Synthesis, characterization and ethylene polymerization activity of titanium aminopyridinato complexes

Three titanium complexes derived from 2-(2,6-difluoroanilino)pyridine and 2-(2-chloroanilino)pyridine were synthesized and characterized by X-ray diffraction or spectroscopic methods. All titanium complexes have been used to catalyze the polymerization of ethylene in the presence of MAO as cocatalyst. The mono(2,6-difluorophenylaminopyridinato) titanium catalyst was found to be more active in ethylene polymerization than the bis(2,6-difluorophenylaminopyridinato) and bis(2-chlorophenylaminopyridinato) titanium catalysts. ortho-Halogens disturbed the β-elimination transition state of ethylene polymerization and formed higher molar mass polyethylene than their unhalogenated congener. Due to fluxionality, the bis(2-chlorophenylaminopyridinato) titanium catalyst formed broader molar mass distribution than the bis(2,6-difluorophenylaminopyridinato) titanium catalysts.     

Phylogenetic and phenotypic structure among Banksia communities in south‐western Australia

Aim Phylogenetic and phenotypic patterns among coexisting banksias (Banksia, Proteaceae) in the infertile, fire‐prone landscapes of south‐western Australia were examined for evidence of community structuring. It was expected that closely related species would be spatially clustered (underdispersed) as a consequence of widespread recent speciation, strong edaphic fidelity and low dispersability. We also expected that edaphic filtering would result in phenotypic clustering of traits related to habitat specialization and that competitive exclusion among closely related species with similar regeneration biology and growth form would result in phenotypic overdispersion of these latter traits. Location Southwest Australian Floristic Region (SWAFR). Methods Based on published data for coexistence (richness and frequency) of Banksia species at 40 sites in the three floristic provinces, phylogenetic, soil type and morphological mean pairwise distance and mean nearest taxon distance were calculated for each site and compared with null communities. Patterns of co‐occurrence were examined at the local and subregional (provincial) scales. Results Of the 40 sites assessed, 21–30 displayed phylogenetic clustering of Banksia species (5–11 significantly) such that, overall, co‐occurring taxa were more closely related than expected by chance. Banksias in the Transitional Rainfall and Southeast Coastal Provinces were more likely to display phylogenetic clustering than in the High Rainfall Province. A significant trend for phylogenetic clustering associated with edaphic specialization (27–30 sites) was observed, as well as a significant trend for phenotypic overdispersion associated with growth form (25–28 sites). Results for regeneration biology depended on the metric used. Main conclusions We demonstrate spatial clustering of closely related banksias at the local and provincial scales, consistent with their restricted distribution (recent widespread speciation, patchy habitat availability and limited dispersability) in this geologically old and stable region. The clustering of closely related species may also be a consequence of habitat filtering linked to edaphic fidelity in the SWAFR flora, while overdispersion in growth form suggests that functional divergence favours coexistence in Banksia communities.     

Climate oscillations and species interactions: large‐scale congruence but regional differences in the phylogeographic structures of an alpine plant and its monophagous insect

Aim To predict the fate of alpine interactions involving specialized species, using a monophagous beetle and its host plant as a case study. Location The Alps. Methods We investigated genetic structuring of the herbivorous beetle Oreina gloriosa and its specific host‐plant Peucedanum ostruthium. We used genome fingerprinting (in the insect and the plant) and sequence data (in the insect) to compare the distribution of the main gene pools in the two associated species and to estimate divergence time in the insect, a proxy for the temporal origin of the interaction. We quantified the similarity in spatial genetic structures by performing a Procrustes analysis, a tool from shape theory. Finally, we simulated recolonization of an empty space analogous to the deglaciated Alps just after ice retreat by two lineages from two species showing unbalanced dependence, to examine how timing of the recolonization process, as well as dispersal capacities of associated species, could explain the observed pattern. Results Contrasting with expectations based on their asymmetrical dependence, patterns in the beetle and plant were congruent at a large scale. Exceptions occurred at a regional scale in areas of admixture, matching known suture zones in Alpine plants. Simulations using a lattice‐based model suggested these empirical patterns arose during or soon after recolonization, long after the estimated origin of the interaction c. 0.5 million years ago. Main conclusions Species‐specific interactions are scarce in alpine habitats because glacial cycles have limited the opportunities for co‐evolution. Their fate, however, remains uncertain under climate change. Here we show that whereas most dispersal routes are paralleled at a large scale, regional incongruence implies that the destinies of the species might differ under changing climate. This may be a consequence of the host dependence of the beetle, which locally limits the establishment of dispersing insects.     

Butterfly Response to Microclimatic Conditions Following Ponderosa Pine Restoration

Efforts to restore ponderosa pine ecosystems to open, park‐like conditions that predominated prior to European‐American settlement result in altered stand structure and increased landscape heterogeneity, potentially altering habitat suitability for invertebrates and other forest organisms. We examined the responses of two butterfly species, Colias eurytheme and Neophasia menapia, to microclimatic changes at structural edges created by experimental restoration treatments in northern Arizona. We monitored microclimate, including air temperature, light intensity, and vapor pressure deficit (VPD), on several mornings during butterfly releases. We placed adult butterflies at east‐ and west‐facing edges approximately one half‐hour before dawn to determine their behavioral response to microclimatic differences between east‐ and west‐facing edges. After sunrise, all three microclimatic variables were higher at east‐facing edges, and the difference in microclimate between the two edge orientations increased through early morning. For both species, butterflies placed at east‐facing edges flew earlier than butterflies at west‐facing edges. Colias eurytheme, an open‐habitat species, tended to move toward the treated forest during initial flight, while movements of Neophasia menapia, a forest‐dwelling species, did not differ from random flight. Our results indicate that butterflies respond to microclimatic factors associated with restoration treatments, while responses to structural changes in habitat vary among species, based on habitat and food plant preferences. These changes in forest structure and microclimate may affect the distribution of many mobile invertebrates in forested landscapes undergoing restoration treatments.     

