Garden Biomass Research Articles

Production of Escovopsis weberi (Ascomycota: Hypocreales) Mycelial Pellets and Their Effects on Leaf-Cutting Ant Fungal Gardens

The maintenance of the symbiosis between leaf-cutting ants and their mutualistic fungus Leucoagaricus gongylophorus Singer (Moller) is vital for the survival of both species. The specialist fungal parasite Escovopsis weberi Muchovej & Della Lucia is a threat to this symbiosis, causing severe damage to the fungal garden. Mycelial pellets are resistant fungal structures that can be produced under laboratory conditions. These structures were studied for use in biological pest control, but the production of mycelial pellets has not previously been documented in Escovopsis. One of the aims of this study was to induce Escovopsis weberi to produce mycelial pellets and investigate the potential of these pellets for the control of leaf-cutting ants. We compared the pathogenicity of Escovopsis weberi mycelial pellets and conidia against mini-colonies of Acromyrmex subterraneus subterraneus Forel when applied in the form of baits. Worker ants were able to distinguish mycelial pellets from conidia, as baits with mycelial pellets were more attractive to workers than those with conidia, causing a greater negative impact on colony health. All types of baits containing Escovopsis weberi influenced the foraging activity but only treatments with viable fungal propagules resulted in an increase in the quantity of waste material, with a significant negative impact on the fungal garden biomass. The results provided novel information regarding Escovopsis recognition by worker ants and differences between conidia and mycelial pellet dynamics in leaf-cutting ant colonies, with new perspectives for the biological control of these important pests.

Variations in lignin monomer contents and stable hydrogen isotope ratios in methoxy groups during the biodegradation of garden biomass

Lignin, a highly polymerized organic component of plant cells, is one of the most difficult aromatic substances to degrade. Selective biodegradation under mild conditions is a promising method, but the dynamic variations in lignin monomers during the biodegradation of lignocellulose are not fully understood. In this study, we evaluated the differences in lignin degradation under different microbial inoculation based on the lignin monomer content, monomer ratio, and stable hydrogen isotope ratio of lignin methoxy groups (δ2HLM). The weight loss during degradation and the net loss of lignocellulosic components improved dramatically with fungal inoculation. Syringyl monolignol (S-lignin), which contains two methoxy groups, was more difficult to degrade than guaiacyl (G-lignin), which contains only one methoxy group. The co-culture of Pseudomonas mandelii and Aspergillus fumigatus produced the greatest decrease in the G/S ratio, but δ2HLM values did not differ significantly among the three biodegradation experiments, although the enrichment was done within the fungal inoculation. The fluctuation of δ2HLM values during the initial phase of biodegradation may be related to the loss of pectic polysaccharides (another methoxy donor), which mainly originate from fallen leaves. Overall, the relative δ2HLM signals were preserved despite decreasing G/S ratios in the three degradation systems. Nevertheless, some details of lignin δ2HLM as a biomarker for biogeochemical cycles need to be explored further.

The ideal habitat for leaf-cutting ant queens to build their nests

Queens of Atta sexdens Forel (Hymenoptera: Formicidae) face biotic and abiotic environmental factors in the environment while establishing their nests. Biotic factors such as predation, microbial pathogens, successful symbiotic fungus regurgitation, excavation effort and abiotic factors such as radiant sunlight, temperature, density, and soil moisture exert selection pressures on ant queens. Biotic factors such as temperature and solar irradiation affect the survival of the initial colony differently, in different environments in the field. Queens of the leaf-cutting ant A. sexdens, were installed in sunny and shaded conditions to test this hypothesis. Two hundred A. sexdens queens were collected and individualized in two experimental areas (sunny and shaded), each in an experimental area (25 m2) in the center of a square (50 × 50 cm). Temperature, irradiance, nest depth, rainfall and queen mortality were evaluated. Atta sexdens colony development was better in the shaded environment, and the depth and volume of the initial chamber, fungus garden biomass and number of eggs, larvae, pupae and workers were greater. The queen masses were similar in both environments but mortality was higher in the sunny environment. The worse parameter values for A. sexdens nests in the sunny environment are due to the greater solar irradiance, increasing the variation range of the internal temperature of the initial chamber of the nest. On the other hand, the more stable internal temperature of this chamber in the shaded environment, is due to the lower incidence of solar irradiance, which is also more advantageous for queen survival and the formation and development of A. sexdens colonies. Shaded environments are a better micro habitat for nesting A. sexdens than sunny ones.

