Can the Cyanobacterial Carbon-Concentrating Mechanism Increase Photosynthesis in Crop Species? A Theoretical Analysis

Experimental elevation of [CO₂] around C₃ crops in the field has been shown to increase yields by suppressing the Rubisco oxygenase reaction and, in turn, photorespiration. Bioengineering a cyanobacterial carbon-concentrating mechanism (CCM) into C₃ crop species provides a potential means of elevating [CO₂] at Rubisco, thereby decreasing photorespiration and increasing photosynthetic efficiency and yield. The cyanobacterial CCM is an attractive alternative relative to other CCMs, because its features do not require anatomical changes to leaf tissue. However, the potential benefits of engineering the entire CCM into a C₃ leaf are unexamined. Here, a CO₂ and HCO₃⁻ diffusion-reaction model is developed to examine how components of the cyanobacterial CCM affect leaf light-saturated CO₂ uptake (A_sat) and to determine whether a different Rubisco isoform would perform better in a leaf with a cyanobacterial CCM. The results show that the addition of carboxysomes without other CCM components substantially decreases A_sat and that the best first step is the addition of HCO₃⁻ transporters, as a single HCO₃⁻ transporter increased modeled A_sat by 9%. Addition of all major CCM components increased A_sat from 24 to 38 µmol m⁻² s⁻¹. Several Rubisco isoforms were compared in the model, and increasing ribulose bisphosphate regeneration rate will allow for further improvements by using a Rubisco isoform adapted to high [CO₂]. Results from field studies that artificially raise [CO₂] suggest that this 60% increase in A_sat could result in a 36% to 60% increase in yield.C₃ species include the major grain crops rice (Oryza sativa) and wheat (Triticum aestivum) and overall accounted for approximately 75% of all primary foodstuff production in 2012 (FAOSTAT, 2013). The yield of many crop species has been substantially improved through breeding and agronomy, but advancement in yield has substantially slowed in many of the major C₃ crops in the last decade, suggesting that limits on yield improvement using these techniques are being reached and that other approaches are needed (Long and Ort, 2010; Ray et al., 2012).One largely unexploited approach would be to improve the efficiency of photosynthesis in these species (Zhu et al., 2010). The photosynthetic enzyme Rubisco catalyzes the reaction of CO₂ with ribulose bisphosphate (RuBP), which eventually forms carbohydrates. However, Rubisco will also react with oxygen as the first step in photorespiration. This reaction is considered wasteful, since energy is consumed to recover RuBP and CO₂ is lost in the process. In C₃ plants at 25°C and current atmospheric [CO₂], photorespiration results in an approximately 30% decrease in net carbon assimilation (Zhu et al., 2010). Thus, it is a large inefficiency in carbon uptake and a target for improvement.Since CO₂ and oxygen act competitively at Rubisco, photorespiration can be decreased by increasing [CO₂] around Rubisco. That this will increase yield is demonstrated by the many studies that have artificially increased atmospheric [CO₂] around C₃ crops growing in the field (Kimball et al., 2002; Long et al., 2006b). Other photosynthetic organisms have evolved mechanisms to internally elevate [CO₂] at Rubisco to decrease or eliminate photorespiration. Such carbon-concentrating mechanisms (CCMs) include C₄ photosynthesis, as in maize (Zea mays), and the carboxysome and pyrenoid CCMs of single-celled cyanobacteria and algae. The C₄ pathway requires the addition of the photosynthetic C₄ dicarboxylate cycle and inner photosynthetic cells (i.e. bundle sheath), where Rubisco is localized. Converting a C₃ crop to a C₄ crop will require a coordination of changes in photosynthetic tissue differentiation and enzyme and transporter localization. In contrast, cyanobacteria achieve the same effect in a single cell by localizing Rubisco to specialized subcellular compartments called carboxysomes, so in theory they would require fewer changes. Carboxysomes are polyhedral bodies with a protein shell that encloses carbonic anhydrase (CA) and Rubisco packed in an ordered or semiordered array (Long et al., 2007; Yeates et al., 2011). Bicarbonate is actively transported from the environment into the cytosol of the cyanobacteria, and CO₂ in the cytosol is actively hydrated to HCO₃⁻ using NADH. CO₂ is also hydrated to HCO₃⁻, which serves to increase the [CO₂] gradient between the medium and cytosol, increasing CO₂ flux, and also serves to refix CO₂ that leaks from the carboxysome. Since the cytosol lacks CA and the plasma membrane has low permeability to HCO₃⁻, a high cytosolic [HCO₃⁻] far from equilibrium with [CO₂] is achieved. Bicarbonate diffuses through the protein shell of the carboxysome, and since CA is localized to the inner side of the shell, it is rapidly converted to CO₂, given the disequilibrium. The resulting high [CO₂] around Rubisco inside the carboxysome accelerates carboxylation and competitively inhibits the oxygenation reaction (for review, see Price et al., 2008, 2011, 2013; Espie and Kimber, 2011).The C₄ pathway has been well characterized, and several projects are attempting to engineer it into C₃ plants with some success (Slewinski, 