Ecological role of hypogeous ectomycorrhizal fungi in Australian forests and woodlands

The Australian continent is characterised by a harsh climate and highly weathered, nutrient-poor soils. Trees and shrubs in these stressful environmental conditions typically form ectomycorrhizae with a variety of fungi, many of which form hypogeous (underground) fruit-bodies. The total number of hypogeous fungi Australia-wide is unknown, although recent systematic studies in the far south-eastern corner of the country suggest that they may number well over a thousand. Similar surveys elswhere are urgently required to clarify the situation. The precise ecological role of many hypogeous fungi remains to be determined, although most presumably facilitate nutrient and water uptake on behalf of their mycorrhizal partners. Others may also protect their plant host from root pathogens. One key function of hypogeous fungi is the role their fruit-bodies play as a food resource for a large range of terrestrial mammals. For a few animals, hypogeous fungi form the single most important dietary item year-round, whereas for others they may only be of seasonal or supplementary value. The extent to which fungi form part of the diet of any mammal species is reflected in the various levels of adaptation toward acquiring, then processing and digesting these cryptic and nutritionally challenging foodstuffs.     

Studies on the Glutathione-Dependent Formaldehyde-Activating Enzyme from Paracoccus denitrificans

Formaldehyde is a toxin and carcinogen that is both an environmental pollutant and an endogenous metabolite. Formaldehyde metabolism, which is probably essential for all aerobic cells, likely proceeds via multiple mechanisms, including via a glutathione-dependent pathway that is widely conserved in bacteria, plants and animals. However, it is unclear whether the first step in the glutathione-dependent pathway (i.e. formation of S-hydroxymethylglutathione (HMG)) is enzyme-catalysed. We report studies on glutathione-dependent formaldehyde-activating enzyme (GFA) from Paracoccus denitrificans, which has been proposed to catalyse HMG formation from glutathione and formaldehyde on the basis of studies using NMR exchange spectroscopy (EXSY). Although we were able to replicate the EXSY results, time course experiments unexpectedly imply that GFA does not catalyse HMG formation under standard conditions. However, GFA was observed to bind glutathione using NMR and mass spectrometry. Overall, the results reveal that GFA binds glutathione but does not directly catalyse HMG formation under standard conditions. Thus, it is possible that GFA acts as a glutathione carrier that acts to co-localise glutathione and formaldehyde in a cellular context.     

Evaluating the role of the Dingo as a trophic regulator: Additional practical suggestions

Summary   A recent review paper by Glen et   al . in Austral Ecology (2007, Volume 32 , 492–501) canvassed anecdotal and scientific evidence relating to the role of the Dingo as regulator of ecosystem processes in Australian landscapes. Their review forms part of an increasing volume of literature about the ecological roles of top-order or apex predators around the globe. Although recognizing the possible functional significance of the Dingo is a noteworthy subject matter, the management of the species at an ecosystem scale is complicated by a range of practical and theoretical issues. Perhaps the most significant challenge is the degree to which the Dingo is hybridized with the domestic Dog gone wild (Feral Dog). We suggest here that there is a range of research questions that need to be experimentally addressed as a matter of urgency. This includes but is not limited to understanding the ecological significance of Dingo–Dog hybridization. Such research should precede other research initiatives suggested by Glen et   al. such as reintroducing individuals of the pure Dingo back into landscapes. This is particularly the case for south-eastern mainland Australia where the incidence of Dingo–Dog hybridization is high and the ecological consequences of this poorly understood. Finally, new terminology may be needed relating to Dingo and/or Wild Dog management that more clearly reflects both the genetic status of the species as well as its ecological function.     

Easily Constructed Soil Percolation Apparatus

The construction of a soil percolator from a disposable Nalgene sterilizing filter is described.     