Disrupted phylogeographical microsatellite and chloroplast DNA patterns indicate a vicariance rather than long‐distance dispersal origin for the disjunct distribution of the Chilean endemic Dioscorea biloba (Dioscoreaceae) around the Atacama Desert

Aim The Chilean endemic Dioscorea biloba (Dioscoreaceae) is a dioecious geophyte that shows a remarkable 600 km north–south disjunction in the peripheral arid area of the Atacama Desert. Its restricted present‐day distribution and probable Neogene origin indicate that its populations have a history linked to that of the Atacama Desert, making this an ideal model species with which to investigate the biogeography of the region. Location Chile, Atacama Desert and peripheral arid area. Methods Two hundred and seventy‐five individuals from nine populations were genotyped for seven nuclear microsatellite loci, and plastid trnL–F and trnT–L sequences were obtained for a representative subset of these. Analyses included the estimation of genetic diversity and population structure through clustering, Bayesian and analysis of molecular variance analyses, and statistical parsimony networks of chloroplast haplotypes. Isolation by distance was tested against alternative dispersal hypotheses. Results Microsatellite markers revealed moderate to high levels of genetic diversity within populations, with those from the southern Limarí Valley showing the highest values and northern populations showing less exclusive alleles. Bayesian analysis of microsatellite data identified three genetic groups that corresponded to geographical ranges. Chloroplast phylogeography revealed no haplotypes shared between northern and southern ranges, and little haplotype sharing between the two neighbouring southern valleys. Dispersal models suggested the presence of extinct hypothetical populations between the southern and northern ranges. Main conclusions Our results are consistent with prolonged isolation of the northern and southern groups, mediated by the life‐history traits of the species. Significant isolation was revealed at both large and moderate distances as gene flow was not evident even between neighbouring valleys. Bayesian analyses of microsatellite and chloroplast haplotype diversity identified the southern area of Limarí as the probable area of origin of the species. Our data do not support recent dispersal of D. biloba from the southern range into Antofagasta, but indicate the fragmentation of an earlier wider range, concomitant with the Pliocene–Pleistocene climatic oscillations, with subsequent extinctions of the Atacama Desert populations and the divergence of the peripheral ones as a consequence of genetic drift.     

Triggering Closure of a Sialic Acid TRAP Transporter Substrate Binding Protein through Binding of Natural or Artificial Substrates

The pathogens Vibrio cholerae and Haemophilus influenzae use tripartite ATP-independent periplasmic transporters (TRAPs) to scavenge sialic acid from host tissues. They use it as a nutrient or to evade the innate immune system by sialylating surface lipopolysaccharides. An essential component of TRAP transporters is a periplasmic substrate binding protein (SBP). Without substrate, the SBP has been proposed to rest in an open-state, which is not recognised by the transporter. Substrate binding induces a conformational change of the SBP and it is thought that this closed state is recognised by the transporter, triggering substrate translocation. Here we use real time single molecule FRET experiments and crystallography to investigate the open- to closed-state transition of VcSiaP, the SBP of the sialic acid TRAP transporter from V. cholerae. We show that the conformational switching of VcSiaP is strictly substrate induced, confirming an important aspect of the proposed transport mechanism. Two new crystal structures of VcSiaP provide insights into the closing mechanism. While the first structure contains the natural ligand, sialic acid, the second structure contains an artificial peptide in the sialic acid binding site. Together, the two structures suggest that the ligand itself stabilises the closed state and that SBP closure is triggered by physically bridging the gap between the two lobes of the SBP. Finally, we demonstrate that the affinity for the artificial peptide substrate can be substantially increased by varying its amino acid sequence and by this, serve as a starting point for the development of peptide-based inhibitors of TRAP transporters.     

An Eight Amino Acid Segment Controls Oligomerization and Preferred Conformation of the two Non-visual Arrestins

G protein coupled receptors signal through G proteins or arrestins. A long-standing mystery in the field is why vertebrates have two non-visual arrestins, arrestin-2 and arrestin-3. These isoforms are ~75% identical and 85% similar; each binds numerous receptors, and appear to have many redundant functions, as demonstrated by studies of knockout mice. We previously showed that arrestin-3 can be activated by inositol-hexakisphosphate (IP₆). IP₆ interacts with the receptor-binding surface of arrestin-3, induces arrestin-3 oligomerization, and this oligomer stabilizes the active conformation of arrestin-3. Here, we compared the impact of IP₆ on oligomerization and conformational equilibrium of the highly homologous arrestin-2 and arrestin-3 and found that these two isoforms are regulated differently. In the presence of IP₆, arrestin-2 forms “infinite” chains, where each promoter remains in the basal conformation. In contrast, full length and truncated arrestin-3 form trimers and higher-order oligomers in the presence of IP₆; we showed previously that trimeric state induces arrestin-3 activation (Chen et al., 2017). Thus, in response to IP₆, the two non-visual arrestins oligomerize in different ways in distinct conformations. We identified an insertion of eight residues that is conserved across arrestin-2 homologs, but absent in arrestin-3 that likely accounts for the differences in the IP₆ effect. Because IP₆ is ubiquitously present in cells, this suggests physiological consequences, including differences in arrestin-2/3 trafficking and JNK3 activation. The functional differences between two non-visual arrestins are in part determined by distinct modes of their oligomerization. The mode of oligomerization might regulate the function of other signaling proteins.