Echolocating bats use cognitive maps of sound to find their way home in the dark

Amazing stuff!

Why did they choose such tiny bats to attach a GPS device? "Study with 6-gram light bats"

"... In a new study, researchers placed GPS trackers on tiny pipistrelle bats living in Israel’s Hula Valley and relocated them to various points within a three-kilometer radius. Some of the animals were also blindfolded or had their sense of smell blocked. Surprisingly, even when forced to rely on echolocation alone, 95% of bats were able to find their way back to their roosts within minutes. The findings suggest that this ability allows bats to create complex mental “maps” of their surroundings, complete with various types of acoustic “landmarks,” which they use to navigate across long distances.

The researchers were also surprised to discover that, when possible, the bats used their vision to enhance navigation. ... even with such small eyes, they can rely on vision under these conditions.” ..."

"... In addition to the field experiments, the team created a detailed map of the entire valley. “We wanted to visualize what each bat experienced during flight and understand how they used acoustic information to navigate,”  ...

The model revealed that bats tend to fly near environmental features with higher ‘echoic entropy'—areas that provide richer acoustic information. “During the localization phase, bats conduct a meandering flight that, at a certain point, changes to a directional flight toward their destination, suggesting they already know where they are ..."

From the editor's summary and abstract:

"Editor’s summary

Insectivorous bats are well known to use echolocation to catch prey and navigate around obstacles. It has also been shown that more visually guided fruit bats have spatial cognitive maps of their environment. Goldshtein et al. placed minuscule GPS trackers on tiny pipistrelle bats in conjunction with temporary blocks of vision and olfaction. The authors found that the bats could still navigate across kilometer scales using only echolocation. Thus, echolocation may not only allow for local navigation, but might also translate into an acoustic cognitive map of the environment that the animals can use to navigate over long distances. —Sacha Vignieri

Abstract

Bats are known for their ability to use echolocation for obstacle avoidance and orientation. However, the extent to which bats utilize their highly local and directional echolocation for kilometer-scale navigation is unknown. In this study, we translocated wild Kuhl’s pipistrelle bats and tracked their homing abilities while manipulating their visual, magnetic, and olfactory sensing and accurately tracked them using a new reverse GPS system. We show that bats can identify their location after translocation and conduct several-kilometer map-based navigation using solely echolocation. This proposition was further supported by a large-scale echolocation model disclosing how bats use environmental acoustic information to perform acoustic cognitive map–based navigation. We also demonstrate that navigation is improved when using both echolocation and vision."

ScienceAdvisor

Echolocating bats use an acoustic cognitive map for navigation

Bats use an acoustic cognitive map for navigation (original news release)

Echolocating bats use an acoustic cognitive map for navigation (no public access)

Duplicated Gene Helps Bats Survive “Arms Race” With Viruses

Recommendable! Good news! Bats (the only flying mammal) are not just hosts of a plethora of viruses, some of them pathogenic! We can still learn so much from them.

"... bats’ ability to survive as so-called viral reservoirs may stem in part from unique mutations, including the duplication of the gene encoding an antiviral protein called protein kinase R (PKR). That second copy stems from an ongoing evolutionary “arms race,” according to the study, resulting in bats’ adaptation to and seeming immunity from a wide range of viruses over the course of their evolutionary history. ..."

From the abstract:

"Several bat species act as asymptomatic reservoirs for many viruses that are highly pathogenic in other mammals. Here, we have characterized the functional diversification of the protein kinase R (PKR), a major antiviral innate defense system. Our data indicate that PKR has evolved under positive selection and has undergone repeated genomic duplications in bats in contrast to all studied mammals that have a single copy of the gene. Functional testing of the relationship between PKR and poxvirus antagonists revealed how an evolutionary conflict with ancient pathogenic poxviruses has shaped a specific bat host-virus interface. We determined that duplicated PKRs of the Myotis species have undergone genetic diversification, allowing them to collectively escape from and enhance the control of DNA and RNA viruses. These findings suggest that viral-driven adaptations in PKR contribute to modern virus-bat interactions and may account for bat-specific immunity."

Duplicated Gene Helps Bats Survive “Arms Race” With Viruses | The Scientist Magazine® Bats are known for staying healthy even while harboring viral infections. Now, research sheds light on how their unusual immune system evolved.

Adaptive duplication and genetic diversification of protein kinase R contribute to the specificity of bat-virus interactions (open access)

Fig. 3. Evolutionary-guided functional approach reveals adaptive within-protein epistasis in bat PKR and a unique C-terminal extension in the bat poxvirus K3.