Nest Architecture and Colony Growth of Atta bisphaerica Grass-Cutting Ants.

Atta grass-cutting ants (Formicidae: Myrmicinae: Attini) are found in the Cerrado biome and build giant nests with hundreds or thousands of large chambers. We assessed for Atta bisphaerica grass-cutting ants whether the total volume of fungus chambers and other nest parameters grow at close or similar proportions to worker numbers in the colony. Data on fungus garden biomass, population, external area, number of entrance holes, number of fungus chambers, total fungus chambers volume, and nest depth were obtained during colony growth/nest development. Our results reveal that the fungus garden biomass, external area, and total fungus chamber volume increased at rates similar to the increase in the number of workers. The total volume of chambers, and external area increased at a similar proportion to the increase in number of workers, probably due to the fungus garden allocation needs of the colony. The number of fungus chambers, number of entrance holes, and nest depth increased less than 4-fold for every 10-fold increase in the worker number. In addition, the height of the fungus chambers increased as the width increased, a pattern not observed for tunnel height and length, and the chamber volume increased according to worker number. Thus, this study demonstrates for A. bisphaerica that nest development in terms of chamber volume is similar to the increase in number of colony workers, and this contributes to a better understanding of Atta nest architecture.

A Comparison Between the Monetary, Resource and Energy Costs of the Conventional Industrial Supply Path and the “Simpler Way” Path for the Supply of Eggs

Global sustainability requires large-scale reductions in rich world per capita resource use rates. Globalised, industrialised and commercialised supply paths involve high resource, energy, dollar and other costs. However, “The Simpler Way” involving small-scale integrated localised settlements and economies can enable enormous reductions in these costs. Most transport, packaging and marketing costs can be eliminated, and various outputs such as animal manures, kitchen scraps, garden biomass, household grey and black water can be transformed from costly “waste” disposal problems into direct inputs to other functions such as methane digesters, composting, and fish and animal feeds. Thus, there are also savings on the cost of inputs of fertilizer and water, etc. In addition the industrial supply path tends to have many negative “co-products”, most obviously pollution effects, whereas the local path avoids these while providing important positive co-products and social benefits. This study uses input–output analysis of one product, eggs, to illustrate how big the difference between the two paths can be. The implications for sustainable development are profound. If the findings of this study are sound and generalizable the Simpler Way would enable very large reductions in resource and ecological impacts for sustainability to be achieved, but only if extremely radical changes are made in economic, political and cultural systems.

Artificial Neural Network Modeling in Pretreatment of Garden Biomass for Lignocellulose Degradation

In this work, Artificial Neural Network (ANN) model was developed for the garden biomass pretreatment process from the available experimental data of previous work. ANN model was studied to compare the results obtained through Response Surface Methodology (RSM), both graphically and numerically. The influence of process variables such as reaction temperature, Fe2+ concentration and H2O2 concentration on lignocellulose degradation of garden biomass were investigated by this model. The ANN analysis using Matlab, R2012a has shown promising results for this nonlinear system with the correlation coefficient of 0.9663 for cellulose and 0.9699 for lignin, indicating good fit. ANN found to be the effective tool for modeling the experimental data of lignin and cellulose degradation from pretreated biomass and showed a good match with experimental data than RSM. We found that reaction temperature 50 °C, Fe2+ concentration 250 ppm and H2O2 concentration 10000 ppm are the optimum conditions for maximum lignin and cellulose degradation i.e. 47.688% of cellulose and 57.529% of lignin from pretreated garden biomass.

