Host-Synthesized Secondary Compounds Influence the In Vitro Interactions between Fungal Endophytes of Maize

Maize produces a suite of allelopathic secondary metabolites, the benzoxazinoids. 2,4-Dihydroxy-7-methoxy-2H-1,4-benzoxazin-3-one and 2,4-dihydroxy-2H-1,4-benzoxazin-3-one reside as glucosides in plant tissue and spontaneously degrade to 6-methoxy-2-benzoxazolinone (MBOA) and 2-benzoxazolinone (BOA) upon plant cell disruption. Several maize-associated fungi in the genus Fusarium can metabolize MBOA and BOA. BOA tolerance levels in 10 species of Fusarium and in the maize endophytes Nigrospora oryzae, Acremonium zeae, and Periconia macrospinosa were characterized. BOA tolerance ranged from 0.25 to 1.10 mg/ml among species. The influence of substrate alteration by one species on the subsequent growth of another species was assessed in the presence and absence of BOA. The colony area of the secondary colonizer in heterospecific interactions was compared to that in autospecific interactions (one isolate follows itself). In the presence of BOA, four of six secondary colonizers had greater growth (facilitation) when primary colonizers had higher BOA tolerance than the secondary colonizer. When the primary colonizer had lower tolerance than the secondary, three of six secondary colonizers were inhibited (competition) and three not significantly affected. In BOA-free medium, the number of isolates that were facilitated or inhibited was the same regardless of the tolerance level of the primary colonizer. Two of six secondary colonizers were facilitated, two inhibited, and two not significantly affected. This study provides some support for facilitation in stressful conditions under the Menge-Sutherland model. The results are not consistent with the corresponding prediction of competition in the absence of stress. The hypothesis drawn from these data is that in the presence of a toxin, fungal species that detoxify their substrate can enhance the colonization rate of less tolerant fungi.     

Do Red Deer Stags (Cervus elaphus) Use Roar Fundamental Frequency (F0) to Assess Rivals?

It is well established that in humans, male voices are disproportionately lower pitched than female voices, and recent studies suggest that this dimorphism in fundamental frequency (F0) results from both intrasexual (male competition) and intersexual (female mate choice) selection for lower pitched voices in men. However, comparative investigations indicate that sexual dimorphism in F0 is not universal in terrestrial mammals. In the highly polygynous and sexually dimorphic Scottish red deer Cervus elaphus scoticus, more successful males give sexually-selected calls (roars) with higher minimum F0s, suggesting that high, rather than low F0s advertise quality in this subspecies. While playback experiments demonstrated that oestrous females prefer higher pitched roars, the potential role of roar F0 in male competition remains untested. Here we examined the response of rutting red deer stags to playbacks of re-synthesized male roars with different median F0s. Our results show that stags’ responses (latencies and durations of attention, vocal and approach responses) were not affected by the F0 of the roar. This suggests that intrasexual selection is unlikely to strongly influence the evolution of roar F0 in Scottish red deer stags, and illustrates how the F0 of terrestrial mammal vocal sexual signals may be subject to different selection pressures across species. Further investigations on species characterized by different F0 profiles are needed to provide a comparative background for evolutionary interpretations of sex differences in mammalian vocalizations.     

Similar regulation of cell surface human T-cell leukemia virus type 1 (HTLV-1) surface binding proteins in cells highly and poorly transduced by HTLV-1-pseudotyped virions

Little is known about the requirements for human T-cell leukemia virus type 1 (HTLV-1) entry, including the identity of the cellular receptor(s). Previous studies have shown that although the HTLV receptor(s) are widely expressed on cell lines of various cell types from different species, cell lines differ dramatically in their susceptibility to HTLV-Env-mediated fusion. Human cells (293, HeLa, and primary CD4(+) T cells) showed higher levels of binding at saturation than rodent (NIH 3T3 and NRK) cells to an HTLV-1 SU immunoadhesin. A direct comparison of the binding of the HTLV-1 surface glycoprotein (SU) immunoadhesin and transduction by HTLV-1 pseudotyped virus revealed parallels between the level of binding and the titer for various cell lines. When cells were treated with phorbol myristate acetate (PMA), which down-modulates a number of cell surface molecules, the level of SU binding was markedly reduced. However, PMA treatment only slightly reduced the titer of murine leukemia virus(HTLV-1) on both highly susceptible and poorly susceptible cells. Treatment of target cells with trypsin greatly reduced binding, indicating that the majority of HTLV SU binding is to proteins. Polycations, which enhance the infectivity of several other retroviruses, inhibited HTLV-1 Env-mediated binding and entry on both human and rodent cells. These results suggest that factors other than the number of primary binding receptors are responsible for the differences in the titers of HTLV-1 pseudotypes between highly susceptible cells and poorly susceptible cells.     

