Dispersal and species’ responses to climate change

Dispersal is fundamental in determining biodiversity responses to rapid climate change, but recently acquired ecological and evolutionary knowledge is seldom accounted for in either predictive methods or conservation planning. We emphasise the accumulating evidence for direct and indirect impacts of climate change on dispersal. Additionally, evolutionary theory predicts increases in dispersal at expanding range margins, and this has been observed in a number of species. This multitude of ecological and evolutionary processes is likely to lead to complex responses of dispersal to climate change. As a result, improvement of models of species’ range changes will require greater realism in the representation of dispersal. Placing dispersal at the heart of our thinking will facilitate development of conservation strategies that are resilient to climate change, including landscape management and assisted colonisation. Synthesis This article seeks synthesis across the fields of dispersal ecology and evolution, species distribution modelling and conservation biology. Increasing effort focuses on understanding how dispersal influences species' responses to climate change. Importantly, though perhaps not broadly widely‐recognised, species' dispersal characteristics are themselves likely to alter during rapid climate change. We compile evidence for direct and indirect influences that climate change may have on dispersal, some ecological and others evolutionary. We emphasise the need for predictive modelling to account for this dispersal realism and highlight the need for conservation to make better use of our existing knowledge related to dispersal.     

Determination of the duty cycle of WLAN for realistic radio frequency electromagnetic field exposure assessment

Wireless Local Area Networks (WLANs) are commonly deployed in various environments. The WLAN data packets are not transmitted continuously but often worst-case exposure of WLAN is assessed, assuming 100% activity and leading to huge overestimations. Actual duty cycles of WLAN are thus of importance for time-averaging of exposure when checking compliance with international guidelines on limiting adverse health effects. In this paper, duty cycles of WLAN using Wi-Fi technology are determined for exposure assessment on large scale at 179 locations for different environments and activities (file transfer, video streaming, audio, surfing on the internet, etc.). The median duty cycle equals 1.4% and the 95th percentile is 10.4% (standard deviation SD = 6.4%). Largest duty cycles are observed in urban and industrial environments. For actual applications, the theoretical upper limit for the WLAN duty cycle is 69.8% and 94.7% for maximum and minimum physical data rate, respectively. For lower data rates, higher duty cycles will occur. Although counterintuitive at first sight, poor WLAN connections result in higher possible exposures. File transfer at maximum data rate results in median duty cycles of 47.6% (SD = 16%), while it results in median values of 91.5% (SD = 18%) at minimum data rate. Surfing and audio streaming are less intensively using the wireless medium and therefore have median duty cycles lower than 3.2% (SD = 0.5–7.5%). For a specific example, overestimations up to a factor 8 for electric fields occur, when considering 100% activity compared to realistic duty cycles.     

Evaluation of electro‐coagulation–flocculation for harvesting marine and freshwater microalgae

Although microalgae are considered as a promising feedstock for biofuels, the energy efficiency of the production process needs to be significantly improved. Due to their small size and low concentration in the culture medium, cost‐efficient harvesting of microalgae is a major challenge. In this study, the use of electro‐coagulation–flocculation (ECF) as a method for harvesting a freshwater (Chlorella vulgaris) and a marine (Phaeodactylum tricornutum) microalgal species is evaluated. ECF was shown to be more efficient using an aluminum anode than using an iron anode. Furthermore, it could be concluded that the efficiency of the ECF process can be substantially improved by reducing the initial pH and by increasing the turbulence in the microalgal suspension. Although higher current densities resulted in a more rapid flocculation of the microalgal suspension, power consumption, expressed per kg of microalgae harvested, and release of aluminum were lower when a lower current density was used. The aluminum content of the harvested microalgal biomass was less than 1% while the aluminum concentration in the process water was below 2 mg L⁻¹. Under optimal conditions, power consumption of the ECF process was around 2 kWh kg⁻¹ of microalgal biomass harvested for Chlorella vulgaris and ca. 0.3 kWh kg⁻¹ for Phaeodactylum tricornutum. Compared to centrifugation, ECF is thus more energy efficient. Because of the lower power consumption of ECF in seawater, ECF is a particularly attractive method for harvesting marine microalgae. Biotechnol. Bioeng. 2011;108: 2320–2329. © 2011 Wiley Periodicals, Inc.     