Leaf-Cutter Ant Fungus Gardens Are Biphasic Mixed Microbial Bioreactors That Convert Plant Biomass to Polyols with Biotechnological Applications

Leaf-cutter ants use plant matter to culture the obligate mutualistic basidiomycete Leucoagaricus gongylophorus. This fungus mediates ant nutrition on plant resources. Furthermore, other microbes living in the fungus garden might also contribute to plant digestion. The fungus garden comprises a young sector with recently incorporated leaf fragments and an old sector with partially digested plant matter. Here, we show that the young and old sectors of the grass-cutter Atta bisphaerica fungus garden operate as a biphasic solid-state mixed fermenting system. An initial plant digestion phase occurred in the young sector in the fungus garden periphery, with prevailing hemicellulose and starch degradation into arabinose, mannose, xylose, and glucose. These products support fast microbial growth but were mostly converted into four polyols. Three polyols, mannitol, arabitol, and inositol, were secreted by L. gongylophorus, and a fourth polyol, sorbitol, was likely secreted by another, unidentified, microbe. A second plant digestion phase occurred in the old sector, located in the fungus garden core, comprising stocks of microbial biomass growing slowly on monosaccharides and polyols. This biphasic operation was efficient in mediating symbiotic nutrition on plant matter: the microbes, accounting for 4% of the fungus garden biomass, converted plant matter biomass into monosaccharides and polyols, which were completely consumed by the resident ants and microbes. However, when consumption was inhibited through laboratory manipulation, most of the plant polysaccharides were degraded, products rapidly accumulated, and yields could be preferentially switched between polyols and monosaccharides. This feature might be useful in biotechnology.

Solar assisted alkali pretreatment of garden biomass: Effects on lignocellulose degradation, enzymatic hydrolysis, crystallinity and ultra-structural changes in lignocellulose

A comprehensive study was carried out to assess the effectiveness of solar assisted alkali pretreatment (SAAP) on garden biomass (GB). The pretreatment efficiency was assessed based on lignocellulose degradation, conversion of cellulose into reducing sugars, changes in the ultra-structure and functional groups of lignocellulose and impact on the crystallinity of cellulose, etc. SAAP was found to be efficient for the removal of lignin and hemicellulose that facilitated enzymatic hydrolysis of cellulose. FTIR and XRD studies provided details on the effectiveness of SAAP on lignocellulosic moiety and crystallinity of cellulose. Scanning electron microscopic analysis showed ultra-structural disturbances in the microfibrils of GB as a result of pretreatment. The mass balance closer of 97.87% after pretreatment confirmed the reliability of SAAP pretreatment. Based on the results, it is concluded that SAAP is not only an efficient means of pretreatment but also economical as it involved no energy expenditure for heat generation during pretreatment.

Pretreatment of garden biomass using Fenton's reagent: influence of Fe(2+) and H2O2 concentrations on lignocellulose degradation.

Garden biomass (GB) is defined as low density and heterogeneous waste fraction of garden rubbish like grass clippings, pruning, flowers, branches, weeds; roots. GB is generally different from other types of biomass. GB is mostly generated through maintenance of green areas. GB can be processed for bio energy production as it contains considerably good amount of cellulose and hemicellulose. However, pretreatment is necessary to delignify and facilitate disruption of cellulosic moiety. The aim of the present investigation was to pretreat GB using Fenton’s reagent and to study the influence of Fe2+ and H2O2 concentrations on degradation of lignin and cellulose. The data were statistically analyzed using ANOVA and numerical point prediction tool of MINITAB RELEASE 14 to optimize different process variables such as temperature, concentration of Fe2+ and H2O2. The results of the present investigation showed that Fenton’s reagent was effective on GB, however, concentration of Fe2+ and H2O2 play crucial role in determining the efficiency of pretreatment. An increase in H2O2 concentration in Fenton’s reagent significantly increased the rate of cellulose and lignin degradation in contrast to increasing concentration of Fe2+ ion which led to a decrease in lignocellulosic degradation.

Pretreatment of garden biomass by alkali-assisted ultrasonication: effects on enzymatic hydrolysis and ultrastructural changes.