2013). However, a primary obstacle has been achieving the necessary two tissue types with the correct localization of the key enzymes (Covshoff and Hibberd, 2012). In this regard, cyanobacterial CCM may provide an attractive parallel approach to eliminating photorespiration in C₃ plants for two reasons. First, the biochemical, structural, and genetic components of the CCM are well understood, in that all of the necessary proteins and their genes have been identified. Second, chloroplasts of higher plants evolved from a common ancestor with modern cyanobacteria (Raven and Allen, 2003) and, therefore, are structurally similar. Thus, engineering carboxysomes into the chloroplast could involve introducing an operon containing the genes associated with the cyanobacterial CCM into the chloroplast genome.There are, however, multiple proteins in the cyanobacterial CCM, and simultaneously transforming all of the required genes into an organism may be particularly challenging. Furthermore, some of the proteins appear to have a similar function, and others may be deleterious if introduced without the full apparatus. A random sequence of gene stacking would likely be inefficient, while the addition of some genes may simply be unnecessary. However, the biophysical reactions involved are well understood, and there are some measurements of the kinetics of the enzymatic reactions and transporters. With this information, a mathematical model can be created to simulate the CCM. Such a model will allow deduction of the minimal component set necessary for an improvement of leaf photosynthetic efficiency and identify a logical sequence of gene additions to deliver progressive improvements and avoid any lethal effects. This model will also be used to determine which aspects of the CCM exert the most control over the overall process of photosynthetic CO₂ assimilation, information that can then be used to optimize the CCM, help identify the ideal set of components, or identify parameters that need to be more accurately measured in order to improve the effectiveness of the CCM model. Similar kinetic models have been applied to propose systems optimization of the Calvin cycle when plants are grown in elevated [CO₂] (Zhu et al., 2007), of the whole C₃ photosynthetic system (Zhu et al., 2013), C₄ photosynthesis (Yu et al., 2014), and to determine the mechanistic basis of mesophyll conductance (Tholen and Zhu, 2011).This paper develops a kinetic model to determine the potential of the cyanobacterial CCM engineered into C₃ crops for improving photosynthesis by determining the necessary components and estimating the potential improvement of CO₂ assimilation rate and efficiency. There are four distinct features to the cyanobacterial CCM: (1) a carboxysome with internally localized Rubisco and CA; (2) active transport of HCO₃⁻ from the medium into the cyanobacterial cytosol (the equivalent compartment in higher plants is the stroma of the chloroplast); (3) active hydration of CO₂ to HCO₃⁻ within the cytosol; and (4) the absence of CA in the cyanobacterial cytosol, in contrast to the higher plant stroma, which contains high activities of CA. Cyanobacteria have three HCO₃⁻ transporters and two CO₂ hydration enzymes that have different kinetics and are induced under different conditions (Price et al., 2011). All of these enzymes were examined, giving a total of seven individual components (listed in Fig. 1A) to the full cyanobacterial CCM model. Because of the common ancestry between cyanobacteria and higher plant chloroplasts, the two have homologous membranes and compartments. Proteins were modeled within a C₃ leaf using locations equivalent to those in cyanobacteria. That is, bicarbonate transporters were localized to the inner chloroplast membrane, and carboxysomes were localized to the stroma. The CO₂ hydration enzymes are bound to the thylakoid and plasma membranes in cyanobacteria, but the reaction for both occurs within the cyanobacterial cytosol; therefore, in this model, hydration of CO₂ by these enzymes was localized to the stroma. This model was used to determine the necessity of each of the features noted above, potential improvements in light-saturated CO₂ uptake (A_sat; irradiance of 1,800 µmol photons m⁻² s⁻¹) that would be achieved on incorporation of each feature in turn, a possible sequence of gene additions that would give an incremental improvement, and the key components of the CCM. The model was also used to test the value of using higher plant isoforms of Rubisco versus prokaryotic isoforms adapted to incorporation within the carboxysome. Sources of uncertainty in the model are also defined.Open in a separate windowFigure 1.A_sat of leaf models with sequential addition of components of the cyanobacterial CCM. Each point represents a leaf that contains the component listed for that column and all of the components in the columns to the left of it. The columns represent the sequence of transformations that produce the fastest increase in A_sat assuming that it is not possible to simultaneously add carboxysomes and remove stromal CA and that it is not desirable to add CO₂ hydration enzymes before removal of stromal CA (A) and assuming that it is possible to simultaneously add carboxysomes and remove stromal CA (B).     

