bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of position, understorey vegetation and coarse woody debris on tree regeneration in two environmentally contrasting forests of north‐western Patagonia: a manipulative approach
Authors: Heinemann Karin , Kitzberger Thomas 
Published: June 2006

AbstractAim  To investigate the differential effects of position within gaps, coarse woody debris and understorey cover on tree seedling survival in canopy gaps in two old‐growth Nothofagus pumilio (Poepp. & Endl.) Krasser forests and the response of this species to gaps in two forests located at opposite extremes of a steep rainfall gradient.Location  Nahuel Huapi National Park, at 41° S in north‐western Patagonia, Argentina.Methods  In both study sites, seedlings were transplanted to experimental plots in gaps in three different positions, with two types of substrate (coarse woody debris or forest floor), and with and without removal of understorey vegetation. Survival of seedlings was monitored during two growing seasons. Soil moisture and direct solar radiation were measured once in mid‐summer. Seedling aerial biomass was estimated at the end of the experiment.Results  Mid‐summer soil water potential was lowest in the centre of gaps, in plots where the understorey had been removed, and highest at the northern edges of gaps. Direct incoming radiation was highest in gap centres and southern edges, and lowest at northern edges. Seedling mortality was highest in gap centres, in both sites. Coarse woody debris had a positive effect on seedling survival during summer in the mesic forest and during winter in the xeric forest. The removal of understorey cover had negative effects in gap centres during summer. Seedling final aerial biomass was positively affected by understorey removal and by soil substrate in both sites. In the dry forest gaps, seedling growth was highest in northern edges, whereas it was highest in gap centres in the mesic forest. Overall growth was positively related to survival in the xeric forest, and negatively related in the mesic forest.Main conclusions  Survival and growth were facilitated by the shade of gap‐surrounding trees only in the xeric forest. Understorey vegetation of both forests facilitated seedling survival in exposed microsites but competed with seedling growth. Nurse logs were an important substrate for seedling establishment in both forests; however, causes of this pattern differed between forests. Water availability positively controls seedling survival and growth in the xeric forest while in the mesic forest, survival and growth are differentially controlled by water and light availability, respectively. These two contrasting old‐growth forests, separated by a relatively short distance along a steep rainfall gradient, had different yet unexpected microenvironmental controls on N. pumilio seedling survival and growth. These results underscore the importance of defining microscale limiting factors of tree recruitment in the context of large‐scale spatial variation in resources.
Potential selection in native grass populations by exotic invasion
Authors: MEALOR BRIAN A. , HILD ANN L. 
Published: June 2006

AbstractEcological impacts of invasive plant species are well documented, but the genetic response of native species to invasive dominance has been often overlooked. Invasive plants can drastically alter site conditions where they reach dominance, potentially exerting novel selective pressures on persistent native plant populations. Do native plant populations in old exotic invasions show evidence of selection when compared to conspecific populations in adjacent, noninvaded areas? We employ amplified fragment length polymorphism (AFLP) analysis to screen a large number of loci from two native grass species (Hesperostipa comata (Trin. & Rupr.) Barkworth and Sporobolus airoides Torr.) that occur in old infestations of the invasive forb Acroptilon repens. We then compare observed locus by locus FST values with distributions of FST estimated from simulation models under expectation of neutrality. We also compare the proportion of loci possibly linked to selection and those not linked to selection which exhibit parallel trends in divergence between two community types (invaded, noninvaded). Few loci (H. comata, 2.6%; S. airoides, 8.7%) in the two native grasses may be linked to genes under the influence of selection. Also, loci linked to selection showed a greater portion of parallel trends in divergence than neutral loci. Genetic similarities between community types were less than genetic similarity within community types suggesting differentiation in response to community alteration. These results indicate that a small portion of scored AFLP loci may be linked to genes undergoing selection tied to community dominance by an invasive species. We propose that native plants in communities dominated by exotic invasives may be undergoing natural selection.
Double hexameric ring assembly of the type III protein translocase ATPase HrcN
Authors: Müller Shirley A. , Pozidis Charalambos , Stone Remington , Meesters Christian , Chami Mohamed , Engel Andreas , Economou Anastassios , Stahlberg Henning 
Published: June 2006

