In 1922, the guttural toad (Sclerophrys gutturalis), a common amphibian in sub-Saharan Africa was introduced to the Republic of Mauritius in an attempt to control cane beetles. They were then moved to the neighbouring Reunion Island around 1927 as a biocontrol for malaria-causing mosquitoes. A new study has shown that these toads, now an invasive population on the two islands has shrunk in size. The female toads on Mauritius and Reunion were 33.9% and 25.9% smaller respectively than their original South African counterparts. The males shrank by 22.4% on Mauritius, but not on Reunion Island. This extraordinary reshaping of morphology has taken place in less than 100 years, a very short evolutionary time. The results were published in Biology Letters.
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Ecosystems and traits
The team from MeaseyLab at the Centre for Invasion Biology in Stellenbosch University, South Africa has been studying these toads in different invasive populations. “My interests in them had to do with looking at how novel ecosystems shift and shape different traits, like body shape, physical abilities, and behaviour. Instances like when animals are moved to islands or colonised urban landscapes, are excellent natural experiments to look for evolutionary change and understand the mechanisms that allow wildlife to adapt to a changing world,” explains lead author James Baxter-Gilbert in an email to The Hindu .
“The really fascinating part is since both island populations came from the same origin (Durban in South Africa) they effectively started with the same basic ‘genetic blueprint’ so any consistent change we see on both islands happening can help shed light on what traits are being repeated on both islands independently. This can provide a lot of insight into what challenges these invading populations faced and how natural selection (or phenotypic plasticity) allowed them to overcome them,” adds Prof. Baxter-Gilbert.
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Nitya Mohanty, one of the authors of the paper explains: “It is important to determine what mechanisms are at play, whether it is natural selection or a part of their repertoire which is just expressed in that environment. We need to study if there are some genetic changes, probably adaptive changes: organisms which are on islands have less need for dispersal, but can allocate that energy to more frequent reproduction or some other trait to survive better.” Dr. Mohanty completed his postdoc from Stellenbosch University.
Garden experiment
He says that one way to find out is to do a common garden experiment where you bring a bunch of toads from the invasive and native populations, and breed them in their native ranges in South Africa and see if it is to do with the environment or it is indeed genetic.
“We have also begun to examine changes in behavioural traits, like boldness and exploration. There are anecdotes of the toads engaging in curiosity behaviour on the island, like climbing trees, and we are also looking into this for future research that might help us explain the reason for this shift in body size,” adds Prof. Baxter-Gilbert.