The role of preadaptation,propagule pressure and competition in the colonization of new habitats

To successfully colonize new habitats, organisms not only need to gain access to it, they also need to cope with the selective pressures imposed by the local biotic and abiotic conditions. The number of immigrants, the preadaptation to the local habitat and the presence of competitors are important factors determining the success of colonization. Here, using two experimental set-ups, we studied the effect of interspecific competition in combination with propagule pressure and preadaptation on the colonization success of new habitats. Our model system consisted of tomato plants (the novel habitat), the two-spotted spider mite Tetranychus urticae as our focal species and the red spider mite Tetranychus evansi as a competitor. Our results show that propagule pressure and preadaptation positively affect colonization success. More successful populations reach larger final population sizes either by having higher per capita growth rates (due to preadaptation effects) or by starting a population with a larger number of individuals. Although populations are more successful colonizing non-competitive environments than competitive ones, propagule pressure and preadaptation counteract the negative effects of competition, promoting colonization success. Our study shows the importance of propagule pressure and preadaptation for successful colonization of new habitats by providing the ability to cope with both the exigencies of new environments and the community context.     

Design and evaluation of a 6-mer amyloid-beta protein derived phage display library for molecular targeting of amyloid plaques in Alzheimer's disease: Comparison with two cyclic heptapeptides derived from a randomized phage display library

Amyloid plaques are the main molecular hallmark of Alzheimer's disease. Specific carriers are needed for molecular imaging and for specific drug delivery. In order to identify new low molecular weight amyloid plaque-specific ligands, the phage display technology was used to design short peptides that bind specifically to amyloid-beta protein, which is the principal component of amyloid plaques. For this purpose, a phage display library was designed from the amino acid sequence of amyloid-beta 1-42. Then, the diversity was increased by soft oligonucleotide-directed mutagenesis. This library was screened against amyloid-beta 1-42 and several phage clones were isolated. Their genomes were sequenced to identify the displayed peptides and their dissociation constants for amyloid-beta 1-42 binding were evaluated by ELISA. The two best peptides, which are derived from the C-terminus hydrophobic domain of amyloid-beta 1-42 that forms a beta-strand in amyloid fibers, were synthesized and biotinylated. After confirming their binding affinity for amyloid-beta 1-42 by ELISA, the specific interaction with amyloid plaques was validated by immunohistochemistry on brain sections harvested from a mouse model of Alzheimer's disease. The thioflavin T aggregation assay has furthermore shown that our peptides are able to inhibit the amyloid fiber formation. They are not toxic for neurons, and some of them are able to cross the blood-brain barrier after grafting to a magnetic resonance imaging contrast agent. To conclude, these peptides have high potential for molecular targeting of amyloid plaques, either as carriers of molecular imaging and therapeutic compounds or as amyloid fiber disrupting agents.     

High-resolution proxies for wood density variations in Terminalia superba

Background and Aims

Density is a crucial variable in forest and wood science and is evaluated by a multitude of methods. Direct gravimetric methods are mostly destructive and time-consuming. Therefore, faster and semi- to non-destructive indirect methods have been developed.

Methods

Profiles of wood density variations with a resolution of approx. 50 µm were derived from one-dimensional resistance drillings, two-dimensional neutron scans, and three-dimensional neutron and X-ray scans. All methods were applied on Terminalia superba Engl. & Diels, an African pioneer species which sometimes exhibits a brown heart (limba noir).

