R-matrix Floquet theory of multiphoton processes:VI. The negative halide ions

The R-matrix Floquet approach is applied to study the negative F and Cl ions in a light field. Detachment rates are obtained for detachment processes involving up to three photons. The results obtained in the present approach are compared to other experimental and theoretical results. For two- and three-photon processes reasonable agreement with other calculations has been found, while for two-photon detachment the results agree with the experimental cross sections. The three-photon results are in less good agreement with experiment although the larger error bars make accurate comparisons more difficult. The changes in the detachment behaviour for these ions are compared to each other as well as to the detachment behaviour of H.

Lifespan, body size and oxygen : aerobic metabolism and oxidative stress in cultured fibroblasts /

The allometric scaling relationship observed between metabolic rate (MR) and species body mass can be partially explained by differences in cellular MR (Porter & Brand, 1995). Here, I studied cultured cell lines derived from ten mammalian species to determine whether cells propagated in an identical environment exhibited MR scaling. Oxidative and anaerobic metabolic parameters did not scale significantly with donor body mass in cultured cells, indicating the absence of an intrinsic MR setpoint. The rate of oxygen delivery has been proposed to limit cellular metabolic rates in larger organisms (West et al., 2002). As such cells were cultured under a variety of physiologically relevant oxygen tensions to investigate the effect of oxygen on cellular metabolic rates. Exposure to higher medium oxygen tensions resulted in increased metabolic rates in all cells. Higher MRs have the potential to produce more reactive oxygen species (ROS) which could cause genomic instability and thus reduced lifespan. Longer-lived species are more resistant to oxidative stress (Kapahi et al, 1999), which may be due to greater antioxidant and/or DNA repair capacities. This hypothesis was addressed by culturing primary dermal fibroblasts from eight mammalian species ranging in maximum lifespan from 5 to 120 years. Only the antioxidant manganese superoxide dismutases (MnSOD) positively scaled with species lifespan (p<0.01). Oxidative damage to DNA is primarily repaired by the base excision repair (BER) pathway. BER enzyme activities showed either no correlation or as in the case of polymerase p correlated, negatively with donor species (p<0.01 ). Typically, mammalian cells are cultured in a 20% O2 (atmospheric) environment, which is several-fold higher than cells experience in vivo. Therefore, the secondary aim of this study was to determine the effect of culturing mammalian cells at a more physiological oxygen tension (3%) on BER, and antioxidant, enzyme activities. Consistently, standard culture conditions induce higher antioxidant and DNA ba.se excision repair activities than are present under a more physiological oxygen concentration. Therefore, standard culture conditions are inappropriate for studies of oxidative stress-induced activities and species differences in fibroblast DNA BER repair capacities may represent differences in ability to respond to oxidative stress. An interesting outcome firom this study was that some inherent cellular properties are maintained in culture (i.e. stress responses) while others are not (i.e. MR).

Seasonal reproductive endothermy in tegu lizards

With some notable exceptions, small ectothermic vertebrates are incapable of endogenously sustaining a body temperature substantially above ambient temperature. This view was challenged by our observations of nighttime body temperatures sustained well above ambient (up to 10°C) during the reproductive season in tegu lizards (~2 kg). This led us to hypothesize that tegus have an enhanced capacity to augment heat production and heat conservation. Increased metabolic rates and decreased thermal conductance are the same mechanisms involved in body temperature regulation in those vertebrates traditionally acknowledged as “true endotherms” : the birds and mammals. The appreciation that a modern ectotherm the size of the earliest mammals can sustain an elevated body temperature through metabolic rates approaching that of endotherms enlightens the debate over endothermy origins, providing support for the parental care model of endothermy, but not for the assimilation capacity model of endothermy. It also indicates that, contrary to prevailing notions, ectotherms can engage in facultative endothermy, providing a physiological analog in the evolutionary transition to true endothermy.

