Eucalyptus Foliage Research Articles

The Eucalyptus terpene synthase gene family.

BackgroundTerpenoids are abundant in the foliage of Eucalyptus, providing the characteristic smell as well as being valuable economically and influencing ecological interactions. Quantitative and qualitative inter- and intra- specific variation of terpenes is common in eucalypts.ResultsThe genome sequences of Eucalyptus grandis and E. globulus were mined for terpene synthase genes (TPS) and compared to other plant species. We investigated the relative expression of TPS in seven plant tissues and functionally characterized five TPS genes from E. grandis. Compared to other sequenced plant genomes, Eucalyptus grandis has the largest number of putative functional TPS genes of any sequenced plant. We discovered 113 and 106 putative functional TPS genes in E. grandis and E. globulus, respectively. All but one TPS from E. grandis were expressed in at least one of seven plant tissues examined. Genomic clusters of up to 20 genes were identified. Many TPS are expressed in tissues other than leaves which invites a re-evaluation of the function of terpenes in Eucalyptus.ConclusionsOur data indicate that terpenes in Eucalyptus may play a wider role in biotic and abiotic interactions than previously thought. Tissue specific expression is common and the possibility of stress induction needs further investigation. Phylogenetic comparison of the two investigated Eucalyptus species gives insight about recent evolution of different clades within the TPS gene family. While the majority of TPS genes occur in orthologous pairs some clades show evidence of recent gene duplication, as well as loss of function.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-1598-x) contains supplementary material, which is available to authorized users.

Diversity and host specificity of Psylloidea (Hemiptera) inhabiting box mistletoe,Amyema miquelii(Loranthaceae) and three of its hostEucalyptusspecies

This study is the first direct comparison of the diversity of phytophagous insects associated with a parasitic plant and its host plants. Specifically, we compared the species composition, density and host specificity of psylloids or jumping plant lice (Hemiptera: Psylloidea), inhabiting hemiparasitic box mistletoe Amyema miquelii, and three of its host Eucalyptus species: Eucalyptus blakelyi, Eucalyptus melliodora and Eucalyptus polyanthemos. Insects were sampled by restricted canopy fogging in remnant Eucalyptus woodlands in an agricultural region of temperate south-eastern Australia. Although most psylloids are understood to be mono- or oligophagous, most species in our survey were found on the foliage of both mistletoes and eucalypts. Nevertheless, analysis of density patterns and reference to previous work on psylloids supports the high degree of host specificity for psylloids, leading to distinct assemblages on these two intimately associated plants. We show that (1) there were two mistletoe-associated species of psylloid and 18 eucalypt-associated species; (2) there were a large number of tourist species, as indicated by known psylloid/plant host associations; and (3) psylloid density was higher on eucalypt than mistletoe leaves. The different psylloid assemblages found on box mistletoes compared with their host plants are likely to be due to differences in the foliar properties implicated in host specificity and host selection by phytophagous insects. Further research is required to understand the ecological dynamics and evolutionary origins of these arboreal assemblages.

Four species of arboreal folivore show differential tolerance to a secondary metabolite.

The marsupials that eat Eucalyptus in south-eastern Australia provide an example of animals with similar niche requirements occurring sympatrically. They certainly differ in size, ranging from about 1 kg in the greater glider (Petauroides volans) and the closely related common ringtail possum (Pseudocheirus peregrinus), to 4 kg (common brushtail possum, Trichosurus vulpecula) and up to 15 kg in the koala (Phascolarctos cinereus). All species, however, may eat considerable amounts of eucalypt foliage, often favouring the same species, and thus appear to compete for food. In order to better understand the degree of competition for food, we measured feeding by the greater glider in response to increasing concentrations of a specific group of eucalypt plant secondary metabolites (PSM), the sideroxylonals, and then compared it to results published for the other species. The greater glider was more resilient than the other species to increasing concentrations of sideroxylonals. We suggest this allows gliders to feed on leaves from the eucalypt subgenus, Symphyomyrtus, while its small size and gliding ability allow it to feed where koalas cannot, on the young leaves on top of the canopy. In contrast, the common ringtail possum is well adapted to feeding from species of the subgenus Eucalyptus, which do not produce sideroxylonals but contain less available nitrogen (AvailN) than do the symphyomyrtles. These 'nutritional niches' segregate the forest and along with other factors, such as generalist and specialist feeding strategies and differences in body size and requirements for shelter, presumably minimise competition between the marsupial species.

