Diet selection in marsupial folivores of Eucalyptus: the role of plant secondary metabolites

Past efforts to explain feeding by eucalypt folivores focussed on three groups of plant secondary metabolites – phenolics, tannins and terpenes. It is yet unkownn if these compounds consistently limit the food available to marsupial folivores or whether they provide a better explanation of food choice or habitat quality than do nutrient concentrations alone. Recently, the formylated phloroglucinolc compounds were shown to defend many eucalypts against the marsupial browsers. This discovery has enhanced our understanding of the interaction between marsupial folivores and Eucalyptus while elaborating its complexity. Some informal subgenera of Eucalyptus, such as Monocalyptus, appear to lack formylated phloroglucinol compounds while others (e.g. Symphyomyrtus) contain a wide variety. Of most importance ecologically, is the huge variation in formylated phloroglucinol compounds between individual trees within species, even within a small area. This makes it impossible to generalize about “food trees” across species. The concentrations of formylated phloroglucinol compounds and terpenes in foliage are positively correlated. It appears that folivores use smell to gauge terpene concentrations and hence that of formylated phloroglucinol compounds, and thus avoid the foliage of some trees and feed from others. Thereafter, a physiological feedback mechanism, involving the emetic system, keeps the dose of formylated phloroglucinol compounds below a threshold. This understanding of formylated phloroglucinol compounds makes it pertinent to re-evaluate the roles of other plant secondary metabolites, particularly tannins, in marsupial feeding. However, the greatest challenge ahead is to extrapolate the results of feeding experiments with captive animals to predicaments of wild marsupial folivores. Near infrared spectroscopy provides a way of measuring formylated phloroglucinol compounds concentrations in samples from hundreds of trees. Preliminary research suggests that it may be possible to measure formylated phloroglucinol compounds at the landscape scale with remote sensing

Genus-wide variation in foliar polyphenolics in eucalypts

Many studies quantify total phenolics or total tannins, but understanding the ecological role of polyphenolic secondary metabolites requires at least an understanding of the diversity of phenolic groups present. We used UPLC-MS/MS to measure concentrations of different polyphenol groups - including the four most common tannin groups, the three most common flavonoid groups, and quinic acid derivatives - in foliage from 628 eucalypts from the genera Eucalyptus, Angophora and Corymbia. We also tested for phylogenetic signal in each of the phenolic groups. Many eucalypts contained high concentrations of polyphenols, particularly ellagitannins, which have been relatively poorly studied, but may possess strong oxidative activity. Because the biosynthetic pathways of many phenolic compounds share either precursors or enzymes, we found negative correlations between the concentrations of several of the constituents that we measured, including proanthocyanidins (PAs) and hydrolysable tannins (HTs), HTs and flavonol derivatives, and HTs and quinic acid derivatives. We observed moderate phylogenetic signal in all polyphenol constituents, apart from the concentration of the prodelphinidin subunit of PAs and the mean degree of polymerisation of PAs. These two traits, which have previously been shown to be important in determining plants' protein precipitation capacity, may have evolved under selection, perhaps in response to climate or herbivore pressure. Hence, the signature of evolutionary history appears to have been erased for these traits. This study is an important step in moving away from analysing "totals" to a better understanding of how phylogenetic effects influence phenolic composition, and how this in turn influences ecological processes.Karen J.Marsh, Carsten Kulheim, Simon P.Blomberg, Andrew H.Thornhill, Joseph T.Miller, Ian R.Wallis, Dean Nicolle, Juha-Pekka Salminen, William J.Fole

Modelling nutritional interactions: from individuals to communities

International audienc

Amino acid digestibility and poultry feed formulation: expression, limitations and application

The nutritional value or quality of dietary proteins used for poultry feed formulation varies: amino acid availability is an important measure of protein quality. Determination of ileal digestibility values has become the preferred method for estimating amino acid availability. This review discusses the different approaches to the expression of digestibility results, including correction for endogenous loss and the derivatisation of standardised values. Sources of variation in values include, the assay protocol, anti-nutritional factors in feedstuffs and feed milling. Feed formulating with ileal digestibility values should allow higher dietary inclusion levels of protein feedstuffs of lower quality provided that values of different feedstuffs are additive, the age of the bird and the use of feed enzymes are considered. An Australian data set of "ileal digestible amino acid values in feedstuffs for poultry" that has recently be published is described. This overview is intended to stimulate interest in the generation and application of ileal digestibility as a method for estimating amino acid availability in poultry nutrition