Intraspecific variation in Eucalyptus secondary metabolites determines food intake by folivorous marsupials

Abstract

Traditional approaches to the question of the effects of plant secondary metabolites on the feeding choices of folivores of Eucalyptus have focused on the tree species level, although numerous field studies of foraging behaviour have identified selection at the level of the individual trees. Attempts to relate these decisions to deterrency resulting from secondary leaf chemistry have been inconclusive because assays used have focused on broad groups of compounds such as "total" phenolics. In this study we have conducted no-choice feeding trials with two arboreal mammalian folivores, the common ringtail possum (Pseudocheirus peregrinus) and the koala (Phascolarctos cinereus), to measure deterrency of individual trees of two species of Eucalyptus, E. ovata and E. viminalis. Average daily intakes of E. ovata foliage by common ringtail possums ranged from 2.5 to 50 g kg body mass. Koala intakes of foliage from the same individual trees ranged from 22.4 to 36.3 g kg body mass. When fed foliage from different individual E. viminalis trees, common ringtail possums ate between 1.26 and 6.28 g kg body mass while koalas ate from 14.3 to 45.9 g kg body mass. Correlative analyses showed no relationships between feeding and several measures of nutritional quality, nor with total phenolics or condensed tannins. They did, however, identify two groups of plant secondary metabolites that may cause deterrency: terpenes, and a defined group of phenolic compounds, the diformylphloroglucinols (DFPs). Further bioassay experiments with common ringtail possums showed that only the DFPs could cause the effects seen with the foliage experiments at concentrations similar to those found in the leaves. We argue that, when in sufficiently high concentrations, DFPs determine the level of food intake by these animals irrespective of other questions of nutritional quality of the leaves.

Coping with chemical complexity in mammal-plant interactions: near-infrared spectroscopy as a predictor of Eucalyptus foliar nutrients and of the feeding rates of folivorous marsupials

“…Field studies of koalas (e.g. Hindell and Lee 1987) and field and laboratory data of ringtail possum food preferences (Cork and Pahl 1984;Lawler et al 1998;this study) suggest that with appropriate calibration and the increased sampling power made possible by NIR spectroscopy, a far greater understanding of the foraging decisions made by individual animals will be developed by examining spectral variation of all individual trees within a study site.…”

Eucalyptus foliar chemistry explains selective feeding by koalas

“…We captured five adult male koalas (6.15-9.2 kg) from a wild population at Sandy Point, Victoria, in November 1997 and held them under standard conditions (Lawler et al 1998). Over 12 nights, we fed the koalas only mature (fully expanded) adult foliage from 12 E. melliodora trees using a standardized no-choice protocol (Lawler et al 2000) in a randomized block design.…”

“…Diet selection studies involving other marsupials considered either the concentration of a single FPC (Lawler et al 2000), or used crude measures of total FPC concentration (e.g. Lawler et al 1998). Likewise, we first studied the effect on koala feeding of a single FPC, sideroxylonal, which is the only FPC found in Eucalyptus melliodora.…”

Marker-Based Quantitative Genetics in the Wild?: The Heritability and Genetic Correlation of Chemical Defenses in Eucalyptus

“…Both insect and vertebrate herbivores of Eucalyptus are deterred by a range of secondary metabolites in Eucalyptus leaves, most importantly the formylated phloroglucinol compounds (FPCs), e.g., sideroxylonal (Lawler et al 1998;Wallis et al 2002;Moore and Foley 2005). Second, the concentration of the volatile terpenoid 1,8-cineole is highly correlated with sideroxylonal, allowing it to act as an indicator of palatability (Lawler et al 1999).…”