What tiny African frogs are teaching us about conservation

Deforestation and climate change are reshaping our ecosystems faster than many species can adapt.

As global wildlife populations decline, scientists are racing to prevent species from going extinct. But even within a species, conservation strategies are often not a one-size-fits-all solution.

To understand this better, an international team of researchers have been studying two species of African reed frogs within the genus Hyperolius.

These closely related amphibians are found across Tanzania, Kenya and Malawi. Although much of their range still supports rich biodiversity, their habitat is under threat from climate change, deforestation and expanding agriculture.

Using cutting-edge technology, the researchers examined the genomes of different populations of the frogs and used this information to predict how they might be affected under various scenarios of environmental change. The results of the study have been published in the journal Evolutionary Applications.

Dr Simon Loader, our Principal Curator and expert in amphibians, was one of the authors on the paper.

“Using the genetic data, we can predict which populations of these frogs we should be the most concerned about,” Simon explains.

“Some populations will likely be able to adapt to projected environmental changes, but others are going to become much more isolated. We can then use this information to say what the most effective conservation strategy might be for that particular population.”

What can genes tell us about a population?

Although the two species of African reed frogs are closely related, they inhabit a wide range of environments from wet coastal forests to cooler mountain ranges.

By studying their DNA, the scientists discovered that different frog populations are likely to show characteristics better suited to their surroundings. So, what helps a frog to survive in one area might not work a few hundred kilometres away.

Genetic diversity refers to all of the millions of characteristics that are encoded within the genomes of living things. This genetic information is inherited from an individual’s ancestors and is often the result of millions of years of evolution.

Populations with high genetic diversity are more likely to be resilient to environmental change because the higher variations within their genes enable them to adapt and evolve more effectively.

Small, isolated populations are more likely to have low genetic diversity due to inbreeding. This reduces their ability to adapt. As species’ habitats become fragmented, populations are likely to become more isolated.

Genes can also tell us how well a population might cope with future changes in its environment. For instance, a group of animals may be well-suited to current climate conditions like temperature, rainfall and humidity. But how well do their genes match what is needed to deal with future change? This is known as genetic offset.

A high genetic offset means a population’s genetic makeup may no longer be fit for future conditions and so may struggle to survive and reproduce. Whereas a low genetic offset means a population’s genes are already close to what will be needed, and so will likely be more resilient.

How can different conservation strategies help these frogs?

By the end of the century, much of the habitat across the range of the reed frogs could disappear. But the genetic samples reveal an interesting story about the potential impact this habitat destruction might have on the amphibians.

The researchers identified three main genetic groups: one in Kenya, one spread across Tanzania and one isolated population in Malawi. Genetic differences identified in the Tanzanian frogs could also justify them being further divided into northern, central and southern populations.

The central and southern Tanzanian populations were found to have a high genetic diversity and a low genetic offset, and so are likely to be resilient to predicted environmental changes.

The team suggest that these populations could serve as genetic reservoirs to help boost diversity in surrounding smaller populations. This would mean protecting forest corridors to allow gene flow across the region.

The Kenyan population is genetically unique from the closest frogs in northern Tanzania. The population’s low genetic diversity and genetic offset could make it particularly vulnerable to environmental changes.

But in this case, researchers advise against mixing them with the Tanzanian amphibians as hybrids could lower genetic diversity even further and impact their local adaptations to the wetter climate. Therefore, for this population, protecting their forest habitat is essential for their future survival.

The Malawi frogs had a very low genetic offset with a local adaption to extreme temperatures and so are likely to be more resilient as the climate warms. But they are also the most geographically isolated frogs in the study and had a very low genetic diversity.

In this case, the researchers recommend conservation initiatives that create and improve habitats designed to help establish new populations, as well as connecting habitats to join other existing populations that were not sampled in this study.

“The African reed frogs are a good model for how we can approach conservation,” says Simon. “Amphibians are particularly sensitive to environmental change, and so they are good indicator species for what is going on in these habitats.”

“I think it would be interesting to test this with other species to see if we observe a similar pattern. But in this study, we wanted to show that if you have the DNA from a population as well as data on current and future environmental conditions, you can understand quite a lot about their needs and use that to inform conservation.”