Topological analysis of the complex formed between neurokinin A and the NK2 tachykinin receptor

Neurokinin A stimulates physiological responses in the peripheral and central nervous systems upon interacting primarily with the tachykinin NK2 receptor (NK2R). In this study, the structure of NKA bound to the NK2R is characterised by use of fluorescence resonance energy transfer. Four fluorescent NKA analogues with Texas red introduced at amino acid positions 1, 4, 7 and 10 were prepared. When bound to a NK2R carrying enhanced green fluorescent protein at the N-terminus, all peptides reduce green fluorescent protein fluorescence from 10% to 50% due to energy transfer. The derived donor-acceptor distances are 46, 55, 59 and 69 A for the fluorophore linked to positions 1-10, respectively. The monotonic increase in distance clearly indicates that the peptide adopts an extended structure when bound to its receptor. The present data are used, in combination with rhodopsin structure, fluorescence studies, photoaffinity labelling and site-directed mutagenesis data to design a computer model of the NKA-NK2R complex. We propose that the N-terminus of NKA is exposed and accessible to the extracellular medium. Subsequent amino acids of the NKA peptide become progressively more buried residues up to approximately one-third of the transmembrane-spanning domain.     

Uncertainty in allometric exponent estimation: a case study in scaling metabolic rate with body mass

Many factors could influence the allometric scaling exponent β estimation, but have not been explored systematically. We investigated the influences of three factors on the estimate of β based on a data set of 626 species of basal metabolic rate and mass in mammals. The influence of sampling error was tested by re-sampling with different sample sizes using a Monte Carlo method. Small random errors were introduced to measured data to examine their influence on parameter estimations. The influence of analysis method was also evaluated by applying nonlinear and linear regressions to the original data. Results showed that a relative large sample size was required to lower statistical inference errors. When sample size n was 10% of the base population size (n=63), 35% of the samples supported β=2/3, 39% supported β=3/4, and 15% rejected β=0.711, even though the base population had a β=0.711. The controversy surrounding the estimation of β in the literature could be partially attributable to such small sample sizes in many studies. Measurement errors in body mass and base metabolic rate, especially in body mass, could largely increase alpha and beta errors. Analysis methods also affected parameter estimations. Nonlinear regressions provided better estimates of the scaling exponent that were significantly higher than these commonly estimated by linear regressions. This study demonstrated the importance of the quantity and quality of data as well as analysis method in power law analysis, raising caution in interpreting power law results. Meta-data synthesis using data from independent studies seems to be a proper approach in the future, but caution should be taken to make sure that such measurements are made using similar protocols.     

Ecological character displacement caused by reproductive interference

We carried out a theoretical investigation of whether ecological character displacement can be caused by reproductive interference. Our model assumes that a quantitative character is associated with both resource use and species recognition, and that heterospecific mating incurs costs. The model shows that ecological character displacement can occur as a consequence of evolution of premating isolation; this conclusion is based on the premise that resource competition is less intense between species than within species and that the ecological character also contributes to premating isolation. When resource competition between species is intense, extinction of either species may occur by competitive exclusion before ecological character divergence. Some observational studies have shown that character displacement in body size is associated with not only resources use but also species recognition. We propose that body size displacement can occur as a consequence of evolution of premating isolation. Our results suggest that ecological character displacement results from reproductive character displacement.     

Diets of Introduced Predators Using Stable Isotopes and Stomach Contents

ABSTRACT In a study of predation on ground-nesting birds at South San Francisco Bay (South Bay), California, USA, we analyzed stomach contents and stable isotopes of carbon and nitrogen to identify commonly consumed prey. We obtained the stomach contents from 206 nonnative red foxes (Vulpes vulpes regalis) collected in the South Bay area and Monterey County during 1995–2001 and from 68 feral cats (Felis silvestris) from the South Bay area during 2001–2002. We determined prey identity, biomass, and frequency, described seasonal diet trends, and derived an Index of Relative Importance. Avian species were the most frequent prey we found in the stomachs of red foxes from South Bay (61%), whereas small rodents were most frequent for red foxes from Monterey County (62%). Small rodents were the most frequent prey we found in feral cats (63%). Carbon and nitrogen isotopic signatures for foxes supported stomach content findings. However, isotope results indicated that cats received a majority of their energy from a source other than rodents and outside the natural system, which differed from the stomach content analysis. We demonstrated the utility of both stable isotope and stomach content analyses to establish a more complete understanding of predators' diets. This information aids natural resource managers in planning and evaluating future predator-removal programs and increases our understanding of the impacts of nonnative foxes and cats on native species.     

