Biomass of primary and secondary vegetation in Rondônia, Western Brazilian Amazon

Biomass estimates of primary and different ages of secondary vegetation are reported for a tropical forest region in Rondônia, Western Brazilian Amazon. The estimates are based on published allometric equations, and on vegetation composition and allometric data collected in areas of primary forest and secondary vegetation of ages 2, 3, 5, 9, 11, 16 and 18 years. Primary forest biomass estimates varied from 290 to 495 t ha^–1. Secondary vegetation biomass estimates accounted for 40–60% of the primary forest biomass after 18 years of abandonment. Secondary growth rates in lightly used areas are estimated to have varied from 6.6 to 8.7 t ha^–1 y^–1 between the third and the eighteenth years after abandonment. CO₂ sequestration by regrowing vegetation is discussed for two scenarios of land abandonment.     

Semiparametric regression estimation in the presence of dependent censoring

We propose a semiparametric estimation procedure for estimatingthe regression of an outcome Y, measured at the end of a fixedfollow-up period, on baseline explanatory variables X, measuredprior to start of follow-up, in the presence of dependent censoringgiven X. The proposed estimators are consistent when the dataare ‘missing at random’ but not ‘missing completelyat random’ (Rubin, 1976), and do not require full specificationof the complete data likelihood. Specifically, we assume thatthe probability of censoring at time t is independent of theoutcome Y conditional on the recorded history up to t of a vectorof time-dependent covariates that are correlated with Y. Ourestimators can be used to adjust for dependent censoring andnonrandom noncompliance in randomised trials studying the effectof a treatment on the mean of a response variable of interest.Even with independent censoring, our methods allow the investigatorto increase efficiency by exploiting the correlation of theoutcome with a vector of time-dependent covariates.     

Geographical variation in floral traits of the tree tobacco in relation to its hummingbird pollinator fauna

Nicotiana glauca , a hummingbird pollinated plant, exhibits geographical variation in several floral traits. We examined whether geographical differentiation occurred for different flower characters and if this differentiation could be explained, at least in part, by the existence or abundance of different hummingbird species in the respective pollinator assemblages. The comparison between five populations showed significant variation in six floral traits and two female fitness measures. The traits that better discriminated between populations were corolla length and corolla width. There were metric correlations between corolla length and style length in all populations studied and, in four of the five populations, both corolla length and width were also correlated. Among plants in each population, seed weight was correlated positively and significantly with style exertion, suggesting that fruit quality is dependent on the degree of cross pollination. Assemblages of hummingbirds differed between populations in species composition, visitation frequencies, and bill length. Linear regression involving bill length of the more frequent hummingbird pollinators and corolla length yielded positive and significant relationships. Thus, there appears to be an adjustment between pollinators and flowers traits that have high incidence in the among population variation.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 657–667.     

Drought resistance of Quercus pubescens as a function of root hydraulic conductance, xylem embolism and hydraulic architecture

Water relations, xylem embolism, root and shoot hydraulic conductance of both young plants in the field and potted seedlings of Quercus pubescens have been studied with the aim of investigating whether these variables may account for the well known adaptation of this oak species to arid habitats. Our data revealed that Q. pubescens is able to maintain high leaf relative water contents under water stress conditions. In fact, relative water contents measured in summer (July) did not differ from those recorded in April. This was apparently achieved by compensating water loss by an equal amount of water uptake. Such a drought avoidance strategy was made possible by the recorded high hydraulic efficiency of stems and roots under water stress. In fact, root hydraulic conductance of field-grown plants was maintained high in summer when the percentage loss of hydraulic conductance of stems was lowest. The hydraulic architecture of young plants of Q. pubescens measured in terms of partitioning of hydraulic resistances along the water pathway revealed that the highest hydraulic resistance was located in stems of the current year's growth. This hydraulic architecture is interpreted as consistent with the adaptation of Q. pubescens to arid habitats as a consequence of the recorded seasonal changes in water relation parameters as well as in root and stem hydraulics.     