Elevated volatile concentrations in high‐nutrient plants: do insect herbivores pay a high price for good food?

1. A tritrophic perspective is fundamental for understanding the drivers of insect–plant interactions. While host plant traits can directly affect insect herbivore performance by either inhibiting or altering the nutritional benefits of consumption, they can also have an indirect effect on herbivores by influencing rates of predation or parasitism.2. Enhancing soil nutrients available to trees of the genus Eucalyptus consistently modifies plant traits, typically improving the nutritional quality of the foliage for insect herbivores. We hypothesised that resulting increases in volatile essential oils could have an indirect negative effect on eucalypt‐feeding herbivores by providing their natural enemies with stronger host/prey location cues.3. Eucalyptus tereticornis Smith seedlings were grown under low‐ and high‐nutrient conditions and the consequences for the release of volatile cues from damaged plants were examined. The influence of 1,8‐cineole (the major volatile terpene in many Eucalyptus species) on rates of predation on model caterpillars in the field was then examined.4. It was found that the emission of cineole increased significantly after damage (artificial or herbivore), but continued only when damage was sustained by herbivore feeding. Importantly, more cineole was emitted from high‐ than low‐nutrient seedlings given an equivalent amount of damage. In the field, predation was significantly greater on model caterpillars baited with cineole than on unbaited models.5. These findings are consistent with the hypothesis that any performance benefits insect herbivores derive from feeding on high‐nutrient eucalypt foliage could be at least partially offset by an increased risk of predation or parasitism via increased emission of attractive volatiles.

Investigation of the koala (Phascolarctos cinereus) hindgut microbiome via 16S pyrosequencing

As a dietary source, the foliage of Eucalyptus spp. is low in available protein and carbohydrate while containing polyphenolic compounds that interfere with enzymatic digestion. To overcome this, the koala (Phascolarctos cinereus) has evolved a range of anatomical and physiological adaptations to assist with digestion and absorption of nutrients from this food source. Microbial fermentation of partially digested eucalyptus leaves is thought to be critical in this process, however, little is known about the composition and diversity of microorganisms that are associated with digestive health in this native species. In this study, we performed 16S rRNA gene pyrosequencing of caecum, colon and faecal pellet samples from two wild, free ranging, Queensland koalas. Our results reveal a highly complex and diverse ecosystem with considerable intra-individual variation. Although samples were dominated by sequences from the Bacteroidetes and Firmicutes phyla there was considerable variation at the genus level. This study is the first non-culture based microbiota analysis, using 454-amplicon pyrosequencing, and provides preliminary data to expand our understanding of the koala hindgut.

The influence of fuel moisture content on the combustion of Eucalyptus foliage

Leaves from three species of Eucalyptus were combusted in a mass-loss calorimeter to characterise the effect of fuel moisture on energy release and combustion products for this genus. Increasing moisture content reduced peak heat release and the effective heat of combustion in a negative exponential pattern while simultaneously increasing time-to-ignition. Estimates of the probability of ignition, based upon time-to-ignition data, indicated that the critical fuel moisture content for a 50% probability of ignition ranged from 81 to 89% on a dry-weight basis. The modified combustion efficiency of leaves (the ratio of CO2 concentration to the sum of the CO2 and CO concentrations) decreased exponentially as fuel moisture increased. This was because CO2 concentrations during combustion declined exponentially while CO concentrations increased exponentially. However, CO2 mixing ratios were always greater by at least one order of magnitude. Emission factors for CO2 declined exponentially with increasing fuel moisture content while CO emission factors increased exponentially to a maximum. The emission factors for volatile organic compounds increased in a pattern similar to that for CO with increasing fuel moisture content. The empirical relationships identified in this study have implications for fire-behaviour modelling and assessing the effect of fire on air quality and climate.

