A recent study from the National Autonomous University of Mexico (UNAM) shows in 1998 there were 6,000 axolotls per square kilometer in Xochimilco. By 2008 that figure had plummeted to 100. And in 2014 researchers found less than one per square kilometer.

There are at least three major causes for its decline: urbanization, water pollution and the massive invasion of exotic predator fish like carp and tilapia, introduced by the Mexican government in the 1980s to help feed local communities. From the first few thousands they introduced, there are now an estimated 900 tons of fish in these canals.

“It’s an amazing amount. About 98 percent of the biomass in the water is made up of just these two fish, and they destroy everything,” said professor Luis Zambrano, an ecologist at UNAM who studies Mexican salamanders and the deterioration of their environment. “The government didn’t know what they were doing. They’ve altered the food chain and the whole ecosystem.”

By examining research on global patterns of amphibian diversification over hundreds of millions of years, De Lisle and Rowe discovered that “sexually dimorphic” species – those in which males and females differ in size, for example – are at lower risk of extinction and better able to adapt to diverse environments.

Their work suggests the ability of males and females in sexually dimorphic amphibian species to independently evolve different traits – such as size – helps them survive extinction threats that kill off others, says De Lisle.

He says classic ecological theory would not have predicted that about amphibians, a class of vertebrates that includes frogs, toads, salamanders, newts and caecilians.

The conventional school of thought believes different-sized sexes of the same species take up more resources and are less able to adapt and diversify than species where ecologically relevant traits like size are basically the same between males and females.

Venom research is a large field, especially due to the pharmaceutical potential of the venom proteins. The idea here is that venom proteins are capable of affecting the body's cells. Excessive amounts can be harmful and even lethal in some circumstances, but if the right dose is used, the venom proteins can be used to treat certain diseases. Snake proteins that normally cause prey to bleed can be used in small doses to treat blood clots, for example.

In the same way, work is currently being done to develop spider venom proteins to provide pain relief. The Aarhus researchers focused on gila lizards, and these are currently being used in pharmaceutical contexts. Gila lizards produce exendin-4, a small venom protein used in the treatment of diabetes and obesity, which is a competitor to Victoza - produced by Novo Nordisk.

To study the impact of these depressions on the reproductive success of the frogs, scientists based at the University of Vienna installed a series of plastic bowls to collect rainwater at regular intervals in a patch of rainforest in French Guiana and monitored frog populations in their test and control plots.

It was found that the frog populations expanded rapidly in both the areas with the bowls and nearby plots, from 148 frogs the season before the bowls were installed to 246 frogs two years later, while no increase was seen in plots far away from the man-made peccary wallows.