A Role for p38 Stress-Activated Protein Kinase in Regulation of Cell Growth via TORC1

The target of rapamycin (TOR) complex 1 (TORC1) signaling pathway is a critical regulator of translation and cell growth. To identify novel components of this pathway, we performed a kinome-wide RNA interference (RNAi) screen in Drosophila melanogaster S2 cells. RNAi targeting components of the p38 stress-activated kinase cascade prevented the cell size increase elicited by depletion of the TOR negative regulator TSC2. In mammalian and Drosophila tissue culture, as well as in Drosophila ovaries ex vivo, p38-activating stresses, such as H₂O₂ and anisomycin, were able to activate TORC1. This stress-induced TORC1 activation could be blocked by RNAi against mitogen-activated protein kinase kinase 3 and 6 (MKK3/6) or by the overexpression of dominant negative Rags. Interestingly, p38 was also required for the activation of TORC1 in response to amino acids and growth factors. Genetic ablation either of p38b or licorne, its upstream kinase, resulted in small flies consisting of small cells. Mutants with mutations in licorne or p38b are nutrition sensitive; low-nutrient food accentuates the small-organism phenotypes, as well as the partial lethality of the p38b null allele. These data suggest that p38 is an important positive regulator of TORC1 in both mammalian and Drosophila systems in response to certain stresses and growth factors.The target of rapamycin, TOR, is a highly conserved serine/threonine kinase that is a critical regulator of cell growth. It is a core component of two signaling complexes, TORC1 and TORC2 (60, 74). TORC1 is defined by the presence of Raptor in the complex, while TORC2 contains Rictor. Rictor and Raptor are mutually exclusive. Activation of the TORC1 pathway leads to increased protein translation, increased cell size, and increased proliferation, making this pathway an important target for emerging cancer therapies. Rapamycin is an inhibitor of TORC1 that is commonly used as an immunosuppressant following kidney transplantation (51). At least three analogs of rapamycin are currently being tested in solid and hematological tumors and have shown some promising results (21).The TORC1 pathway responds to numerous inputs, sensing both the desirability of and the capacity for growth. Many of these pathways control TORC1 signaling through phosphorylation of the tuberous sclerosis protein TSC2. TSC2 associates with TSC1 to form a heterodimeric GTPase-activating protein complex (GAP) that inactivates the small GTPase Rheb (24, 29, 67). While the exact molecular mechanism remains a topic of debate, activation of Rheb promotes the kinase activity of TORC1 (24, 29, 67). Rheb is required for the activation of TORC1 in response to both amino acids and growth factors (55, 62). In Drosophila melanogaster, mutation of either TOR or Rheb inhibits growth, leading to reduced body size and reduced cell size in mutant clones (42, 64). Mutation of either TSC1 or TSC2 has the predicted opposite effect, as tissue deficient for either of these proteins overgrows and contains large cells (49, 66).TORC1 is activated via the phosphatidylinositol 3′ kinase (PI3′K) pathway by growth-promoting mitogens, such as insulin and growth factors. Drosophila mutants with mutations of PI3′K pathway components have size phenotypes similar to those of the TOR and Rheb mutants (71). In mammalian cells, the PI3′K-mediated activation of TORC1 occurs at least in part through the phosphorylation of TSC2 by the PI3′K target AKT (30, 50). Interestingly, mutation of these residues in Drosophila has no impact on TSC2 function in vivo, suggesting that there may be other mechanisms through which PI3′K can activate Drosophila TOR (20). Recent work has suggested that the proline-rich AKT substrate PRAS40 may provide part of this link (23, 59, 69, 70). In addition, signaling through RAS activates extracellular