Aspects of the biology of climbers in southern Africa

This study examines factors that may limit the abundance and distribution of climbers and the influence that climbers may have on the regeneration of forests. The abundance of climbing plants (climbers) was established over a soil nutrient gradient, under standardised light conditions. Abundance was found to be positively correlated with the potassium concentration and the soil S-value, but not with other nutrients. Thus, the association between climbers and soil nutrient levels is challenged. Instead the abundance of climbers was found to be positively correlated with tree canopy architecture and trellis availability. More climbers entered host trees with low canopies (< 15 m) than those with high canopies. Trees with low canopies had more climbers entering vertically into the canopy while trees with high canopies had more climbers entering the canopy horizontally. Evidence was found to suggest that climbers facilitate the entry of each other into tree canopies. Tree and climber saplings were grown under three nutrient and two light treatments to compare the relative growth rates of their terminal shoots under the different conditions. While climbers were found to have greater shoot extension rates than trees, they did not grow relatively faster than trees under any of the combination of treatments. Thus light levels and soil nutrient availability may not influence the competitive ability of climbers compared to trees. Three aspects of the carbon gain capacity (maximum photosynthetic rate, leaf nitrogen concentration and leaf water use efficiency) were compared between climbers and trees. While the climbers had a significantly higher leaf nitrogen concentration than trees, as well as higher leaf water use efficiency; the maximum carbon assimilation rates of climbers and trees did not differ. These differences between trees and climbers are slight and suggest that differences in growth rates between the two growth forms are largely due to differences in carbon allocation in trees (to support structures) and in climbers (shoot elongation), rather than carbon gain mechanisms. Patterns of canopy tree regeneration in gaps and sub-canopy plots were determined for lowland and highland forests to determine whether climbers influenced the regeneration of canopy trees. More canopy trees regenerate in the sub-canopy of highland forests, while in lowland forests treefall gaps are the major sites of canopy tree regeneration. These patterns of regeneration were found not to be related to the density of the ground layer, the extent of the lateral infill of the gap-forming trees or the abundance of woody climbers. Instead, a negative correlation was found between the percentage of regenerating canopy species and the density of the herbaceous and shrubby understory layer in both lowland and highland forests. Thus in both forests the understory layer has an important influence on the regeneration of canopy trees. The role of vertebrate herbivores may be important in providing the necessary release from suppressive effect of the dense understory layer and to enable the regeneration of canopy tree species in the lowland forests

“Gold Would Cure That”: Economic Feminism in Olive Harper’s A Fair Californian

In 1889, Minerva Press published a lost-race fantasy entitled A Fair Californian, by the controversial journalist, author, lecturer, and poet Olive Harper (Ellen Burrell D’Apery, 1842–1915). The novel incorporated its author’s beliefs about “economic feminism”, which advocated expanding economic opportunities for women, rather than on achieving women’s suffrage. There are obvious similarities between the novel and contemporary feminist utopian fiction, but Harper’s emphasis on economic opportunity for women (in particular, the novel’s protagonist, Dolores) clearly distinguishes A Fair Californian from the far more politics-focused work of more widely known feminist utopian writers

Profiles of visuospatial memory dysfunction in opioid exposed and dependent populations

Background . Chronic opioid exposure is common world-wide, but behavioural performance remains under-investigated. This study aimed to investigate visuospatial memory performance in opioid-exposed and dependent clinical populations and its associations with measures of intelligence and cognitive impulsivity. Methods . We recruited 109 participants: (i) patients with a history of opioid dependence due to chronic heroin use (n = 24), (ii) heroin users stabilised on methadone maintenance treatment (n = 29), (iii) participants with a history of chronic pain and prescribed tramadol and codeine (n = 28) and (iv) healthy controls (n = 28). The neuropsychological tasks from the Cambridge Neuropsychological Test Automated Battery included the Delayed Matching to Sample (DMS), Pattern Recognition Memory, Spatial Recognition Memory, Paired Associate Learning, Spatial Span Task, Spatial Working Memory and Cambridge Gambling Task. Pre-morbid general intelligence was assessed using the National Adult Reading Test. Results . As hypothesised, this study identified the differential effects of chronic heroin and methadone exposures on neuropsychological measures of visuospatial memory (p < 0.01) that were independent of injecting behaviour and dependence status. The study also identified an improvement in DMS performance (specifically at longer delays) when the methadone group was compared with the heroin group and also when the heroin group was stabilised onto methadone. Results identified differential effects of chronic heroin and methadone exposures on various neuropsychological measures of visuospatial memory independently from addiction severity measures, such as injecting behaviour and dependence status.PostprintPeer reviewe

