women (-0.33 +/- 0.02 vs -0.03 +/- 0.08 mg/kg per min; P = 0.004). Basal glycerol appearance (0.27 +/- 0.02 vs 0.38 +/- 0.03 mg/kg per min; P = 0.02), palmitate appearance (0.74 +/- 0.09 vs 1.05 +/- 0.09 mg/kg per min; P = 0.03) and palmitate oxidation (0.07 +/- 0.01 vs 0.10 +/- 0.01 mg/kg per min; P = 0.03) were lower in the pGDM women. During the adrenaline infusion, changes in glucose, glycerol and palmitate concentrations and kinetics were similar in both groups. CONCLUSIONS: Sustained glucose production during fasting is an early abnormality in non-obese subjects at risk of type 2 diabetes. Lipolysis and non-esterified fatty acid appearance and oxidation are diminished, suggesting an increased tendency to store fat. The observations are not readily attributable to differences in insulin or catecholamine sensitivity.

Will loss of snow cover during climatic warming expose New Zealand alpine plants to increased frost damage?

If snow cover in alpine environments were reduced through climatic warming, plants that are normally protected by snow-lie in winter would become exposed to greater extremes of temperature and solar radiation. We examined the annual course of frost resistance of species of native alpine plants from southern New Zealand that are normally buried in snowbanks over winter (Celmisia haastii and Celmisia prorepens) or in sheltered areas that may accumulate snow (Hebe odora) and other species, typical of more exposed areas, that are relatively snow-free (Celmisia viscosa, Poa colensoi, Dracophyllum muscoides). The frost resistance of these principal species was in accord with habitat: those from snowbanks or sheltered areas showed the least frost resistance, whereas species from exposed areas had greater frost resistance throughout the year. P. colensoi had the greatest frost resistance (-32.5 degrees C). All the principal species showed a rapid increase in frost resistance from summer to early winter (February-June) and maximum frost resistance in winter (July-August). The loss of resistance in late winter to early summer (August-December) was most rapid in P. colensoi and D. muscoides. Seasonal frost resistance of the principal species was more strongly related to daylength than to temperature, although all species except C. viscosa were significantly related to temperature when the influence of daylength was accounted for. Measurements of chlorophyll fluorescence indicated that photosynthetic efficiency of the principal species declined with increasing daylength. Levels of frost resistance of the six principal alpine plant species, and others measured during the growing season, were similar to those measured in tropical alpine areas and somewhat more resistant than those recorded in alpine areas of Europe. The potential for frost damage was greatest in spring. The current relationship of frost resistance with daylength is sufficient to prevent damage at any time of year. While warmer temperatures might lower frost resistance, they would also reduce the incidence of frosts, and the incidence of frost damage is unlikely to be altered. The relationship of frost resistance with daylength and temperature potentially provides a means of predicting the responses of alpine plants in response to global warming.

Variability in fMRI: a re-examination of inter-session differences.

We revisit a previous study on inter-session variability (McGonigle et al. [2000]: Neuroimage 11:708-734), showing that contrary to one popular interpretation of the original article, inter-session variability is not necessarily high. We also highlight how evaluating variability based on thresholded single-session images alone can be misleading. Finally, we show that the use of different first-level preprocessing, time-series statistics, and registration analysis methodologies can give significantly different inter-session analysis results.

Advances in functional and structural MR image analysis and implementation as FSL.

The techniques available for the interrogation and analysis of neuroimaging data have a large influence in determining the flexibility, sensitivity, and scope of neuroimaging experiments. The development of such methodologies has allowed investigators to address scientific questions that could not previously be answered and, as such, has become an important research area in its own right. In this paper, we present a review of the research carried out by the Analysis Group at the Oxford Centre for Functional MRI of the Brain (FMRIB). This research has focussed on the development of new methodologies for the analysis of both structural and functional magnetic resonance imaging data. The majority of the research laid out in this paper has been implemented as freely available software tools within FMRIB's Software Library (FSL).

Effects of short- and long-term growth hormone replacement on lipoprotein composition and on very-low-density lipoprotein and low-density lipoprotein apolipoprotein B100 kinetics in growth hormone-deficient hypopituitary subjects.

