TrackBeam, a simple tool for estimating potential exposure to the solar beam underneath tree canopies

A simple tool, TrackBeam, for rapid in situ estimates of potential exposure to the solar beam of objects underneath tree canopies is presented, tested and demonstrated to be useful in insect conservation studies. The tool can be used whenever accurate data on sun exposure is of use e.g., in ecological studies of saproxylic insects. TrackBeam draws upon the principles behind the analysis of hemispherical photographs but its use is much less dependent on the weather at the time of sampling. It may be used for detecting canopy openings in directions corresponding to the solar path. Based on this, periods of time with potential beam exposure and/or the proportion of sky that is not obscured by canopy for objects such as dead wood may be estimated. The results of using TrackBeam compares well between operators and with the corresponding results of analysed hemispherical photographs. Results are presented which show that TrackBeam was successfully used to characterise the habitat light requirements of the saproxylic beetle Melanotus castanipes (Coleoptera: Elateridae).     

The “heterolytic hydroperoxide lyase” is an isomerase producing a short-lived fatty acid hemiacetal

To elucidate the reaction mechanism of hydroperoxide lyase (HPL), the enzyme from guava (Psidium guajava) fruits, was incubated for 10–60 s at 0 °C with 13-HPOT. The products were rapidly extracted and derivatized by trimethylsilylation. Two trapping products, namely the trimethylsilyl ether/ester derivatives of the hemiacetal 12-(1′-hydroxy-3′-hexenyloxy)-9,11-dodecadienoic acid and the enol (9Z,11E)-12-hydroxy-9,11-dodecadienoic acid, were detected by gas chromatography-mass spectrometry (GC-MS) analyses. The structural assignments were supported by mass spectra recorded for (a) hydrogenated products; (b) products biosynthesized from [9,10,12,13,15,16] 13-HPOT or [¹⁸O₂]13-HPOT; (c) chemically prepared reference compounds. Kinetic experiments showed that the hemiacetal and enol were both unstable and transiently appearing compounds (half-lives, ca. 20 s and 2 min, respectively). Hemiacetal and enol biosynthesized from [¹⁸O₂]13-HPOT retained two and one ¹⁸O atoms, respectively, whereas no ¹⁸O was incorporated from [¹⁸O]water. The data demonstrated that: (1) the true enzymatic product formed from 13-HPOT in the presence of HPL is a short-lived hemiacetal; (2) the hemiacetal spontaneously dissociates into (3Z)-hexenal and the unstable enol form of (9Z)-12-oxo-9-dodecenoic acid; (3) the enzymatic isomerization of 13-HPOT into the hemiacetal occurs homolytically.     

Host selection patterns in insects breeding in bracket fungi

Abstract.  1. Fungivorous insects are generally viewed as polyphagous, largely because most fungal fruiting bodies constitute an unpredictable resource. To examine the validity of this hypothesis, and degree of phylogenetic relatedness between the preferred hosts of the insects, host selection in the insect fauna of bracket fungi was studied, using data obtained both from the field and the literature.
2. More than half (53%) of the insect species breeding in them appeared to be monophagous.
3. Modern phylogenies explained the host selection patterns better than older classifications, since non-monophagous species of beetles frequently used hosts that are closely related to each other.
4. The hypothesis that polyphagous species use more heavily decayed fruiting bodies than monophagous species was verified for insects breeding in Fomes fomentarius . The results indicate that the chemical composition of the fungi influences host selection.
5. It is suggested that fruiting bodies of bracket fungi differ from most other fungi in that their occurrence is more predictable. Therefore, the primary colonising fungivores generally attack only one host species, or a few hosts that are closely phylogenetically related. Polyphagous species generally colonise fruiting bodies after they have reached a certain stage of decay, thus escaping their chemical defence.     

