Fine‐scale spatiotemporal dynamics of fungal fruiting: prevalence,amplitude, range and continuity

Despite the critical importance of fungi as symbionts with plants, resources for animals, and drivers of ecosystem function, the spatiotemporal distributions of fungi remain poorly understood. The belowground life cycle of fungi makes it difficult to assess spatial patterns and dynamic processes even with recent molecular techniques. Here we offer an explicit spatiotemporal Bayesian inference of the drivers behind spatial distributions from investigation of a Swiss inventory of fungal fruit bodies. The unique inventory includes three temperate forest sites in which a total of 73 952 fungal fruit bodies were recorded systematically in a spatially explicit design between 1992 and 2006. Our motivation is to understand how broad‐scale climate factors may influence spatiotemporal dynamics of fungal fruiting within forests, and if any such effects vary between two functional groups, ectomycorrhizal (ECM) and saprotrophic fungi. For both groups we asked: 1) how consistent are the locations of fruiting patches, the sizes of patches, the quantities of fruit bodies, and of prevalence (occupancy)? 2) Do the annual spatial characteristics of fungal fruiting change systematically over time? 3) Are spatial characteristics of fungal fruiting driven by climatic variation? We found high inter‐annual continuity in fruiting for both functional groups. The saprotrophic species were characterised by small patches with variable fruit body counts. In contrast, ECM species were present in larger, but more distinctly delimited patches. The spatial characteristics of the fungal community were only indirectly influenced by climate. However, climate variability influenced overall yields and prevalence, which again links to spatial structure of fruit bodies. Both yield and prevalence were correlated with the amplitudes of occurrence and of fruit body counts, but only prevalence influenced the spatial range. Summarizing, climatic variability affects forest‐stand fungal distributions via its influence on yield (amount) and prevalence (occupancy), whereas fungal life‐history strategies dictate fine‐scale spatial characteristics.     

Electrical potentials in the ectomycorrhizal fungus Laccaria bicolor after a rainfall event

We measured extracellular bioelectrical activities of the ectomycorrhizal basidiomycete Laccaria bicolor under field conditions to examine its response to environmental factors. Six fruit bodies of L. bicolor in a cluster, to which electrodes were attached, exhibited less electrical potentials at the beginning, probably due to the lack of precipitation for over a week. However, its electrical potential fluctuated after raining, sometimes over 100 mV. The electrical potential of the fruit bodies and its fluctuation were correlated with precipitation. Causality analysis of electrical potential after the rain showed electrical signal transport among fruit bodies, particularly between spatially close ones, with potential directionality. Our preliminary results bring a call for studies on fungal electrical potentials in a more ecological context under field conditions.     

Identification, Characterization, and In Situ Detection of a Fruit-Body-Specific Hydrophobin of Pleurotus ostreatus

Hydrophobins are small (length, about 100 ± 25 amino acids), cysteine-rich, hydrophobic proteins that are present in large amounts in fungal cell walls, where they form part of the outermost layer (rodlet layer); sometimes, they can also be secreted into the medium. Different hydrophobins are associated with different developmental stages of a fungus, and their biological functions include protection of the hyphae against desiccation and attack by either bacterial or fungal parasites, hyphal adherence, and the lowering of surface tension of the culture medium to permit aerial growth of the hyphae. We identified and isolated a hydrophobin (fruit body hydrophobin 1 [Fbh1]) present in fruit bodies but absent in both monokaryotic and dikaryotic mycelia of the edible mushroom Pleurotus ostreatus. In order to study the temporal and spatial expression of the fbh1 gene, we determined the N-terminal amino acid sequence of Fbh1. We also synthesized and cloned the double-stranded cDNA corresponding to the full-length mRNA of Fbh1 to use it as a probe in both Northern blot and in situ hybridization experiments. Fbh1 mRNA is detectable in specific parts of the fruit body, and it is absent in other developmental stages.     