Conséquences de l’acclimatation à différents régimes thermiques sur les taux métaboliques standards des tacons du saumon de l’Atlantique(Salmo salar)

Les poissons vivant au sein d’une rivière sont soumis à des variations circadiennes de température pouvant influencer la croissance, la digestion et le métabolisme standard. Les modèles bioénergétiques utilisant les fonctions métaboliques pour déterminer la croissance d’un poisson ont souvent été élaborés avec des poissons acclimatés à des températures constantes. Ces modèles pourraient sous-estimer l’énergie dépensée par un poisson soumis à des températures fluctuantes. En utilisant la respirométrie par débit intermittent, les objectifs de ce travail étaient : (1) de quantifier les différences entre les taux métaboliques standards de poissons acclimatés à une température constante (20.2 oC ± 0.5 oC) et à des fluctuations circadiennes de température (19.8 oC ± 2.0 oC; 19.5 oC ± 3.0 oC) et (2) comparer deux méthodologies pour calculer les taux métaboliques standards de poissons sujets aux fluctuations circadiennes de températures : respirométrie (a) en température constante ou (b) en température fluctuante. Les poissons acclimatés à des fluctuations circadiennes de température ont des taux métaboliques standards plus élevés que des poissons acclimatés à une température constante. À 20.2 oC ± 0.5 oC, les taux métabolique standards ont été de 25% à 32% plus bas pour des poissons maintenus à une température constante que pour des poissons gardés sous des fluctuations circadiennes de température. Les méthodologies utilisées pour estimer les taux métaboliques standards de poissons sujets aux fluctuations de température offrent des résultats similaires.

Réponse métabolique du saumon Atlantique (Salmo salar) aux fluctuations journalières de température : rôles de la température d’acclimatation et de l’historique thermique

En général, le métabolisme des poissons est estimé à des valeurs de température constantes, mais les effets de fluctuations journalières de température similaires à celles retrouvées en milieu naturel semblent peu connus. Les objectifs du présent mémoire sont de quantifier les effets de la température moyenne d’acclimatation et d’évaluer les effets de l’historique thermique des individus, sur les réponses métaboliques de tacons de saumon Atlantique (Salmo salar) aux fluctuations journalières de la température. Des tacons provenant de deux rivières, une fraîche et une chaude, ont été acclimatés à un maximum de quatre régimes thermiques (constant 15 °C ou 20 °C, fluctuant 15 °C ± 2.5 °C ou 20 °C ± 2.5 °C) et leur taux métabolique standard estimés par respirométrie par débit-intermittent. Les fluctuations journalières de température (15 °C ± 2.5 °C) près de l’optimum thermique pour cette espèce (16 °C) n’affectent pas le taux métabolique standard. À l’opposé, les fluctuations journalières de température plus chaudes (20 °C ± 2.5 °C) augmentent de 35.4% le taux métabolique standard des tacons de la rivière plus chaude, mais pas ceux des poissons de la rivière fraîche. Ainsi, la température moyenne à laquelle sont acclimatés les poissons peut affecter leur réponse métabolique aux fluctuations journalières de température, mais cette réponse peut varier entre populations provenant de rivières présentant des régimes thermiques différents. Enfin, grâce aux données de métabolisme précédemment estimées, un modèle de métabolisme standard a été développé pour des tacons de saumon Atlantique soumis à des fluctuations journalières de température.

Farmers’ knowledge and perceptions of potato pests and their management in Uganda

As we initiate entomological research on potato (Solanum tuberosum L.) in Uganda, there is need to understand farmers’ knowledge of existing insect pest problems and their management practices. Such information is important for designing a suitable intervention and successful integrated pest management (IPM) strategy. A farm household survey using a structured questionnaire was conducted among 204 potato farmers in six districts of Uganda (i.e., Kabale, Kisoro, Mbale, Kapchorwa, Mubende, and Kyegegwa) during August and September 2013. Diseases, insect pests, price fluctuations, and low market prices were the four highest ranked constraints in potato production, in order of decreasing importance. Cutworms (Agrotis spp.), aphids (Myzus persicae (Sulzer)), and potato tuber moth (Phthorimaea operculella (Zeller)) were the three most severe insect pests. Ants (Dorylis orantalis Westwood), whiteflies (Bemisia tabaci (Gennadius)), and leafminer flies (Liriomyza huidobrensis (Blanchard)) were pests of moderate importance. Major yield losses are predominantly due to late blight (Phytophthora infestans (Mont.) de Bary) and reached 100% without chemical control in the districts of Kabale, Kisoro, Mbale, and Kapchorwa. On average, farmers had little to moderate knowledge about pest characteristics. The predominant control methods were use of fungicides (72% of respondents) and insecticides (62% of respondents). On average, only 5% of the 204 farmers knew about insect pests and their natural enemies. This lack of knowledge calls for training of both farmers and extension workers in insect pest identification, their biology, and control. Empowering farmers with knowledge about insect pests is essential for the reduction of pesticide misuse and uptake of more environmentally friendly approaches like IPM. Field surveys would need follow-up in order to assess the actual field infestation rates and intensities of each insect pest and compare the results with the responses received from farmers.

