Subgenus Eucalyptus Research Articles

The nutritional quality of post-fire eucalypt regrowth and its consumption by koalas in the New South Wales Southern Tablelands

Most forests and woodlands of south-eastern Australia are fire prone. These landscapes are typically dominated by tree species of the genus Eucalyptus, and many of these are proficient epicormic resprouters after fire. Several marsupial folivores rely on Eucalyptus foliage, including the koala. Little is known about the nutritional composition of epicormic leaves and whether folivores can utilise them. Following the 2019–20 megafires, we offered koalas epicormic leaves from eight eucalypt species that occur in the New South Wales Southern Tablelands and measured concentrations of foliar chemical constituents known to influence koala feeding (total and available nitrogen, formylated phloroglucinol compounds (FPCs), and unsubstituted B-ring flavanones (UBFs)). Captive koalas ate epicormic leaves from the four eucalypt species belonging to the subgenus Symphyomyrtus but ate relatively little from the species of the subgenus Eucalyptus. Available nitrogen was significantly higher in symphyomyrtle epicormic regrowth than in monocalypts and differed between species. Concentrations of FPCs and UBFs also differed between eucalypt species. Our results suggest that post-fire epicormic regrowth from symphyomyrtle species may be more readily browsed than that of monocalypts by koalas in the NSW Southern Tablelands. Therefore, some burnt areas are likely to be better quality habitat for koalas than others.

Phylogenomics reveals extreme gene tree discordance in a lineage of dominant trees: hybridization, introgression, and incomplete lineage sorting blur deep evolutionary relationships despite clear species groupings in Eucalyptus subgenus Eudesmia

Eucalypts are a large and ecologically important group of plants on the Australian continent, and understanding their evolution is important in understanding evolution of the unique Australian flora. Previous phylogenies using plastome DNA, nuclear-ribosomal DNA, or random genome-wide SNPs, have been confounded by limited genetic sampling or by idiosyncratic biological features of the eucalypts, including widespread plastome introgression. Here we present phylogenetic analyses of Eucalyptus subgenus Eudesmia (22 species from western, northern, central and eastern Australia), in the first study to apply a target-capture sequencing approach using custom, eucalypt-specific baits (of 568 genes) to a lineage of Eucalyptus. Multiple accessions of all species were included, and target-capture data were supplemented by separate analyses of plastome genes (average of 63 genes per sample). Analyses revealed a complex evolutionary history likely shaped by incomplete lineage sorting and hybridization. Gene tree discordance generally increased with phylogenetic depth. Species, or groups of species, toward the tips of the tree are mostly supported, and three major clades are identified, but the branching order of these clades cannot be confirmed with confidence. Multiple approaches to filtering the nuclear dataset, by removing genes or samples, could not reduce gene tree conflict or resolve these relationships. Despite inherent complexities in eucalypt evolution, the custom bait kit devised for this research will be a powerful tool for investigating the evolutionary history of eucalypts more broadly.

Common ringtail possums (

Plant secondary metabolites (PSMs) can influence the consumption of particular plants by herbivores. Unsubstituted B-ring flavanones (UBFs), which are compounds found in the leaves of Eucalyptus species from the Eucalyptus subgenus (common name monocalypt), deter feeding by common brushtail possums (Trichosurus vulpecula) when added to artificial diets at concentrations that reflect those found naturally in foliage. We hypothesised that common ringtail possums (Pseudocheirus peregrinus) would tolerate higher UBF concentrations, because, unlike brushtail possums, they regularly eat monocalypt foliage. This proved to be the case; ringtail possums were not deterred by two different UBFs, pinocembrin and flavanone, at concentrations up to 4.7% dry matter, which is substantially higher than the concentrations that deter brushtail possums. These results extend and refine our understanding of how variation in tolerance or susceptibility to eucalypt PSMs affects the diets of sympatric marsupial folivores, potentially reducing competition for food.

