Major dams have disrupted gene flow between platypus populations, making them more vulnerable to threats, according to new research.
Scientists from the University of New South Wales examined the genetic makeup of platypuses in free-flowing and dammed rivers in that state.
Their results, published in Communications Biology, found there was greater genetic differentiation between platypus populations located above and below dams compared to populations in free-flowing rivers.
They said this indicated large dams were major barriers to the movement of platypuses, resulting in limited or no gene flow between separate populations.
Prof Richard Kingsford, the director of the UNSW Centre for Ecosystem Science and one of the paper’s authors, said the findings had significant implications for platypus conservation.
“This is the first time that we’ve got some really good evidence of what we suspected might be going on,” he said.
The scientists took blood samples from platypus populations above and below five dams in New South Wales: Dartmouth, Eucumbene, Jindabyne, Pindari and Nepean.
They also took samples from populations in adjacent free-flowing rivers without dams.
The researchers extracted DNA from the samples and found large differences between the genetic composition of populations living above dams and those living below. This level of genetic differentiation was not found in the neighbouring rivers without dams.
“By using thousands of molecular markers, we were able to identify a strong signal indicating that genetic differentiation increased rapidly between platypuses below and above these large dams,” said the paper’s lead author, Luis Mijangos, a former UNSW PhD student who is now at the University of Canberra.
The differences were found to be greater the longer the dam had been present.
Kingsford said the results suggested dams prevented platypuses from moving up and down rivers and meeting up with other platypuses. This meant a population below a dam eventually started to change genetically from the group above because they were unable to mix their genes.
He said over the long term this could lead to inbreeding and reduced genetic variability, resulting in populations that were less adaptable and more vulnerable to threats.
The inability to disperse also meant platypuses could not move to areas with more suitable conditions. “In the long term, it can contribute to the local extinction of a population, usually below the dam,” Kingsford said.
Platypuses are declining in many parts of their range in eastern Australia. Dr Gilad Bino, another of the paper’s authors, said the research showed dams were one of the main threats to the species.
The authors said water conservation and management planning should consider alternative approaches to large dams.
Kingsford said some populations might also require human interventions in future, such as translocation from one part of a river to another, to improve their genetic variability.
Dr Melody Serena, a conservation biologist at the Australian Platypus Conservancy, said platypuses were capable of circumventing waterfalls more than 30m high and man-made weirs at least 10m high.
She said the UNSW research suggested a different rule might apply when a platypus encountered a very large weir (more than 70m high).
“However, the good news is that the study also confirmed that inbreeding has not yet actually increased due to restricted movement – platypus populations on both sides of study weirs remain genetically diverse,” she said.