When Does an Alien Become a Native Species? A Vulnerable Native Mammal Recognizes and Responds to Its Long-Term Alien Predator

The impact of alien predators on native prey populations is often attributed to prey naiveté towards a novel threat. Yet evolutionary theory predicts that alien predators cannot remain eternally novel; prey species must either become extinct or learn and adapt to the new threat. As local enemies lose their naiveté and coexistence becomes possible, an introduced species must eventually become ‘native’. But when exactly does an alien become a native species? The dingo (Canis lupus dingo) was introduced to Australia about 4000 years ago, yet its native status remains disputed. To determine whether a vulnerable native mammal (Perameles nasuta) recognizes the close relative of the dingo, the domestic dog (Canis lupus familiaris), we surveyed local residents to determine levels of bandicoot visitation to yards with and without resident dogs. Bandicoots in this area regularly emerge from bushland to forage in residential yards at night, leaving behind tell-tale deep, conical diggings in lawns and garden beds. These diggings were less likely to appear at all, and appeared less frequently and in smaller quantities in yards with dogs than in yards with either resident cats (Felis catus) or no pets. Most dogs were kept indoors at night, meaning that bandicoots were not simply chased out of the yards or killed before they could leave diggings, but rather they recognized the threat posed by dogs and avoided those yards. Native Australian mammals have had thousands of years experience with wild dingoes, which are very closely related to domestic dogs. Our study suggests that these bandicoots may no longer be naïve towards dogs. We argue that the logical criterion for determining native status of a long-term alien species must be once its native enemies are no longer naïve.     

Uprooting and Burial of Invasive Alien Plants: A New Tool in Coastal Restoration?

Invasive alien plants are a problem for conservation management, and control of these species can be combined with habitat restoration. Subsoil burial of uprooted plants is a new method of mechanical control, which might be suitable in disturbed habitats. The method was tested in Rosa rugosa (Japanese Rose), an invasive shrub in north‐western Europe with negative effects on coastal biodiversity. Two months after uprooting and burial in dunes of north‐eastern Denmark, 89% of the 58 shrubs resprouted from roots and rhizomes; on average 41 resprouts per shrub. Resprout density was twice as high at former shrub margins compared with the center; resprouts were taller and originated from more superficial soil layers at the margin than in the center. Resprouting was negatively correlated with fragment depth, and no resprouts were observed from greater than 15 cm depth. The number of resprouts increased with fragment dry mass (0.5–168.5 g). After 18 months with harrowing the species was still resprouting, flowering, and fruiting, albeit with no difference between shrub margin and center. Resprouts were taller (26 cm) and coverage was higher (0–4%) after two compared with three times harrowing, whereas no difference was found in cover of native dune species (1–5%). The results show that even small fragments of R. rugosa resprout, and that resprouting persists despite repeated harrowing. Thus, careful subsoil burial of all fragments is necessary, special attention should be paid to the shrub margin, and follow‐up treatments are needed. The effectiveness of the burial method is discussed for restoration of coastal dunes.     

Does Seeding After Wildfires in Rangelands Reduce Erosion or Invasive Species?

