The duck-billed platypus faces many threats — climate change, loss of habitat, pollution and invasive species among others. Although they are not yet considered endangered, their numbers are declining, and some local populations have become extinct. Now, scientists have found yet another manufactured menace: the construction of dams in the rivers they inhabit.
Platypuses are semiaquatic egg-laying mammals. Despite being only one to two feet long, they can climb over dams, at least smaller ones. And although they can avoid the artificial obstacles by walking on land, predation by red foxes, as well as both feral and domestic cats and dogs presents them with additional risks.
In a study published Thursday in the journal Communications Biology, scientists found that dams are restricting platypus migration and leading to inbreeding. Interference with migration can lead to genetic weaknesses, but until now, there has been no solid data to prove it was happening among platypuses.
Over two years, the study’s researchers examined platypus populations in five rivers with dams and four without in southeast Australia, collecting blood samples from 274 individuals to study their DNA. With this genetic analysis in hand, the scientists could see that dams posed a serious threat, not only because they destroy habitat, but from an evolutionary point of view. On a genetic level, the difference between populations living in dammed and undammed rivers was stark.
“When there is no migration between populations, and the populations are small, the genetic diversity within each group drops quickly,” said Luis Mijangos, a researcher at the University of New South Wales in Australia, and an author of the study. “If there are beneficial mutations that allow individuals to adapt to climate change, these mutations are not spread to other populations.”
Platypuses only live naturally in eastern Australia and Tasmania, and there are an estimated 300,000 left in the world. In dammed rivers, they are divided into small, genetically distinct groups above and below the dam, a recipe for inbreeding and reduced numbers.
“The platypus population has declined by about 30 percent over the last couple of decades, and we knew the dams were a problem,” Dr. Mijangos said, “but we didn’t know how much of a problem.” In his view, along with climate change and platypuses accidentally drowned in fishing nets, dams are one of most significant threats to the animals’ survival.
Platypuses also lack the appeal of more spectacular troubled species like giant pandas or mountain gorillas. Despite being one of only two mammals that lay eggs (the echidna is the other) to make them odd enough, they have several other less-than-adorable characteristics.
A platypus has a tail like a beaver’s, webbed feet, nostrils that close tightly to forage underwater and legs on the sides of its body, which is more like lizards than other mammals, which tend to have legs below their bodies. They can locate prey by detecting electrical fields using receptors on their duck bills. They nurse their young but have no nipples. Instead, they feed the young through pores in their skin. Adult platypuses are toothless, chewing their food with pads made of keratin, fibrous proteins similar to those found in human fingernails and hair.
In 2020, scientists discovered that platypuses have bioluminescent fur that glowed a bluish-green when exposed to ultraviolet light — no one knows why. On top of all this, they are also venomous: The males have spurs on their back legs that secrete a toxin. Although the venom is not strong enough to kill a human, contact can cause swelling and pain that can last for months. Platypuses are not cuddly.
The World Wildlife Fund-Australia is working on a project to restore a wild platypus population in the Royal National Park in Sydney. The group plans to do some other “re-wilding” projects in other areas in the future, none of which involve the dams. To Dr. Mijangos, their future still seems grim. “As far as I am aware,” he said, “the Australian government is taking no steps to reduce the consequences of dams on platypuses.”