signal-regulated kinase (ERK) and ribosomal S6 kinase (RSK), which can phosphorylate TSC2 and Raptor to activate TORC1 (13, 40, 56). There are also likely to be additional mechanisms through which growth factors activate Drosophila TOR that have not yet been identified.TORC1 activity is also controlled by the intracellular building blocks necessary to support cellular growth. The energy-sensing AMP-activated protein kinase (AMPK) pathway relays information about the energy status of the cell to TORC1 by phosphorylating TSC2. Unlike the inactivating phosphorylation of TSC2 by Akt, phosphorylation of TSC2 by AMPK promotes the GAP activity of the TSC complex (31). AMPK also phosphorylates Raptor, leading to decreased TORC1 activity (28). Thus, when energy levels are low, active AMPK inhibits TORC1.Amino acids also activate the TORC1 pathway, through a mechanism that requires Rheb, as well as the type III PI3′K VPS34 and the serine/threonine kinase mitogen-activated protein kinase kinase kinase kinase 3 (MAP4K3) (11, 22, 43). TORC1 thereby integrates information about the availability of amino acids and the amount of energy available for growth with growth factor signaling. Given its ancient function in adapting growth rates to environmental conditions, it is likely that TOR responds to a variety of stimuli, suggesting that many TOR control mechanisms remain to be uncovered. The Rag family of Ras-related small GTPases has recently been identified as a key component of the amino acid-sensing pathway, acting in parallel to Rheb (34, 58). Rag GTPases form heterodimers; RagA or RagB interacts with RagC or RagD. RagA and RagB are active when GTP bound, while RagC and RagD are active when bound to GDP (34, 58). Activation of the Rags by amino acids results in TOR relocalization to Rab7-containing vesicles (58). While the function of these vesicles in TORC1 signaling remains unclear, this relocalization is associated with increased TORC1 activity.TORC1 controls cell growth and translation through the phosphorylation and activation of components of the translational machinery, such as S6 kinase (S6K) and 4EBP1, an inhibitor of eukaryotic translation initiation factor 4E (eIF4E) activity (reviewed in reference 27). S6K phosphorylates the S6 ribosomal subunit, thereby increasing translation. Mice deficient for S6K1 are small and have small pancreatic beta cells and a correspondingly low level of circulating insulin (45). Mutation of the phosphorylation sites on S6 results in a similar phenotype, with small beta cells and fibroblasts (57). In Drosophila, mutation of S6K again reduces both cell and organism size (42), as does the overexpression of 4EBP (41).Interestingly, while mutation of the TORC1 pathway in mammalian cells reduces cell size by 10 to 15%, ablation of core TORC1 pathway components in Drosophila cells can affect cell size by up to 40% (73). In an attempt to identify novel components of the TORC1 pathway, we undertook an RNA interference (RNAi)-based screen of Drosophila S2 cells. We reasoned that the extreme size phenotypes observed in Drosophila cells upon TORC1 manipulations would facilitate the identification of modulators. In order to increase the likelihood of isolating novel regulators of TOR, we uncoupled TOR activity from many of its known nutritional controls by depleting TSC2 and screened for double-stranded RNAs (dsRNAs) that could reverse the cell size increase elicited by loss of TSC2. Depletion of multiple components of the p38 pathway was found to revert the TSC2 RNAi-induced cell size increase. Furthermore, activation of p38 is necessary and sufficient for the activation of TOR. Strikingly, mutation of components of the stress-activated p38 pathway in Drosophila has a similar phenotype to mutations in the TOR and insulin signaling pathway: a cell-autonomous cell size decrease, reduced body size, and a sensitization to the effects of nutritional stress.     