Interactive effects of pre-industrial, current and future [CO2] and temperature on an insect herbivore of Eucalyptus

Both atmospheric [CO2] and average surface temperatures are predicted to increase with potentially different, additive or opposing, effects on leaf quality and insect herbivore activity. Few studies have directly measured the interactive effects of concurrent changes in [CO2] and temperature on insect herbivores. None have done so over the entire developmental period of a tree-feeding insect, and none have compared responses to low pre-industrial [CO2] and present day [CO2] to estimate responses to future increases. Eucalypt herbivores may be particularly sensitive to climate-driven shifts in plant chemistry, as eucalypt foliage is naturally low in [N]. In this study, we assessed the development of the eucalypt herbivore Doratifera quadriguttata exposed concurrently to variable [CO2] (290, 400, 650 μmol mol(-1)) and temperature (ambient, ambient +4 °C) on glasshouse-grown Eucalyptus tereticornis. Overall, insects performed best on foliage grown at pre-industrial [CO2], indicating that modern insect herbivores have already experienced nutritional shifts since industrialisation. Rising [CO2] increased specific leaf mass and leaf carbohydrate concentration, subsequently reducing leaf [N]. Lower leaf [N] induced compensatory feeding and impeded insect performance, particularly by prolonging larval development. Importantly, elevated temperature dampened the negative effects of rising [CO2] on larval performance. Therefore, rising [CO2] over the past 200 years may have reduced forage quality for eucalypt insects, but concurrent temperature increases may have partially compensated for this, and may continue to do so in the future. These results highlight the importance of assessing plant-insect interactions within the context of multiple climate-change factors because of the interactive and potentially opposing effects of different factors within and between trophic levels.

Disentangling respiratory acclimation and adaptation to growth temperature by Eucalyptus

• Respiratory acclimation to growth temperature differs between species, but underlying mechanisms are poorly understood. In the present study, we tested the hypothesis that respiratory acclimation of CO(2) release is a consequence of growth regulation such that growth rates of young foliage of Eucalyptus spp. are similar at contrasting growth temperatures. Further, we tested whether such a response is affected by adaptation of Eucalyptus to different thermal environments via growth at different altitudes in the Australian Alps. • We employed calorimetric methods to relate rates of CO(2) release (mainly from substrate oxidation) and rates of O(2) reduction to conservation of energy. Temperature responses of these processes provided insight into mechanisms that control energy conservation and expenditure, and helped define 'instantaneous enthalpic growth capacity' (CapG). • CapG increased with altitude, but was counteracted by other factors in species adapted to highland habitats. The acclimation response was partly driven by changes in respiratory capacity (CapR(CO2)), and partly by more pronounced dynamic responses of CO(2) release (δ(R(CO2))) to measurement temperature. We observed enhanced temperature sensitivity of O(2) reduction (E(o)(R(O2))) at higher altitudes. • Adaptation to growth temperature included differences in respiration and growth capacities, but there was little evidence that Eucalyptus species vary in metabolic flexibility.

Arthropod assemblages in tree canopies: a comparison of orders on box mistletoe (Amyema miquelii) and its host eucalypts

Parasitic plants, such as mistletoes, are important components of tree canopies, providing food and shelter for a range of vertebrates and invertebrates. Arthropods from several orders are known to inhabit mistletoes but no direct comparisons between these plants and their host plants have been conducted until present. In this study, the composition and abundance of arthropods occurring on hemi-parasitic box mistletoe, Amyema miquelii ((Lehm. ex Miq.) Tiegh., Loranthaceae), on Eucalyptus (L., Myrtaceae) trees from the south-west slopes region of eastern Australia were investigated. Here a comparison of the arthropod assemblages at the ordinal level is presented. Specimens of Insecta and Arachnida were sampled from box mistletoe and three of its most common host species, using restricted canopy fogging, in two consecutive years, in nine remnants of grassy-box woodlands. The same 10 arthropod orders were sampled from the mistletoes and their eucalypt hosts but the total density of arthropods was greater on the eucalypt foliage. The latter result might be attributed to the significantly greater nitrogen content of the eucalypt foliage than the mistletoe foliage. One year after de-faunation, all but one of the arthropod orders had re-colonised the mistletoe plants. The total abundance of arthropods (particularly Hemiptera and Hymenoptera) on the mistletoes was greater in the second year of sampling, in which drought conditions occurred. Future research of arthropod assemblages in tree canopies should be more inclusive of the full range of substrates or habitats within canopies. Furthermore, investigation of the nutritional quality of mistletoe foliage compared with their host trees is required for a better understanding of the factors driving variation in community composition of arthropod assemblages.