Genome-wide association study of myrtle rust (Austropuccinia psidii) resistance in Eucalyptus obliqua (subgenus Eucalyptus)

Myrtle rust (caused by Austropuccinia psidii Beenken) is exotic to Australia, yet specific resistance is present in a range of naive myrtaceous host plants. Resistance to myrtle rust is primarily quantitative in nature and controlled by multiple interacting loci. We undertook a genome-wide association study (GWAS) to discover relationships between nuclear genomic sequence variation and multiple aspects of resistance to A. psidii in Eucalyptus obliqua, a representative species from subgenus Eucalyptus. Sequence variation was assessed with respect to numeric severity, binary symptomatic, hypersensitive, and pustulation responses to inoculation of seedlings with A. psidii. A total of 1.13 million, single-nucleotide polymorphisms (SNPs) were tested for association with the rust resistance responses of 637 phenotyped E. obliqua seedlings, each from different, single mother tree seedlots. Thirty-three highly significant SNP-trait associations were detected, of which 26 associated with the binary symptomatic/asymptomatic response to A. psidii. Comparison of the genomic position of these SNPs with rust resistance loci (Ppr1-5), previously reported in species from subgenus Symphyomyrtus, suggested that several were positioned near the major Ppr1 locus and other Ppr loci. This study provides the first integrated genomic view of A. psidii resistance across the Eucalyptus subgenera and provides the foundation for discovering key resistance genes for use in marker-based resistance breeding.

Insights into speciation and species delimitation of closely related eucalypts using an interdisciplinary approach

Speciation is a central process in evolutionary biology and is responsible for the diversity of life on Earth. Although there has been much progress in evolutionary research over the past 150 years, understanding the many facets of speciation remains a challenge. In this synthesis, I focus on the use of an interdisciplinary approach to examine speciation and species delimitation in a group of closely related eucalypts called the green ashes (Eucalyptus subgenus Eucalyptus section Eucalyptus). The green ashes comprise tall trees on fertile soils (e.g. the tallest angiosperm in the world, E. regnans), as well as medium trees and mallees on low-nutrient soils. Previous phylogenetic and population-genetics analyses based on genome-wide scans showed that species boundaries in the green ashes are not always consistent with classifications based on morphology and there was evidence of gene flow across lineages. Genomic analyses also suggested that the green ashes were at varying stages of speciation, with some species being highly genetically differentiated, whereas others were at earlier stages on the speciation continuum. A previous common garden study showed that inter-specific differences in seedling traits were significant, with traits such as leaf width being highly plastic across resource treatments for most species. Overall, this synthesis demonstrated that an interdisciplinary approach incorporating phylogenomics, population genomics and a common garden experiment can provide insights into speciation and species delimitation in the green ash eucalypts. Such an approach may be useful in understanding the evolutionary history of other closely related species in Eucalyptus, as well as other groups of organisms.

Host susceptibility to Gonipterus platensis (Coleoptera: Curculionidae) of Eucalyptus species

Gonipterus platensis is an important insect pest of eucalypt plantations. Despite biological control by the egg parasitoid Anaphes nitens , economic losses remain high in several areas outside its native range where susceptible eucalypt species are grown in commercial plantations. The susceptibility to G. platensis of 17 Eucalyptus species was evaluated and possible alternatives for reforestation in high pest incidence areas were identified. Gonipterus platensis is an important pest of Eucalyptus worldwide. Despite biological control, it causes significant losses to Eucalyptus plantations in several areas, requiring alternative management options. We analysed host preference of G. platensis towards 17 Eucalyptus species to identify less susceptible plant materials that could be used in areas of high pest incidence. Feeding damage was assessed in field trials in three consecutive years. No-choice and choice tests were conducted with Eucalyptus species of contrasting susceptibility. Within subgenus Symphyomyrtus, all species from section Maidenaria were used by G. platensis for feeding. Within this section, E. globulus was always the preferred species, while E. nitens was the least preferred. Differences in susceptibility were less pronounced at high attack intensity by G. platensis. Eucalyptus saligna (section Latoangulatae) was the least preferred species among Symphyomyrtus. All species from subgenus Eucalyptus had low susceptibility to G. platensis, particularly E. regnans, which was never attacked under field conditions. The results were confirmed by choice and no-choice laboratory and semi-field tests. Significant differences in susceptibility to G. platensis were found between the 17 Eucalyptus species tested, which could be explored for reforestation with less susceptible plant materials.

