Showing papers in "Naturwissenschaften in 2004"

Hydrogen storage methods

Abstract: Hydrogen exhibits the highest heating value per mass of all chemical fuels. Furthermore, hydrogen is regenerative and environmentally friendly. There are two reasons why hydrogen is not the major fuel of today’s energy consumption. First of all, hydrogen is just an energy carrier. And, although it is the most abundant element in the universe, it has to be produced, since on earth it only occurs in the form of water and hydrocarbons. This implies that we have to pay for the energy, which results in a difficult economic dilemma because ever since the industrial revolution we have become used to consuming energy for free. The second difficulty with hydrogen as an energy carrier is its low critical temperature of 33 K (i.e. hydrogen is a gas at ambient temperature). For mobile and in many cases also for stationary applications the volumetric and gravimetric density of hydrogen in a storage material is crucial. Hydrogen can be stored using six different methods and phenomena: (1) high-pressure gas cylinders (up to 800 bar), (2) liquid hydrogen in cryogenic tanks (at 21 K), (3) adsorbed hydrogen on materials with a large specific surface area (at T<100 K), (4) absorbed on interstitial sites in a host metal (at ambient pressure and temperature), (5) chemically bonded in covalent and ionic compounds (at ambient pressure), or (6) through oxidation of reactive metals, e.g. Li, Na, Mg, Al, Zn with water. The most common storage systems are high-pressure gas cylinders with a maximum pressure of 20 MPa (200 bar). New lightweight composite cylinders have been developed which are able to withstand pressures up to 80 MPa (800 bar) and therefore the hydrogen gas can reach a volumetric density of 36 kg·m−3, approximately half as much as in its liquid state. Liquid hydrogen is stored in cryogenic tanks at 21.2 K and ambient pressure. Due to the low critical temperature of hydrogen (33 K), liquid hydrogen can only be stored in open systems. The volumetric density of liquid hydrogen is 70.8 kg·m−3, and large volumes, where the thermal losses are small, can cause hydrogen to reach a system mass ratio close to one. The highest volumetric densities of hydrogen are found in metal hydrides. Many metals and alloys are capable of reversibly absorbing large amounts of hydrogen. Charging can be done using molecular hydrogen gas or hydrogen atoms from an electrolyte. The group one, two and three light metals (e.g. Li, Mg, B, Al) can combine with hydrogen to form a large variety of metal–hydrogen complexes. These are especially interesting because of their light weight and because of the number of hydrogen atoms per metal atom, which is two in many cases. Hydrogen can also be stored indirectly in reactive metals such as Li, Na, Al or Zn. These metals easily react with water to the corresponding hydroxide and liberate the hydrogen from the water. Since water is the product of the combustion of hydrogen with either oxygen or air, it can be recycled in a closed loop and react with the metal. Finally, the metal hydroxides can be thermally reduced to metals in a solar furnace. This paper reviews the various storage methods for hydrogen and highlights their potential for improvement and their physical limitations.

Gluconic acid production and phosphate solubilization by the plant growth-promoting bacterium Azospirillum spp.

Abstract: In vitro gluconic acid formation and phosphate solubilization from sparingly soluble phosphorus sources by two strains of the plant growth-promoting bacteria A. brasilense (Cd and 8-I) and one strain of A. lipoferum JA4 were studied. Strains of A. brasilense were capable of producing gluconic acid when grown in sparingly soluble calcium phosphate medium when their usual fructose carbon source is amended with glucose. At the same time, there is a reduction in pH of the medium and release of soluble phosphate. To a greater extent, gluconic acid production and pH reduction were observed for A. lipoferum JA4. For the three strains, clearing halos were detected on solid medium plates with calcium phosphate. This is the first report of in vitro gluconic acid production and direct phosphate solubilization by A. brasilense and the first report of P solubilization by A. lipoferum. This adds to the very broad spectrum of plant growth-promoting abilities of this genus.

The modern theory of biological evolution: an expanded synthesis.

