Bushfires decrease genetic diversity in frog populations

The increasing intensity and frequency of bushfires in Victoria is having a significant impact on the genetic diversity of the state’s frog populations — the same genetic diversity that gives these frogs the ability to adapt to environmental changes, such as shifts in temperature, rainfall and, ironically, bushfires.

In the past 30 years, bushfires have increased in both frequency and intensity in Australia, and climate change models predict that this will further escalate. The impact of this trend on frogs has until now been poorly understood; however, it was already clear that amphibians are particularly vulnerable to changing environmental conditions.

Scientists from Museums Victoria and the University of Melbourne started surveying Victoria’s Kinglake region for frogs in 2007 — two years prior to 2009’s catastrophic Black Saturday bushfires. This led the scientists to investigate the bushfires’ effect on two particular kinds of frogs — the southern brown tree frog (Litoria ewingii) and the plains brown tree frog (Litoria paraewingi) — with the results published in the Journal of Applied Ecology.

An early count and acoustic surveys indicated there had only been a small decline in the number of breeding males in the region, suggesting that the frog species hadn’t been badly affected by the Black Saturday bushfires and were therefore well adapted to such ecological disturbances. However, the genetic data revealed a different picture.

The effective population size (ie, the number of adults who contribute offspring to the next generation) of both species of frog had decreased and the frogs had become more inbred in the years following the fires. The plains brown tree frog showed an increase in inbreeding of approximately 139%, while the effective population size of the southern brown tree frog decreased by 98% immediately following the fire. Furthermore, modelling indicated that there was an 80% probability that a population of Victorian tree frog could become extinct if subjected to 10 intense fires per 100 years.

“This new understanding of how bushfires affect the persistence of frogs in the Victorian environment should be used by authorities to help them make informed decisions about land management,” said Jane Melville, a senior curator at Museums Victoria and co-author on the study. “Fire authorities should carefully consider the timing of controlled burns and conservation efforts after fires should focus on providing frogs with the ability to move across the landscape to re-established genetically healthy populations.”

Image caption: A southern brown tree frog. Image credit: David Paul.