Geographical patterns of variation in susceptibility of Eucalyptus globulus and Eucalyptus obliqua to myrtle rust

Myrtle rust, caused by the pathogen Austropuccinia psidii, is a disease affecting numerous species of Myrtaceae around the globe. Many Australian ecosystems are dominated by Myrtaceae, making them, along with the industries that rely on them, particularly vulnerable to this disease. With over 800 endemic species, Eucalyptus is a major genus within the Myrtaceae in Australia. Wide variation in response to A. psidii infection, from extreme susceptibility to resistance, has been reported among Eucalyptus species in which any pre-formed resistance to this invasive pathogen is unexpected. This study aims to define and contrast geographical patterns of variation in rust susceptibility within the overlapping, natural ranges of Eucalyptus globulus and Eucalyptus obliqua, two commercially and ecologically important species from different Eucalyptus subgenera. Phenotypic disease screening of seedlings of E. globulus races and E. obliqua forest districts (defined geographically) showed E. obliqua to be more susceptible than E. globulus with significant differences in disease susceptibility and symptomatic trait expression. Eucalyptus globulus showed a trend for decreased susceptibility to A. psidii from south- to north-eastern Tasmania, eastwards along the Otway Ranges and southward from the Strzelecki Ranges to the Wilson Promontory Lighthouse in Victoria, but no such geographical patterns were observed within E. obliqua. No significant correlations were found between climatic conditions (i.e. rainfall, temperature and elevation) and rust susceptibility at provenance levels in either species. Taken together, these results support a hypothesis that population divergence in resistance to A. psidii has not been driven by climate.

Occurrence and distribution of unsubstituted B-ring flavanones in Eucalyptus foliage

A group of plant specialised metabolites (PSMs) collectively known as unsubstituted B-ring flavanones (UBFs) have previously been found in the foliage of some species from the genus Eucalyptus L’Hér. (Myrtaceae), specifically from the subgenus Eucalyptus (monocalypts). Captive feeding studies using artificial diets suggest that these compounds may potentially influence the feeding preferences of marsupial folivores, such as koalas. Understanding natural variation in the composition and concentration of UBFs in eucalypt foliage is a first step to deciding whether, through their effects on herbivory, they might have broader effects on ecosystem dynamics. We used ESI-LCMS/MS and HPLC to characterise and quantify UBFs in 351 individual trees from 25 monocalypt species. We found large variation in the total UBF concentration both between and within species. For example, the mean concentration of UBFs in Eucalyptus muelleriana was 0.2 mg g−1 dry wt, whereas it was 105.7 mg g−1 dry wt, with a range of 78.2–141.3 mg g−1 dry wt, in Eucalyptus mediocris. Different eucalypt species contained different subsets of ten UBFs, and three species showed potential chemotypic variation between individuals within species. Our results suggest that UBFs naturally vary between monocalypt species and individuals at concentrations that could realistically be expected to affect the feeding dynamics of marsupial eucalypt folivores. UBFs could be measured relatively rapidly and cheaply in future studies using near-infrared reflectance (NIR) spectroscopy, as we were able to successfully predict the total UBF concentration of samples from their NIR spectra, with an r2 value of 0.98 and a standard error of prediction (SEP) of 6.07. This work further solidifies NIR spectroscopy as a powerful tool enabling ecologists to analyse the chemical composition of large numbers of samples.

A dated molecular perspective of eucalypt taxonomy, evolution and diversification

The eucalypts, which include Eucalyptus, Angophora and Corymbia, are native to Australia and Malesia and include over 800 named species in a mixture of diverse and depauperate lineages. We assessed the fit of the eucalypt taxonomic classification to a phylogeny of 711 species scored for DNA sequences of plastid matK and psbA–trnH, as well as nuclear internal transcribed spacer and external transcribed spacer. Two broadly similar topologies emerge from both maximum likelihood and Bayesian analyses, showing Angophora nested within Corymbia, or Angophora sister to Corymbia. The position of certain species-poor groups on long branches fluctuated relative to the three major Eucalyptus subgenera, and positions of several closely related species within those subgenera were unstable and lacked statistical support. Most sections and series of Eucalyptus were not recovered as monophyletic. We calibrated these phylogenies against time, using penalised likelihood and constraints obtained from fossil ages. On the basis of these trees, most major eucalypt subgenera arose in the Late Eocene and Early Oligocene. All Eucalyptus clades with taxa occurring in south-eastern Australia have crown ages <20 million years. Several eucalypt clades display a strong present-day geographic disjunction, although these clades did not have strong phylogenetic statistical support. In particular, the estimated age of the separation between the eudesmids (Eucalyptus subgenus Eudesmia) and monocalypts (Eucalyptus subgenus Eucalyptus) was consistent with extensive inland water bodies in the Eocene. Bayesian analysis of macroevolutionary mixture rates of net species diversification accelerated in five sections of Eucalyptus subgenus Symphyomyrtus, all beginning 2–3 million years ago and associated with semi-arid habitats dominated by mallee and mallet growth forms, and with open woodlands and forests in eastern Australia. This is the first time that a calibrated molecular study has shown support for the rapid diversification of eucalypts in the recent past, most likely driven by changing climate and diverse soil geochemical conditions.

