What does the koala genome tell us about the taste of eucalyptus?

New data provides insight into the marsupial's unique feeding habits

Date:  July 10, 2018

Source:  Kyoto University

Summary:

Sequencing of the koala genome has revealed some interesting qualities about these marsupials on their sense of taste. They have more bitter taste receptor genes than any other Australian marsupial, and most mammals. This possibly enables the animals to detect toxic metabolites contained in eucalyptus. Koalas even have functional receptors for both sweetness and umami.

Koalas have long captured people's hearts and minds thanks to their cuddly features and seemingly relaxed demeanor.

Now, in a collaborative study by the Koala Genome Consortium -- involving 54 scientists at 29 institutions, including Kyoto University -- researchers have successfully sequenced the entire koala genome, uncovering much that has been unknown about these mesmerizing marsupials.

Past studies have revealed many unique features of the koala's morphology, physiology and ecology. However, little was known about the animal's genome. With this study published in Nature Genetics, the koala is now the fourth marsupial species to have its genome sequenced, providing further understanding of the genetic background of its biology, and establishing a high-quality genomic reference for marsupial mammals.

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Koalas as picky leaf-eaters

Ask the Eucalyptus connoisseurs

Koalas may be the pickiest marsupials around: They evolved to feed almost exclusively on the leaves of Eucalyptus trees, and they are highly selective when it comes to which species and even which individual trees they visit. When the furry leaf-eater settles on a particular tree, it relies on a number of factors, including taste, to make its selection. In a study published in the November issue of Ecology, a journal of the Ecological Society of America (ESA), researchers used koala feeding preferences to design a new method that could help ecologists and conservationists map habitats.

Ben Moore and colleagues from the Australian National University and the Macaulay Land Use Research Institute in Scotland collected and analyzed leaves from all the trees available to koalas in a Eucalyptus woodland using a near-infrared spectroscopic model. To define "palatability" in koala terms, the researchers tested leaves on captive koalas and recorded how much they ate: They found that the koalas ate less foliage when it contained lots of lipid-soluble phenolic chemicals known as formylated phloroglucinol compounds (FPCs). The researchers then tracked koala tree visits in a Eucalyptus woodland to show that tree preferences of wild koalas could be predicted using the taste preferences of the captive koalas. The researchers also determined the chemical composition of the trees' leaves and other factors such as tree size and neighborhood quality, or how attractive each tree's neighbors were to koalas.

Specifically, koalas spend more time in large trees; however, the individual trees they prefer depend on the taste of the leaves and the "neighborhood" in which the tree is growing. Although tree size and taste are most important to the koalas, the researchers found that trees were visited more often if they were surrounded by smaller, less palatable trees or by larger, more palatable trees. Moore and colleagues explained that trees surrounded by smaller, unpalatable trees were probably more attractive by comparison. At the other extreme, trees surrounded by other large, palatable trees were visited more frequently because koalas were attracted to these high-quality areas.

"This method uses a new technique to combine our understanding of animal behavior with the chemical, spatial and physical aspects of the environment to make a map of koala habitat, as koalas see it," said Moore. "Our approach can aid ecologists in tracking and examining the presence or absence of animal populations in different areas—and it can measure plants' susceptibility to herbivory—by determining the quality and value of a habitat from the herbivore's point of view."

"Palatability mapping: a koala's eye view of spatial variation in habitat quality" from ESA's journal Ecology is open-access and available at http://www.esajournals.org/doi/pdf/10.1890/09-1714.1.

http://www.eurekalert.org/pub_releases/2010-11/esoa-kap112310.php