Mitigation of ecological damage caused by rangeland wildfires has historically been an issue restricted to the western United States. It has focused on conservation of ecosystem function through reducing soil erosion and spread of invasive plants. Effectiveness of mitigation treatments has been debated recently. We reviewed recent literature to conduct a meta‐analysis of seeding after wildfires to determine if seedings may (1) protect ecosystems against soil erosion and (2) reduce invasion or abundance of undesirable nonnative plant species. Effectiveness of postfire seedings was examined in 8 erosion and 19 invasive species cases. Seeding has little effect on erosion during the first year after fire and is highly dependent upon initial establishment and coverage of species in successive years. Among all seeding cases, 28% reduced, 67% were neutral, and 5% increased invasive species abundance. Older seedings were more likely to show reductions in invasives than younger seedings. Seedings with high plant establishment were more likely to reduce invasives than those with low establishment. Studies are needed that examine (1) frequency of adequate establishment of postfire seedings and causal factors of success or failure, (2) long‐term impacts of seeding along a range of initial establishment and concomitant plant coverage over time as it relates to erosion and abundance of invasive plant species, and (3) auxiliary treatments designed to increase likelihood of germination and establishment given the inevitable variability of environmental conditions. These studies would aid land managers in deciding when postfire treatments are required and their likely level of success.     

Does the Order of Invasive Species Removal Matter? The Case of the Eagle and the Pig

Background

Invasive species are recognized as a primary driver of native species endangerment and their removal is often a key component of a conservation strategy. Removing invasive species is not always a straightforward task, however, especially when they interact with other species in complex ways to negatively influence native species. Because unintended consequences may arise if all invasive species cannot be removed simultaneously, the order of their removal is of paramount importance to ecological restoration. In the mid-1990s, three subspecies of the island fox Urocyon littoralis were driven to near extinction on the northern California Channel Islands owing to heightened predation by golden eagles Aquila chrysaetos. Eagles were lured to the islands by an abundant supply of feral pigs Sus scrofa and through the process of apparent competition pigs indirectly facilitated the decline in foxes. As a consequence, both pigs and eagles had to be removed to recover the critically endangered fox. Complete removal of pigs was problematic: removing pigs first could force eagles to concentrate on the remaining foxes, increasing their probability of extinction. Removing eagles first was difficult: eagles are not easily captured and lethal removal was politically distasteful.

Methodology/Principal Findings

Using prey remains collected from eagle nests both before and after the eradication of pigs, we show that one pair of eagles that eluded capture did indeed focus more on foxes. These results support the premise that if the threat of eagle predation had not been mitigated prior to pig removal, fox extinction would have been a more likely outcome.

Conclusions/Significance

If complete eradication of all interacting invasive species is not possible, the order in which they are removed requires careful consideration. If overlooked, unexpected consequences may result that could impede restoration.     

Does Cognitive Function Increase over Time in the Healthy Elderly?

Background

In dementia screening, most studies have focused on early cognitive impairment by comparing patients suffering from mild dementia or mild cognitive impairment with normal subjects. Few studies have focused on modifications over time of the cognitive function in the healthy elderly. The objective of the present study was to analyze the cognitive function changes of two different samples, born > 15 years apart.

Method

A first sample of 204 cognitively normal participants was recruited in the memory clinic of Broca hospital between 1991 and 1997. A second sample of 177 cognitively normal participants was recruited in 2008–2009 in the same institution. Both samples were from the same districts of Paris and were assessed with the same neuropsychological test battery. Mean cognitive test scores were compared between 1991 and 2008 samples, between < 80 years old and ≥ 80 years old in 1991 and 2008 samples, and finally between subjects < 80 year old of 1991 sample and subjects ≥ 80 years old of the 2008 sample. Means were compared with T-tests stratified on gender, age-groups and educational level.

Results

Cognitive scores were significantly higher in the 2008 sample. Participants < 80 years old outperformed those ≥ 80 in both samples. However, participants < 80 years old in 1991 sample and subjects ≥ 80 in the 2008 sample, born on average in 1923, performed mostly identically.

Conclusion

This study showed a significant increase of cognitive scores over time. Further, contemporary octogenarians in the later sample performed like septuagenarians in the former sample. These findings might be consistent with the increase in life expectancy and life span in good health. The study highlights the necessity to take into account factors which may contaminate and artificially inflate the age-related differences in favor of younger to the older adults.     