SummaryThe specialized type III secretion (T3S) apparatus of pathogenic and symbiotic Gram‐negative bacteria comprises a complex transmembrane organelle and an ATPase homologous to the F1‐ATPase β subunit. The T3S ATPase HrcN of Pseudomonas syringae associates with the inner membrane, and its ATP hydrolytic activity is stimulated by dodecamerization. The structure of dodecameric HrcN (HrcN12) determined to 1.6 nm by cryo‐electron microscopy is presented. HrcN12 comprises two hexameric rings that are probably stacked face‐to‐face by the association of their C‐terminal domains. It is 11.5 ± 1.0 nm in diameter, 12.0 ± 2.0 nm high and has a 2.0–3.8 nm wide inner channel. This structure is compared to a homology model based on the structure of the F1‐β‐ATPase. A model for its incorporation within the T3S apparatus is presented.
Identification of genes involved in the biosynthesis and attachment of Methanococcus voltae N‐linked glycans: insight into N‐linked glycosylation pathways in Archaea
Authors: Chaban Bonnie , Voisin Sebastien , Kelly John , Logan Susan M. , Jarrell Ken F. 
Published: June 2006

SummaryN‐linked glycosylation is recognized as an important post‐translational modification across all three domains of life. However, the understanding of the genetic pathways for the assembly and attachment of N‐linked glycans in eukaryotic and bacterial systems far outweighs the knowledge of comparable processes in Archaea. The recent characterization of a novel trisaccharide [β‐ManpNAcA6Thr‐(1‐4)‐β‐GlcpNAc3NAcA‐(1‐3)‐β‐GlcpNAc]N‐linked to asparagine residues in Methanococcus voltae flagellin and S‐layer proteins affords new opportunities to investigate N‐linked glycosylation pathways in Archaea. In this contribution, the insertional inactivation of several candidate genes within the M. voltae genome and their resulting effects on flagellin and S‐layer glycosylation are reported. Two of the candidate genes were shown to have effects on flagellin and S‐layer protein molecular mass and N‐linked glycan structure. Further examination revealed inactivation of either of these two genes also had effects on flagella assembly. These genes, designated agl (archaeal glycosylation) genes, include a glycosyl transferase (aglA) involved in the attachment of the terminal sugar to the glycan and an STT3 oligosaccharyl transferase homologue (aglB) involved in the transfer of the complete glycan to the flagellin and S‐layer proteins. These findings document the first experimental evidence for genes involved in any glycosylation process within the domain Archaea.
Interaction network in cyanobacterial nitrogen regulation: PipX, a protein that interacts in a 2‐oxoglutarate dependent manner with PII and NtcA
Authors: Espinosa Javier , Forchhammer Karl , Burillo Sergio , Contreras Asunción 
Published: June 2006

SummaryCyanobacteria perceive nitrogen status by sensing intracellular 2‐oxoglutarate levels. The global nitrogen transcription factor NtcA and the signal transduction protein PII are both involved in 2‐oxoglutarate sensing. PII proteins, probably the most conserved signal transduction proteins in nature, are remarkable for their ability to interact with very diverse protein targets in different systems. Despite widespread efforts to understand nitrogen signalling in cyanobacteria, the involvement of PII in the regulation of transcription activation by NtcA remains enigmatic. Here we show that PipX, a protein only present in cyanobacteria, interacts with both PII and NtcA and provides a mechanistic link between these two factors. A variety ofin vivoandin vitroapproaches were used to study PipX and its interactions with PII and NtcA. 2‐Oxoglutarate favours complex formation between PipX and NtcA, but impairs binding to PII, suggesting that partner swapping between these nitrogen regulators is driven by the 2‐oxoglutarate concentration. PipX is required for NtcA‐dependent transcriptional activationin vivo, thus implying that PipX may function as a prokaryotic transcriptional coactivator.
The Ischia debris avalanche: first clear submarine evidence in the Mediterranean of a volcanic island prehistorical collapse
Authors: Chiocci Francesco Latino , De Alteriis Giovanni 
Published: June 2006

