Many authors have suggested that the vulnerability of montane biodiversity to climate change worldwide is significantly higher than in most other ecosystems. Despite the extensive variety of studies ...predicting severe impacts of climate change globally, few studies have empirically validated the predicted changes in distribution and population density. Here, we used 17 years (2000-2016) of standardised bird monitoring across latitudinal/elevational gradients in the rainforest of the Australian Wet Tropics World Heritage Area to assess changes in local abundance and elevational distribution. We used relative abundance in 1977 surveys across 114 sites ranging from 0-1500m above sea level and utilised a trend analysis approach (TRIM) to investigate elevational shifts in abundance of 42 species. The local abundance of most mid and high elevation species has declined at the lower edges of their distribution by >40% while lowland species increased by up to 190% into higher elevation areas. Upland-specialised species and regional endemics have undergone dramatic population declines of almost 50%. The "Outstanding Universal Value" of the Australian Wet Tropics World Heritage Area, one of the most irreplaceable biodiversity hotspots on Earth, is rapidly degrading. These observed impacts are likely to be similar in many tropical montane ecosystems globally.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We review the transport, synthesis and catabolism of glutathione in the brain as well as its compartmentation and biochemistry in different brain cells. The major reactions involving glutathione are ...reviewed and the factors limiting its availability in brain cells are discussed. We also describe and critique current methods for measuring glutathione in the human brain using magnetic resonance spectroscopy, and review the literature on glutathione measurements in healthy brains and in neurological, psychiatric, neurodegenerative and neurodevelopmental conditions In summary: Healthy human brain glutathione concentration is ∼1–2 mM, but it varies by brain region, with evidence of gender differences and age effects; in neurological disease glutathione appears reduced in multiple sclerosis, motor neurone disease and epilepsy, while being increased in meningiomas; in psychiatric disease the picture is complex and confounded by methodological differences, regional effects, length of disease and drug-treatment. Both increases and decreases in glutathione have been reported in depression and schizophrenia. In Alzheimer's disease and mild cognitive impairment there is evidence for a decrease in glutathione compared to age-matched healthy controls. Improved methods to measure glutathione in vivo will provide better precision in glutathione determination and help resolve the complex biochemistry of this molecule in health and disease.
The rising global temperature is predicted to expand the distribution of vector-borne diseases both in latitude and altitude. Many host communities could be affected by increased prevalence of ...disease, heightening the risk of extinction for many already threatened species. To understand how host communities could be affected by changing parasite distributions, we need information on the distribution of parasites in relation to variables like temperature and rainfall that are predicted to be affected by climate change.
We determined relations between prevalence of blood parasites, temperature, and seasonal rainfall in a bird community of the Australian Wet Tropics along an elevation gradient. We used PCR screening to investigate the prevalence and lineage diversity of four genera of blood parasites (Plasmodium, Haemoproteus, Leucocytozoon and Trypanosoma) in 403 birds. The overall prevalence of the four genera of blood parasites was 32.3%, with Haemoproteus the predominant genus. A total of 48 unique lineages were detected. Independent of elevation, parasite prevalence was positively and strongly associated with annual temperature. Parasite prevalence was elevated during the dry season.
Low temperatures of the higher elevations can help to reduce both the development of avian haematozoa and the abundance of parasite vectors, and hence parasite prevalence. In contrast, high temperatures of the lowland areas provide an excellent environment for the development and transmission of haematozoa. We showed that rising temperatures are likely to lead to increased prevalence of parasites in birds, and may force shifts of bird distribution to higher elevations. We found that upland tropical areas are currently a low-disease habitat and their conservation should be given high priority in management plans under climate change.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The ascending cholinergic system dynamically regulates sensory perception and cognitive function, but it remains unclear how this modulation is executed in neocortical circuits. Here, we demonstrate ...that the cholinergic system controls the integrative operations of neocortical principal neurons by modulating dendritic excitability. Direct dendritic recordings revealed that the optogenetic-evoked release of acetylcholine (ACh) transformed the pattern of dendritic integration in layer 5B pyramidal neurons, leading to the generation of dendritic plateau potentials which powerfully drove repetitive action potential output. In contrast, the synaptic release of ACh did not positively modulate axo-somatic excitability. Mechanistically, the transformation of dendritic integration was mediated by the muscarinic ACh receptor-dependent enhancement of dendritic R-type calcium channel activity, a compartment-dependent modulation which decisively controlled the associative computations executed by layer 5B pyramidal neurons. Our findings therefore reveal a biophysical mechanism by which the cholinergic system controls dendritic computations causally linked to perceptual detection.
