Glutaminase deficiency in rod photoreceptors disrupts nonessential amino acid levels to activate the integrated stress response and induce rapid degeneration.

The bioenergetic demand of photoreceptors rivals that of cancer cells, and numerous metabolic similarities exist between these cells. Glutamine (Gln) anaplerosis via the tricarboxylic acid (TCA) cycle provides biosynthetic intermediates and is a hallmark of cancer metabolism. In this process, Gln is first converted to glutamate via glutaminase (GLS), which is a crucial pathway in many cancer cells. To date, no study has been undertaken to examine the role of Gln metabolism in vivo in photoreceptors. Here, mice lacking GLS in rod photoreceptors were generated. Animals lacking GLS experienced rapid photoreceptor degeneration with concomitant functional loss. Gln has multiple roles in metabolism including redox balance, biosynthesis of nucleotides and amino acids, and supplementing the TCA cycle. Few alterations were noted in redox balance. Unlabeled targeted metabolomics demonstrated few changes in glycolytic and TCA cycle intermediates, which corresponded with a lack of significant changes in mitochondrial function. GLS deficiency in rod photoreceptors did decrease the fractional labelling of TCA cycle intermediates when provided uniformly labeled 13C-Gln in vivo. However, supplementation with alpha-ketoglutarate provided only marginal rescue of photoreceptor degeneration. Nonessential amino acids, glutamate and aspartate, were decreased in the retina of mice lacking GLS in rod photoreceptors. In accordance with this amino acid deprivation, the integrated stress response (ISR) was found to be activated with decreased global protein synthesis. Importantly, supplementation with asparagine delayed photoreceptor degeneration to a greater degree than alpha-ketoglutarate. These data show that GLS-mediated Gln catabolism is essential for rod photoreceptor amino acid biosynthesis, function, and survival.

The mouse retinal pigment epithelium mounts an innate immune defense response following retinal detachment.

The retinal pigment epithelium (RPE) maintains photoreceptor viability and function, completes the visual cycle, and forms the outer blood-retinal barrier (oBRB). Loss of RPE function gives rise to several monogenic retinal dystrophies and contributes to age-related macular degeneration. Retinal detachment (RD) causes separation of the neurosensory retina from the underlying RPE, disrupting the functional and metabolic relationships between these layers. Although the retinal response to RD is highly studied, little is known about how the RPE responds to loss of this interaction. RNA sequencing (RNA-Seq) was used to compare normal and detached RPE in the C57BL6/J mouse. The naïve mouse RPE transcriptome was compared to previously published RPE signature gene lists and from the union of these 14 genes (Bmp4, Crim1, Degs1, Gja1, Itgav, Mfap3l, Pdpn, Ptgds, Rbp1, Rnf13, Rpe65, Slc4a2, Sulf1 and Ttr) representing a core signature gene set applicable across rodent and human RPE was derived. Gene ontology enrichment analysis (GOEA) of the mouse RPE transcriptome identified expected RPE features and functions, such as pigmentation, phagocytosis, lysosomal and proteasomal degradation of proteins, and barrier function. Differentially expressed genes (DEG) at 1 and 7 days post retinal detachment (dprd) were defined as mRNA with a significant (padj≤0.05) fold change (FC) of 0.67 ≥ FC ≥ 1.5 in detached versus naïve RPE. The RPE transcriptome exhibited dramatic changes at 1 dprd, with 2297 DEG identified. The KEGG pathways and biological process GO groups related to innate immune responses were significantly enriched. Lipocalin 2 (Lcn2) and several chemokines were upregulated, while numerous genes related to RPE functions, such as pigment synthesis, visual cycle, phagocytosis, and tight junctions were downregulated at 1 dprd. The response was largely transient, with only 18 significant DEG identified at 7 dprd, including upregulation of complement gene C4b. Validation studies confirmed RNA-Seq results. Thus, the RPE quickly downregulates cell-specific functions and mounts an innate immune defense response following RD. Our data demonstrate that the RPE contributes to the inflammatory response to RD and may play a role in attraction of immune cells to the subretinal space.

Metabolic Alterations Caused by Simultaneous Loss of HK2 and PKM2 Leads to Photoreceptor Dysfunction and Degeneration.