Abstract: In 1858, two naturalists, Charles Darwin and Alfred Russel Wallace, independently proposed natural selection as the basic mechanism responsible for the origin of new phenotypic variants and, ultimately, new species. A large body of evidence for this hypothesis was published in Darwin's Origin of Species one year later, the appearance of which provoked other leading scientists like August Weismann to adopt and amplify Darwin's perspective. Weismann's neo-Darwinian theory of evolu- tion was further elaborated, most notably in a series of books by Theodosius Dobzhansky, Ernst Mayr, Julian Huxley and others. In this article we first summarize the history of life on Earth and provide recent evidence demonstrating that Darwin's dilemma (the apparent missing Precambrian record of life) has been resolved. Next, the historical development and structure of the "modern synthesis" is described within the context of the following topics: paleobiology and rates of evolution, mass extinctions and species selection, macroevolution and punctuated equilibrium, sexual reproduction and recombination, sexual selection and altruism, endosym- biosis and eukaryotic cell evolution, evolutionary devel- opmental biology, phenotypic plasticity, epigenetic in- heritance and molecular evolution, experimental bacterial evolution, and computer simulations (in silico evolution of digital organisms). In addition, we discuss the expan- sion of the modern synthesis, embracing all branches of scientific disciplines. It is concluded that the basic tenets of the synthetic theory have survived, but in modified form. These sub-theories require continued elaboration, particularly in light of molecular biology, to answer open- ended questions concerning the mechanisms of evolution in all five kingdoms of life.

Fine colour discrimination requires differential conditioning in bumblebees

Abstract: Accurate recognition requires that visual systems must be able to discriminate between target and distractor stimuli. Flowers are learned and recognised by bees using visual cues including colour and shape. We investigated whether bees were able to learn to discriminate between colours differently depending upon absolute or differential conditioning. For absolute conditioning bees were rewarded with sucrose solution for visits to target flowers. When distractor stimuli were subsequently presented, a high level of discrimination was observed if there was a perceptually large colour distance separating distractors and targets, but for a perceptually small colour distance the bees generalised and did not discriminate between stimuli. When provided with differential conditioning where both target and distractors were present, the bees learnt to discriminate stimuli separated by a perceptually small colour distance. This shows that for bees to learn fine colour discrimination tasks it is important to use differential conditioning. The findings are discussed within the context of the necessity for plants to produce distinctive flower colours.

The species flocks of East African cichlid fishes: recent advances in molecular phylogenetics and population genetics.

Abstract: With more than 3,000 species, the fish fami- ly Cichlidae is one of the most species-rich families of vertebrates. Cichlids occur in southern and central Amer- ica, Africa, Madagascar, and India. The hotspot of their biodiversity is East Africa, where they form adaptive ra- diations composed of hundreds of endemic species in several lakes of various sizes and ages. The unparalleled species richness of East African cichlids has been some- thing of a conundrum for evolutionary biologists and ecologists, since it has been in doubt whether these hun- dreds of species arose by allopatric speciation or whether it is necessary to invoke somewhat less traditional models of speciation, such as micro-allopatric, peripatric, or even sympatric speciation or evolution through sexual selection mediated by female choice. Ernst Mayr's analyses of these evolutionary uniquely diverse species assemblages have contributed to a more direct approach to this prob- lem and have led to a deeper understanding of the patterns and processes that caused the formation of these huge groups of species. We review here recent molecular data on population differentiation and phylogenetics, which have helped to unravel, to some extent, the patterns and processes that led to the formation and ecological main- tenance of cichlid species flocks. It is becoming apparent that sexually selected traits do play an important role in speciation in micro-allopatric or even sympatric settings. Species richness seems to be roughly correlated with the surface area, but not the age, of the lakes. We observe that the oldest lineages of a species flock of cichlids are often less species-rich and live in the open water or deepwater habitats. While the species flocks of the Lake Malawai and the Lake Victoria areas were shown to be mono- phyletic, the cichlid assemblage of Lake Tanganyika seems to consist of several independent species flocks. Cichlids emerge as an evolutionary model system in which many fundamental questions in evolution and ecology can be tested successfully, yet for other fish species flocks the relative importance of alternative mechanisms of speciation is likely to differ from that in cichlid fish.

Conditioning procedure and color discrimination in the honeybee Apis mellifera.

Abstract: We studied the influence of the conditioning procedure on color discrimination by free-flying honeybees. We asked whether absolute and differential conditioning result in different discrimination capabilities for the same pairs of colored targets. In absolute conditioning, bees were rewarded on a single color; in differential conditioning, bees were rewarded on the same color but an alternative, non-rewarding, similar color was also visible. In both conditioning procedures, bees learned their respective task and could also discriminate the training stimulus from a novel stimulus that was perceptually different from the trained one. Discrimination between perceptually closer stimuli was possible after differential conditioning but not after absolute conditioning. Differences in attention inculcated by these training procedures may underlie the different discrimination performances of the bees.

Ant-plant-herbivore interactions in the neotropical cerrado savanna.