In this study, we concurrently examined the effects of 8 and 40 weeks of growth hormone replacement (GHR) on lipids, lipoprotein composition, low-density lipoprotein (LDL) size, very-low-density lipoprotein (VLDL) apolipoprotein (apo)B kinetics and LDL apoB kinetics. Eight weeks of GHR did not alter lipid profiles. Forty weeks of GHR increased high-density lipoprotein-cholesterol (HDL-C) concentration (P =.01), nonsignificantly reduced LDL-C (P =.06), and reduced the HDL/LDL-C ratio (P =.04). Forty weeks of GHR increased HDL free cholesterol (P =.03), total cholesterol (P =.01), and cholesterol ester (P <.01) concentrations. No other significant changes in VLDL, LDL, or HDL composition or LDL size were noted at any time. Eight weeks of GHR reduced VLDL apoB absolute secretion rate (ASR, P =.03), with nonsignificant reductions in fractional secretion rate (FSR, P =.09) and pool size (P =.09). After 40 weeks of GHR, the VLDL apoB ASR, FSR, and pool size were not significantly different from baseline. Forty weeks of GHR increased both LDL apoB FSR (P =.02) and LDL apoB ASR (P =.04), with a small decrease in pool size. Thus, GHR may have important antiatherogenic effects; HDL-C increased, LDL-C was nonsignificantly reduced, the total/HDL-C ratio was reduced, VLDL apoB production was reduced, and LDL apoB turnover was increased.

Improved optimization for the robust and accurate linear registration and motion correction of brain images.

Linear registration and motion correction are important components of structural and functional brain image analysis. Most modern methods optimize some intensity-based cost function to determine the best registration. To date, little attention has been focused on the optimization method itself, even though the success of most registration methods hinges on the quality of this optimization. This paper examines the optimization process in detail and demonstrates that the commonly used multiresolution local optimization methods can, and do, get trapped in local minima. To address this problem, two approaches are taken: (1) to apodize the cost function and (2) to employ a novel hybrid global-local optimization method. This new optimization method is specifically designed for registering whole brain images. It substantially reduces the likelihood of producing misregistrations due to being trapped by local minima. The increased robustness of the method, compared to other commonly used methods, is demonstrated by a consistency test. In addition, the accuracy of the registration is demonstrated by a series of experiments with motion correction. These motion correction experiments also investigate how the results are affected by different cost functions and interpolation methods.

Differential accumulation of nutrient elements in some New Zealand mistletoes and their hosts.

It has been generally assumed that differential accumulation of mineral nutrients, leading to greater accumulation of elements in mistletoe tissues, is associated with greater transpiration in the mistletoe than in the host. Only a few investigations have measured both tissue element concentrations and transpiration, or transpiration-related parameters such as carbon isotope ratios (δ13C). Seasonal means for foliar concentrations of Ca, Mg, K, Na, P, N, transpiration and δ13C were obtained from ten mistletoe-host pairs, nine involving the mistletoe Ileostylus micranthus and one with Tupeia antarctica. Annual means of transpiration and δ13C were similar in mistletoes and hosts, but hosts showed greater variation in both transpiration and δ13C than mistletoes. Foliar concentrations of Ca and Mg in mistletoes were similar to those of their hosts, N concentrations were less, and foliar concentrations of K, Na and P were greater in mistletoes than in their hosts. Ratios of foliar concentrations of Ca, Mg and P in mistletoes to those in their hosts (M/H) were greatest when host transpiration was low, when host δ13C was least negative, and when the difference between mistletoe and host δ13C was most negative. The lack of a phloem connection between host and mistletoe, combined with circulation of elements in the host phloem and their transfer into the host xylem, provides a mechanism that explains the accumulation of phloem-mobile elements in the mistletoe.

Water relations of temperate mistletoes on various hosts.