Multiple infestation by seed predators: the effect of loculate fruits on intraspecific insect larval competition

Many morphological features of fruits are important factors affecting predispersal seed predation by insects. This paper analyses the predispersal seed predation process of a major predator (a Noctuidae lepidopteran larvae) in loculate fruits of a bushy perennial plant, Cistus ladanifer. The main aim of the study is to assess the potential effect of internal valvae (which partition groups of seeds) in the intraspecific competition between larvae in multiple-infested fruits.Our results show that larvae do not reject already infested fruits, but they avoid the proximity of other larvae within the fruit, keeping an average minimum distance of one locule. In multiple-infested fruits, larval mortality increases and the proportion of seeds consumed by each larvae decreases. In those situations in which valvae keep apart larvae within a fruit, these only suffer the cost of exploitation competition with a low acquisition of resources. However, when all valvae between them are pierced by the larvae, competition switches to an interference component and larval mortality increases markedly. The existence of valvae within a fruit allows larvae to diminish the cost of intraspecific competition, obtaining high life expectancies (70%), even in triple-infested fruits.     

Effect of cold treatment on survival and development of codling moth (Lepidoptera: Tortricidae) in cherry

'Bing' cherries, Prunus avium L., were obtained from an organic orchard and a conventional commercial orchard. The two groups were examined separately in replicated tests infested with each fruit initially infested with a first-instar codling moth, Cydia pomonella (L.). To simulate commercial postharvest holding conditions, the treatments were 0 (control), 1, 2, 4, 7, 10, and 14 d cold storage at 3.3 degrees C. The fruits were examined three or more times to determine larval survival, life stage, fruit condition, and fungal disease. Survival of first instars was affected only by cold storage durations of > or = 7 d. When infested with codling moth larvae, both organic and conventionally grown cherries quickly deteriorated from fungal diseases. The rate of moth development was estimated from the surviving larvae and was significantly different between organic and conventionally grown cherries for all instars except the second.     

First data on the larval morphology and biology of two Palaearctic species of the genus <Emphasis Type="Italic">Allognosta</Emphasis> Osten-Sacken, 1883 (Diptera,Stratiomyidae)

Data on the morphology and ecology of the immature stages of two Palaearctic species of the genus Allognosta Osten-Sacken, 1883 (Diptera, Stratiomyidae) are given. The sides of the abdominal segments in the larvae of this genus are divided into two sections: the anterior one is shorter and with a conical projection, while the posterior one is more massive and paddle-shaped. The larvae inhabit the humus soil layer and the fruit bodies of polyporus fungi.     

Resource partitioning of the host fungus Coriolus versicolor by two ciid beetles: the role of odour compounds and host ageing

The ciid beetles Octotemnus glabriculus and Cis boleti exploit different developmental stages of fruit bodies of their preferred host fungus Coriolus versicolor . Larvae of the smaller beetle, O. glabriculus , mainly use young, expanding, fruit bodies; adults of O. glabriculus are predominantly found in young fruit bodies. By contrast, adults and larvae of the larger beetle, C. boleti , are prevalent in fully developed fruit bodies of C. versicolor . Because fruit bodies of most genets emerge during spring and early summer and mature by autumn, O. glabriculus and C. boleti breed in separated seasons. Adults and larvae of O. glabriculus are abundant in spring and early summer. By contrast, the number of adults and larvae of C. boleti increases gradually from late spring to summer and peaks in autumn. We conducted a field experiment that suggests that the phenological dynamics of C. versicolor fruit bodies drive the separation of breeding seasons between O. glabriculus and C. boleti . Additionally, laboratory experiments revealed that O. glabriculus and C. boleti have differential behavioural responses to odour compounds from young and mature fruit bodies of C. versicolor . We conclude that age-related changes in the chemical composition of fruit bodies may allow O. glabriculus and C. boleti to discriminate among C. versicolor , thus providing a mechanism for the partitioning of the resource.     

Clash of kingdoms or why Drosophila larvae positively respond to fungal competitors