Alien Invasive Slider Turtle in Unpredicted Habitat: A Matter of Niche Shift or of Predictors Studied?

Background

Species Distribution Models (SDMs) aim on the characterization of a species'' ecological niche and project it into geographic space. The result is a map of the species'' potential distribution, which is, for instance, helpful to predict the capability of alien invasive species. With regard to alien invasive species, recently several authors observed a mismatch between potential distributions of native and invasive ranges derived from SDMs and, as an explanation, ecological niche shift during biological invasion has been suggested. We studied the physiologically well known Slider turtle from North America which today is widely distributed over the globe and address the issue of ecological niche shift versus choice of ecological predictors used for model building, i.e., by deriving SDMs using multiple sets of climatic predictor.

Principal Findings

In one SDM, predictors were used aiming to mirror the physiological limits of the Slider turtle. It was compared to numerous other models based on various sets of ecological predictors or predictors aiming at comprehensiveness. The SDM focusing on the study species'' physiological limits depicts the target species'' worldwide potential distribution better than any of the other approaches.

Conclusion

These results suggest that a natural history-driven understanding is crucial in developing statistical models of ecological niches (as SDMs) while “comprehensive” or “standard” sets of ecological predictors may be of limited use.     

Does Mutualism Drive the Invasion of Two Alien Species? The Case of Solenopsis invicta and Phenacoccus solenopsis

Although mutualism between ants and honeydew-producing hemipterans has been extensively recognized in ecosystem biology, however few attempts to test the hypothesis that mutualism between two alien species leads to the facilitation of the invasion process. To address this problem, we focus on the conditional mutualism between S. invicta and P. solenopsis by field investigations and indoor experiments. In the laboratory, ant colony growth increased significantly when ants had access to P. solenopsis and animal-based food. Honeydew produced by P. solenopsis also improved the survival of ant workers. In the field, colony density of P. solenopsis was significantly greater on plots with ants than on plots without ants. The number of mealybug mummies on plants without fire ants was almost three times that of plants with fire ants, indicating a strong effect of fire ants on mealybug survival. In addition, the presence of S. invicta successfully contributed to the spread of P. solenopsis. The quantity of honeydew consumption by S. invicta was significantly greater than that of a presumptive native ant, Tapinoma melanocephalum. When compared with the case without ant tending, mealybugs tended by ants matured earlier and their lifespan and reproduction increased. T. melanocephalum workers arrived at honeydew more quickly than S. invicta workers, while the number of foraging S. invicta workers on plants steadily increased, eventually exceeding that number of T. melanocephalum foragers. Overall, these results suggest that the conditional mutualism between S. invicta and P. solenopsis facilitates population growth and fitness of both species. S. invicta tends to acquire much more honeydew and drive away native ants, promoting their predominance. These results suggest that the higher foraging tempo of S. invicta may provide more effective protection of P. solenopsis than native ants. Thus mutualism between these two alien species may facilitate the invasion success of both species.     

Does Prison Crowding Predict Higher Rates of Substance Use Related Parole Violations? A Recurrent Events Multi-Level Survival Analysis

Objective

This administrative data-linkage cohort study examines the association between prison crowding and the rate of post-release parole violations in a random sample of prisoners released with parole conditions in California, for an observation period of two years (January 2003 through December 2004).

Background

Crowding overextends prison resources needed to adequately protect inmates and provide drug rehabilitation services. Violence and lack of access to treatment are known risk factors for drug use and substance use disorders. These and other psychosocial effects of crowding may lead to higher rates of recidivism in California parolees.

Methods

Rates of parole violation for parolees exposed to high and medium levels of prison crowding were compared to parolees with low prison crowding exposure. Hazard ratios (HRs) with 95% confidence intervals (CIs) were estimated using a Cox model for recurrent events. Our dataset included 13070 parolees in California, combining individual level parolee data with aggregate level crowding data for multilevel analysis.

Results

Comparing parolees exposed to high crowding with those exposed to low crowding, the effect sizes from greatest to least were absconding violations (HR 3.56 95% CI: 3.05–4.17), drug violations (HR 2.44 95% CI: 2.00–2.98), non-violent violations (HR 2.14 95% CI: 1.73–2.64), violent and serious violations (HR 1.88 95% CI: 1.45–2.43), and technical violations (HR 1.86 95% CI: 1.37–2.53).