AbstractSector or flank collapse with related debris avalanches is increasingly recognized as a relatively common volcanic behaviour, in particular, for large, hot‐spot related oceanic islands. Here, we report the case of a catastrophic collapse that occurred at Ischia volcanic island in prehistorical times and was driven by the volcano‐tectonic uplift of Mt Epomeo, the major relief of the island. The collapse left a subaerial to submarine horseshoe scar on the southern flank of the island and generated a debris avalanche incorporating thousands of giant blocks dispersed as far as 50 km from the island. During the emplacement, part of the debris avalanche evolved into a debris flow covering an area of 250–300 km2. This constitutes the first, clear evidence of a submarine debris avalanche in the Mediterranean Sea. The major collapse was followed, and probably also preceded, by recurrent, less catastrophic terrestrial and underwater failures. Two other undersea hummocky deposits are found north and west of the island and might tentatively be correlated to the major southern collapse. Such volcanic behaviour, previously unknown for Ischia Volcano, has likely triggered tsunami waves over the entire Bay of Naples raising the question of their impact on prehistorical/historical communities.
DOF transcription factor AtDof1.1 (OBP2) is part of a regulatory network controlling glucosinolate biosynthesis in Arabidopsis
Authors: Skirycz Aleksandra , Reichelt Michael , Burow Meike , Birkemeyer Claudia , Rolcik Jakub , Kopka Joachim , Zanor Maria Inès , Gershenzon Jonathan , Strnad Miroslav , Szopa Jan , Mueller‐Roeber Bernd , Witt Isabell 
Published: June 2006

SummaryGlucosinolates are a group of secondary metabolites that function as defense substances against herbivores and micro‐organisms in the plant order Capparales. Indole glucosinolates (IGS), derivatives of tryptophan, may also influence plant growth and development. In Arabidopsis thaliana, indole‐3‐acetaldoxime (IAOx) produced from tryptophan by the activity of two cytochrome P450 enzymes, CYP79B2 and CYP79B3, serves as a precursor for IGS biosynthesis but is also an intermediate in the biosynthetic pathway of indole‐3‐acetic acid (IAA). Another cytochrome P450 enzyme, CYP83B1, funnels IAOx into IGS. Although there is increasing information about the genes involved in this biochemical pathway, their regulation is not fully understood. OBP2 has recently been identified as a member of the DNA‐binding‐with‐one‐finger (DOF) transcription factors, but its function has not been studied in detail so far. Here we report that OBP2 is expressed in the vasculature of all Arabidopsis organs, including leaves, roots, flower stalks and petals. OBP2 expression is induced in response to a generalist herbivore, Spodoptera littoralis, and by treatment with the plant signalling molecule methyl jasmonate, both of which also trigger IGS accumulation. Constitutive and inducible over‐expression of OBP2 activates expression of CYP83B1. In addition, auxin concentration is increased in leaves and seedlings of OBP2 over‐expression lines relative to wild‐type, and plant size is diminished due to a reduction in cell size. RNA interference‐mediated OBP2 blockade leads to reduced expression of CYP83B1. Collectively, these data provide evidence that OBP2 is part of a regulatory network that regulates glucosinolate biosynthesis in Arabidopsis.
Rapid generation of new powdery mildew resistance genes after wheat domestication
Authors: Yahiaoui Nabila , Brunner Susanne , Keller Beat 
Published: June 2006