Disease cycle of Austropuccinia psidii on Eucalyptus globulus and Eucalyptus obliqua leaves of different rust response phenotypes

Myrtle rust poses a significant biosecurity threat to Australia with potential for long‐term damaging impacts on native flora and plant industries. This study describes the disease cycle of Austropuccinia psidii, the myrtle rust pathogen, in Eucalyptus globulus and Eucalyptus obliqua, two commercially and ecologically important species from different subgenera of Eucalyptus. Ontogeny and morphology of infection structures of A. psidii on plants of both Eucalyptus species with different rust response phenotypes, i.e. completely resistant, hypersensitive and highly susceptible, were investigated. Plants were inoculated with single‐uredinium‐derived urediniospores and examined by scanning electron microscopy. No differences between rust response phenotypes were observed in germination of urediniospores, formation of appressoria or length of germ tubes. The growth of germ tubes had no affinity towards stomata of either species. Histological observations indicated direct penetration by infection pegs through the leaf cuticle and no penetration beyond the epidermis on rust‐resistant E. obliqua. Eucalyptus obliqua plants that were identified as susceptible to A. psidii at 3‐ and 6‐months‐old showed no disease when reinoculated with A. psidii at 12‐months‐old; this indicated possible early acquisition of adult plant resistance to A. psidii in this species. In the susceptible phenotype of E. globulus rust inoculation led to rapid colonization of leaf parenchyma cells with the disease cycle completed within 10 days. These findings provide valuable insights into host–pathogen interactions in the Eucalyptus–A. psidii pathosystem, which might be useful for the development of effective rust control strategies across Eucalyptus subgenera.

A revised classification for the predominantly eastern Australian Eucalyptus subgenus Symphyomyrtus sections Maidenaria, Exsertaria, Latoangulatae and related smaller sections (Myrtaceae).

A revised classification for E. sections Maidenaria, Exsertaria, Latoangulatae and five related smaller sections (Liberivalvae, Racemus, Incognitae, Similares and Pumilio) (herein referred to as ‘MEL+5’ lineage for convenience) is provided, based on evidence from a recent phylogenetic study of this group (Jones et al. 2016) and on observations and data from other sources, including our extensive field observations, study of herbarium collections, common garden trials and the findings of other phylogenetic studies. We recognise 153 species and 184 terminal taxa in the ‘MEL+5’ lineage, and classify this group into 6 sections, 23 series and 8 subseries. This new classification mainly involved the repositioning of various terminal taxa into existing higher-level taxonomic groups, as we have attempted to achieve an accurate and useful classification while minimising taxonomic disruption of existing names. Nevertheless, nine new higher-level taxa (eight series and one subseries) are newly described. A full classification of the ‘MEL+5’ lineage is provided, which includes all terminal taxa, taxon authorships, type species, the natural distribution of recognised terminal taxa, and taxonomic and nomenclatural synonyms.

Speciation in the presence of gene flow: population genomics of closely related and diverging Eucalyptus species.