Conclusions

Prison crowding predicted higher rates of parole violations after release from prison. The effect was magnitude-dependent and particularly strong for drug charges. Further research into whether adverse prison experiences, such as crowding, are associated with recidivism and drug use in particular may be warranted.     

Nonlinear Time Series Analysis of Nodulation Factor Induced Calcium Oscillations: Evidence for Deterministic Chaos?

Legume plants form beneficial symbiotic interactions with nitrogen fixing bacteria (called rhizobia), with the rhizobia being accommodated in unique structures on the roots of the host plant. The legume/rhizobial symbiosis is responsible for a significant proportion of the global biologically available nitrogen. The initiation of this symbiosis is governed by a characteristic calcium oscillation within the plant root hair cells and this signal is activated by the rhizobia. Recent analyses on calcium time series data have suggested that stochastic effects have a large role to play in defining the nature of the oscillations. The use of multiple nonlinear time series techniques, however, suggests an alternative interpretation, namely deterministic chaos. We provide an extensive, nonlinear time series analysis on the nature of this calcium oscillation response. We build up evidence through a series of techniques that test for determinism, quantify linear and nonlinear components, and measure the local divergence of the system. Chaos is common in nature and it seems plausible that properties of chaotic dynamics might be exploited by biological systems to control processes within the cell. Systems possessing chaotic control mechanisms are more robust in the sense that the enhanced flexibility allows more rapid response to environmental changes with less energetic costs. The desired behaviour could be most efficiently targeted in this manner, supporting some intriguing speculations about nonlinear mechanisms in biological signaling.     

How Reliable is the Untrained Eye in the Identification of an Invasive Species? The Case of Alien Bee-Hawking Yellow-Legged Hornet in Iberian Peninsula

Biological invasions cause great damage to native ecosystems, therefore, it is extremely important to take measures to contain the progress of existing invasions and prevent new ones. Here, we used the Species Distribution Models approach to compare two independent datasets for the invasive alien species the Yellow-legged hornet in the Iberian Peninsula. One dataset compiles occurrence records gathered by expert people (e.g. environmental services’ technical staff and researchers); and the other compiles occurrence records gathered by non-expert people (e.g. amateur entomologists, beekeepers). The main aim is to assess the effectiveness and reliability of the dataset managed by non-experts when comparing it to the dataset managed by experts. Our results showed a high degree of concordance and similarity between models. Thus, both datasets would have the same reliability to be used in management strategies for this species.     

Does Multimorbidity Influence the Occurrence Rates of Chronic Conditions? A Claims Data Based Comparison of Expected and Observed Prevalence Rates

Objective

Multimorbidity is a complex phenomenon with an almost endless number of possible disease combinations with unclear implications. One important aspect in analyzing the clustering of diseases is to distinguish between random coexistence and statistical dependency. We developed a model to account for random coexistence based on stochastic distribution. We analyzed if the number of diseases of the patients influences the occurrence rates of chronic conditions.

Methods

We analyzed claims data of 121,389 persons aged 65+ using a list of 46 chronic conditions. Expected prevalences were simulated by drawing without replacement from all observed diseases using observed overall prevalences as initial probability weights. To determine if a disease occurs more or less frequently than expected by chance we calculated observed-minus-expected deltas for each disease. We defined clinical relevance as |delta| ≥ 5.0%. 18 conditions were excluded because of a prevalence < 5.0%.

Results

We found that (1) two chronic conditions (e.g. hypertension) were more frequent than expected in patients with a low number of comorbidities; (2) four conditions (e.g. renal insufficiency) were more frequent in patients with many comorbidities; (3) six conditions (e.g. cancer) were less frequent with many comorbidities; and (4) 16 conditions had an average course of prevalences.

Conclusion

A growing extent of multimorbidity goes along with a rapid growth of prevalences. This is for the largest part merely a stochastic effect. If we account for this effect we find that only few diseases deviate from the expected prevalence curves. Causes for these deviations are discussed. Our approach also has methodological implications: Naive analyses of multimorbidity might easily be affected by bias, because the prevalence of all chronic conditions necessarily increases with a growing extent of multimorbidity. We should therefore always examine and discuss the stochastic interrelations between the chronic conditions we analyze.     

