Evidence of evolutionary optimization of fatty acid length and unsaturation.

The lipid composition of cell membranes exerts a crucial influence on cell physiology. Indeed, one double bond triggers membrane fluidity, essential for cell functionality, but additional double bonds increase the susceptibility to peroxidation, which produces reactive compounds that impair the viability of cells. It has therefore been suggested, but never tested in an extensive comparative context, that the composition of membrane fatty acids has been optimized during evolution. A similar prediction has been made for fatty acid chain length, on which susceptibility to peroxidation also depends. Here I tested for stabilizing selection on fatty acid composition by evaluating the fitting of the single stationary peak (SSP) model of evolution to a large data set from 107 species of birds, against alternative evolutionary models. I found that across-species variation in average chain length and in the proportion of monounsaturated fatty acids (MUFAs), but not in the proportion of polyunsaturated (PUFAs) nor saturated (SFAs) fatty acids, was better explained by SSP models than by other models. Results show optimum values of fatty acid chain length and proportion of MUFAs of 18 C atoms and 25.5% mol, respectively, the strength of stabilizing selection being particularly high in chain length. This is the first evidence of evolutionary optimization in fatty acid composition, suggesting that certain values may have been selected because of their adaptive capacity to minimize susceptibility to lipid peroxidation.

Bacteria and Hoverflies (Diptera: Syrphidae) in Tree Hollows From the Iberian Mediterranean Forest.

Saproxylic insect communities inhabiting tree hollows in Mediterranean forests depend on a combination of physical characteristics and interactions occurring between community member species. Despite the need to preserve these organisms, little is known about their interrelationships, in particular those relationships between saproxylic insects and microbiota occurring in these microhabitats. In tree hollows of Quercus rotundifolia Lamark that hold water and contain dead leaves, abundant microbial populations can be found. Developing on them are the larvae of Mallota dusmeti Andréu, 1926 (Diptera: Syrphidae), a vulnerable species (IUCN category: Marcos-García and Quinto 2011). This study provides the first data on the microbiota living inside the gut of the larvae of M. dusmeti, as well as the microbiota in the hollow where these larvae develop. Bacteria were identified by amplification and partial sequencing of the V1-V3 regions and the complete nucleotide sequence of 16S rRNA genes. We found eight species of bacteria living in tree hollows and three species in the gut of M. dusmeti larvae: Bacillus cereus, Bacillus toyonensis, and Lysinibacillus sphaericus. The filter-feeding mechanism characteristic of M. dusmeti larvae is selective in enabling ingestion of bacteria only above 2.1 µm in diameter.

Substituent and solvent effects on the UV-vis absorption spectrum of the photoactive yellow protein chromophore.

Solvent effects on the UV-vis absorption spectra and molecular properties of four models of the photoactive yellow protein (PYP) chromophore have been studied with ASEP/MD, a sequential quantum mechanics/molecular mechanics method. The anionic trans-p-coumaric acid (pCA(-)), thioacid (pCTA(-)), methyl ester (pCMe(-)), and methyl thioester (pCTMe(-)) derivatives have been studied in gas phase and in water solution. We analyze the modifications introduced by the substitution of sulfur by oxygen atoms and hydrogen by methyl in the coumaryl tail. We have found some differences in the absorption spectra of oxy and thio derivatives that could shed light on the different photoisomerization paths followed by these compounds. In solution, the spectrum substantially changes with respect to that obtained in the gas phase. The n → π1* state is destabilized by a polar solvent like water, and it becomes the third excited state in solution displaying an important blue shift. Now, the π → π1* and π → π2* states mix, and we find contributions from both transitions in S1 and S2. The presence of the sulfur atom modulates the solvent effect and the first two excited states become practically degenerate for pCA(-) and pCMe(-) but moderately well-separated for pCTA(-) and pCTMe(-).

Facilitation among saproxylic insects inhabiting tree hollows in a Mediterranean forest: the case of cetonids (Coleoptera: Cetoniidae) and syrphids (Diptera: Syrphidae).

