Subtle Echolocation: The Ancestral Origins of the Barbastelle Bat’s Quiet Hunting Technique

Researchers counter the prevailing notion that the ongoing evolutionary competition between bats and insects led to the barbastelle bat’s subdued calls. They propose instead that these quiet calls are a trait inherited from its ancestors, who were quieter gleaners rather than a direct response to the auditory capabilities of insects.

The subdued calls of the barbastelle bat might be attributable to its lineage rather than a tactical adaptation to elude insects.

Biologists often explain the balance between predators and their prey as a never-ending evolutionary struggle. In this dynamic, both predator and prey constantly adapt to outwit each other.

This concept is especially emphasized in the relationship between bats and their insect prey. Around 50 million years ago, the earliest bats acquired the capability of echolocation, enabling them to hunt in darkness. Correspondingly, certain insects developed ultrasound-sensitive hearing as a countermeasure.

Table of Contents

Questioning the Evolutionary Competition Theory

Associate Professor Lasse Jakobsen of the University of Southern Denmark, a specialist in bat biology, along with his colleagues, has recently published a study in Current Biology that disputes the idea of a continual evolutionary struggle between bats and insects.

Collaborating with Daniel Lewanzik and Holger R. Goerlitz from the Max Planck Institute for Biological Intelligence, and John M. Ratcliffe and Erik Etzler from the University of Toronto, the team delves into this argument.

Supporting the evolutionary competition theory is the observation that some bats, particularly the barbastelles (Barbastella barbastellus), emit calls that are around 20 dB less loud compared to other bats that prey on flying insects. This results in a sound pressure level that is an order of magnitude lower.

Lasse Jakobsen mentions that the barbastelle has often been presented as the bat that has “counteracted” the insects’ adaptations.

Tracing the Lineage of the Barbastelle

Nevertheless, something puzzled the research team: Close relatives of the barbastelle predominantly feed on insects located on surfaces like leaves and branches rather than flying insects. These relatives are notably quieter than species that pursue flying insects.

In the nomenclature of bat research, bats that snatch insects from the air are referred to as hawking bats. Conversely, those that feed on insects found on surfaces are known as gleaning bats. The barbastelle is classified as a hawking bat.

Jakobsen argues that if the majority of the barbastelle’s relatives are gleaners, it is highly probable that their common ancestor was also a gleaner. This makes it unlikely that the barbastelle evolved its quiet calls as a direct response to insects’ auditory defenses.

The True Explanation for the Barbastelle’s Silence

If the barbastelle’s quieter calls are not a result of evolutionary competition with insects, what is their origin?

Jakobsen explains that it is not an evolutionary advantage but rather a morphological limitation. Likely descended from a line of gleaners, the barbastelle has been restricted in its ability to produce louder calls. However, it has found a unique ecological niche where its lower-volume calls are effective.

This specific niche is inhabited by flying nocturnal insects proficient at dodging bats due to their auditory capabilities. Yet, these insects are not adept enough to detect the barbastelle, making them easy targets.

The morphological constraints may be rooted in the method of sound emission among bats. While most bats emit sound through their mouths enabling louder calls, many gleaners emit sound through their noses, resulting in calls that are 20 dB quieter.

In summary, the quiet nature of the barbastelles is not a product of an evolutionary arms race with insects. Instead, it is a characteristic inherited from their ancestors, who were quieter gleaners.

A Note on Nocturnal Flying Insects

Examples of nocturnal flying insects include moths, beetles, and mosquitoes. Many of these insects have developed auditory capabilities, allowing them to detect approaching bats. Prior to the emergence of bats approximately 50 million years ago, nocturnal flying insects faced minimal nocturnal predators. Today, bats remain the primary nocturnal predators of these insects.

Reference: “Subtle Echolocation in Aerial Hawking Bats Reflects a Substrate Gleaning Ancestry,” published in Current Biology on October 27, 2023. DOI: 10.1016/j.cub.2023.10.014

Frequently Asked Questions (FAQs) about Barbastelle Bat’s Quiet Echolocation

What is the main focus of the article?

The main focus of the article is to discuss new research that challenges the commonly held belief that the quiet calls of the barbastelle bat are an evolutionary adaptation to evade detection by insects. Instead, researchers suggest that these quiet calls are inherited traits from the bat’s ancestors, who were quieter gleaners.

Who conducted the research?

The research was conducted by Associate Professor Lasse Jakobsen of the University of Southern Denmark, along with Daniel Lewanzik and Holger R. Goerlitz from the Max Planck Institute for Biological Intelligence, and John M. Ratcliffe and Erik Etzler from the University of Toronto.

What is the evolutionary arms race hypothesis?

The evolutionary arms race hypothesis posits that predators and their prey are continually adapting to outwit each other. In the context of bats and insects, it suggests that the quiet echolocation calls of some bats are a response to insects developing ultrasound-sensitive hearing.

What is the counter-argument to the arms race hypothesis?

The counter-argument is that the barbastelle bat’s quiet calls are not a direct adaptation to evade insect hearing. Rather, they are a trait inherited from the bat’s ancestors, who were quieter gleaners that fed on insects found on surfaces like leaves and branches.

What is a “hawking bat” and what is a “gleaning bat”?

In the context of bat research, a “hawking bat” is one that catches insects in the air, while a “gleaning bat” is one that picks insects from surfaces like leaves and branches. The barbastelle is categorized as a hawking bat.

What is the significance of the barbastelle’s lineage in this context?

The lineage is significant because the barbastelle’s close relatives predominantly feed on surface-dwelling insects and are quieter than bats that hunt flying insects. This suggests that the barbastelle likely inherited its quiet calls from its ancestral gleaners, not as an adaptation to evade insect hearing.

What are the morphological limitations of the barbastelle bat?

The likely morphological limitation is rooted in the method of sound emission among bats. Most bats emit sound through their mouths, allowing for louder calls. However, many gleaners, like the presumed ancestors of the barbastelle, emit sound through their noses, resulting in quieter calls.

What kinds of nocturnal flying insects are discussed?

The nocturnal flying insects discussed in the article include moths, beetles, and mosquitoes. Many of these insects have developed auditory capabilities to detect approaching bats.