Does Testosterone Therapy Increase the Risk of Prostate Cancer?

ObjectiveTo review factors affecting use of testosterone therapy for hypogonadism including the persistent controversial link between testosterone therapy and prostate cancer.MethodsWe reviewed studies investigating the relationship between testosterone therapy and prostate cancer progression and summarized strategies for hypogonadism management and prostate monitoring.ResultsTrials of up to 36 months in length and longitudinal studies consistently fail to demonstrate an increased prostate cancer risk associated with increased testosterone levels. No evidence of an associated relationship between exogenous testosterone therapy and prostate cancer has emerged from clinical trials or adverse event reports. It does not appear that exogenous testosterone accumulates in the prostate or provokes major biologic change in the prostate gland. In addition, preliminary evidence indicates that low endogenous testosterone may confer an increased risk of prostate cancer.ConclusionsMounting evidence demonstrates that there is a lack of association between testosterone therapy and prostate cancer progression. Testosterone therapy may be prescribed for men for whom it was once not considered. Careful monitoring of patients with hypogonadism who are receiving testosterone therapy is imperative. Well-designed, large-scale prospective clinical trials are necessary to adequately address prostate safety in hypogonadal men receiving testosterone therapy. (Endocr Pract. 2008;14:904-911)     

Rewilding Shouldn’t Be Reactive: Fragas do Eume Natural Park in the Face of an Invasive Alien Species

Rewilding is growing worldwide as a conservation approach to face the restoration of all natural processes that are suppressed or degraded by human action. After plenty of theoretical discussion and some limited experimental practices, rewilding remained conceptually open and diverse with regard to its operational framework. However, little was discussed with regards invasive alien species (IAS) management within rewilding. Hence, the aim of this research is to bridge the gap between these two bodies of theory. To do so, this work explores, in situ, a protected area in which rewilding is discoursively expressed as a form of native forest conservation. Based on a qualitative approach, the results gather stakeholders’ discourses on the institutional advocacy for rewilding, expressed as a form of incentivizing land abandonment and hence leading to a decline in the plantation of invasive blue gums (Eucalyptus globulus). The research poses a discussion on the problematic assimilation that rewilding and IAS management may have when informally combined. Lastly, it is concluded that, when executed in coexistence with IAS, rewilding projects should elude reactive positions and, instead, formalize agreed restoration programs, so that conflictive IAS can be consensually treated together with landowners.     

Can Invasive Species Facilitate Native Species? Evidence of How, When, and Why These Impacts Occur

Although the predatory and competitive impacts of biological invasions are well documented, facilitation of native species by non-indigenous species is frequently overlooked. A search through recent ecological literature found that facilitative interactions between invasive and native species occur in a wide range of habitats, can have cascading effects across trophic levels, can re-structure communities, and can lead to evolutionary changes. These are critical findings that, until now, have been mostly absent from analyses of ecological impacts of biological invasions. Here I present evidence for several mechanisms that exemplify how exotic species can facilitate native species. These mechanisms include habitat modification, trophic subsidy, pollination, competitive release, and predatory release. Habitat modification is the most frequently documented mechanism, reflecting the drastic changes generated by the invasion of functionally novel habitat engineers. Further, I predict that facilitative impacts on native species will be most likely when invasive species provide a limiting resource, increase habitat complexity, functionally replace a native species, or ameliorate predation or competition. Finally, three types of facilitation (novel, substitutive, and indirect) define why exotic species can lead to facilitation of native species. It is evident that understanding biological invasions at the community and ecosystem levels will be more accurate if we integrate facilitative interactions into future ecological research. Since facilitative impacts of biological invasions can occur with native endangered species, and can have wide-ranging impacts, these results also have important implications for management, eradication, and restoration.Contribution Number 2293, Bodega Marine Laboratory, University of California at Davis.     

Does Fire Influence the Landscape-Scale Distribution of an Invasive Mesopredator?