The present investigation aims at studying the effectiveness of alkali-assisted ultrasonication on pretreatment of garden biomass (GB). Dry and powdered GB suspended in 1% NaOH was ultrasonicated for 15, 30 and 60 minutes at a frequency of 25 KHZ. The mode of action and effectiveness of alkali-assisted ultrasonication on GB was established through microscopic, scanning electron microscopic and X-ray diffraction studies. A perusal of results showed that alkali-assisted ultrasonication led to fibrillation of GB which ultimately facilitated enzymatic hydrolysis. The results also indicated that alkali-assisted ultrasonication is an efficient means of pretreatment of GB at moderate (45-50°C) working temperature and low (1%) concentration of alkali. The yield of reducing sugar after enzymatic hydrolysis increased almost six times as compared to control due to alkali-assisted ultrasonication.

Instability of novel ant-fungal associations constrains horizontal exchange of fungal symbionts

One of the more fascinating features of fungus-gardening ants (Attini: Formicidae) is their fidelity to their lineage-specific fungal symbionts. Among the derived higher-attine ants (leafcutter ants and close relatives), it is thought that most leaf-cutting ants grow Attamyces fungus whereas most Trachymyrmex ants grow ‘Trachymyces’ fungus, but there exist exceptions to this clade-to-clade correspondence between ants and fungi. The exceptions are inconsistent with strict one-to-one coevolution, which suggests that ants sometimes are able to switch to novel fungi. Such switches appear to be largely constrained and ants are generally faithful to their species-specific fungi. Prior experiments demonstrated no clear fitness consequences of growing novel fungi over the short-term when the ant Trachymyrmex septentrionalis was symbiont-switched by forcing it to grow Attamyces leaf-cutter fungus. We hypothesized that long-term ant-fungal fidelity is constrained either by physiological differences among fungal species or by garden diseases that symbiont-switched ants cannot control. Repeat experiments in a different location show that T. septentrionalis colonies switched to grow Attamyces exhibit sudden declines in garden biomass and consequent fitness reductions due to garden destruction by pathogens, whereas control colonies (Trachymyrmex ants cultivating Trachymyces fungus) do not show parallel garden declines. These patterns are mirrored in symbiont-switch experiments conducted on colonies in Trachymyrmex turrifex. Disease microbes selecting on ant-cultivar combinations therefore can constrain switches to novel cultivars and maintain combinations that are more resistant to disease.

Fitness consequences of nest infiltration by the mutualist‐exploiter Megalomyrmex adamsae

1. Fungus‐growing ants are obligate mutualists. Their nutrient‐rich fungus garden provides a valuable food store that sustains the ant hosts, but can also attract social parasites.2. The ‘guest ant' Megalomyrmex adamsae Longino parasitises the fungus‐growing Trachymyrmex zeteki Weber queen just after nest founding. The parasitic queen infiltrates the incipient nest, builds a cavity in the fungal garden, and lays eggs that develop into workers and reproductive males and females.3. This study compared young parasitised and non‐parasitised laboratory colonies by measuring garden growth and biomass, and the number of host workers and reproductives. Host queen survival and parasite colony growth were also monitored.4. Parasitised Trachymyrmex colonies had reduced host worker and alate numbers, as well as lower garden biomass, compared with non‐parasitised control colonies, confirming that M. adamsae is a xenobiotic social parasite. Host queen survival was not significantly different between parasitised and control colonies.5. This is the first study that experimentally infects host colonies with a xenobiotic social parasite to measure fitness cost to the host. The natural history of M. adamsae and the fungus‐growing ant mutualism are evaluated in the context of three general predictions of (Bronstein, Ecology Letters, 4, 277–287, 2001a) regarding the cost of mutualism exploiters.

Odor, gaseous and PM10 emissions from small scale combustion of wood types indigenous to Central Europe

