Ionic Balance of Root-Shoot Nitrate Transfer in Dwarf Bean

The Dijkshoorn-Ben Zioni model about potassium recycling in higher plants proposes a stoichiometric coupling between the upward transport of nitrate and potassium, and therefore a 1:1 ratio of these ions in the xylem sap. Phaseolus vulgaris grown in media with different NO₃: K⁺ ratios, however, only rarely showed equimolar concentrations of the two ions in the bleeding sap. Ratios between 0.2 and 11 were observed and the ratios between concentrations of the ions in the exudate and in the external solution were positively correlated. An analysis of the major inorganic constituents of the exudate revealed an ionic balance that requires negligible amounts of charges from organic molecules.     

Effect of Plant Growth Regulators on Nitrate Utilization by Roots of Nitrogen-Depleted Dwarf Bean

We examined the effect of pretreatments (18 h at 5 µmoldm^–3) with abscisic acid, the ethylene-releasing substance‘Ethephon’, gibberellic acid, indoleacetic acid,kinetin and zeatin on nitrate uptake and in vivo nitrate reductaseactivity (NRA) in roots of nitrogen-depleted Phaseolus vulgarisL. Nitrate uptake showed an apparent induction pattern witha steady state after about 6 h, in all treatments. The nitrateuptake rate after 6 h was unaffected or at most 30% lower aftertreatments with the plant growth regulators. Gibberellic acid, kinetin and zeatin induced substantial NRAin roots in the absence of nitrate, whereas Ethephon enhancedNRA only during nitrate nutrition. Kinetin-induced NRA (Ki-NRA)was maximal after a pretreatment at 1 µmol dm^–3,and showed a lag phase of 6–8 h. Ki-NRA was additive tonitrate-induced NRA (NO^–₃-NRA) for at least 24 h, independentof the induction sequence. After full induction, Ki-NRA approximated20% of NO-₃-NRA. Abscisic acid counteracted the developmentof Ki-NRA, but not of NO^–₃-NRA. Cycloheximide and tungstatewere equally effective to suppress the development of nitratereductase activity after supply of kinetin or NO^–₃. Our data are consistent with the operation of two independentenzyme fractions (Ki-NRA and NO^–₃-NRA) with apparentlyidentical properties but with separate control mechanisms. Theabsence of major effects of plant growth regulators on the time-courseand rate of nitrate uptake suggests that exogenous regulators,and possibly endogenous phytohormones are of minor importancefor initial nitrate uptake. The differential effect of someregulators on nitrate uptake and root NRA furthermore indicatesthat the processes of uptake and reduction of NO^–₃ arenot obligatory or exclusively coupled to each other.     

A PORTABLE DIGITAL SOUND EMITTER FOR INTERACTIVE PLAYBACK OF ANIMAL VOCALISATIONS

ABSTRACT

A new portable digital sound emitter (DSE) for normal and interactive playback of sound signals in the field and in the laboratory is described together with two examples of applications of the DSE in interactive field experiments. The DSE may be loaded with a broad spectrum of digitised sounds, e.g. artificial signals or natural animal vocalisations, and it is controlled via the keyboard of a portable PC running a dedicated program. This program, which can be tailored to support a vast number of different demands, enables the experimenter to start and stop the analog output from the DSE at any time and to choose freely between the available sounds and playback modes. The use of the DSE for interactive playback experiments therefore is only limited by the ability of the operator to perceive the vocalisations of the participating animal and to operate the keyboard of the PC.     

Relationships Between Fire Response, Morphology, Root Anatomy and Starch Distribution in South-west Australian Epacridaceae

Selected epacrids (92 species in 15 genera) were examined withrespect to fire response type, morphology, root anatomy andstarch storage. Seeders, 75% of the species investigated, possesseda single main stem and a small root system with lateral rootswhich in most cases did not spread beyond the shoot canopy.Resprouter species were generally multi-stemmed with large lignotuberousroot stocks. Certain seeder and resprouter species were intermediatein form and showed small root systems and basally branched mainstems. Amounts of starch in roots of seeders (1.9±0.5mgstarch gd.wt per root) were much less than in resprouters (14.1±3.3)whereas amounts in shoots were similar (1.9±0.5 and 1.6±0.6mgstarch gd.wt per shoot, respectively). Starch storage in rootswas mostly confined to rays of xylem parenchyma and inter-rayxylem parenchyma and the greater storage capacity of resprouterswas generally due to broader rays. Growth zones in root xylemranged from clear, verifiable annual rings, as in many seederspecies, to indistinct growth zones, typical of many resprouterspecies. Shoot:root dry weight ratios were higher in seedersthan resprouters. The study suggests that speciation withinthe Epacridaceae into seeder and resprouter forms involved divergentdifferentiation in terms of morphology, shoot:root dry weightratio root storage of starch. Seeder; starch storage; growth rings; growth zones; south-west Australia; resprouter; Epacridaceae     

Phylogeny,diversification patterns and historical biogeography of euglossine orchid bees (Hymenoptera: Apidae)

