Transport networks are vital components of multicellular organisms, distributing nutrients and removing waste products. Animal and plant transport systems are branching trees whose architecture is linked to universal scaling laws in these organisms. In contrast, many fungi form reticulated mycelia via the branching and fusion of thread-like hyphae that continuously adapt to the environment. Fungal networks have evolved to explore and exploit a patchy environment, rather than ramify through a three-dimensional organism. However, there has been no explicit analysis of the network structures formed, their dynamic behaviour nor how either impact on their ecological function. Using the woodland saprotroph Phanerochaete velutina, we show that fungal networks can display both high transport capacity and robustness to damage. These properties are enhanced as the network grows, while the relative cost of building the network decreases. Thus, mycelia achieve the seemingly competing goals of efficient transport and robustness, with decreasing relative investment, by selective reinforcement and recycling of transport pathways. Fungal networks demonstrate that indeterminate, decentralized systems can yield highly adaptive networks. Understanding how these relatively simple organisms have found effective transport networks through a process of natural selection may inform the design of man-made networks.

The mycelia of two wood decay basidiomycete fungi were grown opposing each other across a 1-microm pore membrane supported on the surface of malt broth, contained within a sealable reaction vessel. Production of volatiles during the time course of interaction was followed by collecting head space samples by solid phase microextraction (100 microm polydimethylsiloxane fiber) on five occasions over 25 d following coinoculation of the fungi: 1, 3 (i.e., immediately prior to mycelial contact), 9 (1-2 d after initiation of pigment production by Resinicium bicolor), 17, and 25 d. Ten volatiles were produced during interactions that were not detected in single species controls. In general, most (18) fungal volatiles were sesquiterpenes eluted between 12.5 and 21 min, with a further two eluted at 29.1 and 33.9 min; a benzoic acid methyl ester, a benzyl alcohol, and a quinolinium type compound with a distinctive fragmentation pattern at m/z 203, 204, 206, and 207 were also identified; three volatiles with m/z maxima of 163, 159, and 206-208, respectively, remained unidentified. The results are discussed in relation to possible ecological roles of volatiles.

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SummaryTransport networks are vital components of multi-cellular organisms, distributing nutrients and removing waste products. Animal cardiovascular and respiratory systems, and plant vasculature, are branching trees whose architecture is thought to determine universal scaling laws in these organisms. In contrast, the transport systems of many multicellular fungi do not fit into this conceptual framework, as they have evolved to explore a patchy environment in search of new resources, rather than ramify through a three-dimensional organism. These fungi grow as a foraging mycelium, formed by the branching and fusion of threadlike hyphae, that gives rise to a complex network. To function efficiently, the mycelial network must both transport nutrients between spatially separated source and sink regions and also maintain its integrity in the face of continuous attack by mycophagous insects or random damage. Here we review the development of novel imaging approaches and software tools that we have used to characterise nutrient transport and network formation in foraging mycelia over a range of spatial scales. On a millimetre scale, we have used a combination of time-lapse confocal imaging and fluorescence recovery after photobleaching to quantify the rate of diffusive transport through the unique vacuole system in individual hyphae. These data then form the basis of a simulation model to predict the impact of such diffusion-based movement on a scale of several millimetres. On a centimetre scale, we have used novel photon-counting scintillation imaging techniques to visualize radiolabel movement in small microcosms. This approach has revealed novel N-transport phenomena, including rapid, preferential N-resource allocation to C-rich sinks, induction

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Per- and polyfluoroalkyl substances (PFASs) are ubiquitous environmental contaminants that have been linked to adverse health effects in wildlife and humans. Here, we report the presence of PFASs in Eurasian otters ( Lutra lutra ) in England and Wales and their association with anthropogenic sources. The following 15 compounds were analyzed: 10 perfluoroalkyl carboxylic acids (PFCAs), 4 perfluoroalkyl sulfonic acids (PFSAs), and perfluorooctane sulfonamide, in livers of 50 otters which died between 2007 and 2009. PFASs were detected in all otters analyzed, with 12/15 compounds detected in ≥80% of otters. Perfluorooctane sulfonate (PFOS) accounted for 75% of the ΣPFAS profile, with a maximum concentration of 6800 μg/kg wet weight (ww). Long-chain (≥C8) PFCAs accounted for 99.9% of the ΣPFCA profile, with perfluorodecanoic acid and perfluorononanoic acid having the highest maxima (369 μg/kg ww and 170 μg/kg ww, respectively). Perfluorooctanoic acid (PFOA) concentrations were negatively associated with the distance from a factory that used PFOA in polytetrafluoroethylene manufacture. Most PFAS concentrations in otters were positively associated with load entering wastewater treatment works (WWTW) and with arable land, suggesting that WWTW effluent and sewage sludge-amended soils are significant pathways of PFASs into freshwaters. Our results reveal the widespread pollution of British freshwaters with PFASs and demonstrate the utility of otters as effective sentinels for spatial variation in PFAS concentrations.

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