BACKGROUND: Competition with filamentous fungi has been demonstrated to be an important cause of mortality for the vast group of insects that depend on ephemeral resources (e.g. fruit, dung, carrion). Recent data suggest that the well-known aggregation of Drosophila larvae across decaying fruit yields a competitive advantage over mould, by which the larvae achieve a higher survival probability in larger groups compared with smaller ones. Feeding and locomotor behaviour of larger larval groups is assumed to cause disruption of fungal hyphae, leading to suppression of fungal growth, which in turn improves the chances of larval survival to the adult stage. Given the relationship between larval density, mould suppression and larval survival, the present study has tested whether fungal-infected food patches elicit communal foraging behaviour on mould-infected sites by which larvae might hamper mould growth more efficiently. RESULTS: Based on laboratory experiments in which Drosophila larvae were offered the choice between fungal-infected and uninfected food patches, larvae significantly aggregated on patches containing young fungal colonies. Grouping behaviour was also visible when larvae were offered only fungal-infected or only uninfected patches; however, larval aggregation was less strong under these conditions than in a heterogeneous environment (infected and uninfected patches). CONCLUSION: Because filamentous fungi can be deadly competitors for insect larvae on ephemeral resources, social attraction of Drosophila larvae to fungal-infected sites leading to suppression of mould growth may reflect an adaptive behavioural response that increases insect larval fitness and can thus be discussed as an anti-competitor behaviour. These observations support the hypothesis that adverse environmental conditions operate in favour of social behaviour. In a search for the underlying mechanisms of communal behaviour in Drosophila, this study highlights the necessity of investigating the role of inter-kingdom competition as a potential driving force in the evolution of spatial behaviour in insects.     

Soil burrowing Muscina angustifrons (Diptera: Muscidae) larvae excrete spores capable of forming mycorrhizae underground

Muscina angustifrons (Diptera: Muscidae) is a mycophagous species that exploits a variety of fungi, including ectomycorrhizal fungi. Larvae of this species have been shown to feed on sporocarps (including spores), and full-grown larvae leave sporocarps and pupate 0–6?cm below the soil surface. In this study, we examined whether M. angustifrons larvae are capable of transporting ectomycorrhizal fungal spores and enhancing ectomycorrhiza growth on host-plant roots. Full-grown larvae were found to move horizontally 10–20?cm from their feeding sites and burrow underground. These wandering larvae retained ectomycorrhizal fungal spores in their intestines, which were excreted following relocation to underground pupation sites. Excreted spores retained germination and infection capacities to form ectomycorrhiza on host-plant roots. In the infection experiments, ectomycorrhizal fungal spores applied in the vicinity of underground host-plant roots were more effective in forming ectomycorrhiza than those applied to the ground surface, suggesting that belowground transportation of spores by M. angustifrons larvae could enhance ectomycorrhizal formation. These results suggested that M. angustifrons larvae act as a short-distance spore transporter of ectomycorrhizal fungi.     

Olfactory responses of Grapholita molesta to different developmental stages of immature fruit of peach,plum, and apple

The Oriental fruit moth, Grapholita molesta (Busck) (Lepidoptera: Tortricidae), is known to shift its host use from stone fruits (the primary hosts) to pome fruits (secondary hosts) as the season progresses. Grapholita molesta recognizes potential hosts by semiochemicals from fruits, but few studies have addressed the olfactory responses of G. molesta to host fruits during the seasonal transition of the moth from stone to pome fruits. So, we investigated the olfactory responses of larvae and gravid females of G. molesta to different fruit stages (collected on May 31, June 11, and June 25) of immature peach, plum, and apple fruits, using both multiple and two choice tests. In the multiple choice tests, for fruits collected after June 11, larvae showed a significant preference for peach as their first choice, compared to plum or apple. The final choice rate (when larvae had stayed on the fruit for more than 1 h) of larvae was also highest for peach fruits collected on June 11 and June 25. In two choice tests (Y-tube test), the response rate and overall choice rate of larvae and mated ovipositing adult females were also highest on peaches collected on May 31 (larvae) and June 25 (adults), respectively. In conclusion, we found that both the adults and larvae of G. molesta were highly attracted to immature peach fruits in laboratory choice tests.     

Combining high-throughput sequencing with fruit body surveys reveals contrasting life-history strategies in fungi