Characteristics of jarrah (Eucalyptus marginata) forest at FORESTCHECK monitoring sites in south-west Western Australia: stand structure, litter, woody debris, soil and foliar nutrients

Summary Species composition, size class distribution and developmental stage of canopy and mid-storey tree species were measured at 48 sampling grids in jarrah (Eucalyptus marginata) forest for the FORESTCHECK monitoring project. Other site attributes quantified at each grid included litter loading and coarse woody debris volume, and concentrations of N, P and K in surface soil and eucalypt foliage. Grids were located in stands treated to release regeneration by gap creation (n = 14), to establish regeneration by shelterwood harvesting (n = 12) and in stands where the outcome of harvesting was a selective cut (n = 3). Grids were also located in coupe buffers (n = 4) and in external reference forest (n =15) that had not been harvested since 1960, with eight grids having no record of previous harvesting or evidence of cut stumps. Live eucalypt basal area in external reference forest and coupe buffers averaged 41 m2 ha−1 (range 13–78 m2 ha−1), with marri (Corymbia calophylla) contributing more than half the basal area on some grids in the Jarrah South and Jarrah Blackwood Plateau ecosystems. On average, basal area was reduced by 14 m2 ha−1 to 17 m2 ha−1 in shelterwood stands and by a similar amount in selectively cut stands. Basal area was reduced by 22 m2 ha−1 to 9 m2 ha−1 in areas cut to gap release. Mature trees greater than 70 cm diameter were retained at a rate of six to seven per hectare in harvested stands. Basal area ingrowth following harvesting averaged 0.5 m2 ha−1 y−1 of jarrah and 0.3 m2 ha−1 y−1 of marri. Harvesting increased the volume of coarse woody debris, with the largest amounts present in stands cut to gap release. The volume of woody debris <250 mm in diameter was significantly less in external reference forest that had never been harvested than in shelterwood or gap release stands. Data collected during the initial 5 y of the FORESTCHECK project demonstrate that gap release treatment has resulted in fully stocked stands with a developing cohort of saplings. Shelterwood treatment has been applied conservatively with a tendency to retain more basal area than required by the silvicultural guidelines, and in areas that may already have had sufficient ground coppice to allow for satisfactorily regeneration by gap release. Shelterwood silviculture does not necessarily result in establishment of sufficient seedlings to satisfy regeneration stocking standards within 10 y of treatment, but further episodic recruitment following fire is expected to achieve this over the longer term.

The effects of plant defensive chemistry on nutrient availability predict reproductive success in a mammal

Plants contain a variety of chemical defenses that strongly affect feeding rates in captive mammals, but their effects on the fitness of wild herbivores are largely unknown. This is because the complexity of defensive compounds, and herbivores' counteradaptations to them, make their effects in the wild difficult to measure. We show how tannins interact with protein to produce spatial variation in the nutritional quality of eucalypt foliage, which is related to demography in a wild population of a marsupial folivore, the common brushtail possum (Trichosurus vulpecula Kerr). Tannins reduced the digestibility of nitrogen (N) in vitro, creating variation in available N concentrations among the home ranges of individual possums in an otherwise homogeneous habitat. This was strongly correlated with reproductive success: females with better quality trees in their home range reproduced more often and had faster-growing offspring. These results demonstrate a powerful mechanism by which spatial variation in plant chemistry may control herbivore population dynamics in nature.

Teratosphaeria nubilosa, a serious leaf disease pathogen of Eucalyptus spp. in native and introduced areas.