Abstract: The Brazilian cerrado savanna covers nearly 2 million km2 and has a high incidence on foliage of various liquid food sources such as extrafloral nectar and insect exudates. These liquid rewards generate intense ant activity on cerrado foliage, making ant–plant–herbivore interactions especially prevalent in this biome. We present data on the distribution and abundance of extrafloral nectaries in the woody flora of cerrado communities and in the flora of other habitats worldwide, and stress the relevance of liquid food sources (including hemipteran honeydew) for the ant fauna. Consumption by ants of plant and insect exudates significantly affects the activity of the associated herbivores of cerrado plant species, with varying impacts on the reproductive output of the plants. Experiments with an ant–plant–butterfly system unequivocally demonstrate that the behavior of both immature and adult lepidopterans is closely related to the use of a risky host plant, where intensive visitation by ants can have a severe impact on caterpillar survival. We discuss recent evidence suggesting that the occurrence of liquid rewards on leaves plays a key role in mediating the foraging ecology of foliage-dwelling ants, and that facultative ant–plant mutualisms are important in structuring the community of canopy arthropods. Ant-mediated effects on cerrado herbivore communities can be revealed by experiments performed on wide spatial scales, including many environmental factors such as soil fertility and vegetation structure. We also present some research questions that could be rewarding to investigate in this major neotropical savanna.

The mechanisms of lift enhancement in insect flight

Abstract: Recent studies have revealed a diverse array of fluid dynamic phenomena that enhance lift production during flapping insect flight. Physical and analytical models of oscillating wings have demonstrated that a prominent vortex attached to the wing’s leading edge augments lift production throughout the translational parts of the stroke cycle, whereas aerodynamic circulation due to wing rotation, and possibly momentum transfer due to a recovery of wake energy, may increase lift at the end of each half stroke. Compared to the predictions derived from conventional steady-state aerodynamic theory, these unsteady aerodynamic mechanisms may account for the majority of total lift produced by a flying insect. In addition to contributing to the lift required to keep the insect aloft, manipulation of the translational and rotational aerodynamic mechanisms may provide a potent means by which a flying animal can modulate direction and magnitude of flight forces for manoeuvring flight control and steering behaviour. The attainment of flight, including the ability to control aerodynamic forces by the neuromuscular system, is a classic paradigm of the remarkable adaptability that flying insects have for utilising the principles of unsteady fluid dynamics. Applying these principles to biology broadens our understanding of how the diverse patterns of wing motion displayed by the different insect species have been developed throughout their long evolutionary history.

Retinal cryptochrome in a migratory passerine bird: a possible transducer for the avian magnetic compass.

Abstract: The currently discussed model of magnetoreception in birds proposes that the direction of the magnetic field is perceived by radical-pair processes in specialized photoreceptors, with cryptochromes suggested as potential candidate molecules mediating magnetic compass information. Behavioral studies have shown that magnetic compass orientation takes place in the eye and requires light from the blue-green part of the spectrum. Cryptochromes are known to absorb in the same spectral range. Because of this we searched for cryptochrome (CRY) in the retina of European robins, Erithacus rubecula, passerine birds that migrate at night. Here, we report three individually expressed cryptochromes, eCRY1a, eCRY1b, and eCRY2. While eCRY1a and eCRY2 are similar to the cryptochromes found in the retina of the domestic chicken, eCRY1b has a unique carboxy (C)-terminal. In light of the 'radical-pair' model, our findings support a potential role of cryptochromes as transducers for the perception of magnetic compass information in birds.

In search of the sky compass in the insect brain.

Abstract: Like many vertebrate species, insects rely on a sun compass for spatial orientation and long- range navigation. In addition to the sun, however, insects can also use the polarization pattern of the sky as a reference for estimating navigational directions. Recent analysis of polarization vision pathways in the brain of orthopteroid insects sheds some light onto brain areas that might act as internal navigation centers. Here I review the significance, peripheral mechanisms, and central processing stages for polarization vision in insects with special reference to the locust Schistocerca gregaria. As in other insect species, polarization vision in locusts relies on specialized photoreceptor cells in a small dorsal rim area of the compound eye. Stages in the brain involved in polarized light signaling include specific areas in the lamina, medulla and lobula of the optic lobe and, in the midbrain, the anterior optic tubercle, the lateral accessory lobe, and the central complex. Integration of polarized-light signals with information on solar position appears to start in the optic lobe. In the central complex, polarization-opponent interneurons form a network of interconnected neurons. The organization of the central complex, its connections to thoracic motor centers, and its involvement in the spatial control of locomotion strongly suggest that it serves as a spatial organizer within the insect brain, including the functions of compass orientation and path integration. Time compensation in compass orientation is possibly achieved through a neural pathway from the internal circadian clock in the accessory medulla to the protocerebral bridge of the central complex.