In this study, we investigated the emissions, including odor, from log wood stoves, burning wood types indigenous to mid-European countries such as Austria, Czech Republic, Hungary, Slovak Republic, Slovenia, Switzerland, as well as Baden-Württemberg and Bavaria (Germany) and South Tyrol (Italy). The investigations were performed with a modern, certified, 8 kW, manually fired log wood stove, and the results were compared to emissions from a modern 9 kW pellet stove. The examined wood types were deciduous species: black locust, black poplar, European hornbeam, European beech, pedunculate oak (also known as “common oak”), sessile oak, turkey oak and conifers: Austrian black pine, European larch, Norway spruce, Scots pine, silver fir, as well as hardwood briquettes. In addition, “garden biomass” such as pine cones, pine needles and dry leaves were burnt in the log wood stove. The pellet stove was fired with softwood pellets.The composite average emission rates for log wood and briquettes were 2030 mg MJ−1 for CO; 89 mg MJ−1 for NOx, 311 mg MJ−1 for CxHy, 67 mg MJ−1 for particulate matter PM10 and average odor concentration was at 2430 OU m−3. CO, CxHy and PM10 emissions from pellets combustion were lower by factors of 10, 13 and 3, while considering NOx – comparable to the log wood emissions. Odor from pellets combustion was not detectable. CxHy and PM10 emissions from garden biomass (needles and leaves) burning were 10 times higher than for log wood, while CO and NOx rise only slightly. Odor levels ranged from not detectable (pellets) to around 19,000 OU m−3 (dry leaves). The odor concentration correlated with CO, CxHy and PM10. For log wood combustion average odor ranged from 536 OU m−3 for hornbeam to 5217 OU m−3 for fir, indicating a considerable influence of the wood type on odor concentration.

Influence of heating source on the efficacy of lignocellulosic pretreatment – A cellulosic ethanol perspective

Three different heating devices (Hot plate (HP), Autoclave (AC) & Microwave (MW)) were tested for their efficiency to pretreat garden biomass (GB), a lignocellulosic substrate. Effectiveness of different modes of heat on pretreatment was assessed taking into consideration the yield of reducing sugar (RS), recovery of cellulose after pretreatment, conversion of hemicellulose into reducing sugar, changes in the ultra structure of GB tissues, changes in the crystallinity of GB etc. The results indicated that all three heating devices are useful for pretreatment, however, the efficacy of MW on GB was found be better than AC and HP. A maximum of 53.95% of cellulose recovery was obtained in case of MW heating along with 46.97% of reducing sugar yield. This when compared to AC and HP is significantly higher (more than 10% increase) and time saving (only 15 min reaction time) as well.

Variation inPseudonocardiaantibiotic defence helps govern parasite‐induced morbidity inAcromyrmexleaf‐cutting ants

Host-parasite associations are potentially shaped by evolutionary reciprocal selection dynamics, in which parasites evolve to overcome host defences and hosts are selected to counteract these through the evolution of new defences. This is expected to result in variation in parasite-defence interactions, and the evolution of resistant parasites causing increased virulence. Fungus-growing ants maintain antibiotic-producing Pseudonocardia (Actinobacteria) that aid in protection against specialized parasites of the ants' fungal gardens, and current evidence indicates that both symbionts have been associated with the ants for millions of years. Here we examine the extent of variation in the defensive capabilities of the ant-actinobacterial association against Escovopsis (parasite-defence interactions), and evaluate how variation impacts colonies of fungus-growing ants. We focus on five species of Acromyrmex leaf-cutting ants, crossing 12 strains of Pseudonocardia with 12 strains of Escovopsis in a Petri plate bioassay experiment, and subsequently conduct subcolony infection experiments using resistant and non-resistant parasite strains. Diversity in parasite-defence interactions, including pairings where the parasites are resistant, suggests that chemical variation in the antibiotics produced by different actinobacterial strains are responsible for the observed variation in parasite susceptibility. By evaluating the role this variation plays during infection, we show that infection of ant subcolonies with resistant parasite strains results in significantly higher parasite-induced morbidity with respect to garden biomass loss. Our findings thus further establish the role of Pseudonocardia-derived antibiotics in helping defend the ants' fungus garden from the parasite Escovopsis, and provide evidence that small molecules can play important roles as antibiotics in a natural system.