Mating failure shapes the patterns of sperm precedence in an insect

Funding: University of St Andrews PhD Apprenticeship (VLB); Laidlaw Scholarship Programme (DB).Estimates of last male sperm precedence (P2) are often used to infer mechanisms of sperm competition, a form of post-copulatory sexual selection. However, high levels of mating failure (i.e. copulations resulting in no offspring) in a population can lead to misinterpretations of sperm competition mechanisms. Through simulations, García-González (2004) illustrated how mating failure could cause bimodal distributions of paternity with peaks at P2 = 0 and 1, under a random sperm mixing mechanism. Here, we demonstrate this effect empirically with the seed bug Lygaeus simulans, a species known to exhibit high levels of mating failure (40–60%), using a morphological marker to estimate paternity. Contrary to previous findings in a sister species, we did not find strong evidence for last male sperm precedence. There was a tendency towards last male precedence (P2 = 0.58) but within the expected range for random sperm mixing. Instead, P2 was highly variable, with a bimodal distribution, as predicted by García-González (2004). After taking mating failure into account, the strongest driver of paternity outcome was copulation duration. Furthermore, we found evidence that mating failure could partly be a female-associated trait. Some doubly-mated females were more likely to produce no offspring or produce offspring from two different sires than expected by chance. Therefore, some females are more prone to experience mating failure than others, a result that mirrors an earlier result in male L. simulans. Our results confirm that mating failure needs to be considered when interrogating mechanisms of post-copulatory sexual selection.Publisher PDFPeer reviewe

Sacramento River Predator Diet Analysis: A Comparative Study

This study examined diets of two predatory fish species, the native Sacramento Pikeminnow (Ptychocheilus grandis) and the introduced Striped Bass (Morone saxatilis), in the Sacramento River, California, USA. Both species have been implicated in native species declines through predation, eliciting our investigation of their diets in the Sacramento River. Sampling occurred between March and November 2017, and was conducted via hook and line on a 35-km reach near Chico, California. Habitat types sampled include engineered structures (water diversions and beam bridges), rip-rapped channel edges, and natural riverbank. Stomach contents were collected via gastric lavage and later processed using visual, gravimetric, and genetic techniques. Diets of Sacramento Pikeminnow and Striped Bass were highly similar as determined through index of relative importance and PERMANOVA modeling. Water temperature was the only variable that significantly affected diet composition. Results reflect similar dietary niches for both species in the Sacramento River

Can females choose to avoid mating failure in the seed bug Lygaeus simulans?

We thank the Natural Environmental Research Council (Ph.D. studentship to E.V.G.) and the Association for the Study of Animal Behaviour (Undergraduate Project Scholarship awarded to V.L.B.) for funding.It is becoming increasingly clear that copulation does not necessarily always lead to offspring production in many organisms, despite fertilization success presumably being under both strong natural and sexual selection. In the seed bug Lygaeus simulans, between 40% and 60% of copulations fail to produce offspring, with this ‘mating failure’ representing a significantly repeatable male-associated trait. Mating has been demonstrated to be costly in this species and, as such, we might expect females to minimize the chance of mating failure by displaying a preference for males with higher insemination success where possible. After assaying males for mating failure, we asked whether females preferred males with a history of successful inseminations versus unsuccessful inseminations in pairwise mate choice trials. Contrary to our expectations, females showed no preference for more successful over less successful males. Moreover, females showed no preference for larger males in the choice trials, even though larger males were significantly more likely to successfully inseminate females in the initial assay. This apparent lack of female precopulatory choice suggests that postcopulatory choice mechanisms may be key to mating failure in this species. However, this does not necessarily explain why females pay the cost of mating with males they will then reject via postcopulatory processes. More generally, our results suggest that mating failure may play a largely underappreciated role in mating systems evolution, influencing both the cost of choosiness, and the costs and benefits of polyandry.Publisher PDFPeer reviewe