•Optogenetic release of ACh positively modulates neocortical principal neuron excitability•Optogenetic release of ACh selectively controls dendritic excitability•Dendritic excitability is transformed by a mAChR-mediated modulation of calcium channels•Cholinergic modulation impacts behaviorally relevant dendritic integration
Williams and Fletcher use optogenetic and high-resolution electrophysiological techniques to demonstrate that the cholinergic system directly controls the electrical excitability of the dendrites of neocortical principal neurons, through the modulation of calcium channels, to powerfully enhance behaviorally relevant associative computations.
Active dendritic synaptic integration enhances the computational power of neurons. Such nonlinear processing generates an object-localization signal in the apical dendritic tuft of layer 5B cortical ...pyramidal neurons during sensory-motor behavior. Here, we employ electrophysiological and optical approaches in brain slices and behaving animals to investigate how excitatory synaptic input to this distal dendritic compartment influences neuronal output. We find that active dendritic integration throughout the apical dendritic tuft is highly compartmentalized by voltage-gated potassium (KV) channels. A high density of both transient and sustained KV channels was observed in all apical dendritic compartments. These channels potently regulated the interaction between apical dendritic tuft, trunk, and axosomatic integration zones to control neuronal output in vitro as well as the engagement of dendritic nonlinear processing in vivo during sensory-motor behavior. Thus, KV channels dynamically tune the interaction between active dendritic integration compartments in layer 5B pyramidal neurons to shape behaviorally relevant neuronal computations.
•Distal tuft input drives pyramidal neuron output by regulating dendritic spike width•Kv channels control the interaction between active integration compartments•High densities of Kv channels are expressed throughout the apical dendritic tree•Interactive integration engages Kv channels during sensory-motor behavior
How does synaptic input to distal dendrites influence neuronal output? Harnett et al. investigate excitability and integration in apical tuft dendrites of layer 5 cortical pyramidal neurons, demonstrating how K+ channels control computation in this compartment to modulate axonal firing.
Extreme weather events, such as unusually hot or dry conditions, can cause death by exceeding physiological limits, and so cause loss of population. Survival will depend on whether or not susceptible ...organisms can find refuges that buffer extreme conditions. Microhabitats offer different microclimates to those found within the wider ecosystem, but do these microhabitats effectively buffer extreme climate events relative to the physiological requirements of the animals that frequent them? We collected temperature data from four common microhabitats (soil, tree holes, epiphytes, and vegetation) located from the ground to canopy in primary rainforests in the Philippines. Ambient temperatures were monitored from outside of each microhabitat and from the upper forest canopy, which represent our macrohabitat controls. We measured the critical thermal maxima (CTmax) of frog and lizard species, which are thermally sensitive and inhabit our microhabitats. Microhabitats reduced mean temperature by 1–2 °C and reduced the duration of extreme temperature exposure by 14–31 times. Microhabitat temperatures were below the CTmax of inhabitant frogs and lizards, whereas macrohabitats consistently contained lethal temperatures. Microhabitat temperatures increased by 0.11–0.66 °C for every 1 °C increase in macrohabitat temperature, and this nonuniformity in temperature change influenced our forecasts of vulnerability for animal communities under climate change. Assuming uniform increases of 6 °C, microhabitats decreased the vulnerability of communities by up to 32‐fold, whereas under nonuniform increases of 0.66 to 3.96 °C, microhabitats decreased the vulnerability of communities by up to 108‐fold. Microhabitats have extraordinary potential to buffer climate and likely reduce mortality during extreme climate events. These results suggest that predicted changes in distribution due to mortality and habitat shifts that are derived from macroclimatic samples and that assume uniform changes in microclimates relative to macroclimates may be overly pessimistic. Nevertheless, even nonuniform temperature increases within buffered microhabitats would still threaten frogs and lizards.