Speciation is a complex process that is fundamental to the origins of biological diversity. While there has been considerable progress in our understanding of speciation, there are still many unanswered questions, especially regarding barriers to gene flow in diverging populations. Eucalyptus is an appropriate system for investigating speciation mechanisms since it comprises species that are rapidly evolving across heterogeneous environments. We examined patterns of genetic variation within and among six closely related Eucalyptus species in subgenus Eucalyptus section Eucalyptus in south-eastern Australia (commonly known as the "green ashes"). We used reduced representation genome sequencing to genotype samples from populations across altitudinal and latitudinal gradients. We found one species, Eucalyptus cunninghamii, to be highly genetically differentiated from the others, and a population of mallees from Mount Banks to be genetically distinct and therefore likely to be a new undescribed species. Only modest levels of differentiation were found between all other species in the study. There was population structure within some species (e.g., E. obstans) corresponding to geographical factors, indicating that vicariance may have played a role in the evolution of the group. Overall, we found that lineages within the green ashes are differentiated to varying extents, from strongly diverged to much earlier stages of the speciation continuum. Furthermore, our results suggest the green ashes represent a group where a range of mechanisms (e.g., reticulate evolution and vicariance) have been operating in concert. These findings not only offer insights into recent speciation mechanisms in Eucalyptus, but also other species complexes.

Phylogeny is a powerful tool for predicting plant biomass responses to nitrogen enrichment.

Increasing rates of anthropogenic nitrogen (N) enrichment to soils often lead to the dominance of nitrophilic plant species and reduce plant diversity in natural ecosystems. Yet, we lack a framework to predict which species will be winners or losers in soil N enrichment scenarios, a framework that current literature suggests should integrate plant phylogeny, functional tradeoffs, and nutrient co-limitation. Using a controlled fertilization experiment, we quantified biomass responses to N enrichment for 23 forest tree species within the genus Eucalyptus that are native to Tasmania, Australia. Based on previous work with these species' responses to global change factors and theory on the evolution of plant resource-use strategies, we hypothesized that (1) growth responses to N enrichment are phylogenetically structured, (2)species with more resource-acquisitive functional traits have greater growth responses to N enrichment, and (3) phosphorus (P) limits growth responses to N enrichment differentially across species, wherein P enrichment increases growth responses to N enrichment more in some species than others. We built a hierarchical Bayesian model estimating effects of functional traits (specific leaf area, specific stem density, and specific root length) and P fertilization on species' biomass responses to N, which we then compared between lineages to determine whether phylogeny explains variation in responses to N. In concordance with literature on N limitation, a majority of species responded strongly and positively to N enrichment. Mean responses ranged three-fold, from 6.21 (E.pulchella) to 16.87 (E.delegatensis) percent increases in biomass per g N·m-2 ·yr-1 added. We identified a strong difference in responses to N between two phylogenetic lineages in the Eucalyptus subgenus Symphyomyrtus, suggesting that shared ancestry explains variation in N limitation. However, our model indicated that after controlling for phylogenetic non-independence, eucalypt responses to N were not associated with functional traits (although post-hoc analyses show a phylogenetic pattern in specific root length similar to that of responses to N), nor were responses differentially limited by P. Overall, our model results suggest that phylogeny is a powerful predictor of winners and losers in anthropogenic N enrichment scenarios in Tasmanian eucalypts, which may have implications for other species.

Climate and geochemistry as drivers of eucalypt diversification in Australia.

Eucalypts cover most of Australia. Here, we investigate the relative contribution of climate and geochemistry to the distribution and diversity of eucalypts. Using geostatistics, we estimate major element concentrations, pH, and electrical conductivity at sites where eucalypts have been recorded. We compare the median predicted geochemistry and reported substrate for individual species that appear associated with extreme conditions; this provides a partial evaluation of the predictions. We generate a site-by-species matrix by aggregating observations to the centroids of 100-km-wide grid cells, calculate diversity indices, and use numerical ecology methods (ordination, variation partitioning) to investigate the ecology of eucalypts and their response to climatic and geochemical gradients. We find that β-diversity coincides with variations in climatic and geochemical patterns. Climate and geochemistry together account for less than half of the variation in eucalypt species assemblages across Australia but for greater than 80% in areas of high species richness. Climate is more important than geochemistry in explaining eucalypts species distribution and change in assemblages across Australia as a whole but there are correlations between the two sets of environmental variables. Many individual eucalypt species and entire taxonomic sections (Aromatica, Longistylus of subgenus Eucalyptus, Dumaria, and Liberivalvae of subgenus Symphyomyrtus) have distributions affected strongly by geochemistry. We conclude that eucalypt diversity is driven by steep geochemical gradients that have arisen as climate patterns have fluctuated over Australia over the Cenozoic, generally aridifying since the Miocene. The diversification of eucalypts across Australia is thus an excellent example of co-evolution of landscapes and biota in space and time and challenges accepted notions of macroecology.