The daily field water relations and gas exchange of the temperate mistletoes Ileostylus micranthus (Hook.f.) Tiegh. and Tupeia antarctica Cham. et Schlecht. on various hosts were examined seasonally in Dunedin, New Zealand during 1996-1998. Mistletoes commonly have higher transpiration rates (E) than their hosts, and this is generally cited as the reason why mistletoes develop lower water potentials (ψ) than their hosts. The mistletoe-host pairs that we examined showed no significant overall differences in E and stomatal conductance (g), and we used them to test the hypothesis that lowered ψ in mistletoes result from higher E. Despite the lack of differences in E and g, osmotic potentials, predawn and daily minimum ψ (ψmin) were significantly more negative in mistletoes, although differences between host and mistletoe ψ were less on hosts with low osmotic potentials and ψ. Mistletoes maintained lower ψ than their hosts both when unshaded and under artificial shading, had lower ψ than hosts at equal E, but had shoot hydraulic resistances similar to that of their hosts. E and ψ of hosts and mistletoes tended to be coordinated only in summer, when hosts were most water-stressed. Mistletoes maintained higher relative water contents at turgor loss, symplastic water contents, and bulk moduli of elasticity (ε) than their hosts. We conclude that the lower ψ in these temperate mistletoes are a consequence of greater mistletoe E only when host ψ are low, but are otherwise maintained by greater succulence and higher ε than in their hosts.

Carbon and nitrogen isotope ratios, nitrogen content and heterotrophy in New Zealand mistletoes.

The carbon isotope ratio (δ13C) of New Zealand mistletoes (-29.51±0.10‰) and their hosts (-28.89±0.12‰) is generally more negative, and shows less difference between mistletoes and their hosts, than found in previous studies. In 37% of the examined pairs, the δ13C of mistletoes was less negative than that of their hosts. These reversals were not associated with the relative position (proximal or distal) of the host material with regard to the mistletoe. Differences between host and mistletoe tended to be greater on hosts with less negative δ13C. Both nitrogen content and isotope ratio (δ15N) of the mistletoe leaves were strongly correlated with those of their hosts. Nitrogen contents of mistletoe leaves were similar to those of their hosts at low nitrogen contents but proportionately less on hosts with a high nitrogen content, whereas δ15N of mistletoes was consistently similar to that of their hosts. The δ13C of mistletoes was related to both host nitrogen content and δ15N, but δ13C in host tissue was related to neither, suggesting that the mistletoes derived both nitrogen and carbon from their hosts. The δ13C of both hosts and mistletoes were significantly related to leaf conductance and carbon dioxide concentration but relationships with transpiration and water use efficiency were not significant. In all cases there was no clear separation between the responses of hosts and mistletoes. This may be related to the similarity of stomatal conductance, transpiration and photosynthesis in the studied mistletoes and their hosts and is consistent with the small differences in δ13C between mistletoes and hosts found in this study. Consequently, the estimation of mistletoe heterotrophy from carbon discrimination is confounded, as the small difference between host and mistletoe carbon discrimination could equally well result from either similarities in photosynthesis and water relations or heterotrophic assimilation of host-derived carbon. The differences between our study and previous studies (which are mostly from seasonally dry or semi-arid to arid environments) may be related to the temperate environment in which these mistletoes grow. Water is freely available so that the mistletoe is able to obtain sufficient water and dissolved nutrients without having to maintain the high transpiration rate and low water potentials that are needed to extract water from a water-stressed host. Similarly, mistletoe photosynthesis is less inhibited by water stress. The physiological similarities between mistletoe and hosts from a temperate environment are reflected in their similar δ13C values.

Nitrogen concentration and mimicry in some New Zealand mistletoes.

The nitrogen concentration in photosynthetic organs of 41 pairs of mistletoes and their respective hosts was compared and found to be higher (in relation to that of their hosts) in cryptic mistletoes and lower in non-cryptic mistletoes. This supports the hypothesis that crypsis may have evolved as a mechanism for avoiding predation by vertebrate herbivores. There were no consistent differences between the nitrogen concentrations of hosts and mistletoes in trees and larger-leaved shrubs (whether native or introduced). The largest differences between mistletoes and their hosts were found on small-leaved divaricate shrubs (Coprosma ssp., Melicope simplex) where the nitrogen concentrations in cryptic mistletoes (Korthalsella spp.) were significantly higher than in their hosts, but significantly lower in prominent mistletoes (Loranthus micranthus, Tupeia antarctica) which apparently "advertise" their unpalatability. If crypsis in New Zealand mistletoes evolved as a protection against herbivory, then it must have evolved in the absence of mammalian herbivores, and the appropriate selection pressures could have been provided only by moas, extinct ratite birds. Otherwise, alternative explanations, such as differing relationships between water use and nitrogen uptake, must be sought for the observed associations of nitrogen concentration and cryptic mimicry in New Zealand mistletoes.