SummaryPlant defence against pathogens is controlled by disease resistance (R) gene products that directly or indirectly detect specific pathogen effectors. Plant–pathogen interactions have been proposed to follow a co‐evolutionary arms‐race model where R genes are recent and evolve rapidly in response to structural changes in matching pathogen effectors. However, the longevity and extensive polymorphism of R genes studied were more consistent with balancing selection maintaining ancient and diverse R genes or alleles. In bread wheat (Triticum aestivum), the Pm3 locus confers race‐specific resistance to wheat powdery mildew (Blumeria graminis f.sp. triticii). Here we describe recently generated Pm3 resistance alleles that all derive from one susceptible allele, Pm3CS, which is widespread among hexaploid bread‐wheat lines. One group of four Pm3 resistance alleles shows few, clearly delimited, polymorphic sequence blocks of ancient origin, embedded in sequences identical to Pm3CS and possibly derived from gene conversion. A second group of three alleles differs from Pm3CS by only two to five mutations, all non‐synonymous, and all in the leucine‐rich repeat‐encoding region. Transient transformation experiments confirmed that Pm3 resistance specificities are based on one or few amino acid changes. The Pm3CS allele was found in wild tetraploid wheat, the ancestor of hexaploid bread wheat, specifically from southern Turkey, a region proposed to be the site of wheat domestication. Based on these data, we propose that the Pm3 resistance alleles were generated in agricultural ecosystems after domestication of wheat 10 000 years ago. The evolution of Pm3 alleles in wheat is best described by the model of evolved recycling, where novel genetic variation is integrated in plant populations together with recycling of old variation.
STY1 regulates auxin homeostasis and affects apical–basal patterning of the Arabidopsis gynoecium
Authors: Sohlberg Joel J. , Myrenås Mattias , Kuusk Sandra , Lagercrantz Ulf , Kowalczyk Mariusz , Sandberg Göran , Sundberg Eva 
Published: June 2006

SummaryGynoecia of the Arabidopsis mutant sty1‐1 display abnormal style morphology and altered vascular patterning. These phenotypes, which are enhanced in the sty1‐1 sty2‐1 double mutant, suggest that auxin homeostasis or signalling might be affected by mutations in STY1 and STY2, both members of the SHI gene family. Chemical inhibition of polar auxin transport (PAT) severely affects the apical–basal patterning of the gynoecium, as do mutations in the auxin transport/signalling genes PIN1, PID and ETT. Here we show that the apical–basal patterning of sty1‐1 and sty1‐1 sty2‐1 gynoecia is hypersensitive to reductions in PAT, and that sty1‐1 enhances the PAT inhibition‐like phenotypes of pin1‐5, pid‐8 and ett‐1 gynoecia. Furthermore, we show that STY1 activates transcription of the flavin monooxygenase‐encoding gene THREAD/YUCCA4, involved in auxin biosynthesis, and that changes in expression of STY1 and related genes lead to altered auxin homeostasis. Our results suggest that STY1 and related genes promote normal development of the style and affect apical–basal patterning of the gynoecium through regulation of auxin homeostasis.
A Sex‐Specific Affiliative Contact Behavior in Indian Ocean Bottlenose Dolphins, Tursiops sp.
Authors: Connor Richard , Mann Janet , Watson‐Capps Jana 
Published: June 2006

AbstractA variety of signals are employed by animals to establish, mediate and advertise social bonds. Gentle contact behaviors, such as grooming in primates, are an important class of affiliative signals that may provide direct benefits (e.g. stress reduction, parasite removal) in addition to their signal information. Unlike other kinds of signals (e.g. male displays) examples of affiliative contact behaviors restricted to one sex are rare. Here we describe a strongly sex‐biased affiliative behavior ‘contact swimming’, in female bottlenose dolphins in Shark Bay, Western Australia. Females were more likely to be observed contact swimming than males and the presence of males likely influenced this behavior. This is surprising given that female relationships have been characterized as weak. Female dolphins are sometimes herded and harassed by males and contact swimming occurs most often between females in male‐biased groups. Contact swimming may serve as a signal of cooperation between females. Possible direct benefits include stress reduction and assisted locomotion.
Host‐Handling Behavior: An Innate Component of Foraging Behavior in the Parasitoid WaspAmpulex compressa
Authors: Keasar Tamar , Sheffer Noa , Glusman Gustavo , Libersat Frederic 
Published: June 2006