Greater Sage-Grouse Population Response to Energy Development and Habitat Loss

ABSTRACT Modification of landscapes due to energy development may alter both habitat use and vital rates of sensitive wildlife species. Greater sage-grouse (Centrocercus urophasianus) in the Powder River Basin (PRB) of Wyoming and Montana, USA, have experienced rapid, widespread changes to their habitat due to recent coal-bed natural gas (CBNG) development. We analyzed lek-count, habitat, and infrastructure data to assess how CBNG development and other landscape features influenced trends in the numbers of male sage-grouse observed and persistence of leks in the PRB. From 2001 to 2005, the number of males observed on leks in CBNG fields declined more rapidly than leks outside of CBNG. Of leks active in 1997 or later, only 38% of 26 leks in CBNG fields remained active by 2004–2005, compared to 84% of 250 leks outside CBNG fields. By 2005, leks in CBNG fields had 46% fewer males per active lek than leks outside of CBNG. Persistence of 110 leks was positively influenced by the proportion of sagebrush habitat within 6.4 km of the lek. After controlling for habitat, we found support for negative effects of CBNG development within 0.8 km and 3.2 km of the lek and for a time lag between CBNG development and lek disappearance. Current lease stipulations that prohibit development within 0.4 km of sage-grouse leks on federal lands are inadequate to ensure lek persistence and may result in impacts to breeding populations over larger areas. Seasonal restrictions on drilling and construction do not address impacts caused by loss of sagebrush and incursion of infrastructure that can affect populations over long periods of time. Regulatory agencies may need to increase spatial restrictions on development, industry may need to rapidly implement more effective mitigation measures, or both, to reduce impacts of CBNG development on sage-grouse populations in the PRB.     

Effect of chronic infusion of olanzapine and clozapine on food intake and body weight gain in male and female rats

Many antipsychotics cause weight gain in humans, but usually not in rats, when injected once or twice daily. Since blood antipsychotic half-lives are short in rats, compared to humans, chronic administration by constant infusion may be necessary to see consistent weight gain in rats. Male and female rats were implanted with mini-pumps for constant infusion of olanzapine (5 mg/kg/day), clozapine (10 mg/kg/day) or vehicle for 11 days. Food intake and body weight were measured; blood drug levels were measured by HPLC. Olanzapine increased food intake and body weight in female, but not male rats. Serum olanzapine concentrations were 30-35 ng/ml. Clozapine had no effect on food intake or body weight in female or male rats. Serum clozapine concentrations were about 75 ng/ml. Single-dose pharmacokinetic analysis revealed a serum terminal half-life of 1.2-1.5 h for each drug, with no sex differences. Despite the fact that olanzapine and clozapine promote weight gain in humans, these drugs appear to have minimal effects on body weight and food intake in rats, except for a modest effect of olanzapine in female rats, even though therapeutic levels of olanzapine are achieved in serum during chronic infusion. Hence, the rapid clearance of drug following single administration in previous studies cannot explain the weak or absent effects of antipsychotics on weight gain in this species. The rat thus appears to be an inadequate model of weight gain produced by some antipsychotics in humans.     

Preferences for masculinity in male bodies change across the menstrual cycle

In human females cyclic shifts in preference have been documented for odour and physical and behavioral male traits. Women prefer the smell of dominant males, more masculine male faces and men behaving more dominantly when at peak fertility than at other times in their menstrual cycle. Here we examine variation in preferences for body sexual dimorphism. Across two studies, both between- and within-participant, we show that women prefer greater masculinity in male bodies at times when their fertility is likely highest, in the follicular phase of their cycle. Shifts were seen when rating for a short-term but not when rating for a long-term relationship. In line with studies showing similar effects for facial sexual dimorphism, we also show that women prefer greater masculinity when they think themselves attractive than when they think themselves less attractive. These results indicate that women's preferences for sexual dimorphism in male bodies follow a similar pattern as found for sexual dimorphism and dominance in other domains and such differences in preference may serve a similar function. Cyclic preferences could influence women to select partners when most likely to become pregnant that possess traits that may be most likely to maximize their offspring's quality via attraction to masculinity or serve to help acquire investment via attraction to femininity.     