Why ant pollination is rare: new evidence and implications of the antibiotic hypothesis

The antibiotic hypothesis proposes that ant pollination is rare at least in part because the cuticular antimicrobial secretions of ants are toxic to pollen grains. We tested this hypothesis by comparing the effects of ants and bees on pollen in two regions: a tropical rainforest in Amazonian Peru and temperate forests and old fields in Canada. We found support for three predictions that follow from the antibiotic hypothesis. (1) For all 10 ant and 11 plant species in our study, contact with ants significantly reduced pollen germination, confirming the generality of this effect. (2) Contact with two bee species did not have similar effects; pollen exposed to bees germinated as well as control pollen. (3) Consistent with the presumed greater abundance of entomopathogens in the tropics, which may have selected for stronger antibiotic secretions in tropical ants, tropical ants had more negative effects on pollen than temperate ants. We speculate that the antibiotic hypothesis contributes not only to the rarity but also to the biogeography of ant pollination, and we discuss whether the negative effects of ants on pollen have resulted in selection for floral defenses against ants.     

Anthropogenic Influences on Conservation Values of White Rhinoceros

White rhinoceros (rhinos) is a keystone conservation species and also provides revenue for protection agencies. Restoring or mimicking the outcomes of impeded ecological processes allows reconciliation of biodiversity and financial objectives. We evaluate the consequences of white rhino management removal, and in recent times, poaching, on population persistence, regional conservation outcomes and opportunities for revenue generation. In Kruger National Park, white rhinos increased from 1998 to 2008. Since then the population may vary non-directionally. In 2010, we estimated 10,621 (95% CI: 8,767–12,682) white rhinos using three different population estimation methods. The desired management effect of a varying population was detectable after 2008. Age and sex structures in sink areas (focal rhino capture areas) were different from elsewhere. This comes from relatively more sub-adults being removed by managers than what the standing age distribution defined. Poachers in turn focused on more adults in 2011. Although the effect of poaching was not detectable at the population level given the confidence intervals of estimates, managers accommodated expected poaching annually and adapted management removals. The present poaching trend predicts that 432 white rhinos may be poached in Kruger during 2012. The white rhino management model mimicking outcomes of impeded ecological processes predicts 397 rhino management removals are required. At present poachers may be doing “management removals,” but conservationists have no opportunity left to contribute to regional rhino conservation strategies or generate revenue through white rhino sales. In addition, continued trends in poaching predict detectable white rhino declines in Kruger National Park by 2016. Our results suggest that conservationists need innovative approaches that reduce financial incentives to curb the threats that poaching poses to several conservation values of natural resources such as white rhinos.     

Satellite data identify decadal trends in the quality of Pygoscelis penguin chick‐rearing habitat

Pygoscelis penguins are experiencing general population declines in their northernmost range whereas there are reported increases in their southernmost range. These changes are coincident with decadal‐scale trends in remote sensed observations of sea ice concentrations (SIC) and sea surface temperatures (SST) during the chick‐rearing season (austral summer). Using SIC, SST, and bathymetry, we identified separate chick‐rearing niche spaces for the three Pygoscelis penguin species and used a maximum entropy approach (MaxEnt) to spatially and temporally model suitable chick‐rearing habitats in the Southern Ocean. For all Pygoscelis penguin species, the MaxEnt models predict significant changes in the locations of suitable chick‐rearing habitats over the period of 1982–2010. In general, chick‐rearing habitat suitability at specific colony locations agreed with the corresponding increases or decreases in documented population trends over the same time period. These changes were the most pronounced along the West Antarctic Peninsula where there has been a rapid warming event during at least the last 50 years.     

Effects of surface texture and interrelated properties on marine biofouling: a systematic review

This systematic review examines effects of surface texture on marine biofouling and characterizes key research methodologies. Seventy-five published articles met selection criteria for qualitative analysis; experimental data from 36 underwent quantitative meta-analysis. Most studies investigated fouling mechanisms and antifouling performance only in laboratory assays with one to several test species. Textures were almost exclusively a single layer of regularly arranged geometric features rather than complex hierarchical or irregular designs. Textures in general had no effect or an inconclusive effect on fouling in 46% of cases. However, effective textures more often decreased (35%) rather than increased (19%) fouling. Complex designs were more effective against fouling (51%) than were regular geometric features (32%). Ratios of feature height, width, or pitch to organism body length were significant influences. The authors recommend further research on promising complex and hierarchical texture designs with more test species, as well as field studies to ground-truth laboratory results.     

The identification of Pcl1-interacting proteins that genetically interact with Cla4 may indicate a link between G1 progression and mitotic exit

In budding yeast, Cla4 and Ste20, two p21-activated kinases, contribute to numerous morphogenetic processes. Loss of Ste20 or Cla4 individually confers distinct phenotypes, implying that they regulate different processes. However, loss of both proteins is lethal, suggesting some functional overlap. To explore the role(s) of Cla4, we and others have sought mutations that are lethal in a cla4 Delta strain. These mutations define >60 genes. Recently, both Ste20 and Cla4 have been implicated in mitotic exit. Here, we identify a genetic interaction between PHO85, which encodes a cyclin-dependent kinase, and CLA4. We further show that the Pho85-coupled G(1) cyclins Pcl1 and Pcl2 contribute to this Pho85 role. We performed a two-hybrid screen with Pcl1. Three Pcl1-interacting proteins were identified: Ncp1, Hms1, and a novel ATPase dubbed Epa1. Each of these proteins interacts with Pcl1 in GST pull-down experiments and is specifically phosphorylated by Pcl1.Pho85 complexes. NCP1, HMS1, and EPA1 also genetically interact with CLA4. Like Cla4, the proteins Hms1, Ncp1, and Pho85 appear to affect mitotic exit, a conclusion that follows from the mislocalization of Cdc14, a key mitotic regulator, in strains lacking these proteins. We propose a model in which the G(1) Pcl1.Pho85 complex regulates mitotic exit machinery.