HK2 and PKM2 are two main regulators of aerobic glycolysis. Photoreceptors (PRs) use aerobic glycolysis to produce the biomass necessary for the daily renewal of their outer segments. Previous work has shown that HK2 and PKM2 are important for the normal function and long-term survival of PRs but are dispensable for PR maturation, and their individual loss has opposing effects on PR survival during acute nutrient deprivation. We generated double conditional (dcKO) mice lacking HK2 and PKM2 expression in rod PRs. Western blotting, immunofluorescence, optical coherence tomography, and electroretinography were used to characterize the phenotype of dcKO animals. Targeted and stable isotope tracing metabolomics, qRT-PCR, and retinal oxygen consumption were performed. We show that dcKO animals displayed early shortening of PR inner/outer segments, followed by loss of PRs with aging, much more rapidly than either knockout alone without functional loss as measured by ERG. Significant alterations to central glucose metabolism were observed without any apparent changes to mitochondrial function, prior to PR degeneration. Finally, PR survival following experimental retinal detachment was unchanged in dcKO animals as compared to wild-type animals. These data suggest that HK2 and PKM2 have differing roles in promoting PR neuroprotection and identifying them has important implications for developing therapeutic options for combating PR loss during retinal disease.

Rod photoreceptor-specific deletion of cytosolic aspartate aminotransferase, GOT1, causes retinal degeneration.

Photoreceptor cell death is the cause of vision loss in many forms of retinal disease. Metabolic dysfunction within the outer retina has been shown to be an underlying factor contributing to photoreceptor loss. Therefore, a comprehensive understanding of the metabolic pathways essential to photoreceptor health and function is key to identifying novel neuroprotective strategies. Glutamic-oxaloacetic transaminase 1 (Got1) encodes for a cytosolic aspartate aminotransferase that reversibly catalyzes the transfer of an amino group between glutamate and aspartate and is an important aspect of the malate-aspartate shuttle (MAS), which transfers reducing equivalents from the cytosol to the mitochondrial matrix. Previous work has demonstrated that the activity of this enzyme is highest in photoreceptor inner segments. Furthermore, ex vivo studies have demonstrated that the retina relies on aspartate aminotransferase for amino acid metabolism. Importantly, aspartate aminotransferase has been suggested to be an early biomarker of retinal degeneration in retinitis pigmentosa and a possible target for neuroprotection. In the present study, we characterized the effect of Got1 deletion on photoreceptor metabolism, function, and survival in vivo by using a rod photoreceptor-specific, Got1 knockout mouse model. Loss of the GOT1 enzyme from rod photoreceptors resulted in age-related photoreceptor degeneration with an accumulation of retinal aspartate and NADH and alterations in the expression of genes involved in the MAS, the tricarboxylic acid (TCA) cycle, and redox balance. Hence, GOT1 is critical to in vivo photoreceptor metabolism, function, and survival.

Hypoxia-Inducible Factor-1α in Rods Is Neuroprotective Following Retinal Detachment.

Purpose: Following retinal detachment (RD) photoreceptors (PRs) sustain hypoxic stress and eventually die. Hypoxia-inducible factor-1α (HIF-1α) plays a central role in cellular adaptation to hypoxia. The purpose of this study is to determine the necessity of HIF-1α on PR cell survival after RD. Methods: Experimental RD was created in mice by injection of hyaluronic acid (1%) into the subretinal space. Mice with conditional HIF-1α knockout in rods (denoted as HIF-1αΔrod) were used. HIF-1α expression in retinas was measured real-time polymerase chain reaction (RT-PCR) and Western blotting. PR cell death after RD was evaluated using TUNEL assay. Optical coherence tomography (OCT) and histology were used to evaluate retinal layer thicknesses and PR cell densities. A hypoxia signaling pathway PCR array was used to examine the expression of HIF-1α target genes after RD. Results: HIF-1α protein levels were significantly increased after RD, and depletion of HIF-1α in rods blunted this increase. A compensatory increase of HIF-2α protein was observed in HIF-1αΔrod mice. Conditional knockout (cKO) of HIF-1α in rods did not lead to any morphologic change in attached retinas but resulted in significantly increased PR cell loss after RD. HIF-1α cKO in rods altered the responses to retinal detachment for 25 out of 83 HIF-1α target genes that were highly enriched for genes involved in glycolysis. Conclusions: Rod-derived HIF-1α plays a key role in the PR response to RD, mediating the transcriptional activity of a battery of genes to promote PR cell survival.