Tree hollows offer an ideal niche for saproxylic insects in mature Mediterranean forests, where Diptera and Coleoptera are the richest groups. Co-occurrence is frequently observed among many species of both groups in these microhabitats, and some of these species have been considered to facilitate the presence of other species by acting as ecosystem engineers. One of the systems that is found in Mediterranean tree hollows is formed by cetonid (Coleoptera: Cetoniidae) and syrphid (Diptera: Syrphidae) larvae. Here, cetonid larvae feed on wood and litter and produce a substrate that is easier to decompose. To assess the possible role of these larvae as facilitating agents for the saproxylic guild, we studied whether the presence of saprophagous Syrphidae inside tree hollows is associated with the activity of cetonid larvae. Furthermore, in laboratory conditions, we tested whether cetonid larvae activity can improve the development and fitness of the saprophagous syrphid species. Our results show that "cetonid activity" was the variable that best explained the presence of saprophagous syrphid species in natural conditions. Myathropa florea (L., 1758) was one of the species most influenced by this activity. The laboratory experiment gave similar results, demonstrating that an enriched substrate with Cetonia aurataeformis Curti, 1913 larval feces improves syrphid larval growth rate and fitness of adults (measured as longer wing length) of M. florea.

Testicular melanization has evolved in birds with high mtDNA mutation rates.

Melanin is mainly found in the integument of animals, but it also appears in several extracutaneous tissues. The presence of melanin in testes has been anecdotally reported in all vertebrate groups, but the causes and functions of this melanin remain unknown. Similar to other extracutaneous melanins, testicular melanin may protect male germ cells from oxidative stress. Given the high respiratory activity of spermatozoa, oxidative stress generated by mitochondrial dysfunction as a consequence of mtDNA mutations directly affects sperm viability. Thus, natural selection may favour testicular melanization in males of species with high historical mutation rates in the mitochondrial genome. Here, we tested this hypothesis using information on occurrence of testicular melanization and mutation accumulation as reflected by cytochrome b mtDNA base pair substitution rates in a large set of 134 species of birds, controlling for the confounding effects of body mass, reproductive activity and phylogeny. We found that testicular melanization has evolved in species with high rates of accumulated mitochondrial mutations and propose that this is an adaptive response related to the protective capacity of melanin against oxidative stress. In support of this hypothesis, testicular melanization was more frequently observed during the breeding season of birds (i.e. when spermatogenesis is likely to occur) than during reproductive inactivity. In contrast to other extracutaneous melanins whose abundance seems to reflect skin and coat colour, we did not find a correlation between the proportion of plumage coloured by melanins and occurrence of testicular melanization. Whereas future experimental studies should test these hypotheses, our study highlights for the first time that melanization patterns in animals may evolve as a response to historical mutation rates.

Brain size and the expression of pheomelanin-based colour in birds.

Eumelanin and pheomelanin are the most common vertebrate pigments. They generate different colours and are synthesized under different physiological conditions. While pheomelanogenesis requires high levels of a key intracellular antioxidant (glutathione, GSH), eumelanogenesis is inhibited by GSH. This implies that species that present the molecular basis to produce large amounts of pheomelanin might be more limited to perform other costly processes that generate oxidative stress than species that produce eumelanin. Brain development requires large amounts of energy and antioxidants during ontogeny, so that large-brained species may be constrained in their simultaneous synthesis of large amounts of pheomelanin, but not in their synthesis of eumelanin. Here, we tested this hypothesis in a large dataset of 323 bird species. After controlling for the effects of phylogeny, latitude and sexual dichromatism, the proportion of pheomelanic plumage colour was strongly negatively related to the relative brain mass of species, whereas no relationship was found for the proportion of eumelanic colour. This indicates that the production of pheomelanin is a costly process that cannot evolve together with complex neural structures and thus with large cognitive capacity. This is the first time that the expression of melanic traits is found to correlate with another phenotypic character across species.

Quantum mechanical methods applied to excitation energy transfer: a comparative analysis on excitation energies and electronic couplings.