Teratosphaeria nubilosa is a serious leaf pathogen of several Eucalyptus spp. This review considers the taxonomic history, epidemiology, host associations and molecular biology of T. nubilosa. Kingdom Fungi; Phylum Ascomycota; Class Dothideomycetes; Order Capnodiales; Family Teratosphaeriaceae; genus Teratosphaeria; species nubilosa. Pseudothecia hypophyllous, less so amphigenous, ascomata black, globose becoming erumpent, asci aparaphysate, fasciculate, bitunicate, obovoid to ellipsoid, straight or incurved, eight-spored, ascospores hyaline, non-guttulate, thin walled, straight to slightly curved, obovoid with obtuse ends, medially one-septate, slightly constricted at the median septum, tapering to both ends, ascospore germination type F, germinating from both ends, germ tubes growing parallel to the long axis of the spore with distortion of the primary ascospore cell. Teratosphaeria nubilosa is a primary pathogen of several Eucalyptus spp., including E. botryoides, E. bicostata, E. bridgesiana, E. cypellocarpa, E. dunnii, E. globulus ssp. bicostata, E. globulus ssp. globulus, E. globulus ssp. maidenii, E. globulus ssp. pseudoglobulus, E. grandis, E. gunnii, E. nitens, E. pilularis, E. quadrangulata, E. viminalis, E. grandis x E. resinifera and E. urophylla x E. globulus. Leaf spots predominantly occur on juvenile Eucalyptus foliage; however, T. nubilosa has also recently been found on mature Eucalyptus foliage. Leaf spots are amphigenous, varying in size from small spots that are round to irregular. Lesions enlarge and coalesce to form larger blotches over the leaf surface. Initial lesions appear as pale-green spots surrounded by purple margins and, once mature, are generally yellow to pale brown with dark-brown raised borders. Mycobank, http://www.mycobank.org; Mycosphaerella identification website, http://www.cbs.knaw.nl/mycosphaerella/BioloMICS.aspx.

Volatile constituents of the flowers and leaves of Eucalyptus oleosa cultivated in central Iran

Eucalyptus oleosa, which belonges to the Myrtaceae family, is native to Australia. Eucalyptus leaves contain essential oil and this oil gives the leaves their characteristic fragrance. From the time of European settlement, there has been considerable interest in the properties of essential oils of indigenous Australian plants, in particular Eucalyptus. In 1788, this genus was named Eucalyptus by L′Heriter. The word is derived from the Greek words eu (well) and kalypto (I cover) and is alladed to the observation that the flower-bud covers the stamens until they are fully developed. Medicinally, Eucalyptus oil is used for the treatment of bronchial ailments, where it works by stimulating mucous secretion, and as an antiseptic agent [1]. Eucalyptus contains many chemical compounds that play several roles in the plant. These include defense against insect and vertebrate herbivores and protection against uv radiation and against cold stress. The best known compounds are the terpenoids, which form most of the essential oil, giving Eucalyptus foliage its characteristic smell. However, Eucalyptus is also a rich source of phenolic constituents such as tannins and simpler phenolics. Some of these have formed the basis of industries in the past. For example, tannins were extracted from E. astringens and rutin from E. macrorhyncha [2]. Eucalyptus species are widely planted throughout the world; they yield oils as by products with considerable economic value. Although about 300 species of Eucalyptus have been shown to contain volatile oils in their leaves, only a few are important as far as commercial production of essential oils is concerned. The oils of these species are classified for trade in three broad types according to their composition and main end-use: medicinal (cineole-rich), perfumery (citronella), and industrial (rich in phellandrene and piperitone) [3].

Survey of tropical cut flower and foliage responses to irradiation

The sensitivity of cut flowers and foliage to irradiation used for insect disinfestation varies from species to species and to a lesser extent variety to variety. Flowers with low sensitivity to 250 Gy of electron-beam irradiation were Red ginger ( Alpinia purpurata) and Bird-of-Paradise ( Strelitzia reginae) inflorescences, and Oncidium ( Oncidium spp.–Gower Ramsey) sprays. Medium sensitive flowers were Dendrobium ( Dendrobium spp.) ‘Royal Purples’, Protea hybrid ‘Pink Ice’ and heliconia ‘Red Stricta’ ( Heliconia stricta). Flowers that showed high sensitivity to 250 Gy were Heliconia ‘Keanae’, ‘Beehive’ ginger ( Zingiber spectabilis), ‘Barbatus’ ginger ( Costus barbatus), and ‘Indian head’ ginger ( Costus woodsonii) inflorescences. White (UH 306) dendrobium was more sensitive than the Pink (UH 232) to irradiation (150 Gy). Pretreatment of UH 306 with 1-methylcyclopropene (1-MCP: 50 μg L −1, 3 h) extended the vase life of dendrobium sprays and mitigated the effects of irradiation (250 Gy) on dendrobium vase life. Hot water at 40 °C for 30 min or up to 47.5 °C for 20–30 min reduced the minimal irradiation injury to Bird-of-Paradise inflorescences. For the heliconia ‘Keanae’ inflorescences, a hot water treatment at 45–47.5 °C for 40 min effectively reduced irradiation injury. Red ginger infloresences were able to withstand 500 Gy if pretreated with benzyladenine (BA) before irradiation. Green Ti ( Cordyline terminalis) was not sensitive to irradiation doses from 0 to 500 Gy. Leather-leaf fern ( Dryopteris erythrosora) and baby eucalyptus ( Eucalyptus pulverulenta) foliage showed little or no sensitivity to irradiation. Lycopodium ( Lycopodium taxifolium) and Bracken fern ( Pteridium aquilinum) were sensitive. Ruscus leaves ( Ruscus aeulectus L.) showed chlorosis after irradiation and leaves treated with BA had less chlorosis compared to the non-irradiated foliage. ‘Pink Ice’ protea foliage withstood up to 500 Gy, if first pulsed with 2% glucose solution for 12 h.

