Same species, different sizes: rare evolutionary behavior of island bats

A University of Melbourne researcher has discovered that a rare evolutionary phenomenon occurred instantly and rapidly in bats living in the Solomon Islands.

Dr. Tyrone Lavery is publishing on evolution Two groups of leaf-nosed bats with very different body sizes are thought to be different species, a rare example of parallel evolution. Parallel evolution occurs when different groups living in similar environments independently evolve similar characteristics.

The smaller bat, Hipposideros diadema, is found on six main islands and many smaller islands. It is also common in Southeast Asia, Papua New Guinea, and parts of northern Australia. This much larger bat was named H. dinops, or ferocious leaf-nosed bat, in 1905 and is found only in the Solomon Islands. Both sizes live simultaneously on most islands, which share similar forest habitats.

“Although they are very different in size, their DNA is very similar. They use different sonar frequencies, they probably eat different foods, and even if they live together in the same cave, they don’t interbreed. That’s why No one has ever really questioned whether they are different species,” Dr Lively said.

Dr Lively said that despite their independent origins, the larger bats in each group evolved to look the same, weighing on average more than twice as much as the smaller bats. “Our study shows that larger bats evolved rapidly and repeatedly from smaller bats, each occurring independently on different islands,” he said.

“When we used bat DNA to create a family tree, we found that what we thought was just one large bat in the Solomon Islands was actually larger bats evolving multiple times from smaller species on different islands.”

This type of parallel evolution arising from different populations of the same species has only been observed in action a few times before, and it is believed to be the first time it has been documented live in a mammal.

In parts of the world, parallel evolution is found when populations are geographically separated but live in similar environments, such as different islands or lakes. A common type of parallel evolution is convergent evolution. For example, the thylacine and the wolf are two different species with different origins that each evolved to look similar. But Dr Lively said it was rare to see two isolated groups of the same species going through the same evolutionary process.

“Something very powerful is driving or selecting these large bats, and it’s powerful enough to happen multiple times on different islands. We think these larger bats may be evolving to take advantage of prey that smaller bats don’t eat. Although they may interbreed, for some reason they don’t,” he said.

Across the islands, larger bats have lower sonar frequencies, suitable for hunting larger prey, while smaller bats use higher frequencies. Dr Lively said this could mean larger bats were eating larger insects, or even frogs.

Dr Lavery measured 103 bat specimens from the Australian Museum, the Queensland Museum, the University of Kansas Museum of Natural History and the Bernice Pauahi Bishop Museum in Hawaii and found there was no overlap in body size between the two groups – the smaller ‘species’ always Easily distinguished from larger bats.

“Over time, larger body size may have been part of the behavioral and physical adaptations required to hunt larger prey. This may mean that larger and smaller bats no longer see each other as mates, so they live independently life.

Dr Lively said this parallel evolutionary pattern in leaf-nosed bats was observed in the Solomon Islands and Western Provinces of Guadalcanal, and more research was needed to see if the same pattern occurred on other islands.

“We might think of evolution as a very slow process, but when conditions are right and two populations separate and stop interbreeding, it can happen quickly. They can start evolving along different pathways,” he said.

“Islands are famous for helping us observe and understand the evolution of species in real time. They are also places that are very vulnerable to disturbance caused by humans. It is important that we look after these incredible landscapes in the Solomon Islands before we lose these stories , even before we find them.