The orchid bees constitute a clade of prominent insect pollinators distributed throughout the Neotropical region. Males of all species collect fragrances from natural sources, including flowers, decaying vegetation and fungi, and store them in specialized leg pockets to later expose during courtship display. In addition, orchid bees provide pollination services to a diverse array of Neotropical angiosperms when foraging for food and nesting materials. However, despite their ecological importance, little is known about the evolutionary history of orchid bees. Here, we present a comprehensive molecular phylogenetic analysis based on ～4.0 kb of DNA from four loci [cytochrome oxidase (CO1), elongation factor 1‐α (EF1‐α), arginine kinase (ArgK) and RNA polymerase II (Pol‐II)] across the entire tribe Euglossini, including all five genera, eight subgenera and 126 of the approximately 200 known species. We investigated lineage diversification using fossil‐calibrated molecular clocks and the evolution of morphological traits using disparity‐through‐time plots. In addition, we inferred past biogeographical events by implementing model‐based likelihood methods. Our dataset supports a new view on generic relationships and indicates that the cleptoparasitic genus Exaerete is sister to the remaining orchid bee genera. Our divergence time estimates indicate that extant orchid bee lineages shared a most recent common ancestor at 27–42 Mya. In addition, our analysis of morphology shows that tongue length and body size experienced rapid disparity bursts that coincide with the origin of diverse genera (Euglossa and Eufriesea). Finally, our analysis of historical biogeography indicates that early diversification episodes shared a history on both sides of Mesoamerica, where orchid bees dispersed across the Caribbean, and through a Panamanian connection, thus reinforcing the hypothesis that recent geological events (e.g. the formation of the isthmus of Panama) contributed to the diversification of the rich Neotropical biota. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 552–572.     

Wolf Movement Patterns: a Key to Estimation of Kill Rate?

Abstract: To estimate wolf (Canis lupus) kill rates from fine-scale movement patterns, we followed adult wolves in 3 territories of the Scandinavian wolf population using Global Positioning Systems (GPS) during the winters of 2001–2003. The resulting 6 datasets of 62–84 study days gave a total of 8,747 hourly GPS positions. We visited clusters of positions in the field on average 8.8 days after positioning and found moose (Alces alces) killed by wolves during the study period on 74 (8%) of the 953 clusters. The number of positions and visits to a cluster, their interaction, and the proportion of afternoon positions were significant fixed effects in mixed logistic-regression models predicting the probability of a cluster containing a wolf-killed moose. The models, however, displayed a poor goodness-of-fit and were not a suitable tool for estimating kill rates from positioning data alone. They might be used to reduce fieldwork by excluding unlikely clusters, although the reduction was not substantial. We discuss proximate factors (i.e., human disturbance and access to prey) as well as ultimate factors (i.e., social organization, intra-guild dominance, and litter size) as potential causes of the observed high temporal and spatial variation in prey-handling. For similar future kill-rate studies, we recommend increasing field efforts and shortening positioning intervals.     

Multistage,Long-Range Natal Dispersal by a Global Positioning System-Collared Scandinavian Wolf

Abstract: We document a new record dispersal for wolves worldwide. The natal straight-line dispersal distance of a Global Positioning System-collared female wolf from the Scandinavian population was 1,092 km from southeast Norway to northeast Finland, with a multistage actual travel distance of >10,000 km. Natural gene flow to the isolated, inbred Scandinavian wolf population may occur if survival of dispersers is improved.     

ZmCPK1, a calcium‐independent kinase member of the Zea mays CDPK gene family,functions as a negative regulator in cold stress signalling

Calcium‐dependent protein kinases (CDPKs) have been shown to play important roles in plant environmental stress signal transduction. We report on the identification of ZmCPK1 as a member of the maize (Zea mays) CDPK gene family involved in the regulation of the maize cold stress response. Based upon in silico analysis of the Z. mays cv. B73 genome, we identified that the maize CDPK gene family consists of 39 members. Two CDPK members were selected whose gene expression was either increased (Zmcpk1) or decreased (Zmcpk25) in response to cold exposure. Biochemical analysis demonstrated that ZmCPK1 displays calcium‐independent protein kinase activity. The C‐terminal calcium‐binding domain of ZmCPK1 was sufficient to mediate calcium independency of a previously calcium‐dependent enzyme in chimeric ZmCPK25‐CPK1 proteins. Furthermore, co‐transfection of maize mesophyll protoplasts with active full‐length ZmCPK1 suppressed the expression of a cold‐induced marker gene, Zmerf3 (ZmCOI6.21). In accordance, heterologous overexpression of ZmCPK1 in Arabidopsis thaliana yielded plants with altered acclimation‐induced frost tolerance. Our results identify ZmCPK1 as a negative regulator of cold stress signalling in maize.     

Geographical and seasonal gradients in hatching failure in Eastern Bluebirds Sialia sialis reinforce clutch size trends

Eggs untended during the laying phase can lose viability if exposed to high temperatures, such as those common at lower latitudes and late in the nesting season. The egg‐viability hypothesis states that constraints on viability during the laying phase could account for latitudinal and seasonal gradients in clutch size. We used 7 years’ worth of data collected by volunteers (The Birdhouse Network, co‐ordinated by the Cornell Laboratory of Ornithology) to look simultaneously at populations across the temperate breeding range of Eastern Bluebirds Sialia sialis in order to test three predictions of the egg‐viability hypothesis: the probability of hatching failure decreases at higher latitude and increases later in the season, and that these trends are strongest among large clutches. The overall average number of unhatched eggs relative to the total number of eggs laid was similar to that found by other studies (7.8%; range 6.8–8.9% annually; n = 32 567 eggs from 7231 nests from 530 study sites). Using generalized linear mixed models that controlled for the non‐independence of eggs within a clutch, we found that the ‘per‐egg’ probability of hatching failure was highest late in the season, highest at lower latitudes, and highest for both small (three‐egg) and large (six‐egg) clutches. The seasonal and geographical gradients in egg hatching failure reinforce documented seasonal and geographical trends in clutch size. Loss of egg viability prior to incubation currently provides the most parsimonious and consistent explanation of the observed patterns of hatching failure. However, alternative explanations for large‐scale patterns, particularly those not consistent with the egg‐viability hypothesis, warrant further research into other causes of hatching failure, such as microbes and infertility (related to extra‐pair mating). Our results demonstrate that investigating causes of variation in demography among local populations across a geographical gradient provides a potential means of identifying selection pressures on life‐history traits.