Behavioural contributions to the regulated intake of plant secondary metabolites in koalas

In a given period of time, herbivores often eat less as dietary plant secondary metabolite (PSM) concentrations increase. This reduction in total food intake is interpreted as a need for the herbivore to regulate PSM ingestion in order to avoid toxication. However, regulation of PSM ingestion involves more than the reduction of total intake; it involves an alteration of meal patterns, through a reduction in the number and/or the size of the meals eaten. Despite this, studies of how herbivores alter their meal patterns when offered varying concentrations of PSMs are rare. We investigated whether koalas adjust the number and/or the size of their meals when offered eucalypt foliage varying naturally in concentrations of formylated phloroglucinol compounds (FPCs), a group of PSMs that have previously been shown to inhibit total food intake. High FPC concentrations caused koalas to eat more slowly, eat shorter meals and eat less per meal, which resulted in a reduced total intake. Because increasing FPC concentrations did not cause koalas to alter the number of meals that they ate, clear individual differences between koalas were observed, where some consistently ate fewer larger meals and others ate many smaller meals. Thus, different feeding strategies may still achieve the same outcome of a regulated intake of PSMs. The changes observed match the meal patterns of other herbivores ingesting PSMs known to stimulate nausea and emetic pathways, supporting the idea that feedback signals from nausea are an important way that koalas avoid toxication when eating eucalypt foliage.

Estimating Nitrogen in Eucalypt Foliage by Automatically Extracting Tree Spectra from HyMap™ Data

Airborne HyMap™ data obtained from the crown reflectance of Eucalyptus melliodora were used to estimate nitrogen in the foliage. Estimating chemical concentrations in individual crowns by remote sensing is especially difficult for eucalypts because, first, there is marked variation between individual crowns and, secondly, separating leaf and background spectral information is difficult. We developed an automatic method to select relatively pure tree pixels for each tree. In this method, the background materials are modeled, and the pixels within a crown that do not resemble the background clusters are regarded as target pixels. A modified partial least squares gave an R 2 value for predicted versus determined nitrogen concentrations of 0.79, with an RMSE of 0.69 mg/g, less than half the standard deviation of the measured values. Automatically selecting tree pixels was more accurate than manual selection, while the study confirmed that using the maximum spectrum gives results that are as accurate as those from the mean spectrum.

Botryosphaeria species from Eucalyptus in Australia are pleoanamorphic, producing Dichomera synanamorphs in culture

Species within the genus Botryosphaeria include some of the most widespread and important pathogens of woody plants, and have been the focus of numerous taxonomic studies in recent years. It is currently accepted that anamorphs of Botryosphaeria belong to two distinct genera, Fusicoccum and Diplodia. Species within the genus Fusicoccum commonly produce aseptate, hyaline conidia. In the present study, fungi were isolated from foliage and wood of Eucalyptus in native forests and plantations in Australia. Although these fungi produced Dichomera anamorphs in culture, they clustered within the Fusicoccum clade of Botryosphaeria based on their ITS sequence data. Four species, Botryosphaeria dothidea, B. parva, B. ribis and B. australis produced Dichomera conidia in culture. The Dichomera synanamorphs are described for these four species of Botryosphaeria. In addition, falling within the Fusicoccum clade of Botryosphaeria, two species were found to be distinct from previously described Botryosphaeria spp. based on their ITS sequences, but synonymous with D. versiformis and D. eucalypti. These observations are currently unique to isolates from host trees within the genus Eucalyptus in Australia, and the pleoanamorphic nature of these species is discussed.