The effect of stress on the expression of the amyloid precursor protein in rat brain

AbstractThe abnormal processing of the amyloid precursor protein (APP) is a pivotal event in the development of the unique pathology that defines Alzheimer's disease (AD). Stress, and the associated increase in corticosteroids, appear to accelerate brain ageing and may increase vulnerability to Alzheimer's disease via altered APP processing. In this study, rats were repeatedly exposed to an unavoidable stressor, an open elevated platform. Previous studies in this laboratory have shown that a single exposure produces a marked increase in plasma corticosterone levels but animals develop tolerance to this effect between 10 and 20 daily sessions. Twenty-four hours after stress, there was an increase in the ratio of the deglycosylated form of APP in the particulate fraction of the brain, which subsequently habituated after 20 days. The levels of soluble APP (APPs) tended to be lower in the stress groups compared to controls except for a significant increase in the hippocampus after 20 days of platform exposure. Since APPs is reported to have neurotrophic properties, this increased release may represent a neuroprotective response to repeated stress. It is possible that the ability to mount this response decreases with age thus increasing the vulnerability to stress-induced AD-related pathology

Studies on the effects of drugs on the properties of synaptosomes

1. Synaptosomes have been isolated from guiuea-pig cerebral cortex and their appearance and enzymic and respiratory properties found to be similar to those reported for synaptosomes by other workers. 2. The effects of the convulsants, strychnine and pentamethylene tetrazol, and the anticonvulsants, phenobarbitone and acetazolamide, on some of the properties of synaptosomes have been examined. 3. The resting respiratory rate of synaptosomes was found to be insensitive to the convulsants and anticonvulaants and to a variety of other compounds which affect excitable neuronal membranes *in vivo*. The possible significance of these results has been discussed. 4. The incorporation of 14C in to synaptosomes from (U-14C)-glucose was inhibited by pentamethylene tetrazol and enhanced by phenobarbitone. 5. The uptake of xylose, which did not seem to occur by means of a simple diffusion process, was unaffected by phenobarbitone and pentamethylene tetrazol. 6. The concentration of xylose in the synaptosomes, once xylose uptake was complete, was unaffected by 2, 4-dinitroplienol. 7. The release of osmotically active constituents from synaptosomes suspended in warm sucrose was very much reduced by phenobsrbitone at relatively low concentrations and by acetaszolamide at concentrations which were substantially greater than those found 'in vivo'. 8. 45 per cent of the Na+ and 27 per cent of the K+ was lost to the medium if freshly prepared synaptosomes were incubated in sucrose at 25&deg;C for 30 minutes, Phenobarbitone prevented the loss of these ions during the incubation. 9. Phenobarbitone had no effect on the release of xylose from synaptosomes which were suspended in warm sucrose

Table-like magnetocaloric effect in Gd56Ni15Al27Zr2 alloy and its field independence feature

In order to obtain “table-like” magnetocaloric effect (MCE), multiple-phase Gd56Ni15Al27Zr2 alloy was prepared by arc-melting followed by suck-casting method. Powder x-ray diffraction and calorimetric measurements reveal that the sample contains both glassy and crystalline phases. The fraction of the glassy phase is about 62%, estimated from the heat enthalpy of the crystallization. The crystalline phases, Gd2Al and GdNiAl further broadened the relatively wider magnetic entropy change (−ΔSM) peak of the amorphous phase, which resulted in the table-like MCE over a maximum temperature range of 52.5 K to 77.5 K. The plateau feature of the MCE was found to be nearly independent of the applied magnetic field from 3 T to 5 T. The maximum −ΔSMvalue of the MCE platforms is 6.0 J/kg K under applied magnetic field change of 5 T. Below 3 T, the field independence of the table-like feature disappears. The relatively large constant values of −ΔSM for the respective applied magnetic fields have promising applications in magnetic refrigeration using regenerative Ericsson cycle