Beaked whales respond to simulated and actual navy sonar

Beaked whales have mass stranded during some naval sonar exercises, but the cause is unknown. They are difficult to sight but can reliably be detected by listening for echolocation clicks produced during deep foraging dives. Listening for these clicks, we documented Blainville's beaked whales, Mesoplodon densirostris, in a naval underwater range where sonars are in regular use near Andros Island, Bahamas. An array of bottom-mounted hydrophones can detect beaked whales when they click anywhere within the range. We used two complementary methods to investigate behavioral responses of beaked whales to sonar: an opportunistic approach that monitored whale responses to multi-day naval exercises involving tactical mid-frequency sonars, and an experimental approach using playbacks of simulated sonar and control sounds to whales tagged with a device that records sound, movement, and orientation. Here we show that in both exposure conditions beaked whales stopped echolocating during deep foraging dives and moved away. During actual sonar exercises, beaked whales were primarily detected near the periphery of the range, on average 16 km away from the sonar transmissions. Once the exercise stopped, beaked whales gradually filled in the center of the range over 2-3 days. A satellite tagged whale moved outside the range during an exercise, returning over 2-3 days post-exercise. The experimental approach used tags to measure acoustic exposure and behavioral reactions of beaked whales to one controlled exposure each of simulated military sonar, killer whale calls, and band-limited noise. The beaked whales reacted to these three sound playbacks at sound pressure levels below 142 dB re 1 μPa by stopping echolocation followed by unusually long and slow ascents from their foraging dives. The combined results indicate similar disruption of foraging behavior and avoidance by beaked whales in the two different contexts, at exposures well below those used by regulators to define disturbance.     

Delphinid whistle production and call matching during playback of simulated military sonar

In 2007 and 2008, controlled exposure experiments were performed in the Bahamas to study behavioral responses to simulated mid‐frequency active sonar (MFA) by three groups of odontocetes: false killer whales, Pseudorca crassidens; short‐finned pilot whales, Globicephala macrorhynchus; and melon‐headed whales, Peponocephala electra. An individual in each group was tagged with a Dtag to record acoustic and movement data. During exposures, some individuals produced whistles that seemed similar to the experimental MFA stimulus. Statistical tests were thus applied to investigate whistle‐MFA similarity and the relationship between whistle production rate and MFA reception time. For the false killer whale group, overall whistle rate and production rate of the most MFA‐like whistles decreased with time since last MFA reception. Despite quite low whistle rates overall by the melon‐headed whales, statistical results indicated minor transient silencing after each signal reception. There were no apparent relationships between pilot whale whistle rates and MFA sounds within the exposure period. This variability of responses suggests that changes in whistle production in response to acoustic stimuli depend not only on species and sound source, but also on the social, behavioral, or environmental contexts of exposure.     

Diversity and habitat relationships of hypogeous fungi. III. Factors influencing the occurrence of fire-adapted species

Among the huge array of hypogeous ectomycorrhizal fungi so far documented from Australia, six genera and more than 30 species occur within the family Mesophelliaceae, all of which show various adaptations for surviving in fire-prone landscapes. These mostly endemic fungi are critical to postfire reestablishment of regenerating vegetation, and their fruit-bodies provide essential food resources for diverse ground-dwelling fauna. We developed habitat models for five common representatives of the Mesophelliaceae based on repeat collections of their fruit-bodies from 136 study plots situated along a series of environmental gradients across the south-eastern mainland of Australia. At a meso- or landscape scale, temperature influenced the occurrence of Castoreum radicatum, Mesophellia clelandii and Nothocastoreum cretaceum, with the type of response varying. Below a threshold, C. radicatum preferred sites with cooler mean annual temperatures. In contrast, M. clelandii and N. cretaceum had optimal ranges of temperature, above and below which the probability of detecting them dropped. Also at a landscape scale, C. radicatum was more likely to be detected at sites with lower levels of precipitation during the driest quarter of the year. At a micro-site scale, M. clelandii and N. cretaceum were more likely to occur in stands with an intermediate number of host eucalypt stems, likely relating to successional age of the stand. Sites with a higher number of large fallen trees were more likely to have N. cretaceum, while sites with intermediate litter depths were more likely to have C. radicatum and M. clelandii. Mesophellia glauca and M. trabalis showed no consistent patterns. They are apparently the most broadly adaptable in terms of the independent variables tested. Although fire has been previously suggested to be heavily implicated in the life cycle of several members of the Mesophelliaceae, we found no relationship between time since disturbance by fire and other factors and likelihood of occurrence. Instead, other habitat attributes appeared to be more important in explaining their distribution. The complex and differing responses of the species of Mesophelliaceae studied here, to features of their environment, reinforce the need to manage multiple-use forest landscapes across the region for a diversity of attributes.