A deep dive into past climates paints a grim outlook for fish species

Climate stability over millions of years allowed ancient and isolated freshwater fish to thrive in areas such as the 356,000 square kilometers from Shark Bay to Esperance in southwestern Western Australia.

But now accelerating climate change is threatening the biodiversity hotspot and its native fish species, according to new research in the journal heredity led by Matthew Flinders Professor Luciano Beheregaray and Ph.D. Sean Buckley.

Consisting of temperate forests and grasslands, the corner of the continent hosts more than 8,000 species of plants, of which almost half are endemic, and more than 500 recorded vertebrate species.

Unfortunately, the southwestern section of WA is also a climate change hotspot because of warmer, drier conditions, a journal summary explains.

Since the 1970s, precipitation has decreased by 10–15% and is expected to worsen in the coming decades. Over the past century, the region has also experienced a 1.1°C increase in temperature.

“This amazing biodiversity is already suffering the consequences, including species declines and recent forest die-offs,” said Flinders University Molecular Ecology Lab researcher Dr. Buckley, now Lecturer in Molecular Ecology and Environmental Management at Edith Cowan University, WA.

“It is especially about whether historically stable climates have been key to the development of this biodiversity: climate change presents a novel threat to this incredible ecosystem, and endemic species are may not have changed the capacity to respond.

“Understanding the role of historical climate stability is necessary to better predict the potential impacts of climate change on the region.”

The research focused on two small freshwater fish endemic to the region: the western (Nannoperca vittata) and small (Nannoperca pygmaea) pygmy perches.

The western pygmy perch is found throughout the region, while the lesser pygmy perch is found only in a few rivers (and is listed as Endangered on state, national and global conservation lists).

“Based on our previous research, we know that these species are likely to have existed in the landscape for a very long time and would be ideal models to look at the interaction of climate history and evolutionary patterns,” said Professor Beheregaray .

The Molecular Ecology Lab study generated genomic data from nine populations accessed through museum collections, assessing their evolutionary relationships, divergence histories, and gene flow in passage of time.

He said, “We combined these methods with environmental techniques—specifically, species distribution modeling—to see how the climate history of the region shaped their evolution.

“Using a time calibration derived from previous studies, we found that these two cryptic species last shared an ancestor about nine million years ago, with no evidence for gene flow between them . This indicates that they have been separated for a very long time.”

Environmental approaches supported this conclusion.

Using reconstructions of past climates in the region, the study found relatively little change in species range over time: except for a small expansion towards the coast during periods of lower sea levels during the ice age, pygmy perch have been found in the same areas since the Pliocene.

“These patterns reflect the climate itself, which has remained relatively stable over the same time period, especially when compared to the rest of Australia,” added Dr. Buckley.

“However, modeling these distributions under future climate change produced a clear picture, with significant range declines in species. In a business-as-usual scenario, this would include the complete loss of suitable climate for one of these enigmatic species within the next few decades.”

Conservation management actions that enhance resilience, such as genetic rescue, may be necessary to maintain the unique diversity of this part of WA.

Other ambitious strategies, such as captive breeding and reintroduction programs have been successful for other endangered pygmy perches, and may be needed in the future, the researchers said.