Inflammatory resolution and vascular barrier restoration after retinal ischemia reperfusion injury.

BACKGROUND: Several retinal pathologies exhibit both inflammation and breakdown of the inner blood-retinal barrier (iBRB) resulting in vascular permeability, suggesting that treatments that trigger resolution of inflammation may also promote iBRB restoration. METHODS: Using the mouse retinal ischemia-reperfusion (IR) injury model, we followed the time course of neurodegeneration, inflammation, and iBRB disruption and repair to examine the relationship between resolution of inflammation and iBRB restoration and to determine if minocycline, a tetracycline derivative shown to reverse microglial activation, can hasten these processes. RESULTS: A 90-min ischemic insult followed by reperfusion in the retina induced cell apoptosis and inner retina thinning that progressed for approximately 2 weeks. IR increased vascular permeability within hours, which resolved between 3 and 4 weeks after injury. Increased vascular permeability coincided with alteration and loss of endothelial cell tight junction (TJ) protein content and disorganization of TJ protein complexes. Shunting of blood flow away from leaky vessels and dropout of leaky capillaries were eliminated as possible mechanisms for restoring the iBRB. Repletion of TJ protein contents occurred within 2 days after injury, long before restoration of the iBRB. In contrast, the eventual re-organization of TJ complexes at the cell border coincided with restoration of the barrier. A robust inflammatory response was evident a 1 day after IR and progressed to resolution over the 4-week time course. The inflammatory response included a rapid and transient infiltration of granulocytes and Ly6C+ classical inflammatory monocytes, a slow accumulation of Ly6Cneg monocyte/macrophages, and activation, proliferation, and mobilization of resident microglia. Extravasation of the majority of CD45+ leukocytes occurred from the superficial plexus. The presence of monocyte/macrophages and increased numbers of microglia were sustained until the iBRB was eventually restored. Intervention with minocycline to reverse microglial activation at 1 week after injury promoted early restoration of the iBRB coinciding with decreased expression of mRNAs for the microglial M1 markers TNF-α, IL-1ß, and Ptgs2 (Cox-2) and increased expression of secreted serine protease inhibitor Serpina3n mRNA. CONCLUSIONS: These results suggest that iBRB restoration occurs as TJ complexes are reorganized and that resolution of inflammation and restoration of the iBRB following retinal IR injury are functionally linked.

Conditional Knock out of High-Mobility Group Box 1 (HMGB1) in Rods Reduces Autophagy Activation after Retinal Detachment.

After retinal detachment (RD), the induction of autophagy protects photoreceptors (PR) from apoptotic cell death. The cytoplasmic high-mobility group box 1 (HMGB1) promotes autophagy. We previously demonstrated that the deletion of HMGB1 from rod PRs results in a more rapid death of these cells after RD. In this work, we tested the hypothesis that the lack of HMGB1 accelerates PR death after RD due to the reduced activation of protective autophagy in the retina after RD. The injection of 1% hyaluronic acid into the subretinal space was used to create acute RD in mice with a rhodopsin-Cre-mediated conditional knockout (cKO) of HMGB1 in rods (HMGB1Δrod) and littermate controls. RD sharply increased the number of apoptotic cells in the outer nuclear layer (ONL), and this number was further increased in HMGB1Δrod mouse retinas. The activation of autophagy after RD was reduced in the HMGB1Δrod mouse retinas compared to controls, as evidenced by diminished levels of autophagy regulatory proteins LC3-II, Beclin1, ATG5/12, and phospho-ATG16L1. The cKO of HMGB1 in rods increased the expression of Fas and the Bax/Bcl-2 ratio in detached retinas, promoting apoptotic cell death. In conclusion, endogenous HMGB1 facilitates autophagy activation in PR cells following RD to promote PR cell survival and reduce programmed apoptotic cell death.

Effects of nutrient addition on endophyte-associated grass invasion in a long-term, old-field community experiment.