Symbiont Interactions in a Tripartite Mutualism: Exploring the Presence and Impact of Antagonism between Two Fungus-Growing Ant Mutualists

Mutualistic associations are shaped by the interplay of cooperation and conflict among the partners involved, and it is becoming increasingly clear that within many mutualisms multiple partners simultaneously engage in beneficial interactions. Consequently, a more complete understanding of the dynamics within multipartite mutualism communities is essential for understanding the origin, specificity, and stability of mutualisms. Fungus-growing ants cultivate fungi for food and maintain antibiotic-producing Pseudonocardia actinobacteria on their cuticle that help defend the cultivar fungus from specialized parasites. Within both ant-fungus and ant-bacterium mutualisms, mixing of genetically distinct strains can lead to antagonistic interactions (i.e., competitive conflict), which may prevent the ants from rearing multiple strains of either of the mutualistic symbionts within individual colonies. The success of different ant-cultivar-bacterium combinations could ultimately be governed by antagonistic interactions between the two mutualists, either as inhibition of the cultivar by Pseudonocardia or vice versa. Here we explore cultivar-Pseudonocardia antagonism by evaluating in vitro interactions between strains of the two mutualists, and find frequent antagonistic interactions both from cultivars towards Pseudonocardia and vice versa. To test whether such in vitro antagonistic interactions affect ant colonies in vivo, we performed sub-colony experiments using species of Acromyrmex leaf-cutting ants. We created novel ant-fungus-bacterium pairings in which there was antagonism from one, both, or neither of the ants' microbial mutualists, and evaluated the effect of directional antagonism on cultivar biomass and Pseudonocardia abundance on the cuticle of workers within sub-colonies. Despite the presence of frequent in vitro growth suppression between cultivars and Pseudonocardia, antagonism from Pseudonocardia towards the cultivar did not reduce sub-colony fungus garden biomass, nor did cultivar antagonism towards Pseudonocardia reduce bacteria abundance on the cuticle of sub-colony workers. Our findings suggest that inter-mutualist antagonism does not limit what combinations of cultivar and Pseudonocardia strains Acromyrmex fungus-growing ants can maintain within nests.

Parasites may help stabilize cooperative relationships.

BackgroundThe persistence of cooperative relationships is an evolutionary paradox; selection should favor those individuals that exploit their partners (cheating), resulting in the breakdown of cooperation over evolutionary time. Our current understanding of the evolutionary stability of mutualisms (cooperation between species) is strongly shaped by the view that they are often maintained by partners having mechanisms to avoid or retaliate against exploitation by cheaters. In contrast, we empirically and theoretically examine how additional symbionts, specifically specialized parasites, potentially influence the stability of bipartite mutualistic associations. In our empirical work we focus on the obligate mutualism between fungus-growing ants and the fungi they cultivate for food. This mutualism is exploited by specialized microfungal parasites (genus Escovopsis) that infect the ant's fungal gardens. Using sub-colonies of fungus-growing ants, we investigate the interactions between the fungus garden parasite and cooperative and experimentally-enforced uncooperative ("cheating") pairs of ants and fungi. To further examine if parasites have the potential to help stabilize some mutualisms we conduct Iterative Prisoner's Dilemma (IPD) simulations, a common framework for predicting the outcomes of cooperative/non-cooperative interactions, which incorporate parasitism as an additional factor.ResultsIn our empirical work employing sub-colonies of fungus-growing ants, we found that Escovopsis-infected sub-colonies composed of cheating populations of ants or fungi lost significantly more garden biomass than sub-colonies subjected to infection or cheating (ants or fungi) alone. Since the loss of fungus garden compromises the fitness of both mutualists, our findings suggest that the potential benefit received by the ants or fungi for cheating is outweighed by the increased concomitant cost of parasitism engendered by non-cooperation (cheating). IPD simulations support our empirical results by confirming that a purely cooperative strategy, which is unsuccessful in the classic IPD model, becomes stable when parasites are included.ConclusionHere we suggest, and provide evidence for, parasitism being an external force that has the potential to help stabilize cooperation by aligning the selfish interests of cooperative partners in opposition to a common enemy. Specifically, our empirical results and IPD simulations suggest that when two mutualists share a common enemy selection can favor cooperation over cheating, which may help explain the evolutionary stability of some mutualisms.

