A throat-throated toad in Tanzania. Image credit: Shutterstock/Chedko
uux.cn According to a study published in biology newspaper on November 18, the toad that invaded two tropical islands shrank by 1/3 in less than a century, which is very fast in terms of evolutionary timescale.
The throat-headed toad is native to much of Africa. In 1922 and 1927, throated toads from Durban, South Africa, were introduced to the islands of Mauritius and Reunion in the Indian Ocean. Between June 2019 and March 2020, James Baxter-Gilbert's team at Stenlingbush University in South Africa captured and measured 158, 186 and 151 toads on the islands of Mauritius, Reunion and Durban, respectively.
They found that female toads on the island of Mauritius were 33.9 per cent smaller than those in Durban, while female toads on Reunion Were 25.9 per cent less in size than they had been. The male toad on the island of Mauritius has also shrunk in size, but this is not the case for the male toad on Reunion Island, and the size of amphibians on the islands usually takes thousands or millions of years to shrink.
The island has long been considered a unique testing ground for observing how animals adapt and evolve, such as dwarfism and gigantism exhibited by giant turtles in the Galapagos Islands, though it's hard to know how long this change will take. But studying the species that humans have recently introduced to the islands will make those changes easier to track.
Baxter-Gilbert said it's unclear how and why the island's throated toads shrink. This mechanism may be natural selection, or it may be that the species has the ability to shrink (phenotypic plasticity) as long as the environment changes appropriately.
"If this is the product of natural selection and functional adaptation, then the speed of this change is quite surprising." Baxter-Gilbert said.
One possible driver of the change, the researchers analyzed, was that these toads appeared to breed year-round on the island, while elsewhere they were seasonal. If female toads don't need to get fat and store more energy in a short period of time in order to lay a lot of eggs, they probably don't need to grow that big.
Next, the team will try to explore whether the shrinkage and shape of these toads' unique body shapes and shapes is due to adaptation to natural selection or phenotypic plasticity, or the interaction between the two.
Related thesis information: http://doi.org/10.1098/rsbl.2020.0651
