Abstract
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.
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Acknowledgements
Dr. Kath Handasyde, Dr. Ben Moore and Parks Victoria staff assisted with the capture and release of the koalas. Phillip Island Nature Park, and Marg Healy, in particular, kindly allowed us to use their koala pens and eucalypt plantation. Thanks also to Linda Merrin, Owen and Jan Marsh, and Cora Shiroyama, who helped with some of the care of the koalas. Dr. Ann Cowling and Ms. Christine Donnelly from the Statistical Consulting Unit at the Australian National University gave advice on statistical analyses. This research was approved by the Victorian Department of Sustainability and Environment and the Animal Experimentation Ethics Committee of the Australian National University and conforms to the Australian Code of Practice for the Care and Use of Animals for Scientific Purposes.
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Communicated by Ulrich Sommer.
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Marsh, K.J., Wallis, I.R. & Foley, W.J. Behavioural contributions to the regulated intake of plant secondary metabolites in koalas. Oecologia 154, 283–290 (2007). https://doi.org/10.1007/s00442-007-0828-6
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DOI: https://doi.org/10.1007/s00442-007-0828-6