Predation and fire shape the structure and function of ecosystems globally. However, studies exploring interactions between these two processes are rare, especially at large spatial scales. This knowledge gap is significant not only for ecological theory, but also in an applied context, because it limits the ability of landscape managers to predict the outcomes of manipulating fire and predators. We examined the influence of fire on the occurrence of an introduced and widespread mesopredator, the red fox (Vulpes vulpes), in semi-arid Australia. We used two extensive and complimentary datasets collected at two spatial scales. At the landscape-scale, we surveyed red foxes using sand-plots within 28 study landscapes – which incorporated variation in the diversity and proportional extent of fire-age classes – located across a 104 000 km² study area. At the site-scale, we surveyed red foxes using camera traps at 108 sites stratified along a century-long post-fire chronosequence (0–105 years) within a 6630 km² study area. Red foxes were widespread both at the landscape and site-scale. Fire did not influence fox distribution at either spatial scale, nor did other environmental variables that we measured. Our results show that red foxes exploit a broad range of environmental conditions within semi-arid Australia. The presence of red foxes throughout much of the landscape is likely to have significant implications for native fauna, particularly in recently burnt habitats where reduced cover may increase prey species’ predation risk.     

Does Tropical Forest Fragmentation Increase Long-Term Variability of Butterfly Communities?

Habitat fragmentation is a major driver of biodiversity loss. Yet, the overall effects of fragmentation on biodiversity may be obscured by differences in responses among species. These opposing responses to fragmentation may be manifest in higher variability in species richness and abundance (termed hyperdynamism), and in predictable changes in community composition. We tested whether forest fragmentation causes long-term hyperdynamism in butterfly communities, a taxon that naturally displays large variations in species richness and community composition. Using a dataset from an experimentally fragmented landscape in the central Amazon that spanned 11 years, we evaluated the effect of fragmentation on changes in species richness and community composition through time. Overall, adjusted species richness (adjusted for survey duration) did not differ between fragmented forest and intact forest. However, spatial and temporal variation of adjusted species richness was significantly higher in fragmented forests relative to intact forest. This variation was associated with changes in butterfly community composition, specifically lower proportions of understory shade species and higher proportions of edge species in fragmented forest. Analysis of rarefied species richness, estimated using indices of butterfly abundance, showed no differences between fragmented and intact forest plots in spatial or temporal variation. These results do not contradict the results from adjusted species richness, but rather suggest that higher variability in butterfly adjusted species richness may be explained by changes in butterfly abundance. Combined, these results indicate that butterfly communities in fragmented tropical forests are more variable than in intact forest, and that the natural variability of butterflies was not a buffer against the effects of fragmentation on community dynamics.     

Heterotrophic Compensation: A Possible Mechanism for Resilience of Coral Reefs to Global Warming or a Sign of Prolonged Stress?

Thermally induced bleaching has caused a global decline in corals and the frequency of such bleaching events will increase. Thermal bleaching severely disrupts the trophic behaviour of the coral holobiont, reducing the photosynthetically derived energy available to the coral host. In the short term this reduction in energy transfer from endosymbiotic algae results in an energy deficit for the coral host. If the bleaching event is short-lived then the coral may survive this energy deficit by depleting its lipid reserves, or by increasing heterotrophic energy acquisition. We show for the first time that the coral animal is capable of increasing the amount of heterotrophic carbon incorporated into its tissues for almost a year following bleaching. This prolonged heterotrophic compensation could be a sign of resilience or prolonged stress. If the heterotrophic compensation is in fact an acclimatization response, then this physiological response could act as a buffer from future bleaching by providing sufficient heterotrophic energy to compensate for photoautotrophic energy losses during bleaching, and potentially minimizing the effect of subsequent elevated temperature stresses. However, if the elevated incorporation of zooplankton is a sign that the effects of bleaching continue to be stressful on the holobiont, even after 11 months of recovery, then this physiological response would indicate that complete coral recovery requires more than 11 months to achieve. If coral bleaching becomes an annual global phenomenon by mid-century, then present temporal refugia will not be sufficient to allow coral colonies to recover between bleaching events and coral reefs will become increasingly less resilient to future climate change. If, however, increasing their sequestration of zooplankton-derived nutrition into their tissues over prolonged periods of time is a compensating mechanism, the impacts of annual bleaching may be reduced. Thus, some coral species may be better equipped to face repeated bleaching stress than previously thought.