Key Results

The use of X-ray tomography combined with a reference material permitted direct estimates of wood density. These X-ray-derived densities overestimated gravimetrically determined densities non-significantly and showed high correlation (linear regression, R² = 0·995). When comparing X-ray densities with the attenuation coefficients of neutron scans and the amplitude of drilling resistance, a significant linear relation was found with the neutron attenuation coefficient (R² = 0·986) yet a weak relation with drilling resistance (R² = 0·243). When density patterns are compared, all three methods are capable of revealing the same trends. Differences are mainly due to the orientation of tree rings and the different characteristics of the indirect methods.

Conclusions

High-resolution X-ray computed tomography is a promising technique for research on wood cores and will be explored further on other temperate and tropical species. Further study on limba noir is necessary to reveal the causes of density variations and to determine how resistance drillings can be further refined.     

A role for Piwi and piRNAs in germ cell maintenance and transposon silencing in Zebrafish

Piwi proteins specify an animal-specific subclass of the Argonaute family that, in vertebrates, is specifically expressed in germ cells. We demonstrate that zebrafish Piwi (Ziwi) is expressed in both the male and the female gonad and is a component of a germline-specifying structure called nuage. Loss of Ziwi function results in a progressive loss of germ cells due to apoptosis during larval development. In animals that have reduced Ziwi function, germ cells are maintained but display abnormal levels of apoptosis in adults. In mammals, Piwi proteins associate with approximately 29-nucleotide-long, testis-specific RNA molecules called piRNAs. Here we show that zebrafish piRNAs are present in both ovary and testis. Many of these are derived from transposons, implicating a role for piRNAs in the silencing of repetitive elements in vertebrates. Furthermore, we show that piRNAs are Dicer independent and that their 3' end likely carries a 2'O-Methyl modification.     

Both Ca2+ -dependent and -independent pathways are involved in rat hepatic stellate cell contraction and intrahepatic hyperresponsiveness to methoxamine

In chronic liver injury, hepatic stellate cells (HSCs) have been implicated as regulators of sinusoidal vascular tone. We studied the relative role of Ca(2+)-dependent and Ca(2+)-independent contraction pathways in rat HSCs and correlated these findings to in situ perfused cirrhotic rat livers. Contraction of primary rat HSCs was studied by a stress-relaxed collagen lattice model. Dose-response curves to the Ca(2+) ionophore A-23187 and to the calmodulin/myosin light chain kinase inhibitor W-7 served to study Ca(2+)-dependent pathways. Y-27632, staurosporin, and calyculin (inhibitors of Rho kinase, protein kinase C, and myosin light chain phosphatase, respectively) were used to investigate Ca(2+)-independent pathways. The actomyosin interaction, the common end target, was inhibited by 2,3-butanedione monoxime. Additionally, the effects of W-7, Y-27632, and staurosporin on intrahepatic vascular resistance were evaluated by in situ perfusion of normal and thioacetamide-treated cirrhotic rat livers stimulated with methoxamine (n = 25 each). In vitro, HSC contraction was shown to be actomyosin based with a regulating role for both Ca(2+)-dependent and -independent pathways. Although the former seem important, an important auxiliary role for the latter was illustrated through their involvement in the phenomenon of "Ca(2+) sensitization." In vivo, preincubation of cirrhotic livers with Y-27632 (10(-4) M) and staurosporin (25 nM), more than with W-7 (10(-4) M), significantly reduced the hyperresponsiveness to methoxamine (10(-4) M) by -66.8 +/- 1.3%, -52.4 +/- 2.7%, and -28.7 +/- 2.8%, respectively, whereas in normal livers this was significantly less: -43.1 +/- 4.2%, -40.2 +/- 4.2%, and -3.8 +/- 6.3%, respectively. Taken together, these results suggest that HSC contraction is based on both Ca(2+)-dependent and -independent pathways, which were shown to be upregulated in the perfused cirrhotic liver, with a predominance of Ca(2+)-independent pathways.