The origin and early evolution of birds: discoveries, disputes, and perspectives from fossil evidence

Abstract: The study of the origin and early evolution of birds has never produced as much excitement and public attention as in the past decade. Well preserved and abundant new fossils of birds and dinosaurs have provided unprecedented new evidence on the dinosaurian origin of birds, the arboreal origin of avian flight, and the origin of feathers prior to flapping flight. The Mesozoic avian assemblage mainly comprises two major lineages: the prevalent extinct group Enantiornithes, and the Ornithurae, which gave rise to all modern birds, as well as several more basal taxa. Cretaceous birds radiated into various paleoecological niches that included fish- and seed-eating. Significant size and morphological differences and variation in flight capabilities, ranging from gliding to powerful flight among early birds, highlight the diversification of birds in the Early Cretaceous. There is little evidence, however, to support a Mesozoic origin of modern avian groups. Controversy and debate, nevertheless, surround many of these findings, and more details are needed to give a better appreciation of the significance of these new discoveries.

Symmetry is in the eye of the ‘beeholder’: innate preference for bilateral symmetry in flower-naïve bumblebees

Abstract: Bilateral symmetry has been considered as an indicator of phenotypic and genotypic quality supporting innate preferences for highly symmetric partners. Insect pollinators preferentially visit flowers of a particular symmetry type, thus leading to the suggestion that they have innate preferences for symmetrical flowers or flower models. Here we show that flower-naive bumblebees (Bombus terrestris), with no experience of symmetric or asymmetric patterns and whose visual experience was accurately controlled, have innate preferences for bilateral symmetry. The presence of color cues did not influence the bees' original preference. Our results thus show that bilateral symmetry is innately preferred in the context of food search, a fact that supports the selection of symmetry in flower displays. Furthermore, such innate preferences indicate that the nervous system of naive animals may be primed to respond to relevant sensory cues in the environment.

Communal nesting and kinship in degus ( Octodon degus )

Abstract: Communal nesting is a fundamental component of many animal societies. Because the fitness consequences of this behavior vary with the relatedness among nest mates, understanding the kin structure of communally nesting groups is critical to understanding why such groups form. Observations of captive degus (Octodon degus) indicate that multiple females nest together, even when supplied with several nest boxes. To determine whether free-living degus also engage in communal nesting, we used radiotelemetry to monitor spatial relationships among adult females in a population of O. degus in central Chile. These analyses revealed that females formed stable associations of > 2–4 individuals, all of whom shared the same nest site at night. During the daytime, spatial overlap and frequency of social interactions were greatest among co-nesting females, suggesting that nesting associations represent distinct social units. To assess kinship among co-nesting females, we examined genotypic variation in our study animals at six microsatellite loci. These analyses indicated that mean pairwise relatedness among members of a nesting association (r=0.25) was significantly greater than that among randomly selected females (r=−0.03). Thus, communally nesting groups of degus are composed of female kin, making it possible for indirect as well as direct fitness benefits to contribute to sociality in this species.

Bonitasaura salgadoi gen. et sp. nov.: a beaked sauropod from the Late Cretaceous of Patagonia

Abstract: Ornithischian and theropod dinosaurs were morphologically diverse during the Cretaceous In contrast, sauropods were relatively more conservative The anatomy of Bonitasaura salgadoi, a new 9-m titanosaurian sauropod from Upper Cretaceous beds of Patagonia, suggests that sauropod anatomical diversity would have included unexpected items Its unusual, rectangular lower jaw possesses narrow, anteriorly restricted teeth and shows evidence of a sharp keratinous sheath over the non-dentigerous region that probably worked to guillotine plant material This discovery definitely demonstrates that titanosaurs acquired a mandibular configuration similar to that of some basal diplodocoids, as had already been suggested by the lower jaw of the controversial genus Antarctosaurus This oral configuration, plus the beak-like structure and the skull shape, resemble some traits more commonly seen in Laurasian ornithischians, mostly unexpressed in southern continents A high sauropod morphological diversity seems to be in agreement with the poorly represented ornithischian clades of the southern hemisphere

Spectrographic analysis of the ultrasonic vocalisations of adult male and female BALB/c mice

Abstract: In this study, a spectrographic analysis was designed to improve the description of the shape, the modulations, the rate, length and frequencies of BALB/c mouse calls in different behavioural situations. Male and female calls emitted during investigation of cages with clean bedding, soiled with male or female bedding, and during same-sex encounters, were recorded and described. BALB/c male mice uttered different types of vocalisations both when investigating counterpart odour cues and when interacting with same-sex counterparts. BALB/c female mice vocalised solely during same-sex counterpart encounters and it appeared that calls were uttered mainly by the resident females. Male and female mice present a complex array of calls, which seem to be linked to particular behavioural situations. Further studies using this technology may help to improve our understanding of the role of vocal communication in natural rodent populations.

