1,721,027 research outputs found
La pianificazione urbanistica e le infrastrutture verdi
Full text linkIl presente lavoro di ricerca esamina come sia venuto ad evolversi il modo di concepire il verde all’interno dei contesti urbani. Per una ricostruzione in questo senso, un’attenzione è posta sugli strumenti che l’ordinamento nazionale mette a disposizione per tutelare gli elementi verdi nei contesti urbani, per garantirne una più ampia diffusione ovvero la creazione in aree in cui essi sono assenti. Gli strumenti considerati si distinguono in due macrocategorie, laddove alla prima possono essere ricondotti tutti quelli che orbitano intorno all’attività di pianificazione urbanistica, mentre alla seconda quelli che esulano da tale attività, senza, tuttavia, porsi in contrapposizione ad essa. Con riferimento alla prima categoria, è nel PRG, comunque denominato, che viene individuato lo strumento più efficace che gli enti locali hanno a disposizione per garantire la diffusione delle infrastrutture verdi all’interno del territorio comunale e, in generale, per garantire una tutela all’ambiente urbano
Microclimate drives intraspecific thermal specialization: conservation perspectives in freshwater habitats
Full text linkEndemic and relict species are often confined to ecological refugia or over fragmented distributions, representing priority conservation subjects. Within these sites, the individual population may realize distinct niches to a varying degree of specialization. An emblematic example is provided by freshwater species segregated in thermal-mineral springs, where individuals may face highly diverse microclimates in limited geographic areas. Downscaling the characterization of physiological traits to microclimatic niches becomes pivotal to adopt effective conservation measures in these heterogeneous habitats. Melanopsis etrusca (Brot, 1862) is an endangered relict snail endemic to a small number of thermal-mineral streams in central Italy. Here we describe the thermal tolerance of two populations of M. etrusca inhabiting streams with distinctly different thermal regimes, investigating the extent of physiological and behavioural specialization to such diverse microclimatic niches. The comparison of oxygen consumption rates of a population dwelling in temperate streams, characterized by seasonal temperature fluctuations (12-27 degrees C), with a population experiencing constantly hot water (35-38 degrees C) revealed the absence of any seasonal or geographic effect on metabolic compensation. Conversely, mobility performances were maximized in the population inhabiting the hot stream. Interestingly, here, the snails exhibited emersion behaviour outside the water, triggered by temperatures above 37 degrees C. In the field, individuals of this population are observed inactive on stream banks, conceivably to minimize the metabolic cost that otherwise would be induced by remaining in the hot water. Only a few individuals from the temperate stream exhibited the same behaviour when exposed to elevated temperatures, suggesting the exaptation of a preexisting trait during the evolutionary process of adaptation to hot waters. The present results provide elements for the best practice in future programmes aimed at reintroducing stocks of threatened species across heterogeneous habitats. Our study further underlines the relevance of downscaling data collection for endangered species conservation in order to recognize microclimatic specializations
Study of the critical dynamics of active matter models to explain anomalous relaxation in natural swarms
No full textA major challenge of modern physics and mathematics is the theoretical modeling of living systems. Recently, methods of condensed matter physics have been successfully applied to biological systems, providing an accurate description of the statistical laws governing active matter. Systems of interest in active matter are made of a large number of entities interacting locally and leading to large-scale collective behavior. Manifestations of this appear at multiple scales of living systems, from cell migration to swarming of insects and flocking of birds. Interestingly, though these systems are microscopically very different, they exhibit common macroscopic features. The study of active matter through the lens of statistical physics aims at developing a unified description of these behaviors. A fruitful approach uses the theory of critical phenomena, developed in condensed matter physics to study phase transitions in inanimate systems. This theory has allowed a systematic description of equilibrium phenomena through the introduction of concepts like long-range correlations, scaling laws, and renormalization. A major result of this theory states that an equilibrium system close to a second-order phase transition exhibits a macroscopic behavior independent of the microscopic details. This notion of universality has inspired the use of the same methods to study non-equilibrium collective behaviors in biology. Hydrodynamics, active matter models, and non-equilibrium statistical physics are paramount to the study of self-organization in biological systems. Several questions are still open. To what extent can the search for universality be applied to biological collective behavior? How should equilibrium theories be transformed