Ontogenetic Change of the PSI- and PSII-Distribution in the Thylakoid System of Euglena gracilis

The thylakoid membranes of isolated Euglena chloroplasts wereseparated into two fractions by aqueous two-phase-partitioning(mixture of dextran 500 and poly(ethylene glycol) 4000) followingpress disruption. These two fractions differ in many respectsduring most of the cell cycle of this alga in comparison withthe thylakoid characteristics of higher plants or green algae.The amount of thylakoid membranes with separation characteristicscomparable with inside-out-vesicles of higher plant chloroplastschanges depending on the cell cycle stage of Euglena gracilis.Photosystems II and I are not restricted to one fraction. Boththylakoid membrane fractions evolve oxygen photosynthetically.When chloroplast differentiation in Euglena gracilis is complete(i.e. at the end of the light-time) the composition and thephotosynthetic efficiency of the two thylakoid fractions aregenerally equal. Photosystem I-related LHCI is present in bothfractions. Photosystem II-related CP29, however, was only detectedin unfractionated thylakoid membranes. The implications forthylakoid organization in Euglena chloroplasts are discussed. Key words: Euglena gracilis, photosystem I, photosystem II, stacking, thylakoids     

Adipokinetic hormone counteracts oxidative stress elicited in insects by hydrogen peroxide: in vivo and in vitro study

The role of adipokinetic hormone (AKH) in counteracting oxidative stress elicited in the insect body is studied in response to exogenously applied hydrogen peroxide, an important metabolite of oxidative processes. In vivo experiments reveal that the injection of hydrogen peroxide (8 µmol) into the haemocoel of the firebug, Pyrrhocoris apterus L. (Heteroptera: Pyrrhocoridae) increases the level of AKH by 2.8‐fold in the central nervous system (CNS) and by 3.8‐fold in the haemolymph. The injection of hydrogen peroxide also increases the mortality of experimental insects, whereas co‐injection of hydrogen peroxide with Pyrap‐AKH (40 pmol) reduces mortality to almost control levels. Importantly, an increase in haemolymph protein carbonyl levels (i.e. an oxidative stress biomarker) elicited by hydrogen peroxide is decreased by 3.6‐fold to control levels when hydrogen peroxide is co‐injected with Pyrap‐AKH. Similar results are obtained using in vitro experiments. Oxidative stress biomarkers such as malondialdehyde and protein carbonyls are significantly enhanced upon exposure of the isolated CNS to hydrogen peroxide in vitro, whereas co‐treatment of the CNS with hydrogen peroxide and Pyrap‐AKH reduces levels significantly. Moreover, a marked decrease in catalase activity compared with controls is recorded when the CNS is incubated with hydrogen peroxide. Incubation of the CNS with hydrogen peroxide and Pyrap‐AKH together curbs the negative effect on catalase activity. Taken together, the results of the present study provide strong support for the recently published data on the feedback regulation between oxidative stressors and AKH action, and implicate AKH in counteracting oxidative stress. The in vitro experiments should facilitate research on the mode of action of AKH in relation to oxidative stress, and could help clarify the key pathways involved in this process.     

Leaf architecture of South American Nothofagus (Nothofagaceae) using traditional and new methods in morphometrics

Leaf morphology has been the subject of several studies in NoNothofagur especially in the context of the taxonomy and evolutionary relationships of taxa within the genus, which are still controversial. The leaf architecture of 8 dombgi , N. betuloides and N. nitida , dominant trees of temperate forest in southern South America, is compared using venation patterns, landmarks, and entire outlines. In terms of venation patterns N. dombgi and N. betuloides were more similar to each other than to N. nitida. Similar results were found when differences in shape were analysed by discriminant analyses of shape coordinates (landmarks) and Fourier coefficients (outlines). For both analyses, the fwst discriminant function separated N. nitida from the other two species; these were also distinguished but showed greater overlap with each other. This study, in concert with information from allozyme data confirms the hypothesis of a more ancestral position for N. nitida with N. dombgi and N. betuloides being more recently derived. In addition to differences in shape, the size component of leaf morphology indicated that whereas N. betuloides had the smallest leaves, N. dombgi spanned the greatest range and has the biggest leaves. Given that the data shown here were obtained from seedlings grown under common-garden conditions, differences in both shape and size, seem to be important components of leaf morphology that may warrant consideration in characterizing these and other species of Nothofagus.     