Before the recent revolution in molecular biology, field studies on fungal communities were mostly confined to fruit bodies, whereas mycelial interactions were studied in the laboratory. Here we combine high-throughput sequencing with a fruit body inventory to study simultaneously mycelial and fruit body occurrences in a community of fungi inhabiting dead wood of Norway spruce. We studied mycelial occurrence by extracting DNA from wood samples followed by 454-sequencing of the ITS1 and ITS2 regions and an automated procedure for species identification. In total, we detected 198 species as mycelia and 137 species as fruit bodies. The correlation between mycelial and fruit body occurrences was high for the majority of the species, suggesting that high-throughput sequencing can successfully characterize the dominating fungal communities, despite possible biases related to sampling, PCR, sequencing and molecular identification. We used the fruit body and molecular data to test hypothesized links between life history and population dynamic parameters. We show that the species that have on average a high mycelial abundance also have a high fruiting rate and produce large fruit bodies, leading to a positive feedback loop in their population dynamics. Earlier studies have shown that species with specialized resource requirements are rarely seen fruiting, for which reason they are often classified as red-listed. We show with the help of high-throughput sequencing that some of these species are more abundant as mycelium in wood than what could be expected from their occurrence as fruit bodies.     

Larval isolation and brood care in Acromyrmex leaf-cutting ants

The larvae of leaf-cutting ants are maintained within the fungus gardens of their colonies and are fed pieces of fungus by the adult workers. However, little else is known about the nature of the worker-larva interaction in these ecologically important ants. To examine whether workers can gauge the needs of individual larvae, we isolated larvae without adult workers for different lengths of time. We then placed workers with the larvae and recorded the type and frequency of the subsequent behaviours of the workers. Workers scraped the mouthparts of larvae, ingested their faecal fluid, fed them with fungal hyphae, transported them around the fungus garden and, most frequently, licked their bodies. The workers were also observed to ‘plant’ fungal hyphae on the bodies of larvae. Workers interacted more frequently with larvae that had been isolated without workers than with those that had not, but there was no effect of the length of isolation. The results suggest that the interactions are complex, involving a number of behaviours that probably serve different functions, and that workers are to some extent able to assess the individual needs of larvae. Received 8 November 2004; revised 31 March 2005; accepted 22 April 2005.     

How does the richness of wood-decaying fungi relate to wood microclimate?

Microclimatic conditions in dead wood influence fungal growth and hence also species composition, but it remains unclear how they influence species richness in nature. We analysed fungal species richness based on the occurrence of fruit bodies on 2 m long segments of both standing and lying trunks of Norway spruce (Picea abies). The number of non-red-listed species was related positively to moisture, and negatively to both temperature extremes and fluctuations. The numbers of both red-listed and non-red-listed species were further differently influenced by trunk diameter and by trunk properties related to the progression in wood decay. These results indicate that the richness of fungal communities in dead wood is shaped by an interaction of wood decay, moisture and temperature fluctuations.     

Bacterial Community Analysis and Potential Functions of Core Taxa in Different Parts of the Fungus Cantharellus cibarius

Cantharellus cibarius is a widely distributed, popular, edible fungus with high nutritional and economic value. However, significant challenges persist in the microbial ecology and artificial cultivation of C. cibarius. Based on the 16S rRNA sequencing data, this study analyzed bacterial community structures and diversity of fruit bodies and rhizomorph parts of C. cibarius and mycosphere samples (collected in the Wudang District, Guiyang, Guizhou Province, China). It explored the composition and function of the core bacterial taxa. The analyzed results showed that the rhizomorph bacterial community structure was similar to mycosphere, but differed from the fruit bodies. Members of the Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium complex had the highest abundance in the fruit bodies. However, they were either absent or low in abundance in the rhizomorphs and mycosphere. At the same time, members of the Burkholderia-Caballeronia-Paraburkholderia complex were abundant in the fruit bodies and rhizomorphs parts of C. cibarius, as well as mycosphere. Through functional annotation of core bacterial taxa, we found that there was an apparent trend of potential functional differentiation of related bacterial communities in the fruit body and rhizomorph: potential functional groups of core bacterial taxa in the fruit bodies centered on nitrogen fixation, nitrogen metabolism, and degradation of aromatic compounds, while those in rhizomorphs focused on aerobic chemoheterotrophy, chemoheterotrophy, defense against soil pathogens, decomposition of complex organic compounds, and uptake of insoluble inorganic compounds. The analysis of functional groups of bacteria with different structures is of great significance to understand that bacteria promote the growth and development of C. cibarius. Open in a separate window     

Ultrastructural studies on the fungus,Nomuraea rileyi,infecting the velvetbean caterpillar,Anticarsia gemmatalis