The evolutionary ecology of resistance to parasitoids by Drosophila

Parasitoids are the most important natural enemies of many insect species. Larvae of many Drosophila species can defend themselves against attack by parasitoids through a cellular immune response called encapsulation. The paper reviews recent studies of the evolutionary biology and ecological genetics of resistance in Drosophila, concentrating on D. melanogaster. The physiological basis of encapsulation, and the genes known to interfere with resistance are briefly summarized. Evidence for within- and between-population genetic variation in resistance from isofemale line, artificial selection and classical genetic studies are reviewed. There is now firm evidence that resistance is costly to Drosophila, and the nature of this cost is discussed, and the possibility that it may involve a reduction in metabolic rate considered. Comparative data on encapsulation and metabolic rates across seven Drosophila species provides support for this hypothesis. Finally, the possible population and community ecological consequences of evolution in the levels of host resistance are examined.

Structural modeling of high-affinity thyroid receptor-ligand complexes

Understanding the molecular basis of the binding modes of natural and synthetic ligands to nuclear receptors is fundamental to our comprehension of the activation mechanism of this important class of hormone regulated transcription factors and to the development of new ligands. Thyroid hormone receptors (TR) are particularly important targets for pharmaceuticals development because TRs are associated with the regulation of metabolic rates, body weight, and circulating levels of cholesterol and triglycerides in humans. While several high-affinity ligands are known, structural information is only partially available. In this work we obtain structural models of several TR-ligand complexes with unknown structure by docking high affinity ligands to the receptors` ligand binding domain with subsequent relaxation by molecular dynamics simulations. The binding modes of these ligands are discussed providing novel insights into the development of TR ligands. The experimental binding free energies are reasonably well-reproduced from the proposed models using a simple linear interaction energy free-energy calculation scheme.

Mitochondrial ATP-sensitive K(+) channels as redox signals to liver mitochondria in response to hypertriglyceridemia

We have recently demonstrated that hypertriglyceridemic (HTG) mice present both elevated body metabolic rates and mild mitochondrial uncoupling in the liver owing to stimulated activity of the ATP-sensitive potassium channel (mitoK(ATP)). Because lipid excess normally leads to cell redox imbalance, we examined the hepatic oxidative status in this model. Cell redox imbalance was evidenced by increased total levels of carbonylated proteins, malondialdehydes, and GSSG/GSH ratios in HTG livers compared to wild type. In addition, the activities of the extramitochondrial enzymes NADPH oxidase and xanthine oxidase were elevated in HTG livers. In contrast, Mn-superoxide dismutase activity and content, a mitochondrial matrix marker, were significantly decreased in HTG livers. isolated HTG liver mitochondria presented lower rates of H(2)O(2) production, which were reversed by mitoK(ATP) antagonists. In vivo antioxidant treatment with N-acetylcysteine decreased both mitoKATP activity and metabolic rates in HTG mice. These data indicate that high levels of triglycerides increase reactive oxygen generation by extramitochondrial enzymes that promote MitoK(ATP) activation. The mild uncoupling mediated by mitoK(ATP) increases metabolic rates and protects mitochondria against oxidative damage. Therefore, a biological role for mitoK(ATP) is a redox sensor is shown here for the first time in an in vivo model of systemic and cellular lipid excess, (C) 2009 Elsevier Inc. All rights reserved.