Fungus garden platforms improve hygiene during nest establishment in Acromyrmex ants (Hymenoptera, Formicidae, Attini)

Physically isolating organisms from disease agents should reduce the likelihood of disease transmission and infection, and increase survival and growth, particularly in more vulnerable, early ontogenetic stages. During nest founding in fungus-growing ants, foundresses of most genera use a garden platform to isolate the incipient fungal garden from the soil of the underground chamber. We studied nest founding in Acromyrmex octospinosus to test the hypotheses that the use of a platform (rootlets used to suspend the fungus garden): (i) reduces the likelihood that the garden will be contaminated by soil-borne microbial pathogens; (ii) results in more rapid growth of a young colony; and (iii) increases colony survival. We manipulated natural incipient nests to have gardens either in contact with or isolated from soil surrounding the chamber, and nests with and without foundresses present. We found a higher incidence of infection in gardens that were in contact with the chamber soil and without queens, compared with gardens isolated from the chamber soil with and without foundresses. The production of eggs, larvae and pupae, as well as leaf area harvested, were significantly different between nests with and without platforms, but there were no differences in the production of workers nor garden biomass. Likewise, there were no differences between treatments in colony survival rates over 8 weeks. Using smaller incipient gardens, however, gardens with and without platforms differed in survivorship rates after 24 hours. The results indicate that the use of a platform to cultivate an incipient fungal garden is an adaptation to reduce soil-borne diseases and increase colony performance.

Cooperation, conflict, and coevolution in the attine ant-fungus symbiosis

Fungus-growing ants in the tribe Attini represent a classic example of a mutualism. These ants obligately depend on fungus as their major food source, while the fungus receives both vegetative substrate (nourishment) from the ants and protection from pathogens. Here, we try to identify both benefits and costs of the association by using cultivar switch experiments. We assessed the benefits to each mutualistic partner by replacing the native fungus (cultivar) used by the primitive attine ant species Cyphomyrmex muelleri with a novel cultivar, that of the closely related ant species Cyphomyrmex longiscapus. We show that interspecific cultivar switches caused a significant decline in worker number, garden biomass, and the number of reproductives produced by colonies. In contrast, these effects were not seen in intraspecific switches. We also examined possible costs of the mutualistic association. We estimated colony sex ratios for C. longiscapus to determine whether cultivars can bias reproductive allocation toward females; such bias may evolve because only female reproductives can disperse the fungus, and males are therefore of no value to the fungus. However, intraspecific cultivar switches did not significantly affect ant sex ratios. Cultivar switch experiments represent a new tool for studying cooperation, conflict, and coevolution between mutualistic partners in the attine ant-fungus symbiosis.

Estimation of gaseous products and particulate matter emission from garden biomass combustion in a simulation fire test chamber

Air quality in many of the cities in India is gradually deteriorated due to various activities. One of such activities is open burning of garden biomasses in cities. This study was aimed to estimate the emissions from various types of garden biomasses namely grass, leaves, twigs and mixtures of these three in a controlled SIFT chamber. Although the particulate emission (1.51 g kg−1) was lowest from grass, the particle size distribution indicates that the emission contains 10% of fine particulates (<2.5 μm) and significant quantity (70%) of respirable fraction (<10 μm). On the other hand leaves, though generating 32.3 g kg−1 particulate matter contained major portion in non-respirable range (around 40%). CO2 emission from leaves (1064.6 g kg−1) and twigs (897.3 g kg−1) are significantly lower than the emission from mixture (1423 g kg−1) of equal proportion of these two. Similar trend is followed in case of carbon monoxide and nitrogen oxides emissions. However, hydrocarbon emission followed a reverse trend of emitting high emission load (11.4 g kg−1) in the mixture of leaves and twigs than their individual type 2.4 g kg−1 (leaves) and 0.2 g kg−1 (twigs). The toxicity indices for all categories were very low (0.06–0.12). However, out of the five categories grass was found to have lowest toxicity index (0.06) and followed by mixtures (1:1:1) having 0.07. The particulate matter emission load computed for the cities of India shows that the leaves contribute 97 tons day−1 and 4.5 tons day−1 contribution from grass. Among gaseous pollutants CO2 emission was highest, as the computed values were 3212 tons day−1 from leaves and 92 tons day−1 from grass.