Electrostatic interactions and hydrogen bond dynamics in chloride pumping by halorhodopsin

Translocation of negatively charged ions across cell membranes by ion pumps raises the question as to how protein interactions control the location and dynamics of the ion. Here we address this question by performing extensive molecular dynamics simulations of wild type and mutant halorhodopsin, a seven-helical transmembrane protein that translocates chloride ions upon light absorption. We find that inter-helical hydrogen bonds mediated by a key arginine group largely govern the dynamics of the protein and water groups coordinating the chloride ion.     

INVESTIGATING PROCESSES OF NEOTROPICAL RAIN FOREST TREE DIVERSIFICATION BY EXAMINING THE EVOLUTION AND HISTORICAL BIOGEOGRAPHY OF THE PROTIEAE (BURSERACEAE)

Andean uplift and the collision of North and South America are thought to have major implications for the diversification of the Neotropical biota. However, few studies have investigated how these geological events may have influenced diversification. We present a multilocus phylogeny of 102 Protieae taxa (73% of published species), sampled pantropically, to test hypotheses about the relative importance of dispersal, vicariance, habitat specialization, and biotic factors in the diversification of this ecologically dominant tribe of Neotropical trees. Bayesian fossil‐calibrated analyses date the Protieae stem at 55 Mya. Biogeographic analyses reconstruct an initial late Oligocene/early Miocene radiation in Amazonia for Neotropical Protieae, with several subsequent late Miocene dispersal events to Central America, the Caribbean, Brazil's Atlantic Forest, and the Chocó. Regional phylogenetic structure results indicate frequent dispersal among regions throughout the Miocene and many instances of more recent regional in situ speciation. Habitat specialization to white sand or flooded soils was common, especially in Amazonia. There was one significant increase in diversification rate coincident with colonization of the Neotropics, followed by a gradual decrease consistent with models of diversity‐dependent cladogenesis. Dispersal, biotic interactions, and habitat specialization are thus hypothesized to be the most important processes underlying the diversification of the Protieae.     

Thank you for not flowering: conservation genetics and gene flow analysis of native and non-native populations of Fraxinus (Oleaceae) in Ireland

The risks of gene flow between interfertile native and introduced plant populations are greatest when there is no spatial isolation of pollen clouds and phenological patterns overlap completely. Moreover, invasion probabilities are further increased if introduced populations are capable of producing seeds by selfing. Here we investigated the mating system and patterns of pollen-mediated gene flow among populations of native ash (Fraxinus excelsior) and mixed plantations of non-native ash (F. angustifolia and F. excelsior) as well as hybrid ash (F. excelsior × F. angustifolia) in Ireland. We analysed the flowering phenology of the mother trees and genotyped with six microsatellite loci in progeny arrays from 132 native and plantation trees (1493 seeds) and 444 potential parents. Paternity analyses suggested that plantation and native trees were pollinated by both native and introduced trees. No signs of significant selfing in the introduced trees were observed and no evidence of higher male reproductive success was found for introduced trees compared with native ones either. A small but significant genetic structure was found (φ_ft=0.05) and did not correspond to an isolation-by-distance pattern. However, we observed a significant temporal genetic structure related to the different phenological groups, especially with early and late flowering native trees; each phenological group was pollinated with distinctive pollen sources. Implications of these results are discussed in relation to the conservation and invasiveness of ash and the spread of resistance genes against pathogens such as the fungus Chalara fraxinea that is destroying common ash forests in Europe.     

Peripheral administration of oxytocin increases social affiliation in the naked mole-rat (Heterocephalus glaber)

The neuropeptide oxytocin regulates a wide variety of social behaviors across diverse species. However, the types of behaviors that are influenced by this hormone are constrained by the species in question and the social organization that a particular species exhibits. Therefore, the present experiments investigated behaviors regulated by oxytocin in a eusocial mammalian species by using the naked mole-rat (Heterocephalus glaber). In Experiment 1, adult non-breeding mole-rats were given intraperitoneal injections of either oxytocin (1 mg/kg or 10 mg/kg) or saline on alternate days. Animals were then returned to their colony and behavior was recorded for minutes 15–30 post-injection. Both doses of oxytocin increased huddling behavior during this time period. In Experiment 2, animals received intraperitoneal injections of either oxytocin (1 mg/kg), an oxytocin-receptor antagonist (0.1 mg/kg), a cocktail of oxytocin and the antagonist, or saline across 4 testing days in a counterbalanced design. Animals were placed in either a 2-chamber arena with a familiar conspecific or in a small chamber with 1 week old pups from their home colony and behaviors were recorded for minutes 15–30 post-injection. Oxytocin increased investigation of, and time spent in close proximity to, a familiar conspecific; these effects were blocked by the oxytocin antagonist. No effects were seen on pup-directed behavior. These data suggest that oxytocin is capable of modulating affiliative-like behavior in this eusocial species.     