The impact of parasites on the life history evolution of guppies (Poecilia reticulata): the effects of host size on parasite virulence

There is large spatial and temporal variation in the Gyrodactylus parasite fauna across natural guppy (Poecilia reticulata) populations in Trinidad. The life history evolution of these fish could be affected differently in the various habitats depending on the local parasite selection pressure. Here, we experimentally infected three guppy populations with three gyrodactylid strains in the laboratory and monitored the infection by recording the number of parasites and host mortality in a full factorial design. The origin of the guppy population and parasite strain, and the size of the hosts explained significant variation in the survival of hosts. Larger fish carried the highest parasite loads and experienced the highest mortality rates, which suggests that parasite-mediated selection may favour smaller phenotypes, possibly counter-balancing selection pressures by gape-limited predators, mate choice and female fecundity. We observed significant variation in virulence between parasite strains with the captive-bred experimental strain (Gt3) causing the highest mortality of hosts whilst reaching only relatively low maximum burdens. This suggests that adaptations to the captive environment and/or inbreeding depression may alter the virulence of such captive-bred parasites. There were significant differences in survival rate between guppy populations, with infected guppies from the large population of the Lower Aripo River showing a higher survival rate than the fish from the small and genetically less diverse Upper Aripo River population.     

Filamentous temperature-sensitive Z (FtsZ) isoforms specifically interact in the chloroplasts and in the cytosol of Physcomitrella patens

Plant filamentous temperature-sensitive Z (FtsZ) proteins have been reported to be involved in biological processes related to plastids. However, the precise functions of distinct isoforms are still elusive. Here, the intracellular localization of the FtsZ1-1 isoform in a moss, Physcomitrella patens, was examined. Furthermore, the in vivo interaction behaviour of four distinct FtsZ isoforms was investigated. Localization studies of green fluorescent protein (GFP)-tagged FtsZ1-1 and fluorescence resonance energy transfer (FRET) analyses employing all dual combinations of four FtsZ isoforms were performed in transient protoplast transformation assays. FtsZ1-1 is localized to network structures inside the chloroplasts and exerts influence on plastid division. Interactions between FtsZ isoforms occur in distinct ordered structures in the chloroplasts as well as in the cytosol. The results expand the view of the involvement of Physcomitrella FtsZ proteins in chloroplast and cell division. It is concluded that duplication and diversification of ftsZ genes during plant evolution were the main prerequisites for the successful remodelling and integration of the prokaryotic FtsZ-dependent division mechanism into the cellular machineries of distinct complex processes in plants.     

Linking global warming to amphibian declines through its effects on female body condition and survivorship

There is general consensus that climate change has contributed to the observed decline, and extinction, of many amphibian species throughout the world. However, the mechanisms of its effects remain unclear. A laboratory study in 1980–1981 in which temperate zone amphibians that were prevented from hibernating had decreased growth rates, matured at a smaller size and had increased mortality compared with those that hibernated suggested one possible mechanism. I used data from a field study of common toads (Bufo bufo) in the UK, between 1983 and 2005, to determine whether this also occurs in the field. The results demonstrated two pathways by which global warming may cause amphibian declines. First, there was a clear relationship between a decline in the body condition of female common toads and the occurrence of warmer than average years since 1983. This was paralleled by a decline in their annual survival rates with the relationship between these two declines being highly correlated. Second, there was a significant relationship between the occurrence of mild winters and a reduction in female body size, resulting in fewer eggs being laid annually. Climate warming can, therefore, act on wild temperate zone amphibians by deleteriously affecting their physiology, during and after hibernation, causing increased female mortality rates and decreased fecundity in survivors.