Sideroxylonal in Eucalyptus foliage influences foraging behaviour of an arboreal folivore

Plant secondary metabolites (PSMs) offer plants chemical defences against herbivores, and are known to influence intake and diet choice in both insect and mammalian herbivores. However, there is limited knowledge regarding how PSMs influence herbivore foraging decisions. Herbivore foraging decisions, in turn, directly impact on which individual plants, and plant species, are selected for consumption. We took advantage of the natural variation in sideroxylonal concentrations in the foliage of Eucalyptus melliodora (Cunn. ex Schauer) to investigate feeding patterns of a marsupial folivore, the common ringtail possum, Pseudocheirus peregrinus (Boddaert 1785). Foliage, collected from six trees, contained between 0.32 and 12.97 mg g-DM(-1) sideroxylonal. With increasing sideroxylonal concentrations, possums decreased their total intake, rate of intake and intake per feeding bout, and increased their cumulative time spent feeding. Possums did not alter their total feeding time, number of feeding bouts or time per feeding bout in response to increasing sideroxylonal concentrations. Results demonstrate important behavioural changes in foraging patterns in response to sideroxylonal. These behavioural changes have important implications, in relation to altered foraging efficiency and potential predation risk, for herbivores foraging in the field. As a result, the spatial distribution of dietary PSMs across a landscape may directly influence herbivore fitness, and ultimately habitat selection of mammalian herbivores.

Eucalyptus foliar chemistry explains selective feeding by koalas

The koala is the quintessential specialist herbivore, feeding almost exclusively on Eucalyptus foliage. Consequently, the limitations imposed on the koala's diet by plant defences indicate the extent to which evolutionary adaptations allow mammalian herbivores to circumvent such defences. We tested whether a recently discovered group of plant secondary metabolites, the formylated phloroglucinol compounds (FPCs), deters koalas from feeding on some eucalypt foliage. We found that captive koalas ate less foliage in a single night from trees with high FPC concentrations. Individual trees also differ in the types of FPC they possess, but for a given eucalypt species, most FPCs were similarly effective deterrents. Two closely related and sympatric eucalypt species could be clearly separated by the amounts that koalas ate from each; however, this difference could not be explained by total FPC concentrations alone. We suggest, that in this case, the presence of a distinct type of FPC deters koala herbivory on the less palatable species, and may have facilitated the evolutionary divergence of these species. We conclude that plant defences probably play an important role in determining the distribution and abundance of koalas.

Effects of terpenes and tannins on some physiological and biochemical parameters in two species of phalangerid possums (Marsupialia : Phalangeridae)

The common brushtail possum (Trichosurus vulpecula) and the short-eared possum (T. caninus) are closely related but differ in several aspects of their life-history strategy, habitat and diet preferences. Both are generalist herbivores, but T. vulpecula consumes significant amounts of Eucalyptus spp. foliage, while T. caninus instead feeds mainly on Acacia spp. Eucalypt foliage is protected against herbivory by several classes of plant secondary compounds, including terpenes and tannins, while acacia foliage is protected mainly by tannins. We compared the responses of these two possum species to the addition of either sesquiterpenes or a hydrolysable tannin to a basal diet free of these compounds. In both species, sesquiterpenes tended to reduce food intake, and increased plasma concentrations of albumin and decreased concentrations of bicarbonate, the latter consistent with changes in acid–base balance. Tannic acid significantly depressed food intake in both species, and depressed plasma concentrations of total protein, albumin, glucose, sodium and chloride, consistent with dehydration. T. vulpecula increased urinary glucuronic acid excretion three-fold in response to dietary sesquiterpenes but there was no increase in T. caninus. T. vulpecula had five- to six-fold greater plasma concentrations of bilirubin, a potent antioxidant, than did T. caninus across all treatments. Results suggest that T. vulpecula can better withstand the detrimental effects of plant secondary compounds, consistent with its wider spectrum of foods and broader habitat preferences.