The comparative energetics and growth strategies of sympatric Antarctic and subantarctic fur seal pups at Iles Crozet

The period of maternal dependence is a time during which mammalian infants must optimise both their growth and the development of behavioural skills in order to successfully meet the demands of independent living. The rate and duration of maternal provisioning, post-weaning food availability and climatic conditions are all factors likely to influence the growth strategies of infants. While numerous studies have documented differences in growth strategies at high taxonomic levels, few have investigated those of closely related species inhabiting similar environments. The present study examined the body composition, metabolism and indices of physiological development in pups of Antarctic fur seals (Arctocephalus gazella) and subantarctic fur seals (Arctocephalus tropicalis), congeneric species with different weaning ages (4 months and 10 months, respectively), during their overlap in lactation at a sympatric breeding site in the Iles Crozet. Body lipid reserves in pre-moult pups were significantly greater (t₂₈=2.73, P<0.01) in subantarctic (26%) than Antarctic fur seals (22%). Antarctic fur seal pups, however, had significantly higher (t₂₆=3.82, P<0.001) in-air resting metabolic rates (RMR; 17.1±0.6 ml O₂ kg^-1 min^-1) than subantarctic fur seal pups (14.1±0.5 ml O2 kg^-1 min^-1). While in-water standard metabolic rate (SMR; 22.9±2.5 ml O2 kg^-1 min^-1) was greater than in-air RMR for Antarctic fur seal pups (t₉=2.59, P<0.03), there were no significant differences between in-air RMR and in-water SMR for subantarctic fur seal pups (t₁₂=0.82, P>0.4), although this is unlikely to reflect a greater ability for pre-moult pups of the latter species to thermoregulate in water. Pup daily energy expenditure was also significantly greater (t₂₇=2.36, P<0.03) in Antarctic fur seals (638±33 kJ kg^-1 day^-1) than in subantarctic fur seals (533±33 kJ kg^-1 day^-1), which corroborates observations that pups of the former species spend considerably more time actively learning to swim and dive. Consistent with this observation is the finding that blood oxygen storage capacity was significantly greater (t₉=2.81, P<0.03) in Antarctic (11.5%) than subantarctic fur seal (8.9%) pups. These results suggest that, compared with subantarctic fur seals, Antarctic fur seal pups adopt a strategy of faster lean growth and physiological development, coupled with greater amounts of metabolically expensive behavioural activity, in order to acquire the necessary foraging skills in time for their younger weaning age.

Water repellency, near-saturated infiltration and preferential solute transport in a macroporous clay soil

Little attention has been paid to the possibility that soil water repellency could enhance non-equilibrium water flow and solute transport through macropores present in structured clay soils. In this study, we measured infiltration and solute transport in a clay soil under near-saturated conditions in both the field using tension infiltrometers and in the laboratory on undisturbed soil columns. Measurements were made on adjacent plots under grass and continuous arable cultivation. Steady-state field infiltration rates measured using water and ethanol as the infiltrating fluids demonstrated that the soil macroporosity under grass was better developed, but that much of the structural pore system was inactive due to water repellency. No water repellency was detected on the arable plot disturbed by tillage. Dye tracing showed that the conducting macroporosity was largely comprised of earthworm channels in the grassed plot and inter-aggregate voids resulting from ploughing in the arable plot. Tracer breakthrough curves measured on field-dry soil indicated rapid macropore transport in columns taken from both plots, although the degree of non-equilibrium transport appeared somewhat stronger under grass. This result, which was attributed to water repellency, was also consistent with the larger flow-weighted mean pore size found in the field infiltration experiments. It is concluded that water repellency in undisturbed structured clay soils can have significant effects on the occurrence of non-equilibrium water and solute transport in macropores.

Size matters : extraordinary rodent abundance on an Australian tropical floodplain

Published estimates of the total biomass of natural populations of mammalian herbivores generally have ignored small-bodied taxa (especially, rodents). Including such taxa may dramatically change our understanding of total biomass and energy flow in such systems. Dusky rats (Rattus colletti) are small (up to 210 g) native Australian mammals, and our 5-year mark-recapture study on a tropical flood plain (Adelaide River, Northern Territory) revealed that rat biomass can reach extraordinary levels (up to 4.7 t km⁻²). Because their small body size results in high mass-specific metabolic rates, a given biomass of rodents has a several-fold higher total energy requirement than the same mass of large-bodied herbivores. Accordingly, during some years dusky rat biomass can be double that estimated for large herbivores on the world's most productive savannas in eastern and southern Africa. The huge rodent biomass strongly suggests that the Adelaide River flood plain must be an incredibly productive habitat. Considering the immense biological importance of these productive ecosystems, flood plain conservation must be placed high on the priority list of habitats that require immediate protection.

