Science to the rescue of the chorus frog

It has just been declared an endangered species in Quebec, while its future is more uncertain than ever. If the trend continues, the chorus frog’s chances of survival could well depend on the work of a team of researchers who want to help the smallest of frogs to regain their place in the wild.

Officially threatened in Quebec

Since June 21, 2023, the Western Chorus Frog has been officially a threatened species in Quebec, a status it has held federally since 2008. Tiny amphibian measuring less than 3 cm and weighing barely 1 g at adult, this species has only four populations still viable in the province, said Tommy Montpetit, director of conservation at Ciel et Terre.

Find the right recipe

For three years now, a team of scientists has been carrying out a research project to reintroduce the species into the wild. The University of Ottawa, the Montreal Biodôme, the Quebec Ministry of the Environment and Laval University hope to find the right “recipe” to ensure the survival of the chorus frog. A mission that is all the more important since less than a quarter of the populations that remain today “would be able to maintain themselves in the medium term if the conditions remained as they are”, estimates a report from the former Ministry of Forests, Wildlife and des Parcs (MFFP), published in 2021.

The Challenge of Captive Breeding

Every spring, biologist Lyne Bouthillier, from the Quebec Ministry of the Environment, goes to a wood in Longueuil to capture adult tree frogs, male and female, which will be sent to the Montreal Biodôme. In the wild, it is at this time of year that the males begin their song to seduce the females. But in captivity, it’s a different story. For years, the Biodôme unsuccessfully tried various methods to promote the reproduction of tree frogs. It is finally thanks to the work of researcher Vance Trudeau, of the University of Ottawa, that we were able to adapt to the species a technique which was first intended for northern leopard frogs.

A love potion for tree frogs only

Under the supervision of Émiko Wong, veterinarian and senior scientist at the Biodôme, each tree frog is injected with a cocktail of hormones to promote mating. A female can lay up to 500 eggs. Tadpoles, once hatched, have gills, like a fish. In a few weeks, they transform and reach the stage of shapeshifters. At this time, future tree frogs change their digestive and respiratory systems and can begin to breathe in the open air. This is where some of the “frogettes” are transferred to Parc du Mont-Saint-Bruno in bins called mesocosms.

Reproduce a natural environment

With these mesocosms, we are trying to reproduce the natural environment of chorus frogs, explains Jeanne Dudemaine, master’s student in wood science at Laval University. “We have noticed that the shifters transform more quickly in the natural environment,” she explains. During their transformation, which lasts a few days, the amphibians stop feeding since their digestive system also changes. They survive thanks to the food reserves stored in their tail, an appendage that will also eventually disappear.

temporary ponds

A few kilometers from the location of the mesocosms, the research team had four ponds set up for the chorus frog. These ponds should be temporary, that is, they should dry up naturally over the summer. It is not for nothing that the tree frog chooses this type of ephemeral wetland to reproduce there: the chances of finding predators such as fish or green frogs are lower. Once adults, the tree frogs leave the wetland for the mainland where they will spend the rest of the year.

300 new recruits

It is in these ponds that the team released more than 300 young tree frogs on June 21st. These come from the Biodôme where they grew up in a controlled environment. The young in the mesocosms are released into the ponds almost daily at this time of year. Beforehand, the amphibians were identified using a tiny transponder injected under the skin. This will be the way to find those who will have survived the following year. Those that have not been eaten by a predator during the summer, however, must survive the winter. Despite its tiny size, the species has an amazing ability to go into hibernation. Despite everything, only 40% of individuals survive Quebec winters.

Prepare for the worst

“The objective is to accumulate knowledge to eventually be able to act if necessary, explains biologist Lyne Bouthillier. We test things. Maybe one day, we will have to do population support with our project. But the biologist is well aware that the habitat of this species, which is becoming increasingly rare, must first be protected. However, the research project is coming to an end: for lack of funding, it will not be renewed. Funded jointly by the federal and provincial governments, it benefited from an envelope of $120,000. The whole team is crossing its fingers for next year.