Who flies first? – habitat‐specific phenological shifts of butterflies and orthopterans in the light of climate change: a case study from the south‐east Mediterranean

1. Insects undergo phenological change at different rates, showing no consistent trend between habitats, time periods, species or groups. Understanding how and why this variability occurs is crucial. 2. Phenological patterns of butterflies and Orthoptera were analysed using a novel approach of standardised major axis (SMA) analysis. It was investigated whether: (i) phenology (the mean date and duration of flight) of butterflies and Orthoptera changed from one survey (1998 and 1999 respectively) to another (2011), (ii) the rate at which phenology changed differed between taxa and (iii) phenological change was significantly different across habitat types (agriculture fields, grasslands, and forests). Using the 2011 dataset, we investigated relationships between habitat‐specific variables and species phenology. 3. For both groups, late‐emerging species had an advanced onset on the second survey while the duration showed no consistent trend for butterflies and did not change for Orthoptera. Although the rate at which phenology changed was consistent between the two groups, at the habitat level, a longer duration of flight period emerged for butterflies in agriculture fields while Orthoptera showed no differentiation in flight duration between habitats. We found an earlier emergence of butterflies in grasslands compared to forests, attributed to habitat‐specific temperature, whereas spatial variation in humidity had a significantly lower effect on butterflies' phenology in grasslands compared to forests. A gradual delay of butterfly appearances as the canopy cover increased was also found. 4. The utility of SMA analysis was demonstrated in phenological studies and evidence was detected that both habitat type and habitat‐specific variables refine species' phenological responses.     

Molecular phylogeny of fungus gnats (Diptera: Mycetophilidae) revisited: position of Manotinae,Metanepsiini, and other enigmatic taxa as inferred from multigene analysis

The phylogeny of selected genera from four subfamilies of fungus gnats (Diptera: Mycetophilidae) – Manotinae, Leiinae, Sciophilinae and Gnoristinae (including Metanepsiini) – is reconstructed based on the combined analysis of five mitochondrial (12S, 16S, COI, COII, cytB) and two nuclear (28S, ITS2) gene markers. Results of the different analyses all support Manotinae as a monophyletic group, with Leiinae as the sister group. Allactoneura DeMeijere is nested in the monophyletic and strongly supported clade of Leiinae. The tribe Metanepsiini is revealed as paraphyletic and the genera Metanepsia Edwards and Chalastonepsia Søli do not appear to be closely related. The genera Docosia Winnertz, Ectrepesthoneura Enderlein, Novakia Strobl and Syntemna Winnertz were placed with a group of genera included traditionally in the Gnoristinae. The monophyly of Dziedzickia Johannsen and Phthinia Winnertz is not supported. The genera of Sciophilinae (excluding Paratinia Mik but including Eudicrana Loew) form a monophyletic group in the Bayesian model.     

Size-related shifts in the physical habitat of two mayfly species (Ephemeroptera)

1. The spatial niche shifts of the nymphs of two mayfly species (Rhithrogena semicolorata and Ecdyonurus sp, gr. venosus) in relation to their growth were investigated in two lowland springs of northern Italy where they are dominant species. 2. Ordination of the different size classes of the two species revealed a canonical trend related to season and bottom roughness. 3. Larger nymphs of both species colonized rougher substrata. Differences between species in the roughness of areas colonized by small nymphs, which were very numerous, may have been due to competition for space.