in order to study non-equilibrium living systems? Only a combination of theory and experiments can provide answers to these problems. In this thesis I try to tackle these questions, focusing on the collective behavior of natural swarms. Recent field experiments unveiled long-range correlations in swarms of midges in absence of collective motion [1], thus suggesting that the system is disordered but with a near-critical phenomenology [2]. Moreover, experiments confirmed the emergence of dynamical scaling laws in the spatio-temporal correlation functions of different swarms [3], providing additional evidence about the universality of their behavior. Dynamical scaling stems from the study of time-dependent critical phenomena of equilibrium systems [4]. It affirms that, close to criticality, the correlation length ξ is the only relevant length scale of the system, ruling also its dynamical relaxation [4]. This phenomenon is known as critical slowing down, and it is expressed by the power law τ ∼ ξ^z, where τ is the characteristic time scale and z is called dynamical critical exponent [5]. When this property holds, the exponent determines the dynamical universality class of the system, containing all the information on its macroscopic dynamical behavior. Natural swarms obey this law with a dynamical critical exponent z ≃ 1.2, a value not found in any other statistical model [3]. Moreover, the relaxation reflects an anomalous underdamped decay of velocity correlation functions, which is not compatible with standard models. This thesis proposes to combine classic and novel active matter models with standard statistical field theory tools, with the purpose of rationalizing this experimental finding. The validity of scaling laws suggests that a description in terms of out-of-equilibrium critical phenomena is legitimate, therefore our study will employ Renormalization Group (RG) techniques and numerical simulations of active matter models in a near-critical regime. The investigation focuses on two active matter models. The first is the Vicsek model that describes self-propelled dissipative dynamics in the velocities. An analytical calculation on the respective hydrodynamic incompressible field theory reveals that activity lowers the value of the dynamical critical exponent with respect to the equilibrium universality class through a mechanism of crossover. Numerical simulations confirm that this result is valid also for compressible systems. The second studied theory is the Inertial Spin Model, which formulates a second-order dynamics in the velocities able to qualitatively reproduce the swarms’ relaxation. A fixed-network RG calculation unveils the role of inertia in determining the critical dynamics of weakly damped systems: through a dynamical crossover they can exhibit a z = 1.5 critical exponent, a value lower than the dissipative case. The information acquired with these studies is combined in a theoretical model that includes self-propulsion and inertial dynamics, ingredients that both lower the value of the critical exponent finally arriving at consistency with experimental data
Nothing in experimental biology makes sense except in the light of ecology and evolution - correspondence on J. Exp. Biol. 216, 2771-2782
Full text linkEffects of ocean acidification on embryonic respiration and development of a temperate wrasse living along a natural CO2 gradient
Full text linkVolcanic CO2 seeps provide opportunities to investigate the effects of ocean acidification on organisms in the wild. To understand the influence of increasing CO2 concentrations on the metabolic rate (oxygen consumption) and the development of ocellated wrasse early life stages, we ran two field experiments, collecting embryos from nesting sites with different partial pressures of CO2 [pCO2; ambient (400 µatm) and high (800-1000 µatm)] and reciprocally transplanting embryos from ambient- to high-CO2 sites for 30 h. Ocellated wrasse offspring brooded in different CO2 conditions had similar responses, but after transplanting portions of nests to the high-CO2 site, embryos from parents that spawned in ambient conditions had higher metabolic rates. Although metabolic phenotypic plasticity may show a positive response to high CO2, it often comes at a cost, in this case as a smaller size at hatching. This can have adverse effects because smaller larvae often exhibit a lower survival in the wild. However, the adverse effects of increased CO2 on metabolism and development did not occur when embryos from the high-CO2 nesting site were exposed to ambient conditions, suggesting that offspring from the high-CO2 nesting site could be resilient to a wider range of pCO2 values than those belonging to the site with present-day pCO2 levels. Our study identifies a crucial need to increase the number of studies dealing with these processes under global change trajectories and to expand these to naturally high-CO2 environments, in order to assess further the adaptive plasticity mechanism that encompasses non-genetic inheritance (epigenetics) through parental exposure and other downstream consequences, such as survival of larvae
Closely related crabs from opposite niches adopt different mechanisms to adjust oxygen transport
No full textThe molecular heterogeneity of hemocyanin: the role in crustacean adaptive plasticity.