Strictly vertically transmitted (hereditary) Epichloë spp. fungal endophytes are symbionts with cool-season pooid host grasses. Such endophytes may increase host invasiveness in the non-native, introduced ranges. However, because costs and benefits for the host can vary with the growing conditions, the endophyte may become locally or temporally extinct when costs outweigh benefits. Our long-term field experiment involved the introduction of seven Schedonorus pratensis (meadow fescue) cultivars hosting Epichloë uncinata endophyte, which represent host-grass populations differing in genetic backgrounds and Epichloë infection frequencies, to an unmanaged old field. In the first 6 years, the host grasses persisted but did not become invasive in the plant community, regardless of their endophyte infection frequency. Subsequently, we hypothesized that increasing nutrient availability would decrease endophyte costs and thus increase the host's success and abundance. We fertilized half of the plots for four additional years and re-examined S. pratensis invasiveness. We predicted that increased nutrient availability would increase S. pratensis abundance and E. uncinata frequency and concentration, as well as decrease plant community diversity, relative to unfertilized plots. Fertilization increased endophyte concentrations in three low-endophyte host populations. However, E. uncinata did not enable S. pratensis populations to achieve high abundance or to reduce plant community diversity in the old field, with or without fertilization. Thus, nutrient availabililty and host invasiveness appear to be decoupled in this study system.

Examining the Impacts of CO2 Concentration and Genetic Compatibility on Perennial Ryegrass-Epichloë festucae var lolii Interactions.

Perennial ryegrass (Lolium perenne) is the most cultivated cool-season grass worldwide with crucial roles in carbon fixation, turfgrass applications, and fodder for livestock. Lolium perenne forms a mutualism with the strictly vertically transmitted fungal endophyte, Epichloë festucae var lolii. The fungus produces alkaloids that protect the grass from herbivory, as well as conferring protection from drought and nutrient stress. The rising concentration of atmospheric CO2, a proximate cause of climatic change, is known to have many direct and indirect effects on plant growth. There is keen interest in how the nature of this plant-fungal interaction will change with climate change. Lolium perenne is an obligately outcrossing species, meaning that the genetic profile of the host is constantly being reshuffled. Meanwhile, the fungus is asexual implying both a relatively constant genetic profile and the potential for incompatible grass-fungus pairings. In this study, we used a single cultivar, "Alto", of L. perenne. Each plant was infected with one of four strains of the endophyte: AR1, AR37, NEA2, and Lp19 (the "common strain"). We outcrossed the Alto mothers with pollen from a number of individuals from different ryegrass cultivars to create more genetic diversity in the hosts. We collected seed such that we had replicate maternal half-sib families. Seed from each family was randomly allocated into the two levels of the CO2 treatment, 400 and 800 ppm. Elevated CO2 resulted in an c. 18% increase in plant biomass. AR37 produced higher fungal concentrations than other strains; NEA2 produced the lowest fungal concentrations. We did not find evidence of genetic incompatibility between the host plants and the fungal strains. We conducted untargeted metabolomics and quantitative proteomics to investigate the grass-fungus interactions between and within family and treatment groups. We identified a number of changes in both the proteome and metabalome. Taken together, our data set provides new understanding into the intricacy of the interaction between endophyte and host from multiple molecular levels and suggests opportunity to promote plant robustness and survivability in rising CO2 environmental conditions through application of bioprotective epichloid strains.

Hexokinase 2 is dispensable for photoreceptor development but is required for survival during aging and outer retinal stress.

Photoreceptor death is the ultimate cause of vision loss in many retinal degenerative conditions. Identifying novel therapeutic avenues for prolonging photoreceptor health and function has the potential to improve vision and quality of life for patients suffering from degenerative retinal disorders. Photoreceptors are metabolically unique among other neurons in that they process the majority of their glucose via aerobic glycolysis. One of the main regulators of aerobic glycolysis is hexokinase 2 (HK2). Beyond its enzymatic function of phosphorylating glucose to glucose-6-phosphate, HK2 has additional non-enzymatic roles, including the regulation of apoptotic signaling via AKT signaling. Determining the role of HK2 in photoreceptor homeostasis may identify novel signaling pathways that can be targeted with neuroprotective agents to boost photoreceptor survival during metabolic stress. Here we show that following experimental retinal detachment, p-AKT is upregulated and HK2 translocates to mitochondria. Inhibition of AKT phosphorylation in 661W photoreceptor-like cells results in translocation of mitochondrial HK2 to the cytoplasm, increased caspase activity, and decreased cell viability. Rod-photoreceptors lacking HK2 upregulate HK1 and appear to develop normally. Interestingly, we found that HK2-deficient photoreceptors are more susceptible to acute nutrient deprivation in the experimental retinal detachment model. Additionally, HK2 appears to be important for preserving photoreceptors during aging. We show that retinal glucose metabolism is largely unchanged after HK2 deletion, suggesting that the non-enzymatic role of HK2 is important for maintaining photoreceptor health. These results suggest that HK2 expression is critical for preserving photoreceptors during acute nutrient stress and aging. More specifically, p-AKT mediated translocation of HK2 to the mitochondrial surface may be critical for protecting photoreceptors from acute and chronic stress.

