Mac gets a leg up on frog research

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Sulawesi is a small island in the Indonesian archipelago. Its geographic location makes it a hotbed of biodiversity, and it is home to species not found anywhere else on the planet. Many biologists have looked there to solve some of the mysteries of evolution, including McMaster’s Ben Evans.

“I’ve been interested in evolutionary processes in general and this has been an arena to explore things like how species disperse across marine barriers, how they compete with one another when they arrive in a novel habitat, and how adaptation occurs and what it depends on,” said Evans, whose work over the last 15 years has focused on endemic primate and frog species exclusive to Sulawesi.

The species garnering the most attention is the fanged frog, which Evans explained has been divided into subspecies based on body size. The larger frogs are found in fast-flowing water, while small frogs are found on land. These smaller frogs spend more time on land than in water, and have undergone a unique adaptation that Evans and his colleagues believe has occurred to combat predation.

Most frogs reproduce by laying eggs that are externally fertilized. One species of fanged frogs, however, gives birth to live tadpoles, while another lays eggs with jelly coats on leaves. Evans finds these discoveries fascinating, but he claims it is not the most interesting aspect of this adaptation.

“I think the more important message offered by this new species is that there’s a lot of diversity we don’t even know about and therefore that there’s a lot more research to be done,” he explained.

The unique reproduction of fanged frogs has been compared to that of placental and marsupial mammals.

“If you look at it coarsely, it’s quite similar in that internal fertilization and internal gestation in mammals is advantageous because it increases offspring survival,” Evans said.

However, there are still important distinctions to make between the two groups. The phenomenon of fanged frogs giving birth to live young has evolved separately from mammals’ ability to reproduce in the same way.

“It uses a distinct set of genetic tools and probably someway comparable to mammals but it’s an independent evolution of a similar characteristic,” Evans explained.

He added that a female fanged frog has been observed giving birth in standing water already containing tadpoles. He admits it cannot be confirmed yet whether or not the tadpoles came from the same female, though he believes it is unlikely.

“It’s probably the case that she doesn’t provision the tadpoles, so she doesn’t come and bring them food like a mammal would.”

This discovery opens many doors in the fields of evolutionary biology and genetics. Evans discussed his desire to better understand the specific details of how female fanged frogs are able to give birth to live tadpoles as well as the larger scale of species diversity on Sulawesi.

“That’s going to involve field work, genetic work, it’s going to involve careful ecological studies and comparison to other species of frogs, and even other vertebrates.”

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