Ellen Phiddian
Cosmos science journalist
The tiny mammals in the antechinus genus have a big reputation in ecology. The males literally mate themselves to death: they all perish in a few weeks around breeding season from uncontrollable hormone levels. And now these cute, mouse-like carnivores have another weird trait to their name.
It turns out that during this breeding frenzy, antechinuses are also partial to a bite or two – of each other!
“What’s an orgy without a feast?” says Dr Andrew Baker, an associate professor at Queensland University of Technology.
A “serendipitous” finding has allowed Baker to confirm that at least one antechinus species – mainland dusky antechinus, or Antechinus mimetes – engages in cannibalism. It could be a behaviour that appears in the other 14 species of antechinus, too.
“We’d sort of suspected that it could happen – we know that antechinuses are generalist feeders,” Baker tells Cosmos.
“Because the antechinuses have this die-off where all the males just drop dead over a period of about 1-3 weeks, the same time every year at a given location, there’s got to be a lot of dead bodies around – and it’s just a free meal. There’s no reason why they wouldn’t eat one of their own, because they’re pretty ferocious.”
But no-one had recorded any evidence of antechinus cannibalism until August last year, when Elliot Bowerman, a plant ecologist with the Sunshine Coast council, spotted something unusual on a walk at Point Lookout in New England National Park.
“[He] heard a rustle in the bushes and watched it, and then this little mammal popped out. It was dragging a carcass of something else and eating it,” says Baker.
“He didn’t realise the significance of it, but he thought, well, it’s weird to see a small mammal during the day. So he whipped out his phone and took a video.”
A mainland dusky antechinus eating a mainland dusky antechinus. Credit: Elliot Bowerman
The video, plus pictures of other dead males – some partially eaten – made their way to Baker, who identified both the devourer and the devoured as mainland dusky antechinus.
“It was great bit of naturalism from [Bowerman],” says Baker.
Baker, Bowerman and fellow ecologist Dr Ian Gynther have published a paper on the observation in Australian Mammalogy.
“It wouldn’t surprise me if it occurs in all the antechinus species,” says Baker.
“But because mostly they’re active at night, when the males fall to bits, they probably just want to crawl into a hole and die.
“And then, if they’re discovered, they’ll be discovered at night, in a hole somewhere, and eaten down there and you just won’t get to see it.”
Baker has his own experience studying antechinus to back this up. “I’ve done a fair bit of antechinus work during the breeding season, and it’s actually pretty rare that you come across a dead male,” he says.
“It’s happened to me a few times, but given the amount of males that must be around at that time, they’re going into holes and dying in private – because you just don’t see many lying on the ground.”
Baker suspects the cannibalism was “just one of nature’s secrets”.
The breeding season for antechinuses varies from place to place and species to species. Baker and colleagues had previously done fieldwork around Point Lookout and suspected that this population bred in August, but Bowerman’s data allowed them to confirm it.
The researchers believe that the eating antechinus was a male, and it was showing signs of the inevitable stress-related death that befalls all male antechinuses once their testosterone levels have spiked and they’ve bred. The mammal was missing an eye and had lost hair on its arms and shoulders, both of which are consistent with stress-induced antechinus death.
“He was probably just desperate – that’s why he was around during the day,” says Baker.
“They do weird things when they when they get towards die-off, so I think he was probably destined to be dead in a few days anyway. Maybe someone else’s meal.”
Shortly after the feeding session was observed, all the surviving dusky antechinus in that area would be female, and almost all of those females would be pregnant. The male die-off is a rare example of semelparity (suicidal reproduction) in mammals. Semelparity is more common in other living things – particularly plants, like bamboo.
Baker believes the cannibalism they’ve reported could be providing an energy boost to more than one species of antechinus.
“Often antechinus species co-occur, so there’ll be two species in the same place,” he says.
“And whenever that happens, their breeding is never quite at the same time – we think for evolutionary reasons and resource access. But it’s usually within a few weeks of each other that it happens.
“That brings up an intriguing notion. For the species breeding earlier, those males that are dying could be being eaten by their own species, but also by the other species.
“The later of the breeding species would eat those dead males because they’d be interested in putting on pounds before their own breeding is about to start.”
Breeding sessions among antechinus can last up to 14 hours, as the males seek to monopolise the females’ attention.
“Once you get to the later breeding species, when they’re dying off, the females from the earlier breeding species will be pregnant or lactating, which is an incredibly energy-sapping time,” says Baker.
“So they might be eating the dead males of the other species as well.”
Baker is part of a research team that’s found 5 new species of antechinus over the course of 10 years. His own fascination with the tiny mammals has stretched back two decades.
“You’re constantly fascinated by this life history – and I guess this is just another twist,” he says.
Alongside working to conserve some threatened antechinus populations, Baker is interested in finding ways to check these cannibalism theories.
“It’s got me thinking,” he says.
“A couple of [species] are endangered, so we’re worried about their conservation. But at the same time, I’m now wondering how we might be able to test some of those ideas.”