We present a comparative study on the influence of the quantum mechanical (QM) method (including basis set) on the evaluation of transition energies, transition densities and dipoles, and excitation energy transfer (EET) electronic couplings for a series of chromophores (and the corresponding pairs) typically found in organic electro-optical devices and photosynthetic systems. On these systems we have applied five different QM levels of description of increasing accuracy (ZINDO, CIS, TD-DFT, CASSCF, and SAC-CI). In addition, we have tested the effects of a surrounding environment (either mimicking a solvent or a protein matrix) on excitation energies, transition dipoles, and electronic couplings through the polarizable continuum model (PCM) description. Overall, the results obtained suggest that the choice of the QM level of theory affects the electronic couplings much less than it affects excitation energies. We conclude that reasonable estimates can be obtained using moderate basis sets and inexpensive methods such as configuration interaction of single excitations or time-dependent density functional theory when appropriately coupled to realistic solvation models such as PCM.

Feather mites and birds: an interaction mediated by uropygial gland size?

Feather mites (Arachnida: Acari: Astigmata) feed mainly on secretions of the uropygial gland of birds. Here, we use analyses corrected for phylogeny and body size to show that there is a positive correlation between the size of this gland and mite abundance in passerine birds at an interspecific level during the breeding season, suggesting that the gland mediates interactions between mites and birds. As predicted on the basis of hypothesized waterproofing and antibiotic functions of uropygial gland secretions, riparian/marsh bird species had larger glands and higher mite loads than birds living in less mesic terrestrial environments. An unexpected pattern was a steeper relationship between mite load and gland size in migratory birds than in residents. If moderate mite loads are beneficial to a host but high loads detrimental, this could create complex selection regimes in which gland size influences mite load and vice versa. Mites may exert selective pressures on gland size of their hosts that has resulted in smaller glands among migratory bird species, suggesting that smaller glands may have evolved in these birds to attenuate a possible detrimental effect of feather mites when present in large numbers.

Comparison of three effective Hamiltonian models of increasing complexity: triazene in water as a test case.

A critical comparison of widely used solvation models is reported. It is illustrated by a study of the triazene molecule in liquid water. We consider the following approaches: (1) a continuum model based on multicentric multipole expansions of the charge distribution, (2) the averaged solvent electrostatic potential from molecular dynamics (ASEP/MD) method, and (3) molecular dynamics simulations using a combined quantum mechanics/molecular mechanics potential (QM/MM/MD). We find that the solvation induces appreciable changes in the geometry and charge distribution of triazene. These changes are only qualitatively reproduced by the dielectric continuum model, which clearly underestimates induced dipole moments and solute-solvent interaction energy. We also show that the use of effective point charges placed on solute nuclei during the classical simulations may cause significant errors in the description of the solvent structure. The addition of charges representing nitrogen atom lone pairs is compulsory to reproduce the QM/MM/MD simulation results. Moreover, our results validate the use of the mean field approximation in the study of solvent effects. A major conclusion of this study is that the ASEP/MD method constitutes a reliable alternative to the much more computationally demanding QM/MM/MD methods.

Theoretical study of the 1,3-hydrogen shift of triazene in water.

The 1,3-hydrogen shift of triazene in aqueous solution was studied with a combination of QM/MM methods. First, the different species involved were characterized and the activation free-energies calculated with ASEP/MD, a method that makes use of the mean field approximation. Then the reaction dynamics was simulated with a QM/MM/MD method. A very strong influence of the solvent was observed, both specific, with the participation of a water molecule, and from the rest of the solvent. The effect of solvation on the geometry and electron distribution of triazene is important: N-N bond lengths tend to be more similar and the molecule acquires a planar structure. For the transition state structure, a substantial degree of ionic nature was found. Dynamic solvent effects were also analyzed.

A theoretical study of solvent effects on the 1(n-->pi*) electron transition in acrolein.

The (1)(n-->pi(*)) electron transition of acrolein in liquid water was studied theoretically by using the averaged solvent electrostatic potential/molecular dynamics method. The model combines a multireference perturbational treatment in the description of the solute molecule with molecular dynamics calculations in the description of the solvent. We demonstrate the importance of the solvent electron polarization, bulk solvent effects, and the use of relaxed geometries in solution on the calculated solvent shift. It is also shown that the inclusion of the dynamic correlation does not change the solvent shift although it must be used to reproduce the transition energy.

A new method to locate saddle points for reactions in solution by using the free-energy gradient method and the mean field approximation.