From bivalves to birds : oxidative stress and longevity

1. The oxidative stress theory of ageing predicts that animals living longer will have less cumulative oxidative damage together with structural characteristics that make them more resistant to oxidative damage itself.
2. Although a general relationship between body size, metabolism and longevity does not exist in marine invertebrates, they are generally characterized by low rates of metabolism and reactive oxygen species (ROS) formation associated with lower antioxidant enzyme activities compared to vertebrates.
3. Birds and mammals have very similar size-affected metabolic rates and their metabolic intensity explains only some of the variation in maximum lifespan potential (MLSP).Within each class, smaller animals have higher rates of metabolism and ROS production and membranes that are more susceptible to oxidative damage and autocatalytic propagation of free radicals than larger ones.
4. Although the high variation in life-history strategies is accompanied by substantial variation in MLSP, there is a consistent positive correlation between rates of ROS formation and antioxidant levels among most animals examined so far for these traits. The consensus of these studies is that ROS and antioxidant levels are inversely related to MLSP.
5. The lack of a clear stoichiometric relation between variables contributing to oxidative stress limits our capacity to infer longevity consequences from measures of pro-oxidant or antioxidant status among or within species

Life histories of the Insectivora : the role of phylogeny, metabolism and sex differences

Life-history data for 63 species from the mammalian order Insectivora have been collated from the literature. These data were analysed for covariation and for correlations with body mass, brain mass and mass-specific resting metabolic rate. An independent contrasts method has been used to remove the effect of phylogeny. Due to uncertainties surrounding their evolutionary relationships, 22 different phylogenies of insectivores have been used as a basis for comparative analysis. The results show that several key correlations between life-history variables are only significant when certain phylogenies are used, highlighting the problems of such analyses when the phylogeny used is inaccurate. After removing the effect of phylogeny, relatively few significant correlations remain. Insectivores that have a high body mass have relatively lower metabolic rates, longer lifespans and longer gestation lengths. There is some support for a fast±slow continuum in insectivore life-history evolution: there are some significant positive correlations between measures of growth rates (e.g. gestation length and age at weaning) and lifespan, and some negative correlations between growth rates and measures of reproductive output. It is suggested that the seasonality of life of many insectivores may have played an influential role in the evolution of the group, in particular in delaying the onset of sexual maturity. There is little indication that brain size influences life-history evolution in this order, but metabolism may play an important role. The energetic requirements of maintaining high metabolic rates in small mammals such as insectivores may be constraining life histories to a greater extent than occurs in larger mammals. This effect may have obscured the relationship between metabolic rate and life histories in wider inter-order analyses. Finally, there is considerable evidence that sex differences play a large role in shaping insectivore evolution, and it is suggested that this factor must be considered more often in future studies of mammalian life histories in general.

Inexplicable inefficiency of avian molt? Insights from an opportunistically breeding arid-zone species, Lichenostomus penicillatus

The majority of bird species studied to date have molt schedules that are not concurrent with other energy demanding life history stages, an outcome assumed to arise from energetic trade-offs. Empirical studies reveal that molt is one of the most energetically demanding and perplexingly inefficient growth processes measured. Furthermore, small birds, which have the highest mass-specific basal metabolic rates (BMR_m), have the highest costs of molt per gram of feathers produced. However, many small passerines, including white-plumed honeyeaters (WPHE; Lichenostomus penicillatus), breed in response to resource availability at any time of year, and do so without interrupting their annual molt. We examined the energetic cost of molt in WPHE by quantifying weekly changes in minimum resting metabolic rate (RMR_min) during a natural-molt period in 7 wild-caught birds. We also measured the energetic cost of feather replacement in a second group of WPHEs that we forced to replace an additional 25% of their plumage at the start of their natural molt period. Energy expenditure during natural molt revealed an energy conversion efficiency of just 6.9% (±0.57) close to values reported for similar-sized birds from more predictable north-temperate environments. Maximum increases in RMR_min during the molt of WPHE, at 82% (±5.59) above individual pre-molt levels, were some of the highest yet reported. Yet RMR_min maxima during molt were not coincident with the peak period of feather replacement in naturally molting or plucked birds. Given the tight relationship between molt efficiency and mass-specific metabolic rate in all species studied to date, regardless of life-history pattern (Efficiency (%) = 35.720•10^-0.494BMRm; r² = 0.944; p =<0.0001), there appears to be concomitant physiological costs entrained in the molt period that is not directly due to feather replacement. Despite these high total expenditures, the protracted molt period of WPHE significantly reduces these added costs on a daily basis.