Multilevel selection and social evolution of insect societies

Abstract: How sterile, altruistic worker castes have evolved in social insects and how they are maintained have long been central topics in evolutionary biology. With the advance of kin selection theory, insect societies, in particular those of haplodiploid bees, ants, and wasps, have become highly suitable model systems for investigating the details of social evolution and recently also how within-group conflicts are resolved. Because insect societies typically do not consist of clones, conflicts among nestmates arise, for example about the partitioning of reproduction and the allocation of resources towards male and female sexuals. Variation in relatedness among group members therefore appears to have a profound influence on the social structure of groups. However, insect societies appear to be remarkably robust against such variation: division of labor and task allocation are often organized in more or less the same way in societies with high as in those with very low nestmate relatedness. To explain the discrepancy between predictions from kin structure and empirical data, it was suggested that constraints—such as the lack of power or information—prevent individuals from pursuing their own selfish interests. Applying a multilevel selection approach shows that these constraints are in fact group-level adaptation preventing or resolving intracolonial conflict. The mechanisms of conflict resolution in insect societies are similar to those at other levels in the biological hierarchy (e.g., in the genome or multicellular organisms): alignment of interests, fair lottery, and social control. Insect societies can thus be regarded as a level of selection with novelties that provide benefits beyond the scope of a solitary life. Therefore, relatedness is less important for the maintenance of insect societies, although it played a fundamental role in their evolution.

A female-specific attractant for the codling moth, Cydia pomonella , from apple fruit volatiles

Abstract: Host plant-derived esters were investigated as potential female-specific attractants for the codling moth (CM), Cydia pomonella (L.), a key pest of apples worldwide. The behavioural effects of single and combined volatile compounds and of a natural odour blend were examined using olfactometry and wind-tunnel bioassays. The apple-derived volatile butyl hexanoate attracted mated females while it was behaviourally ineffective for males over a dosage range of more than three orders of magnitude in olfactometer assays. Female CM preferred this kairomone to the headspace volatiles from ripe apples. Both no-choice and choice trials in the wind-tunnel suggested that female moths might be effectively trapped by means of this compound. In contrast, headspace volatiles collected from ripe apple fruits as well as a blend containing the six dominant esters from ripe apples were behaviourally ineffective. A female-specific repellency was found for the component hexyl acetate in the olfactometer, but this ester had no significant effect in the wind-tunnel. Butyl hexanoate with its sex-specific attraction should be further evaluated for monitoring and controlling CM females in orchards.

New Early Cretaceous fossil from China documents a novel trophic specialization for Mesozoic birds

Abstract: We report on a new Mesozoic bird, Longirostravis hani, from the Early Cretaceous Jehol Biota of northeastern China. The new taxon has a long, slender rostrum and mandible, and a small number of rostralmost teeth. Postcranial characters such as a furcular ramus wider ventrally than dorsally, a centrally concave proximal margin of the humeral head, and a minor metacarpal that projects distally more than the major metacarpal, support the placement of Longirostravis within euenantiornithine Enantiornithes, the most diverse clade of Mesozoic birds. The morphology of the skull, however, suggests that Longirostravis had a probing feeding behavior, a specialization previously unknown for Enantiornithes. Indeed, this discovery provides the first evidence in support of the existence of such a foraging behavior among basal lineages of Mesozoic birds.

The importance of crossroads in faecal marking behaviour of the wolves (Canis lupus).

Abstract: For wolves (Canis lupus) scats play an important function in territorial marking behaviour. Depositing scats at strategic sites such as crossroads and on conspicuous substrates probably increases their effectiveness as visual and olfactory marks. It is therefore likely that scats will be deposited, and will accumulate, at particular crossroads where the probability of being detected by other wolves is greatest. To check this hypothesis, a wolf population in NW Spain was studied for two consecutive years, from May 1998 to March 2000, and the spatial distribution of 311 scats detected along roads (both at and away from crossroads) was analysed. This study was conducted over an area of 12,000 ha in Montes do Invernadeiro Natural Park. The results confirm that wolves preferably deposit their scats at crossroads (60.1%) and on conspicuous substrates (72.1%). Significantly more scats were found at intersections with numerous, easily passable roads connecting distant territories. Thus, wolves preferably deposit their faeces at crossroads with high accessibility and driveability. The larger the surface area of the crossroads, the more scats were found. Crossroads are therefore highly strategic points that facilitate the detection of scats.