Evolutionary history shapes the susceptibility of an island tree flora to an exotic pathogen

With globalisation, the world’s native biotas are increasingly exposed to disease, parasitism, herbivory and competition from exotic organisms. The vulnerability of native biota to these exotic invasions is exacerbated by human disturbance and global climate change. Rust pathogens are some of the most important plant pathogens, including Puccinia psidii (myrtle rust or guava rust) that is now spreading worldwide at an alarming rate. P. psidii is native to South America and affects species in the family Myrtaceae, including the economically and ecologically important eucalypts. The Australian continent has a rich myrtaceous flora and is the centre of origin of most eucalypt species. P. psidii was first detected in Australia in 2010 and has since rapidly spread along its east coast. We assess the risk this exotic pathogen poses to the eucalypt flora of the southern Australian island of Tasmania, where the first incursion of P. psidii was detected in early 2015. Specifically, we tested the relative importance of phylogenetic history, habitat, endemism, and range size in predicting host susceptibility.Rust screening of seedlings from one to four populations of each of the 30 eucalypt species which are native to Tasmania, revealed significant genetic-based variation in response among host species and populations within the species. Significant population differences in susceptibility were detected in threatened, rare and endemic eucalypt species, as well as Australia’s main plantation eucalypt (Eucalyptus globulus) and the world’s tallest angiosperm species (Eucalyptus regnans). A significant proportion of the variation in host species susceptibility to this exotic pathogen was explained by phylogenetic history, while factors such as habitat, endemism and range size had no detectable effect. Species from subgenus Eucalyptus (13 species) were more susceptible than those from subgenus Symphyomyrtus (17 species) due to differences between the subgenera in the proportion of plants showing a symptomless response. These subgenera are here shown to differ in their leaf oil and wax chemistry. The potential contribution of these differences and other possible mechanisms causing these subgeneric differences in susceptibility are discussed. This study demonstrates the power of a phylogenetic approach to risk assessment for biosecurity and highlights the need for broader resistance screening within and between populations of species of high conservation or economic value.

Use of genetic markers to build a new generation of Eucalyptus pilularis breeding population

Abstract Tree improvement generally proceeds by incremental gains obtained from recurrent selection in large diverse populations but is slow due to long generation times and delay till trees reach assessment age. This places a premium upon extracting data from historic introductions used to found landraces when reinstating modern breeding programs. The value of such resources, however, may be degraded due to a lack of records on germplasm origins, pedigrees and early performance, but DNA technology may help recoup some of this value. Eucalyptus pilularis (subgenus Eucalyptus) is regarded as a premier hardwood plantation species for saw log and poles in Australia, but has not been used extensively despite early introductions and testing in many countries overseas. Here we use DNA fingerprinting to assess genetic diversity and inbreeding in historic introductions of E. pilularis to evaluate this resource in advance of a reinvigorated breeding effort for this species in Brazil. As expected, based on the available documentation for the introductions, genetic diversity relative to Australian reference populations does not appear to be compromised, and there was unlikely to be excessive inbreeding. Also, favorable, was the likelihood that further selections should not unduly increase the relationship in the next generation. Interestingly, we note the importance of testing widely adapted sources of germplasm when making introductions, as provenances which performed poorly in tests on productive sites in Australia, may have value when matched with lower fertility sites overseas.

From Leaf Metabolome to In Vivo Testing: Identifying Antifeedant Compounds for Ecological Studies of Marsupial Diets.