Loss of High-Mobility Group Box 1 (HMGB1) Protein in Rods Accelerates Rod Photoreceptor Degeneration After Retinal Detachment.

Purpose: Retinal detachment (RD) disrupts the nutritional support and oxygen delivery to photoreceptors (PRs), ultimately causing cell death. High-mobility group box 1 (HMGB1) can serve as an extracellular alarmin when released from stressed cells. PRs release HMGB1 after RD. The purpose of this study was to investigate the relationship between HMGB1 and PR survival after RD. Methods: Acute RD was created by injection of hyaluronic acid (1%) into the subretinal space in C57BL/6 mice and mice with a rhodopsin-Cre-mediated conditional knockout (cKO) of HMGB1 in rods (HMGB1ΔRod). Immunofluorescence (IF) in retinal sections was used to localize HMGB1, rhodopsin, and Iba-1 proteins. Optical coherence tomography and electroretinography were used to quantify retinal thickness and function, respectively. The morphology of the retina was assessed by hematoxylin and eosin. Results: HMGB1 protein was localized to the nuclei of all retinal neurons, including PRs, with cones staining more intensely than rods. HMGB1 protein was also found in the inner and outer segments of cones but not rods. Creation of RD caused a dramatic increase of HMGB1 protein IF in rods. cKO of HMGB1 in rods did not affect retinal structure or function. However, after RD, loss of rods and reduction in the thickness of the outer nuclear layer were significantly increased in the HMGB1ΔRod retinas as compared to the control. Interestingly, depletion of HMGB1 in rods did not affect the activation and mobilization of microglia/macrophages normally seen after RD. Conclusions: Increased HMGB1 expression in stressed rods may represent an intrinsic mechanism regulating their survival after RD.

Effects of elevated CO2 on competition between native and invasive grasses.

Elevated atmospheric CO2 concentration increases the performance of invasive plants relative to natives when grown in monoculture, but it is unclear how that will affect the relative competitive abilities per se of invasive and native grasses grown together. We tested competitive outcomes for four native and four invasive perennial C3 and C4 grasses under ambient (390 ppm) and elevated (700 or 1000 ppm) CO2 concentrations in the greenhouse with non-limiting water and nutrients. We predicted that elevated CO2 would increase the competitive suppression of native grasses by invasive grasses. To test this, we determined the relative interaction intensity of biomass allocation for natives grown alone vs. those grown in native-invasive species pairs. We also measured photosynthetic traits that contribute to plant invasiveness and may be affected by elevated CO2 concentrations for species pairs in mixture to determine native-invasive relative performance. We found no effect of CO2 for the aboveground biomass and tiller production measures of interaction intensity or for relative performance for most of the measured photosynthetic traits. In competition, the invaders nearly always outperform natives in biomass and tiller production, regardless of CO2 level. The results suggest that increasing CO2 concentration alone has little effect on grass competitive outcomes under controlled conditions.

Small molecule activation of metabolic enzyme pyruvate kinase muscle isozyme 2, PKM2, circumvents photoreceptor apoptosis.

Photoreceptor cell death is the ultimate cause of vision loss in many retinal disorders, and there is an unmet need for neuroprotective modalities to improve photoreceptor survival. Similar to cancer cells, photoreceptors maintain pyruvate kinase muscle isoform 2 (PKM2) expression, which is a critical regulator in aerobic glycolysis. Unlike PKM1, which has constitutively high catalytic activity, PKM2 is under complex regulation. Recently, we demonstrated that genetically reprogramming photoreceptor metabolism via PKM2-to-PKM1 substitution is a promising neuroprotective strategy. Here, we explored the neuroprotective effects of pharmacologically activating PKM2 via ML-265, a small molecule activator of PKM2, during acute outer retinal stress. We found that ML-265 increased PKM2 activity in 661 W cells and in vivo in rat eyes without affecting the expression of genes involved in glucose metabolism. ML-265 treatment did, however, alter metabolic intermediates of glucose metabolism and those necessary for biosynthesis in cultured cells. Long-term exposure to ML-265 did not result in decreased photoreceptor function or survival under baseline conditions. Notably, though, ML-265-treatment did reduce entrance into the apoptotic cascade in in vitro and in vivo models of outer retinal stress. These data suggest that reprogramming metabolism via activation of PKM2 is a novel, and promising, therapeutic strategy for photoreceptor neuroprotection.