AbstractThe reproductive success of parasitoids depends on their ability to locate, select, and handle hosts quickly and efficiently. Learning has been shown to play a role in host finding and host choice, but the role of learning in the handling of hosts has received little attention. We tested whether the speed and accuracy of host handling improve with experience in the waspAmpulex compressa. This parasitoid performs an elaborate behavioral sequence when parasitizing its host, the cockroachPeriplaneta americana. We provide a quantitative description of the behavioral sequence, and show that: (a) the duration of the whole sequence, (b) the number of completed stages, and (c) the precision of an important stage in the handling sequence, host antennal cutting, are similar in inexperienced and experienced individuals. We discuss features ofA. compressa’s life history that may select for innate host handling.
Increased Susceptibility to Predation for Autotomized House Crickets (Acheta domestica)
Authors: Bateman Philip W. , Fleming Patricia A. 
Published: June 2006

AbstractWhen attacked, crickets may shed or ‘autotomize’ an entrapped limb in order to escape a would‐be predator. We examined the relationship between limb autotomy, running speed and susceptibility to future predation in house crickets (Acheta domestica). Hind limb autotomy resulted in a significant reduction in escape speed and ability to jump during the escape run, and greater predation by both lizards (striped skink Mabuya striata punctatissima) and mice (pouched mouse Saccostomus campestris). Although limb autotomy may enable a house cricket to escape a predatory encounter, autotomy of even one hind limb results in immediate costs to escape speed in crickets and makes the animal more vulnerable to subsequent predator encounters.
A Field Study of Spatial Memory in Green‐Backed Firecrown Hummingbirds (Sephanoides sephaniodes)
Authors: González‐Gómez Paulina L. , Vásquez Rodrigo A. 
Published: June 2006

AbstractThe foraging ecology of hummingbirds involves the exploitation of a high number of patchily distributed flowers. This scenario seems to have influenced capabilities related to learning and memory, which help to avoid recently visited flowers and to allocate exploitation to the most rewarding flowers, once learning has occurred. We carried out two field experiments with the green‐backed firecrown hummingbird (Sephanoides sephaniodes, Trochilidae) in order to examine the ability of birds, first, to recall a nectar location, and secondly, to remember the location of the most rewarding flower among lower quality flowers. The first experiment showed that subjects were able to recall the location of nectar among flowers of identical appearance. In the second experiment, hummingbirds were also able to recall the location of the most rewarding nectar among less rewarding flowers with the same appearance. The results of this study suggest that S. sephaniodes can remember the location of the most rewarding patch, facilitating efficient exploitation of flowers in the absence of visual cues related to nectar quality.
Coexistence in a metacommunity: the competition–colonization trade‐off is not dead
Authors: Calcagno V. , Mouquet N. , Jarne P. , David P. 
Published: June 2006

AbstractThe competition–colonization trade‐off model is often used to explain the coexistence of species. Yet its applicability has been severely criticized, mainly because the original model assumed a strict competitive hierarchy of species and did not allow for any preemptive effect. We considered the impact of relaxing both of these limitations on coexistence. Relaxing trade‐off intensity makes coexistence less likely and introduces a minimum colonization rate below which any coexistence is impossible. Allowing for preemption introduces a limit to dissimilarity between species. Surprisingly, preemption does not impede coexistence as one could presume from previous studies, but can actually increase the likelihood of coexistence. Its effect on coexistence depends on whether or not species in the regional pool are strongly limited in their colonization ability. Preemption is predicted to favour coexistence when: (i) species are not strongly limited in their colonization ability; and (ii) the competitive trade‐off is not infinitely intense.