A General Framework To Assess the Vulnerability of Species to Global Climate Change Vulnerability is a function of the species' sensitivity and their exposure to climatic change, mediated by the ...adaptive potential of the species (both ecological and evolutionary), the resilience of the species, and the capacity for adaptive management to either reduce vulnerability, treat the impacts, mitigate regional exposure, or maximise the system resilience via resource management to increase buffering or reduce other threats. Importantly, physiological limits are often phylogenetically constrained 25,26, meaning tolerances may only need to be estimated for representatives of many taxa.\n Such management options could include, for example, maintenance of canopy cover and buffered microhabitats such as fallen debris through fire management, or the provision of thermally buffered shelters such as nest boxes for high-risk birds and mammals.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The structure of the neocortex varies across the neocortical mantle to govern the physical size of principal neurons. What impact such anatomical variation has on the computational operations of ...principal neurons remains unknown. Here, we demonstrate within a functionally defined area that neocortical thickness governs the anatomical, electrophysiological, and computational properties of the principal output neurons of the neocortex. We find that neocortical thickness and the size of layer 5B pyramidal neurons changes as a gradient across the rostro-caudal axis of the rat primary visual cortex. Simultaneous somato-dendritic whole-cell recordings and compartmental modeling revealed that the electrical architecture of principal neurons was not preserved; rather, primary visual cortex site-dependent differences in intracellular resistivity accentuated a gradient of the electrical behavior of layer 5B pyramidal neurons to influence the emergence of active dendritic computations. Our findings therefore reveal an exquisite relationship between neocortical structure and neuronal computation.
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•Neocortical thickness varies as a gradient across the rat primary visual cortex•Neocortical structure governs apical dendritic morphology of V1 principal neurons•Principal neurons exhibit a gradient of dendritic information processing across V1•Neocortical structure and biophysics enforce a computational gradient across V1
Fletcher and Williams demonstrate that neuronal computations are determined by neocortical location. Dendritic integration in the primary visual cortex is governed by neuronal morphology and biophysics, creating a gradient of information processing that challenges the idea of stereotyped microcircuit operation.
Ecologists seek to understand patterns of distribution and abundance of species. Studies of distribution often use occurrence data to build models of the environmental niche of a species. ...Environmental suitability (ES) derived from such models may be used to predict the potential distributions of species. The ability of such models to predict spatial patterns in abundance is unknown; we argue that there should be a positive relationship between ES and local abundance. This will be so if ES reflects how well the species’ physiological and ecological requirements are met at a site and if those factors also determine local abundance. However, the presence of other factors may indicate that potential abundance is not attained at all sites. Therefore, ES should predict the upper limit of abundance, and the observed relationship with ES should be wedge shaped. We tested the relationship of ES with local abundance for 69 rain forest vertebrates in the Australian wet tropics. Ordinary least squares and quantile regressions revealed a positive relationship between ES and local abundance for most species (>84%). The relationships for these species were wedge shaped. We conclude that ES modeled from presence‐only data provides useful information on spatial patterns of abundance, and we discuss implications of this in addressing important problems in ecology.
There is broad consensus that the diversity of functional traits within species assemblages drives several ecological processes. It is also widely recognized that rare species are the first to become ...extinct following human-induced disturbances. Surprisingly, however, the functional importance of rare species is still poorly understood, particularly in tropical species-rich assemblages where the majority of species are rare, and the rate of species extinction can be high. Here, we investigated the consequences of local and regional extinctions on the functional structure of species assemblages. We used three extensive datasets (stream fish from the Brazilian Amazon, rainforest trees from French Guiana, and birds from the Australian Wet Tropics) and built an integrative measure of species rarity versus commonness, combining local abundance, geographical range, and habitat breadth. Using different scenarios of species loss, we found a disproportionate impact of rare species extinction for the three groups, with significant reductions in levels of functional richness, specialization, and originality of assemblages, which may severely undermine the integrity of ecological processes. The whole breadth of functional abilities within species assemblages, which is disproportionately supported by rare species, is certainly critical in maintaining ecosystems particularly under the ongoing rapid environmental transitions.
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