A new method for calculating saddle points of reactions in solution is presented. The main characteristics of the method are: (1) the solute-solvent system is described by the averaged solvent electrostatic potential/molecular dynamics method (ASEP/MD). This is a quantum mechanics/molecular mechanics method (QM/MM) that makes use of the mean field approximation (MFA) and that permits one to simultaneously optimize the electronic structure and geometry of the solute molecule and the solvent structure around it. (2) The transition state is located by the joint use of the free-energy gradient method and the mean field approximation. An application to the study of the Menshutkin reaction between NH(3) and CH(3)Cl in aqueous solution is discussed. The accuracy and usefulness of the proposed method is checked through comparison with other methods.

A selective learning method to improve the generalization of multilayer feedforward neural networks.

Multilayer feedforward neural networks with backpropagation algorithm have been used successfully in many applications. However, the level of generalization is heavily dependent on the quality of the training data. That is, some of the training patterns can be redundant or irrelevant. It has been shown that with careful dynamic selection of training patterns, better generalization performance may be obtained. Nevertheless, generalization is carried out independently of the novel patterns to be approximated. In this paper, we present a learning method that automatically selects the training patterns more appropriate to the new sample to be predicted. This training method follows a lazy learning strategy, in the sense that it builds approximations centered around the novel sample. The proposed method has been applied to three different domains: two artificial approximation problems and a real time series prediction problem. Results have been compared to standard backpropagation using the complete training data set and the new method shows better generalization abilities.

Controlled pilot study of piracetam for pediatric opsoclonus-myoclonus.

Piracetam is an effective symptomatic treatment for some types of myoclonus in adults. To survey the efficacy and safety of piracetam in pediatric opsoclonus-myoclonus, we conducted an open, randomized, two-period, dose-ranging, double-blind, crossover, clinical trial of five children comparing the antimyoclonic properties of oral piracetam to placebo. We devised and validated a new rating scale, specifically for pediatric opsoclonus-myoclonus. Two parents while blinded were able to identify the active phase by improvement in behavior, but another thought the behavior was worse. None of the patients showed improvement in myoclonus. The adult-equivalent dose of piracetam used in this study, which is threefold higher than that used in previous pediatric studies, was well tolerated and safe. We found our rating scale to be a reliable and useful tool for future studies of opsoclonus-myoclonus in children.

Human brainstem serotonin receptors: characterization and implications for subcortical myoclonus.

The immediate serotonin (5-HT) precursor, 5-hydroxy-L-tryptophan (L-5-HTP), is an investigational treatment for myoclonic disorders. Its mechanism of action in humans is incompletely understood. We measured the density of subtypes of 5-HT1 and 5-HT2 receptors and the affinity of 5-HT and L-5-HTP in vitro in the human brainstem and cortex, regions associated with subcortical and cortical myoclonus, respectively. In the cortex, the rank order of 5-HT receptor subtype Bmax was 5-HT2A (low-affinity), 5-HT1A, 5-HT uptake sites, 5-HT1D, 5-HT2C, 5-HT1E/F, and 5-HT2A (high-affinity) sites. In the brainstem, the rank order was 5-HT uptake sites, 5-HT1D, 5-HT2C, 5-HT1A, and 5-HT2A(L) sites. Specific binding at 5-HT1E/F and high-affinity 5-HT2A sites was too low for characterization. In competition studies, 5-HT had high affinity for 5-HT1A and 5-HT2C sites in the brainstem and cortex, but L-5-HTP was > 1,000-fold less active. These data support the hypothesis that in humans L-5-HTP stimulates 5-HT receptors in the CNS only after conversion to 5-HT. They also indicate in the human brainstem a prominence of 5-HT1A sites and paucity of 5-HT1D, 5-HT1E/F, and 5-HT2A sites, which has implications for brainstem-mediated myoclonus and response to serotonergic drugs.

A controlled trial of 5-hydroxy-L-tryptophan for ataxia in progressive myoclonus epilepsy.