Overestimates of black carbon in soils and sediments.

Abstract: Several recent reports suggest that black carbon (BC), which broadly encompasses charcoal, soot, and other forms of pyrogenic carbon, may constitute a significant proportion of the refractory carbon in soil and sedimentary organic matter. BC is a sink for biospheric and atmospheric carbon dioxide, and is intimately tied to the biogeochemical cycling of both carbon and oxygen through its role in organic matter cycling. Additionally, BC may represent a large fraction of the “missing carbon sink” in global carbon accounting. Here, we demonstrate that documented measurements of BC may be the result of methodological artifacts, which inadvertently overestimate the amount of BC. We found that a widely used thermal oxidative method can create a residue that falls under the operational definition of BC in samples that are relatively BC-free. Moreover, during this procedure, labile organic matter constituents are condensed into pyrogenic carbon, implying that the labile components are present in lesser quantities. These methodological deficiencies are promoting overestimates in the amount of refractory carbon in soil and sedimentary organic matter and may endorse inaccuracies in the rates of carbon fluxes, the mean residence times of terrestrial carbon, and organic matter burial rates in oceanic environments.

Regulation of bone morphogenetic proteins in early embryonic development.

Abstract: Bone morphogenetic proteins (BMPs), a large subgroup of the TGF-beta family of secreted growth factors, control fundamental events in early embryonic development, organogenesis and adult tissue homeostasis. The plethora of dose-dependent cellular processes regulated by BMP signalling demand a tight regulation of BMP activity. Over the last decade, a number of proteins have been identified that bind BMPs in the extracellular space and regulate the interaction of BMPs with their cognate receptors, including the secreted BMP antagonist Chordin. In the early vertebrate embryo, the localized secretion of BMP antagonists from the dorsal blastopore lip establishes a functional BMP signalling gradient that is required for the determination of the dorsoventral - or back to belly - body axis. In particular, inhibition of BMP activity is essential for the formation of neural tissue in the development of vertebrate and invertebrate embryos. Here we review recent studies that have provided new insight into the regulation of BMP signalling in the extracellular space. In particular, we discuss the recently identified Twisted gastrulation protein that modulates, in concert with metalloproteinases of the Tolloid family, the interaction of Chordin with BMP and a family of proteins that share structural similarities with Chordin in the respective BMP binding domains. In addition, genetic and functional studies in zebrafish and frog provide compelling evidence that the secreted protein Sizzled functionally interacts with the Chd-BMP pathway, despite being expressed ventrally in the early gastrula-stage embryo. These intriguing discoveries may have important implications, not only for our current concept of early embryonic patterning, but also for the regulation of BMP activity at later developmental stages and tissue homeostasis in the adult.

The eyes of oilbirds (Steatornis caripensis): pushing at the limits of sensitivity

Abstract: An extreme example of a low light-level lifestyle among flying birds is provided by the oilbird, Steatornis caripensis (Steatornithidae, Caprimulgi- formes). Oilbirds breed and roost in caves, often at sufficient depth that no daylight can penetrate, and forage for fruits at night. Using standard microscopy techniques we investigated the retinal structure of oilbird eyes and used an ophthalmoscopic reflex technique to determine the parameters of these birds' visual fields. The retina is dominated by small rod receptors (diameter 1.3€0.2 mm; length 18.6€0.6 mm) arranged in a banked structure that is unique among terrestrial vertebrates. This arrangement achieves a photoreceptor density that is the highest so far recorded (1,000,000 rods mm �2 ) in any vertebrate eye. Cone photoreceptors are, however, present in low num- bers. The eye is relatively small (axial length 16.1€0.2 mm) with a maximum pupil diameter of 9.0€0.0 mm, achieving a light-gathering capacity that is the highest recorded in a bird (f-number 1.07). The binocular field has a maximum width of 38� and extends vertically through 100� with the bill projecting towards the lower periphery; a topography that suggests that vision is not used to control bill position. We propose that oilbird eyes are at one end of the continuum that juxtaposes the conflicting fundamental visual capacities of sensitivity and resolution. Thus, while oilbird visual sensitivity may be close to a maximum, visual resolution must be low. This explains why these birds employ other sensory cues, including olfaction and echolocation, in the control of their behaviour in low-light-level environ- ments.