Combined scanning and transmission electron microscopy was used to study the fine structure of the developmental stages of Nomuraea rileyi infecting host larvae of Anticarsia gemmatalis. Larvae were dusted with large numbers of fungal conidia, which germinated and penetrated the cuticle within 6 hr post-treatment. Within 24 hr, penetration hyphae had reached the cuticular epidermis and, via a budding process, initiated the hyphal body stage in the hemocoel. The hyphal bodies, suspended in hemolymph, multiplied and spread throughout the host larvae. By 6–7 days post-treatment, the majority of larvae were mummified. Within 12 hr postmortem numerous conidiophores emerged producing a confluent mycelial mat over the entire cuticular surface. Numerous hydrophobic conidia were formed on phialides present on the aerial conidiophores.     

Inapparent infection ofDiatraea grandiosella byHeliothis virescens cytoplasmic polyhedrosis virus

The terminal stage of infection with cytoplasmic polyhedrosis viruses (CPVs) is formation of crystal-like inclusion bodies (polyhedra) in host insects. The degree of susceptibility of larvae to CPV, based on light microscopy and presence of polyhedra, varies with the host species.Heliothis virescens (F.) andSpodoptera exigua (Hübner) are highly susceptible to CPV. In CPV treatedDiatraea grandiosella (Dyar), polyhedra were absent in all 400 + insects examined with light and electron microscopy. However,H. virescens larvae became infected when fed haemolymph ofD. grandiosella larvae or pupae (36±10 days post treatment) developed from CPV-treated larvae. No difference in pathology was observed betweenH. virescens larvae infected with CPV polyhedra and haemolymph fromD. grandiosella. This study provides evidence thatD. grandiosella can serve as a symptomless (no occlusion bodies) carrier of a CPV which is fully expressed inH. virescens species. The observation is interesting because it reveals a potentially important aspect of the epizootiology of this insect virus.     

Effect of entomopathogenic nematodes on different developmental stages of <Emphasis Type="Italic">Drosophila suzukii</Emphasis> in and outside fruits

Drosophila suzukii Matsumura (Diptera: Drosophilidae) is a harmful invasive fruit pest, which is currently spreading in Europe. Since its arrival in 2008, the spotted wing drosophila has caused major losses in several soft-skinned fruit crops. This critical situation urgently requires efficient practices of residue-free pest control. In the present laboratory study, entomopathogenic nematodes (EPNs) were investigated for their ability to infect larvae and pupae of D. suzukii within directly sprayed fruit, fruit placed on soil, and soil. Steinernema feltiae Filipjev (Rhabditida: Steinernematidae), and Steinernema carpocapsae Weiser (Rhabditida: Steinernematidae) were more efficient at infecting soil-pupating host larvae than Heterorhabditis bacteriophora Poinar (Rhabditida: Heterorhabditidae) at application rates ranging from 25 to 400 EPN cm^?2. Applied as a soil drench, S. feltiae and S. carpocapsae were able to infect D. suzukii larvae in the soil as well as hidden inside fruit. Direct application of EPNs on the fruit was less successful, although emergence of flies was significantly reduced.     

Increasing oxidative stress tolerance and subculturing stability of Cordyceps militaris by overexpression of a glutathione peroxidase gene

Like other filamentous fungi, the medicinal ascomycete Cordyceps militaris frequently degenerates during continuous maintenance in culture by showing loss of the ability to reproduce sexually or asexually. Degeneration of fungal cultures has been related with cellular accumulation of reactive oxygen species (ROS). In this study, an antioxidant glutathione peroxidase (Gpx) gene from Aspergillus nidulans was engineered into two C. militaris strains, i.e., the Cm01 strain which can fruit normally and the Cm04 strain which has lost the ability to form fruiting bodies on different media through subculturing. The results showed that the mitotically stable mutants had higher Gpx activities and stronger capacity to scavenge cellular ROS than their parental strains. Most significantly, the fruiting ability of Cm04 strain was restored by overexpression of the antioxidant enzyme. However, after being successively transferred for up to ten generations, two of three Cm04 mutants again lost the ability to fruit on insect pupae while Cm01 transformants remained fertile. This study confirms the relationship between fungal culture degeneration and cellular ROS accumulation. Our results indicate that genetic engineering with an antioxidant gene can be an effective way to reverse fungal degeneration during subculturing.