To study the role of serotonin in the ataxia of progressive myoclonus epilepsy, eight patients received oral 5-hydroxy-L-tryptophan (L-5-HTP) or placebo plus carbidopa for 1 month in a controlled, double-blinded, dose-ranging, cross-over, add-on study. Ataxia was evaluated using objective and subjective scales. All of the subjects had significantly slower motor performance on timed, repetitive tasks than controls and had moderately severe ataxia. L-5-HTP was not efficacious for ataxia or speed of motor performance. Serotonergic drugs that work through mechanisms different than L-5-HTP may be more effective in correcting the abnormal serotonergic neurotransmission suggested by reduction of serotonin metabolites in cerebrospinal fluid in patients with progressive myoclonus epilepsy.

Red blood cell indices in a high altitude hospital population.

It is currently accepted that the red blood cell indices (MCV, MCH and MCHC) are the same in general care hospital populations throughout the world. The aim of the study was to explore whether the internationally accepted values for red cell indices are the same in a hospital located in Mexico City at 2240 meters above sea level (7352 feet). The setting for the study was a third level specialized care hospital for adults with chronic degenerative problems (trauma and obstetric cases were not seen). Each day, for a period of 139 working days, 120 EDTA blood samples of patients were assayed within 3h of extraction in a flow cytometer analyzer (Coulter STKR). Using the moving average approach of Bull (Reference 3) in batches of 20 samples, a raw daily value for each indice was obtained with the mean of the six daily moving averages. The daily raw value was multiplied by a ratio (assigned/observed ratio) of the corresponding daily value obtained in a normal preserved blood control (Coulter's 4C): we refer to them as corrected values in this paper. A total of seven batches of the Coulter control were used to obtain the corrected values during the 139 days of observation. The results were as follows. The mean (SD) of correction values in the 139 days were: MCV = 90.33 (.810) fl, MCH = 30.75 (.582) pg, MCHC = 33.38 (.630) g/dl. The indices showed significant changes in mean as a function of batch of the Coulter control used (F tests, p < 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)

Ontogeny of [125I]iodocyanopindolol-labelled 5-hydroxytryptamine1B-binding sites in the rat CNS.

Little is known about the ontogeny of the 5-hydroxytryptamine1B (5-HT1B) receptor, a putative terminal autoreceptor in the CNS. To learn more about the regional development of 5-HT1B sites and how early these sites may become functional, we studied [125I]iodocyanopindolol ([125I]ICYP)-labelled central 5-HT1B sites in developing postnatal rat brain and spinal cord. Significant ontogenic changes in Bmax were found in neocortex, hippocampus, striatum and brainstem. Maximum binding-site density was reached by 21 days in hippocampus and cortex, but not until 28 days in striatum. The rank order of binding site density changed with rat age, but Bmax was consistently high in brainstem and low in cerebellum. The percent increases in Bmax also varied with brain region, ranging from a 2-fold increase in brainstem up to 8-fold increases in cortex and striatum. In competition studies, the Ki for 5-HT and for RU 24969 was the same in 5-day-old and adult rat brain. These data indicate regional differences in the ontogeny of 5-HT1B-binding sites and suggest that 5-HT1B receptors are functional early in the postnatal period.

Leukocytes of rainbow trout (Oncorhynchus mykiss) pronephros: cell types producing superoxide anion.

Fish pronephric and blood leukocytes yield a chemiluminescent response (CL) when stimulated appropriately. This response reflects the production of highly reactive oxygen derivatives which contribute to oxygen-dependent killing of targets such as pathogens and parasites. From suspensions of pronephric cells of the Rainbow trout, Oncorhynchus mykiss, we have obtained populations enriched for CL-positive cells. Four bands of cells were obtained using continuous gradients generated with 60% Percoll. The leukocytes of band II showed a very strong PMA-induced CL response, the magnitude of which was several times higher than that observed with equivalent numbers of cells form unseparated pronephric cell suspensions. Cells present in other bands were not significantly chemiluminescent. Flow cytometric analysis showed that band II contained large granular cells and small granular cells. Cytochemical analysis showed that this subpopulation was greatly enriched with neutrophils. Many band II cells adhere to glass whereas few band III cells do so. The glass-adherent cells loose their CL potential after a few days in vitro, whereas the nonadherent cells retain their CL responsiveness for at least a week in vitro.