Sleepiness and performance in response to repeated sleep restriction and subsequent recovery during semi-laboratory conditions

There is an ongoing debate of how best to measure the effects of sleep loss in a reliable and feasible way, partly because well controlled laboratory studies and field studies have come to different conclusions. The aims of the present study were to investigate both sleepiness and performance in response to long-term sleep restriction and recovery in a semi-laboratory environment, investigate order effects (i.e., whether levels return to baseline) in a study with seven days of recovery, and characterize individual differences in tolerance to restricted sleep. Nine healthy men (age 23-28 yrs) participated in the protocol, which included one habituation day (sleep 23:00-07:00 h), two baseline days (23:00-07:00 h), five days with restricted sleep (03:00-07:00 h), and seven recovery days (23:00-07:00 h). Participants went outdoors at least twice each day. Reaction-time tests were performed at 08:00, 14:00, and 20:00 h each day in the laboratory. Sleepiness was self-rated by the Karolinska Sleepiness Scale (KSS)after each test. The mixed-effect regression models showed that each day of restricted sleep resulted in an increase of sleepiness by 0.64+/- .05 KSS units (a nine-step scale, p < .001), increase of median reaction times of 6.6+/- 1.6 ms ( p = .003), and increase of lapses/test of 0.69 +/- .16 ms ( p < .001). Seven days of recovery allowed participants to return to the baseline for sleepiness and median reaction time, but not for lapses. The individual differences were larger for performance measures than for sleepiness; the between-subject standard deviation for the random intercept was in the magnitude of the effects of 1.1 days of restricted sleep for sleepiness, 6.6 days of restricted sleep for median reaction time, and 3.2 days for lapses. In conclusion, the present study shows that sleepiness is closely related to sleep pressure, while performance measures, to a larger extent, appear determined by specific individual traits. Moreover, it is suggested to measure sleepiness in a standardized situation so as to minimize the influences of contextual factors.     

Evidence for communality in the primary determinants of CYP74 catalysis and of structural similarities between CYP74 and classical mammalian P450 enzymes

In silico structural analysis of CYP74C3, a membrane-associated P450 enzyme from the plant Medicago truncatula (barrel medic) with hydroperoxide lyase (HPL) specificity, showed that it had strong similarities to the structural folds of the classical microsomal P450 enzyme from rabbits (CYP2C5). It was not only the secondary structure predictions that supported the analysis but site directed mutagenesis of the substrate interacting residues was also consistent with it. This led us to develop a substrate-binding model of CYP74C3 which predicted three amino acid residues, N285, F287, and G288 located in the putative I-helix and distal haem pocket of CYP74C3 to be in close proximity to the preferred substrate 13-HPOTE. These residues were judged to be in equivalent positions to those identified in SRS-4 of CYP2C5. Significance of the residues and their relevance to the model were further assessed by site directed mutagenesis of the three residues followed by EPR spectroscopic and detailed kinetic investigations of the mutated proteins in the presence and absence of detergent. Although point mutation of the residues had no effect on the haem content of the mutated proteins, significant effects on the spin state equilibrium of the haem iron were noted. Kinetic effects of the mutations, which were investigated using three different substrates, were dramatic in nature. In the presence of detergent with the preferred substrate (13-HPOTE), the catalytic center activities and substrate binding affinities of the mutant proteins were reduced by a factor of 8-32 and 4-12, respectively, compared with wild-type--a two orders of magnitude reduction in catalytic efficiencies. We believe this is the first report where primary determinants of catalysis for any CYP74 enzyme, which are fully consistent with our model, have been identified. Our working model predicts that N285 is close enough to suggest that a hydrogen bond with the peroxy group of the enzyme substrate 13-HPOTE is warranted, whereas significance of F287 may arise from a strong hydrophobic interaction between the alkyl group(s) of the substrate and the phenyl ring of F287. We believe that G288 is crucial because of its size. Any other residue with a relatively bulky side chain will hinder the access of substrate to the active site. The effects of the mutations suggests that subtle protein conformational changes in the putative substrate-binding pocket regulate the formation of a fully active monomer-micelle complex with low-spin haem iron and that structural communication exists between the substrate- and micelle-binding sites of CYP74C3. Conservation in CYP74 sequence alignments suggests that N285, F287, and G288 in CYP74C3 and the equivalent residues at positions in other CYP74 enzymes are likely to be critical to catalysis. To support this we show that G324 in CYP74D4 (Arabidopsis AOS), equivalent to G288 in CYP74C3, is a primary determinant of positional specificity. We suggest that the overall structure of CYP74 enzymes is likely to be very similar to those described for classical P450 monooxygenase enzymes.     

