Rare type of parallel evolution found in island bats

In the Solomon Islands, a team of scientists led by the University of Melbourne has identified a swift and unusual type of evolutionary change among local bat populations. The experts suggest that two distinct groups of leaf-nosed bats, initially thought to be different species due to their significant size differences, are actually proof of a rare case of parallel evolution.

Different sizes, similar DNA

Although these two species share the same environment, they have independently developed similar traits. The smaller species, Hipposideros diadema, is widespread, inhabiting not only the Solomon Islands but also regions in Southeast Asia, Papua New Guinea, and northern Australia. In contrast, the larger species, named Hipposideros dinops or the Fierce Leaf-Nosed Bat in 1905, is exclusive to the Solomon Islands.

“Although they are very different sizes, the bats’ DNA is very 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,” explained lead author Tyrone Lavery, a mammalogist at the University of Melbourne. 

Rapid evolution of larger-bodied bats

According to the scientists, despite their independent origins, each group of larger bats has evolved to look the same, averaging more than double the weight of the small bat. “Our research suggests the rapid and repeated evolution of larger bodied bats from smaller bats, each happening independently on separate islands,” said Lavery.

“When we created family trees using the bats’ DNA, 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.”

Parallel bat evolution 

This phenomenon of parallel evolution, where separated populations of the same species evolve similar traits in similar environments, is exceedingly rare and seldomly observed in real-time, especially among mammals. 

The experts suggest that these larger bats might be evolving to exploit food sources not accessible to their smaller counterparts, although they are theoretically capable of interbreeding.

“Something very strong is pushing or selecting for these big bats, and it is strong enough for it to happen multiple times on different islands. We think these larger bats might be evolving to take advantage of prey that the smaller bats aren’t eating. Although they could probably interbreed, they don’t for some reason,” Lavery said.

Diverse dietary preferences 

The differences in sonar frequencies between the groups suggest diverse dietary preferences, with the larger bats likely targeting bigger prey such as larger insects or even frogs. 

The study, which included measuring 103 bat specimens from various international museums, confirmed no overlap in body size between the two groups, reinforcing their distinct developments despite genetic similarities.

Islands and bat evolution

According to Lavery, this pattern of parallel evolution in leaf-nosed bats has been observed in the Solomon Islands on Guadalcanal and in the Western Province, but more research is needed to see if the same pattern occurs on other islands. 

“We may think of evolution as a very slow process, but it can happen rapidly when the conditions are right and two groups are separated and stop interbreeding. They can begin to evolve on different pathways,” he said.

“Islands are famous for helping us to observe and understand the processes for how species evolve in real time. They’re also places that are very vulnerable to the types of disturbance that humans create. It’s important that we look after these incredible landscapes in Solomon Islands before we lose these stories even before we find them,” he concluded.

More about bat evolution

Bats represent a remarkable example of mammalian evolution, having developed unique adaptations that allow them to thrive across diverse environments globally. The evolution of bats is particularly notable for their development of flight and echolocation, which have played crucial roles in their ability to occupy ecological niches that other mammals cannot.

Early bats

The fossil record suggests that bats first appeared at least 50 million years ago during the Eocene epoch. These early bats already possessed the wing structures necessary for flight, indicating that their ability to fly evolved quite rapidly in evolutionary terms. 

This quick adaptation to flight is believed to have significantly contributed to their global spread and diversification.

Echolocation

Echolocation, the ability to navigate and find food using sound waves, is another key evolutionary development in bats, although it is not universal among all bat species. 

Echolocation likely developed after flight, with different bat species evolving this ability independently. This suggests a strong evolutionary pressure to optimize feeding strategies in dark environments, like night skies or dense forests.

Convergent evolution

Molecular studies have provided insights into bat phylogeny, showing that bats are divided into two main suborders: the largely fruit-eating megabats and the echolocating microbats. 

Interestingly, some megabats have also developed echolocation, albeit through different mechanisms than microbats, showcasing convergent evolution – where different species independently evolve similar traits.

Morphological changes and diet

Bats have also adapted to a wide range of dietary preferences, from insects and fruit to vertebrates and blood, each adaptation allowing bats to exploit new or underserved ecological niches.

These dietary adaptations are accompanied by morphological changes, such as tooth and jaw structure, digestive enzymes, and flight adaptations, enabling them to specialize and thrive.

The study is published in the journal Evolution.

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