Current and potential future distribution of the American dog tick (Dermacentor variabilis, Say) in North America.

The American dog tick (Dermacentor variabilis) is medically and economically important in North America. This species is found across central and eastern North America from the Gulf Coast of Mexico through southern Canada. In parts of this region, D. variabilis is a vector for pathogens that cause diseases in humans and animals. Our aim was to determine whether climate change would affect the distribution of the climatically suitable area for D. variabilis in North America, to aid monitoring for potential future spread of tick-borne pathogens. We developed a species distribution model for D. variabilis to project where climate will likely be suitable for the tick in North America using a maximum entropy method, occurrence records from museum and laboratory archives, and 10 environmental variables relevant to climate requirements for the tick. We used four emissions scenarios from the Intergovernmental Panel on Climate Change's Fifth Assessment Report and 10 climate models from the Coupled Model Intercomparison Project (phase 5) to estimate potential future climate suitability and determine how the tick's distribution could change. Our consensus model projected that the area of suitable climate in North America could increase from present by approximately 50% by 2070. In areas beyond the current northern limit of D. variabilis, climate could become more suitable for the tick than at present, possibly resulting in a northward expansion in Canada, but the potential suitability of the southern range of D. variabilis could decrease, depending on the region and climate model. Due to the ability of D. variabilis to harbor and transmit pathogens, a change in the distribution of this species could also affect the risk of human and animal diseases throughout North America, particularly in the northern range of the tick.

Photoreceptor metabolic reprogramming provides survival advantage in acute stress while causing chronic degeneration.

Photoreceptor death is the root cause of vision loss in many retinal disorders, and there is an unmet need for neuroprotective modalities to improve photoreceptor survival. The biosynthetic requirement of photoreceptors is among the highest in the body, and to meet this demand, photoreceptors maintain their ability to perform aerobic glycolysis. This highly regulated form of glycolysis allows cells to efficiently budget their metabolic needs and may be a critical link between photoreceptor function and survival. Pyruvate kinase muscle isozyme 2 (PKM2) is a key regulator of aerobic glycolysis. In the present study, we characterized the effect of PKM2 deletion on baseline functioning and survival of photoreceptors over time by utilizing a photoreceptor-specific, PKM2 knockout mouse model. We found that upon PKM2 deletion, PKM1 is upregulated in the outer retina and there is increased expression of genes involved in glucose metabolism, which led to chronic degenerative changes in the outer retina of these mice. We also discovered that this metabolic reprogramming provided a survival advantage to photoreceptors in an experimental model of retinal detachment. This study strongly supports the hypothesis that reprogramming metabolism may be a novel therapeutic strategy for photoreceptor neuroprotection during acute stress.

Assessing environmental attributes and effects of climate change on Sphagnum peatland distributions in North America using single- and multi-species models.

The fate of Northern peatlands under climate change is important because of their contribution to global carbon (C) storage. Peatlands are maintained via greater plant productivity (especially of Sphagnum species) than decomposition, and the processes involved are strongly mediated by climate. Although some studies predict that warming will relax constraints on decomposition, leading to decreased C sequestration, others predict increases in productivity and thus increases in C sequestration. We explored the lack of congruence between these predictions using single-species and integrated species distribution models as proxies for understanding the environmental correlates of North American Sphagnum peatland occurrence and how projected changes to the environment might influence these peatlands under climate change. Using Maximum entropy and BIOMOD modelling platforms, we generated single and integrated species distribution models for four common Sphagnum species in North America under current climate and a 2050 climate scenario projected by three general circulation models. We evaluated the environmental correlates of the models and explored the disparities in niche breadth, niche overlap, and climate suitability among current and future models. The models consistently show that Sphagnum peatland distribution is influenced by the balance between soil moisture deficit and temperature of the driest quarter-year. The models identify the east and west coasts of North America as the core climate space for Sphagnum peatland distribution. The models show that, at least in the immediate future, the area of suitable climate for Sphagnum peatland could expand. This result suggests that projected warming would be balanced effectively by the anticipated increase in precipitation, which would increase Sphagnum productivity.