Coordinated gene expression for pheromone biosynthesis in the pine engraver beetle, Ips pini (Coleoptera: Scolytidae)

Abstract: In several pine bark beetle species, phloem feeding induces aggregation pheromone production to coordinate a mass attack on the host tree. Male pine engraver beetles, Ips pini (Say) (Coleoptera: Scolytidae), produce the monoterpenoid pheromone component ipsdienol de novo via the mevalonate pathway in the anterior midgut upon feeding. To understand how pheromone production is regulated in this tissue, we used quantitative real-time PCR to examine feeding-induced changes in gene expression of seven mevalonate pathway genes: acetoacetyl-coenzyme A thiolase, 3-hydroxy-3-methylglutaryl coenzyme A synthase, 3-hydroxy-3-methylglutaryl coenzyme A reductase, mevalonate 5-diphosphate decarboxylase, isopentenyl-diphosphate isomerase, geranyl-diphosphate synthase (GPPS), and farnesyl-diphosphate synthase (FPPS). In males, expression of all these genes significantly increased upon feeding. In females, the expression of the early mevalonate pathway genes (up to and including the isomerase) increased significantly, but the expression of the later genes (GPPS and FPPS) was unaffected or decreased upon feeding. Thus, feeding coordinately regulates expression of the mevalonate pathway genes necessary for pheromone biosynthesis in male, but not female, midguts. Furthermore, basal mRNA levels were 5- to 41-fold more abundant in male midguts compared to female midguts. This is the first report of coordinated regulation of mevalonate pathway genes in an invertebrate model consistent with their sex-specific role in de novo pheromone biosynthesis.

Floral CO(2) emission may indicate food abundance to nectar-feeding moths

Abstract: As part of a study of the roles of the sensory subsystem devoted to CO(2) in the nectar-feeding moth Manduca sexta, we investigated CO(2) release and nectar secretion by flowers of Datura wrightii, a preferred hostplant of Manduca. Datura flowers open at dusk and wilt by the following noon. During the first hours after dusk, when Manduca feeds, the flowers produce considerable amounts of nectar and emit levels of CO(2) that should be detectable by moths nearby. By midnight, however, both nectar secretion and CO(2) release decrease significantly. Because nectar production requires high metabolic activity, high floral CO(2) emission may indicate food abundance to the moths. We suggest that hovering moths could use the florally emitted CO(2) to help them assess the nectar content before attempting to feed in order to improve their foraging efficiency.

Brain mechanisms that control sleep and waking.

Abstract: This review paper presents a brief historical survey of the technological and early research that laid the groundwork for recent advances in sleep-waking research. A major advance in this field occurred shortly after the end of World War II with the discovery of the ascending reticular activating system (ARAS) as the neural source in the brain stem of the waking state. Subsequent research showed that the brain stem activating system produced cortical arousal via two pathways: a dorsal route through the thalamus and a ventral route through the hypothalamus and basal forebrain. The nuclei, pathways, and neurotransmitters that comprise the multiple components of these arousal systems are described. Sleep is now recognized as being composed of two very different states: rapid eye movements (REMs) sleep and non-REM sleep. The major findings on the neural mechanisms that control these two sleep states are presented. This review ends with a discussion of two current views on the function of sleep: to maintain the integrity of the immune system and to enhance memory consolidation.

Individual protein balance strongly influences δ15N and δ13C values in Nile tilapia, Oreochromis niloticus

Abstract: Although stable isotope ratios in animals have often been used as indicators of the trophic level and for the back-calculation of diets, few experiments have been done under standardized laboratory conditions to investigate factors influencing δ15N and δ13C values. An experiment using Nile tilapia [Oreochromis niloticus (L.)] was therefore carried out to test the effect of different dietary protein contents (35.4, 42.3, and 50.9%) on δ15N and δ13C values of the whole tilapia. The fish were fed the isoenergetic and isolipidic semi-synthetic diets at a relatively low level. δ15N and δ13C values of the lipid-free body did not differ between the fish fed the diets with different protein contents, but the trophic shift for N and C isotopes decreased with increasing protein accretion in the individual fish, for N from 6.5‰ to 4‰ and for C in the lipid-free body from 4‰ to 2.5‰. This is the first study showing the strong influence of the individual protein balance to the degree to which the isotopic signature of dietary protein was modified in tissue protein of fish. The extrapolation of the trophic level or the reconstruction of the diet of an animal from stable isotope ratios without knowledge of the individual physiological condition and the feeding rate may lead to erroneous results.