No full textCrustacean hemocyanin (He) represents a unique case of molecular heterogeneity among oxygen-carrying proteins. The existence of different genes, encoding single polypeptide chains, constitutes the genetic basis for the inter- and intra-specific polymorphism. In addition, the large number of He subunits within crustacean species, together with their flexible expression, provides an efficient intrinsic mechanism of modulation of oxygen transport. This review presents a description and classification of the various aspects of crustacean He heterogeneity and defines its role in a perspective of crustacean adaptive physiolog
Unusual oxygen binding behavior of a 24-meric crustacean hemocyanin
No full textHemocyanins from Crustacea usually are found as 1 × 6 or 2 × 6-meric assemblies. An exception is the hemocyanin isolated from thalassinidean shrimps where the main component is a 24-meric structure. Our analysis of oxygen binding data of the thalassinidean shrimp Upogebia pusilla based on a three-state MWC-model revealed that despite the 24-meric structure the functional properties can be described very well based on the hexamer as allosteric unit. In contrast to the hemocyanins from other thalassinidean shrimps the oxygen affinity of hemocyanin from U. pusilla is increased upon addition of l-lactate. A particular feature of this hemocyanin seems to be that l-lactate already enhances oxygen affinity under resting conditions which possibly compensates the rather low intrinsic affinity observed in absence of l-lactate. The fast rate of oxygen dissociation might indicate that in this hemocyanin a higher cooperativity is less important than a fast response of saturation level to changes in oxygen concentration. © 2010 Elsevier Inc. All rights reserved
Coping with cyclic oxygen availability: Evolutionary aspects.
Full text linkBoth the gradual rise in atmospheric oxygen over the Proterozoic Eon as well as episodic fluctuations in oxygen over several million-year time spans during the Phanerozoic Era, have arguably exerted strong selective forces on cellular and organismic respiratory specialization and evolution. The rise in atmospheric oxygen, some 2 billion years after the origin of life, dramatically altered cell biology and set the stage for the appearance of multicelluar life forms in the Vendian (Ediacaran) Period of the Neoproterozoic Era. Over much of the Paleozoic, the level of oxygen in the atmosphere was near the present atmospheric level (21%). In the Late Paleozoic, however, there were extended times during which the level of atmospheric oxygen was either markedly lower or markedly higher than 21%. That these Paleozoic shifts in atmospheric oxygen affected the biota is suggested by the correlations between: (1) Reduced oxygen and the occurrences of extinctions, a lowered biodiversity and shifts in phyletic succession, and (2) During hyperoxia, the corresponding occurrence of phenomena such as arthropod gigantism, the origin of insect flight, and the evolution of vertebrate terrestriality. Basic similarities in features of adaptation to hyopoxia, manifest in living organisms at levels ranging from genetic and cellular to physiological and behavioral, suggest the common and early origin of a suite of adaptive mechanisms responsive to fluctuations in ambient oxygen. Comparative integrative approaches addressing the molecular bases of phenotypic adjustments to cyclic oxygen fluctuation provide broad insight into the incremental steps leading to the early evolution of homeostatic respiratory mechanisms and to the specialization of organismic respiratory function
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