Biologists working to save an endangered kitten-sized Australian marsupial may have put those animals in danger — at least once they return back to their home range. The species is the endangered northern quoll. Scientists moved some quolls to an island free of the poison toads that had threatened their survival. But a new study finds this appears to have undermined a key survival instinct: fear of those toads.
The quoll spent 13 generations — just 13 years — on the island. But that’s all the time it took to lose their fear response to predators. Researchers described the finding June 5 in Biology Letters.
“Evolution can happen very rapidly” for animals with fast breeding times, says Rick Shine. He’s an evolutionary biologist at the University of Sydney in Australia. He was not involved in the study.
Separating endangered species from predators is a common conservation technique. Zoos sometimes do this by raising animals in captivity. Other groups may raise animals in safely fenced enclosures. Such isolation allows an endangered species to build up its numbers before eventually being released back into the wild.
Populations of northern quolls have been falling drastically in recent decades. Invasive poisonous cane toads have been a big cause. Quolls and other animals that attempt to eat the poisoned toads quickly die. In 2003, Australia’s Northern Territory Government tried to preserve the quolls. Their tactic was to move 45 quolls to toad-free Astell Island. (It’s located off the north coast of Australia’s mainland.)
Christopher Jolly is a biologist in Australia at the University of Melbourne. In 2016, he was part of a team that tried to release some island-reared quolls back to the mainland after 13 years in isolation. But they quickly put a halt to the program. Feral cats and dingoes (a type of wild dog) killed many of the new arrivals.
To figure out why, the researchers tested the fear responses of four groups of quolls. These worked with wild mainland quolls, island-born quolls and the offspring from both groups. Quolls from each group were given boxes of mealworms, a food quolls like. Some mealworms had no scent. Others were tainted with the scent of either feral cats or dingoes.
Wild quolls shied away from worms that smelled like their natural predators. The island quolls, however, gobbled up the worms. Quoll babies from each group responded the same way the adults had. That suggests the fear response was not something the animals had learned from their parents. It appeared natural to the wild quolls — but had been lost in the island-living animals.
The study’s findings may have lessons for other programs that aim to save endangered animals. Australia is home to plenty of unique animals found nowhere else. And an increasing number of these have become threatened or endangered with extinction. “For many of Australia’s mammals, the future is fenced,” says Alexandra Carthey, who was not involved in the study. She’s an ecologist at Australia’s Macquarie University in Sydney.
There may be a few other solutions. Mainland quolls might be trained to avoid the cane toad. That wouldn’t require taking them from their native habitat. That’s one finding from a study by Jolly and his colleagues. They published it last October in Austral Ecology. Another option: A small number of predators might be added to the isolation locations. Too many would threaten the ability of quolls populations to grow to healthy numbers. But just enough might just put a healthy fear of those predators back into them.
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behavior The way something, often a person or other organism, acts towards others, or conducts itself.
biology The study of living things. The scientists who study them are known as biologists.
colleague Someone who works with another; a co-worker or team member.
ecology A branch of biology that deals with the relations of organisms to one another and to their physical surroundings. A scientist who works in this field is called an ecologist.
dingo A type of wild dog (Canis dingo), native to Australia, with a tan or reddish coat. It may be a subspecies of the domestic dog C. familiaris dingo.
endangered An adjective used to describe species at risk of going extinct.
evolution (v. to evolve) A process by which species undergo changes over time, usually through genetic variation and natural selection. These changes usually result in a new type of organism better suited for its environment than the earlier type. The newer type is not necessarily more “advanced,” just better adapted to the particular conditions in which it developed. Or the term can refer to changes that occur as some natural progression within the non-living world (such as computer chips evolving to smaller devices which operate at an ever faster speed).
evolutionary An adjective that refers to changes that occur within a species over time as it adapts to its environment. Such evolutionary changes usually reflect genetic variation and natural selection, which leave a new type of organism better suited for its environment than its ancestors. The newer type is not necessarily more “advanced,” just better adapted to the conditions in which it developed.
evolutionary biologist Someone who studies the adaptive processes that have led to the diversity of life on Earth. These scientists can study many different subjects, including the microbiology and genetics of living organisms, how species change to adapt, and the fossil record (to assess how various ancient species are related to each other and to modern-day relatives).
feral Animals that were once domesticated but now run wild. Examples may include feral dogs, horses or pigs.
generation A group of individuals (in any species) born at about the same time or that are regarded as a single group. Your parents belong to one generation of your family, for example, and your grandparents to another. Similarly, you and everyone within a few years of your age across the planet are referred to as belonging to a particular generation of humans. The term also is sometimes extended to year classes of other animals or to types of inanimate objects (such as electronics or automobiles).
habitat The area or natural environment in which an animal or plant normally lives, such as a desert, coral reef or freshwater lake. A habitat can be home to thousands of different species.
mammal A warm-blooded animal distinguished by the possession of hair or fur, the secretion of milk by females for feeding their young, and (typically) the bearing of live young.
marsupial A type of mammal that carries its young for a period after birth in external pouches. There the developing babies have access to their mother’s nipples — and milk. Most of these species evolved in Australian and have especially long hind-legs. Examples of marsupials include kangaroos, opossums and koalas.
mealworm A wormlike larval form of darkling beetles. These insects are found throughout the world. The ever-hungry wormlike stage of this insect helps break down — decompose, or recycle — nutrients back into an ecosystem. These larvae also are commonly used as a food for pets and some lab animals, including chickens and fish.
native Associated with a particular location; native plants and animals have been found in a particular location since recorded history began. These species also tend to have developed within a region, occurring there naturally (not because they were planted or moved there by people). Most are particularly well adapted to their environment.
population (in biology) A group of individuals from the same species that lives in the same area.
predator (adjective: predatory) A creature that preys on other animals for most or all of its food.
quoll A small, meat-eating marsupial that has a spotted coat and looks similar to a cat. These animals are native to Australia and New Guinea.
species A group of similar organisms capable of producing offspring that can survive and reproduce.
strategy A thoughtful and clever plan for achieving some difficult or challenging goal.
threatened (in conservation biology) A designation given to species that are at high risk of going extinct. These species are not as imperiled however, as those considered “endangered.”
unique Something that is unlike anything else; the only one of its kind.
Journal: C. Jolly, J. Webb and B. Phillips. The perils of paradise: An endangered species conserved on an island loses antipredator behaviors within 13 generations. Biology Letters. Published online June 6, 2018. doi: 10.1098/rsbl.2018.0222.
Journal: C. Jolly et al. Out of the frying pan: Reintroduction of toad-smart northern quolls to southern Kakadu National Park. Austral Ecology. Vol 43, October 24 2017, p. 139-149. doi: 10.1111/aec.12551.