Predatory spider mimics acquire colony-specific cuticular hydrocarbons from their ant model prey.

Abstract: The integrity of social insect colonies is maintained by members recognising and responding to the chemical cues present on the cuticle of any intruder. Nevertheless, myrmecophiles use chemical mimicry to gain access to these nests, and their mimetic signals may be acquired through biosynthesis or through contact with the hosts or their nest material. The cuticular hydrocarbon profile of the myrmecophilous salticid spider Cosmophasis bitaeniata closely resembles that of its host ant Oecophylla smaragdina. Here, we show that the chemical resemblance of the spider does not arise through physical contact with the adult ants, but instead the spider acquires the cuticular hydrocarbons by eating the ant larvae. More significantly, we show that the variation in the cuticular hydrocarbon profiles of the spider depends upon the colony of origin of the ant larvae prey, rather than the parentage of the spider.

European Atlantic: the hottest oil spill hotspot worldwide.

Abstract: Oil spills caused by maritime transport of petroleum products are still an important source of ocean pollution, especially in main production areas and along major transport routes. We here provide a historical and geographic analysis of the major oil spills (>700 t) since 1960. Spills were recorded from several key marine ecosystems and marine biodiversity hotspots. The past four decades have been characterized by an overall decrease in the number of accidents and tones of oil spilled in the sea, but this trend was less distinct in the European Atlantic area. Recent black tides from the Erika and Prestige vessels provided new evidence for the high risk of accidents with serious ecological impact in this area, which according to our analysis is historically the most important oil spill hotspot worldwide. The English Channel and waters around Galicia in Spain were the areas with most accidents. Maritime transport in European Atlantic waters has been predicted to continue increasing. Together with our own results this suggests that, in addition to measures for increased traffic safety, deployment of emergency capacities in the spill hotspot areas may be crucial for a sustainable conservation of sea resources and ecosystems.

The evolutionary processes of mitochondrial and chloroplast genomes differ from those of nuclear genomes

Abstract: This paper first introduces our present knowledge of the origin of mitochondria and chloroplasts, and the organization and inheritance patterns of their genomes, and then carries on to review the evolutionary processes influencing mitochondrial and chloroplast genomes. The differences in evolutionary phenomena between the nuclear and cytoplasmic genomes are highlighted. It is emphasized that varying inheritance patterns and copy numbers among different types of genomes, and the potential advantage achieved through the transfer of many cytoplasmic genes to the nucleus, have important implications for the evolution of nuclear, mitochondrial and chloroplast genomes. Cytoplasmic genes transferred to the nucleus have joined the more strictly controlled genetic system of the nuclear genome, including also sexual recombination, while genes retained within the cytoplasmic organelles can be involved in selection and drift processes both within and among individuals. Within-individual processes can be either intra- or intercellular. In the case of heteroplasmy, which is attributed to mutations or biparental inheritance, within-individual selection on cytoplasmic DNA may provide a mechanism by which the organism can adapt rapidly. The inheritance of cytoplasmic genomes is not universally maternal. The presence of a range of inheritance patterns indicates that different strategies have been adopted by different organisms. On the other hand, the variability occasionally observed in the inheritance mechanisms of cytoplasmic genomes reduces heritability and increases environmental components in phenotypic features and, consequently, decreases the potential for adaptive evolution.

Nest excavation in ants: group size effects on the size and structure of tunneling networks

Abstract: Collective digging activity was studied in the ant Messor sancta Forel in laboratory conditions and with a two dimensional set-up. We analyzed the digging dynamics and topology of tunneling networks excavated by groups of workers ranging from 50 to 200 individuals over 3 days. In all conditions, the dynamics of excavated sand volume were clearly non-linear. Excavation began with an exponential growth and after 3 days reached a saturation phase in which activity was almost totally stopped. The final volume of sand excavated was positively correlated with the number of workers. At the end of the experiments, the two-dimensional tunneling networks were mapped onto planar graphs where the vertices represent small chambers or intersections between tunnels and the edges represent tunnels. We found that all the networks belonged to a same topological family and exhibited several striking invariants such as the distribution of vertex degree that follows a power law. When increasing the number of ants, some changes occurred in the network structure, mainly an increase in the number of edges and vertices, and the progressive emergence of enlarged and highly connected vertices.