Effects of elevated CO2 on photosynthetic traits of native and invasive C3 and C4 grasses.

BACKGROUND: Rising CO2 is expected to result in changes in plant traits that will increase plant productivity for some functional groups. Differential plant responses to elevated CO2 are likely to drive changes in competitive outcomes, with consequences for community structure and plant diversity. Many of the traits that are enhanced under elevated CO2 also confer competitive success to invasive species, and it is widely believed that invasive species will be more successful in high CO2. However, this is likely to depend on plant functional group, and evidence suggests that C3 plants tend to respond more strongly to CO2. RESULTS: We tested the hypothesis that invasive species would be more productive than noninvasive species under elevated CO2 and that stronger responses would be seen in C3 than C4 plants. We examined responses of 15 grass species (eight C3, seven C4), classified as noninvasive or invasive, to three levels of CO2 (390, 700 and 1000 ppm) in a closed chamber experiment. Elevated CO2 decreased conductance and %N and increased shoot biomass and C/N ratio across all species. Differences between invasive and noninvasive species depended on photosynthetic mechanism, with more differences for traits of C3 than C4 plants. Differences in trait means between invasive and noninvasive species tended to be similar across CO2 levels for many of the measured responses. However, noninvasive C3 grasses were more responsive than invasive C3 grasses in increasing tiller number and root biomass with elevated CO2, whereas noninvasive C4 grasses were more responsive than invasive C4 grasses in increasing shoot and root biomass with elevated CO2. For C3 grasses, these differences could be disadvantageous for noninvasive species under light competition, whereas for C4 grasses, noninvasive species may become better competitors with invasive species under increasing CO2. CONCLUSIONS: The ecophysiological mechanisms underlying invasion success of C3 and C4 grasses may differ. However, given that the direction of trait differences between invasive and noninvasive grasses remained consistent under ambient and elevated CO2, our results provide evidence that increases in CO2 are unlikely to change dramatically the competitive hierarchy of grasses in these functional groups.

Effects of Miscanthus × giganteus and Wheat Straw on Behavior, Survival, and Growth of Alphitobius diaperinus (Coleoptera: Tenebrionidae).

The lesser mealworm, Alphitobius diaperinus (Panzer), damages poultry barns, vectors poultry diseases, inhibits poultry weight gain, and consumes poultry feed. Management of the pest is a challenge because of its resistance to several insecticides, difficulty in treating infestations that can be concealed in locations within barns, and the high populations that occur around spilled poultry feed. However, few A. diaperinus were observed in Miscanthus × giganteus straw in a case where it was used as an alternative bedding material in open-floor poultry production in Ontario. To investigate this, we tested the effects of Miscanthus × giganteus and wheat straw on A. diaperinus behavior, survival, and growth in laboratory experiments. In these experiments, adult beetles preferred to inhabit wheat straw, whereas late-instar larvae preferred Miscanthus × giganteus . As a result, more adult beetles emerged from pupae in Miscanthus × giganteus than in wheat, but there was no difference in emerged beetle weight. Early-instar larvae survived and increased in weight at similar rates in both straw types. Thus, while adult A. diaperinus strongly preferred wheat straw given a choice, late-instar preference and pupae emergence suggest that Miscanthus × giganteus may not be useful for suppressing A. diaperinus populations.

Effects of the Epichloë fungal endophyte symbiosis with Schedonorus pratensis on host grass invasiveness.

Initial studies of grass-endophyte mutualisms using Schedonorus arundinaceus cultivar Kentucky-31 infected with the vertically transmitted endophyte Epichloë coenophiala found strong, positive endophyte effects on host-grass invasion success. However, more recent work using different cultivars of S. arundinaceus has cast doubt on the ubiquity of this effect, at least as it pertains to S. arundinaceus-E. coenophiala. We investigated the generality of previous work on vertically transmitted Epichloë-associated grass invasiveness by studying a pair of very closely related species: S. pratensis and E. uncinata. Seven cultivars of S. pratensis and two cultivars of S. arundinaceus that were developed with high- or low-endophyte infection rate were broadcast seeded into 2 × 2-m plots in a tilled, old-field grassland community in a completely randomized block design. Schedonorus abundance, endophyte infection rate, and co-occurring vegetation were sampled 3, 4, 5, and 6 years after establishment, and the aboveground invertebrate community was sampled in S. pratensis plots 3 and 4 years after establishment. Endophyte infection did not enable the host grass to achieve high abundance in the plant community. Contrary to expectations, high-endophyte S. pratensis increased plant richness relative to low-endophyte cultivars. However, as expected, high-endophyte S. pratensis marginally decreased invertebrate taxon richness. Endophyte effects on vegetation and invertebrate community composition were inconsistent among cultivars and were weaker than temporal effects. The effect of the grass-Epichloë symbiosis on diversity is not generalizable, but rather specific to species, cultivar, infection, and potentially site. Examining grass-endophyte systems using multiple cultivars and species replicated among sites will be important to determine the range of conditions in which endophyte associations benefit host grass performance and have subsequent effects on co-occurring biotic communities.

