Old World Fruit Bats May Have Once Relied on Echolocation

fruit bat

Story at-a-glance -

  • Most fruits bats rely not on echolocation to find their food, but on their large eyes and excellent sense of smell.
  • Researchers have long puzzled over why fruit bats have such distinct methods of finding their food compared to the laryngeal echolocation used by most bats
  • New research suggests that at some point in history even fruit bats may have relied on laryngeal echolocation, but the ability was lost over time

By Dr. Becker

There are more than 1,300 species of bats around the world, which together make up 1 out of every 5 mammalian species.1 Each night, bats feast on thousands of insects, which they easily locate in the dark night sky using laryngeal echolocation, which works similar to sonar.

As bats fly, they make high-frequency calls (too high-pitched for human ears to hear) that bounce off of physical objects in their surroundings. By listening to the returning echos, bats can form an acoustical map of their surroundings.2

In most bats, echolocation sounds are produced by contracting their larynx (voice box), although fruit bats are different — in a number of ways. It was long believed that pteropodids, or Old World fruit bats, did not echolocate, but it turned out some of the bats use echolocation produced via tongue or wing clicks.3

The wing-click echolocation is used to detect large surfaces and is described as a "rudimentary form of echolocation."4 This may suffice for fruit bats since, unlike many other bats, their meals are not moving targets; fruit bats, as their name implies, eat fruit and flower products, not flying insects.

Fruit Bats May Have Once Relied on Laryngeal Echolocation

Most fruits bats rely not on echolocation to find their food, but on their large eyes and excellent sense of smell.

Researchers have long puzzled over why fruit bats have such distinct methods of finding their food, especially since fruit bats have been found to be closely related to certain groups of echolocating bats (this ruled out the theory that fruit bats and echolocating bats may come from highly diverged lineages).

New research published in the journal Nature Ecology & Evolution offers some clues, namely that at some point in history even fruit bats may have relied on echolocation, but the trait was lost over time.5

The size of the cochlea, an inner ear structure, is associated with bat echolocation, in that a bigger cochlea in relation to its skull helps bats better hear high-frequency sounds. As adults, non-laryngeal echolocating bats like fruit bats have much smaller cochleas.

When the researchers examined fruit bats' and laryngeal echolocating bats' cochleas during fetal development, however, they found their size to be similar. The Christian Science Monitor reported:6

"As the bat fetuses grew, the growth of a pteropodid's cochlea slowed down to a crawl so that in adulthood it was the same size relative to its skull as in other mammals that don't echolocate. The researchers suggest that this large fetal cochlea is a vestige of the ancestral echolocation trait."

Fruit Bats' Large Size May Explain Why They Stopped Echolocating

As for why the fruit bats may have lost laryngeal echolocation, their large size may have played a role. "It's thought that there is a body-size constraint for echolocators, as bigger bodies tend to make lower frequency sounds and laryngeal echolocation requires high-frequency sounds," The Christian Science Monitor reported.7

Bats are grouped into two categories: microbats and megabats. Fruit bats (including flying foxes) fall into the latter category, but the names are not necessarily indicative of their size (some microbats are larger than some megabats and vice versa).

Studies on bat genetics have been painting a more complex picture of bat relationships, however, such that the Bat Conservation Trust notes that dividing bats into these two categories is no longer appropriate. They note:8

"Studies of genetics have identified different relationships between some families of bats, for example the horseshoe bat family (that are insect eating and tend to be small bats) are genetically more closely related to the families of fruit bats we previously called megabats than they are those families we called microbats…

There are two alternative proposals for the new groupings of families of bats: Yinpterochiroptera and Yangochiroptera, and Vespertilioniformes and Pteropodiformes; currently researchers do not all agree which is correct and both sets of names are used.

Some scientists now also believe that echolocation was used by a common ancestor of all the bats that exist in the world today.

Echolocation might have then been lost in 'megabats,' only to re-evolve in some of these species [via tongue-clicking] — including greater horseshoe bats and lesser horseshoe bats, which live in the U.K."

It's also interesting to note that bats are the only flying mammal. Their wings are thought to have evolved from hands, which makes them extremely flexible and able to move independently. As a result, some experts believe bats are even better flyers than birds.9

Bats Are Important — and Threatened

Bats are incredibly important to the environment, offering significant benefits via pollination and pest reduction. More than 500 different types of tropical plants are pollinated by bats every year, for instance, including bananas, peaches, cloves, carob and agave (used to make tequila).10

By eating insects and reducing fungal damage, bats also save farmers more than $1 billion worldwide — and that's only for corn crops. The value of bats to the agriculture industry is estimated at $23 billion to $53 billion a year.11

Fruit-eating bats offer unique benefits of their own, as they are incredibly efficient at dispersing seeds. Bats cover large distances while feeding at night and defecate while flying, which means the fruit and flower seeds in their feces are scattered across the vast open expanses of clear-cut rainforests.

"Without bats' pollination and seed-dispersing services, local ecosystems could gradually collapse as plants fail to provide food and cover for wildlife species near the base of the food chain," Bat Conservation International reported.12

"Consider the great baobab tree of the East African savannah. It is so critical to the survival of so many wild species that it is often called the 'African Tree of Life.' Yet it depends almost exclusively on bats for pollination. Without bats, the Tree of Life could die out, threatening one of our planet's richest ecosystems."

Unfortunately, due to habitat loss and fragmentation, pesticide usage, wind turbines, the fungal disease white-nose syndrome (WNS) and other threats, 1 in every 5 bat species is at risk of extinction in the next five decades.13 If you'd like to get involved, the following steps may help protect bats worldwide:14

  • Avoid caves and mines where bats are hibernating during winter.
  • Encourage natural bat habitats around your home by reducing outdoor lighting, minimizing tree clearing and protecting streams and wetlands. Install a bat house.
  • Adhere to cave closures. Check with your state and federal agencies or a local chapter of the National Speleological Society for the status of caves and caving in your area.
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