A case of mistaken identity,Opuntia abjecta,long-lost in synonymy under the Caribbean species,O. triacantha,and a reassessment of the enigmatic O. cubensis

Opuntia abjecta and O. militaris have been placed in synonymy under the Caribbean species O. triacantha for the past 30 years. Recent molecular phylogenetic evidence has shown, however, that O. abjecta and O. triacantha are actually in two very different clades suggesting that the Floridian endemic O. abjecta should be recognized as a distinct species. Here, we summarize major morphological differences between O. abjecta and O. triacantha. We also include new sequence data from the rare Cuban taxon, O. militaris, in a molecular phylogenetic analysis to determine its relationship to O. triacantha and O. abjecta. We discuss the putative hybrid taxa O. cubensis and O. ochrocentra, which currently are treated as synonyms. We also show through analysis of morphological and molecular characters that these two taxa were derived from two independent origins from divergent maternal progenitors, confirming that O. ochrocentra should not be treated as synonymous with O. cubensis. A key is provided for identifying these taxonomically confusing taxa and their close relatives. This study emphasizes the distinctions among O. abjecta, O. militaris, and O. triacantha and illustrates that extreme caution must be employed when using herbarium specimens for identifying species of Opuntia. It also indicates that broad phytogeographic assumptions regarding species’ relationships in Opuntia may sometimes be misleading. Hybridization and polyploidy are common in Opuntia and have played a role in the formation of new species in this group as well. A neotype is here designated for O. triacantha.     

Bursera pereirae,a new species and generic record for the Cerrado complex of Brazil. Studies in neotropical Burseraceae XVIII

Bursera pereirae is described and illustrated, and an updated key to Bursera in South America is provided. This new species, which should be considered threatened, is the first record of Bursera for the Cerrado region and the only species of tribe Bursereae endemic to Brazil.     

Application of the Kwei equation to model the Tg behavior of binary blends of sugars and salts

Vitrification of sugar-based solutions plays an important role in cryopreservation, lyophilization, and the emerging field of anhydrous preservation. An understanding of the glass transition characteristics of such formulations is essential for determining an appropriate storage temperature to ensure an extended shelf life of vitrified products. To better understand the effect of salts on the glass transition temperature (T_g) of glass-forming sugars, we investigated several data-fitting models (Fox, Gordon–Taylor and Kwei) for sugar–salt formulations using data from the literature, as well as new data generated on blends of trehalose and choline dihydrogen phosphate (CDHP). CDHP has recently been shown to have promise as a stabilizing agent for proteins and DNA. The Kwei equation, which has a specific parameter characterizing intermolecular interactions, provides good fits to the T_g data for sugar–salt blends, and complements other commonly used models that are frequently used to model T_g data.     

Extended High Circular Polarization in the Orion Massive Star Forming Region: Implications for the Origin of Homochirality in the Solar System

We present a wide-field (∼6′ × 6′) and deep near-infrared (K _s band: 2.14 μm) circular polarization image in the Orion nebula, where massive stars and many low-mass stars are forming. Our results reveal that a high circular polarization region is spatially extended (∼0.4 pc) around the massive star-forming region, the BN/KL nebula. However, other regions, including the linearly polarized Orion bar, show no significant circular polarization. Most of the low-mass young stars do not show detectable extended structure in either linear or circular polarization, in contrast to the BN/KL nebula. If our solar system formed in a massive star-forming region and was irradiated by net circularly polarized radiation, then enantiomeric excesses could have been induced, through asymmetric photochemistry, in the parent bodies of the meteorites and subsequently delivered to Earth. These could then have played a role in the development of biological homochirality on Earth.