A framework to guide the conservation of species hybrids based on ethical and ecological considerations.

Species hybrids have long been undervalued in conservation and are often perceived as a threat to pure species. Recently, the conservation value of hybrids, especially those of natural origin, has gained recognition; however, hybrid conservation remains controversial. We reviewed hybrid management policies, including laws, regulations, and management protocols, from a variety of organizations, primarily in Canada and the United States. We found that many policies are based on limited ethical and ecological considerations and provide little opportunity for hybrid conservation. In most policies, hybrids are either unrepresented or considered a threat to conservation goals. This is problematic because our review of the hybrid conservation literature identified many ethical and ecological considerations relevant to determining the conservation value of a hybrid, all of which are management-context specific. We also noted a lack of discussion of the ethical considerations regarding hybrid conservation. Based on these findings, we created a policy framework outlining situations in which hybrids could be eligible for conservation in Canada and the United States. The framework comprises a decision tree that helps users determine whether a hybrid should be eligible for conservation based on multiple ecological and ethical considerations. The framework may be applied to any hybrid and is flexible in that it accommodates context-specific management by allowing different options if a hybrid is a threat to or could benefit conservation goals. The framework can inform policy makers and conservationists in decision-making processes regarding hybrid conservation by providing a systematic set of decision criteria and guidance on additional criteria to be considered in cases of uncertainty, and it fills a policy gap that limits current hybrid management.

Un Marco de Referencia para Guiar a la Conservación de Híbridos de Especies con base en Consideraciones Éticas y Ecológicas Jackiw et al. 12526 Resumen Los híbridos de especies han sido subvalorados en la conservación durante mucho tiempo y frecuentemente se perciben como una amenaza para las especies puras. Recientemente, el valor de conservación de los híbridos, especialmente aquellos de origen natural, ha ganado reconocimiento; sin embargo, la conservación de híbridos sigue siendo controversial. Revisamos las políticas de manejo de híbridos de una variedad de organizaciones, principalmente en Canadá y en los Estados Unidos, incluyendo las leyes, regulaciones y protocolos de manejo. Encontramos que muchas políticas se basan en consideraciones éticas y ecológicas limitadas y proporcionan pocas oportunidades para la conservación de híbridos. En la mayoría de las políticas, los híbridos están mal representados o se consideran una amenaza para los objetivos de conservación. Esto es problemático porque nuestra revisión de la literatura sobre la conservación de híbridos identificó muchas consideraciones éticas y ecológicas relevantes para la determinación del valor de conservación de un híbrido, de las cuales todas son específicas para el manejo de contexto específico. También notamos una falta de discusión sobre las consideraciones éticas con respecto a la conservación de híbridos. Con base en estos hallazgos, creamos un marco de referencia político que resalta situaciones en las que los híbridos pueden ser elegibles para la conservación en Canadá y en los Estados Unidos. El marco de referencia consta de un árbol de decisión que ayuda a los usuarios a determinar si un híbrido debe ser elegible para la conservación con base en múltiples consideraciones éticas y ecológicas. El marco de referencia puede aplicarse a cualquier híbrido y es flexible, ya que acomoda el manejo de contexto específico al permitir diferentes opciones si un híbrido es una amenaza o si podría beneficiar a los objetivos de conservación. El marco de referencia puede informar a quienes hacen las políticas y a los conservacionistas sobre los procesos de toma de decisiones con respecto a la conservación de híbridos al proporcionar un conjunto sistemático de criterios de decisión y una guía de los criterios adicionales a ser considerados en casos de incertidumbre y llena un vacío político que limita al manejo actual de los híbridos.