H.diadama. Credit: Tyrone Lavery
Studying bats living in the Solomon Islands, scientists have recorded a rare evolutionary phenomenon occurring in real-time. The phenomenon, called parallel evolution, has only been observed in action a few times before—and this is believed to be the first observed in real-time in mammals.
Parallel evolution is when different populations living in similar environments evolve similar features independently. According to a research team from the University of Melbourne, this is what has happened in two groups of leaf-nosed bats.
Because the bats have vastly different body sizes, they were always thought to be separate species. Additionally, while they live in similar forested habitats on islands, one species is more spread out than the other. The smaller bats, Hipposideros diadema, are common across the six main islands of the Solomon Islands, as well as South East Asia, Papua New Guinea and parts of northern Australia. Meanwhile, the much larger bats, known as H. dinops or Fierce Leaf-Nosed Bat, are found only in the Solomon Islands.
But when Melbourne mammalogist Tyrone Lavery created a family tree from the DNA of 103 bats he uncovered a surprising fact—the bats belonged to the same species.
“We found that what we thought was just one species of large bat in the Solomon Islands was actually a case where bigger bats had evolved from the smaller species multiple times across different islands,” said Lavery.
Parallel evolution has been found in parts of the world where populations are geographically separated but live in similar environments, such as different islands or lakes. But, Lavery said, it’s rare to see two isolated populations of the same species go through the same evolutionary process.
“Although they are very different sizes, the bats’ DNA is similar. They use very different sonar frequencies, they probably eat different food, and even when they live in the same cave together, they don’t interbreed. That is why no one has ever really questioned whether they were different species,” he explained.
“Something very strong is pushing” for the bigger bats, possibly prey selection, according to the study, published in Evolution. Across the islands, for instance, the sonar frequencies of the larger bats are lower—thereby suited to hunting bigger prey—while the smaller bats use a higher frequency. This probably means the larger bats are eating larger insects or even frogs.
“These larger bats might be evolving to take advantage of prey that the smaller bats aren’t eating,” said Lavery. “Over time larger body size may have been part of behavioral and physical adaptations needed to hunt larger prey. This might mean the bigger and smaller bats no longer recognize each other as mates, and so they live separate lives.”
As evidenced by the world-famous Galapagos Islands and the critical observations made there, islands are the perfect blueprint to observe and understand the evolutionary process in real-time.
“We may think of evolution as a very slow process, but it can happen rapidly when the conditions are right,” Lavery concluded.