A lipoxygenase-divinyl ether synthase pathway in flax (Linum usitatissimum L.) leaves

Incubation of linoleic acid with an enzyme preparation from leaves of flax (Linum usitatissimum L.) led to the formation of a divinyl ether fatty acid, i.e. (9Z,11E,1'Z)-12-(1'-hexenyloxy)-9,11-dodecadienoic [(omega5Z)-etheroleic] acid, as well as smaller amounts of 13-hydroxy-9(Z),11(E)-octadecadienoic acid. The 13-hydroperoxide of linoleic acid afforded the same set of products, whereas incubations of alpha-linolenic acid and its 13-hydroperoxide afforded the divinyl ether (9Z,11E,1'Z,3'Z)-12-(1',3'-hexadienyloxy)-9,11-dodecadienoic [(omega5Z)-etherolenic] as the main product. Identification of both divinyl ethers was substantiated by their UV, mass-, (1)H NMR and COSY spectral data. In addition to the 13-lipoxygenase and divinyl ether synthase activities demonstrated by these results, flax leaves also contained allene oxide synthase activity as judged by the presence of endogenously formed (15Z)-cis-12-oxo-10,15-phytodienoic acid in all incubations.     

Trends in major and trace elements in decomposing needle litters during a long-term experiment in Swedish forests

The dynamics of 47 major and trace elements were examined during a long-term (up to 8 years between 1979 and 1988) litter decomposition experiment in European boreal and nemoboreal forests (Sweden). Litterbags were incubated in 11 monocultural stands at 10 different locations including seven with Norway spruce (Picea abies (L.) H. Karst.) and four with Scots pine (Pinus sylvestris L.). Principal component analysis and manual scatter plots revealed groups of elements behaving in a similar manner. One group consisted mainly of nutrients, but also of the unessential or toxic elements Rb, Sc, Sr and Tl, and had a general trend with decreasing mass-normalised (mn) concentrations during decomposition. Another group contained mostly unessential and potentially toxic elements, whose concentrations generally increased during the decay process. An exception from this increasing trend was found for Cd, Hf, Hg, Ta and Zr, for which the mn-concentrations increased initially followed by a net leaching from the litter. The influence of sea spray was identified in the early stages of the experiment (in particular for Na), and the impact of the anthropogenic component of atmospheric deposition was clearly visible (e.g. Pb, Cd, Hg). A regional northern Sb source is indicated in the pine, but not in the spruce, needles. The fact that the samples were collected at a time of higher atmospheric metal deposition than at present provides additional information and usefulness of the results.     

Intraspecific variation in resistance of frog eggs to fungal infection

Documenting sources of variation in host viability at pathogen exposure within and among populations is an important task in order to predict host-pathogen evolutionary dynamics. In the present study, we investigated family and population variation in the degree of embryonic infection of the pathogenic fungus Saprolegnia spp., by infecting moor frog (Rana arvalis) eggs from six populations and exposing them to two different temperatures. We found a significant family effect on the degree of Saprolegnia-infection of eggs and embryos, suggesting that there is genetic variation in resistance among embryos, or variation among females in some aspect of maternally induced resistance. Furthermore, infection level differed significantly between temperatures, with most families having more infected eggs in the relatively colder temperature. However, eggs and embryos from the different populations showed different degrees of Saprolegnia-infection in the two temperatures, i.e., there was a significant population × temperature interaction on the proportion of infected eggs. Thus, the degree of Saprolegnia-infection is sensitive to variation at the level of the family, population and environmental conditions, suggesting that responses to fungal outbreaks will vary geographically and will be difficult to predict.     

Evolution of condition-dependent dispersal under kin competition

Dispersers often differ in body condition from non-dispersers. The social dominance hypothesis explains dispersal of weak individuals, but it is not yet well understood why strong individuals, which could easily retain their natal site, are sometimes exposed to risky dispersal. Based on the model for dispersal under kin competition by Hamilton and May, we construct a model where dispersal propensity depends on body condition. We consider an annual species that inhabits a patchy environment with varying patch qualities. Offspring body condition corresponds to the quality of the natal patch and competitive ability increases with body condition. Our main general result balances the fitness benefit from not dispersing and retaining the natal patch and the benefit from dispersing and establishing somewhere else. We present four different examples for competition, which all hint that dispersal of strong individuals may be a common outcome under the assumptions of the present model. In three of the examples, the evolutionarily stable dispersal probability is an increasing function of body condition. However, we found an example where, counterintuitively, the evolutionarily stable dispersal probability is a non-monotone function of body condition such that both very weak and very strong individuals disperse with high probability but individuals of intermediate body condition do not disperse at all.