Identifying specific plant secondary metabolites that influence feeding behavior can be challenging, but a solid understanding of animal preferences can guide efforts. Common brushtail possums (Trichosurus vulpecula) predominantly eat Eucalyptus species belonging to the subgenus Symphyomyrtus, and avoid eating those belonging to the Monocalyptus subgenus (also called subgenus Eucalyptus). Using an unbiased (1)H NMR metabolomics approach, a previous study identified unsubstituted B ring flavanones in most species of monocalypts examined, whereas these compounds were absent from symphyomyrtles. We hypothesised that unsubstituted B ring flavanones act as feeding deterrents for common brushtail possums. In the current study, we tested this hypothesis by comparing how much possums ate of a basal diet, with diets containing one of four structurally related compounds; pinocembrin, flavanone (unsubstituted B ring flavanones), chrysin (the flavone analogue of pinocembrin), and naringenin (a flavanone with B ring substitution). We found that pinocembrin and flavanone deterred feeding relative to the basal diet, but that chrysin and naringenin did not at equivalent concentrations. Thus, unsubstituted B-ring flavanones may explain why brushtail possums avoid eating monocalypt species. Furthermore, small differences in the structure of secondary compounds can have a large impact on antifeedant properties. These results demonstrate that metabolomics can be a valuable tool for ecologists seeking to understand herbivore feeding preferences.

Feeding and oviposition behaviour of a gall inducing species of Glycaspis (Synglycaspis) (Hemiptera: Psylloidea: Aphalaridae) and development of galls on the leaves of Eucalyptus macrorhyncha (Myrtaceae) in central western New South Wales, Australia

Glycaspis (Synglycaspis) confined to Australia includes gall-inducing and lerp-forming species that are probably highly specific to different species of Eucalyptus subgenus Eucalyptus. Based on available information, their distribution appears restricted to temperate, south-eastern and southern Australia. This paper reports the biology of an unnamed (suspected new species) of Glycaspis (Synglycaspis) that induces spherical, ostiolate galls on the leaves of Eucalyptus macrorhyncha in central western tablelands of NSW. This species completes two generations in a year. Oviposition elicits a passive response in the leaves of E. macrorhyncha. In this work we demonstrate that the host tissue not only supplies water, but also nutrients to the developing embryo via the embedded pedicel. Feeding action of the first instar initiates the gall and morphogenetic gradients become apparent around the feeding site. These gradients direct gall growth. The gall attains its near final spherical shape during the second instar and this spherical gall remains plugged with sugary material, which all the immature stages secrete from the last abdominal segment. No significant gall growth occurs during the occupation of the gall by the third, fourth and fifth instars. The first and second instars feed on the newly differentiated parenchyma tissue in galls, whereas the third, fourth and fifth instars feed on phloem of galls. Consequently the multi-layer parenchymatous nutritive tissue that initially develops lining the chamber dries and shrivels, when the later instars inhabit galls. This shrinkage induces a gradual thinning of gall walls, which is also aggravated by modest expansive growth of the gall.

Evolutionary history and novel biotic interactions determine plant responses to elevated CO2 and nitrogen fertilization.

A major frontier in global change research is predicting how multiple agents of global change will alter plant productivity, a critical component of the carbon cycle. Recent research has shown that plant responses to climate change are phylogenetically conserved such that species within some lineages are more productive than those within other lineages in changing environments. However, it remains unclear how phylogenetic patterns in plant responses to changing abiotic conditions may be altered by another agent of global change, the introduction of non-native species. Using a system of 28 native Tasmanian Eucalyptus species belonging to two subgenera, Symphyomyrtus and Eucalyptus, we hypothesized that productivity responses to abiotic agents of global change (elevated CO2 and increased soil N) are unique to lineages, but that novel interactions with a non-native species mediate these responses. We tested this hypothesis by examining productivity of 1) native species monocultures and 2) mixtures of native species with an introduced hardwood plantation species, Eucalyptus nitens, to experimentally manipulated soil N and atmospheric CO2. Consistent with past research, we found that N limits productivity overall, especially in elevated CO2 conditions. However, monocultures of species within the Symphyomyrtus subgenus showed the strongest response to N (gained 127% more total biomass) in elevated CO2 conditions, whereas those within the Eucalyptus subgenus did not respond to N. Root:shoot ratio (an indicator of resource use) was on average greater in species pairs containing Symphyomyrtus species, suggesting that functional traits important for resource uptake are phylogenetically conserved and explaining the phylogenetic pattern in plant response to changing environmental conditions. Yet, native species mixtures with E. nitens exhibited responses to CO2 and N that differed from those of monocultures, supporting our hypothesis and highlighting that both plant evolutionary history and introduced species will shape community productivity in a changing world.

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.