Alterations in Immune Genes Make Bats Great Viral Hosts

Very recommendable! Why do bats not get sick given all the pathogenic and lethal viruses they host? There is something to be learnt here!

"Researchers reported in PNAS yesterday (October 26 [2020]) that various species of bats have slightly different ways of suppressing inflammation, all centered on changes in genes responsible for triggering innate immune responses. ...
The authors demonstrate a number of the mechanisms in bats that seem to support their capacity to tolerate viruses that make other mammals really sick, ... “This follows a series of other publications that really highlight a dampened inflammatory response in bats that suggests that they are uniquely resistant and resilient to the consequences of immunopathology . . . and don’t experience the kind of autoimmune disease that we often incur against ourselves
In a study published in 2013 ... compared the genomes of two bat species: the fruit bat (Pteropus alecto) and insectivorous bat (Myotis davidii). They found that both species had lost a gene called AIM2, which in other mammals encodes a protein that senses pathogenic DNA and triggers inflammasomes ...
In contrast, they found, the Myotis genus of bats has functional caspase-1, but these animals’ genomes instead contain mutations in IL-1β that prevent the cytokine’s cleavage and subsequent for cellular secretion. A third species, the cave nectar bat (Eonycteris spelaea) had diminished, though not completely suppressed, function of both caspase-1 and IL-1β, resulting from a handful of mutations. ..."

From the abstract:

"... Restoration of AIM2 in bat cells led to intact ASC speck formation, but intriguingly resulted in a lack of caspase-1 or consequent IL-1β activation. We further identified two residues undergoing positive selection pressures in Pteropus alecto caspase-1 that abrogate its enzymatic function and are crucial in human caspase-1 activity. Functional analysis of another bat lineage revealed a targeted mechanism for loss of Myotis davidii IL-1β cleavage and elucidated an inverse complementary relationship between caspase-1 and IL-1β, resulting in overall diminished signaling across bats of both suborders. Thus we report strategies that additionally undermine downstream inflammasome signaling in bats, limiting an overactive immune response against pathogens while potentially producing an antiinflammatory state resistant to diseases such as atherosclerosis, aging, and neurodegeneration."

Alterations in Immune Genes Make Bats Great Viral Hosts | The Scientist Magazine® Bat species use different strategies to dampen immune activation in response to viruses.

Complementary regulation of caspase-1 and IL-1β reveals additional mechanisms of dampened inflammation in bats (public access)

Lessons from the host defenses of bats, a unique viral reservoir

Amazing stuff! Why are bats capable of hosting so many viruses without getting sick? Why are bats so unique? Why do we still not know more about bats?

"There have been several major outbreaks of emerging viral diseases, including Hendra, Nipah, Marburg and Ebola virus diseases, severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS)—as well as the current pandemic of coronavirus disease 2019 (COVID-19). Notably, all of these outbreaks have been linked to suspected zoonotic transmission of bat-borne viruses. Bats—the only flying mammal—display several additional features that are unique among mammals, such as a long lifespan relative to body size, a low rate of tumorigenesis and an exceptional ability to host viruses without presenting clinical disease. ... Recent studies suggest that 64 million years of adaptive evolution have shaped the host defence system of bats to balance defence and tolerance, which has resulted in a unique ability to act as an ideal reservoir host for viruses. ... Studying the mechanisms of immune tolerance in bats could lead to new approaches to improving human health. ... The ability of bats to harbour many viruses—and zoonotic coronaviruses in particular—may result from their ability to efficiently regulate host responses to infection, although species richness may also have a role ...
bats represent 1,423 of the more than 6,400 known species of mammal ...
Bats have been associated with infectious diseases for centuries. Their role in the transmission of rabies virus led Metchnikov to investigate fruit bat macrophages and their immune responses in 1909 ...
By contrast, infected bats show no or minimal signs of disease even when high viral titres are detected in tissues or sera, which suggests that they are tolerant of viral diseases ...
Humans express minimal baseline levels of type I interferons (IFNs), and they are highly inducible upon stimulation. By comparison, the black flying fox (Pteropus alecto) constitutively expresses some baseline IFNα, and many species of bats express several IFN-stimulated genes before stimulation. ... The kinetics of the IFN response in bats also differs from those of other mammals, with a faster decline phase for some bat interferon-stimulated genes. In addition, several antiviral genes ... are IFN-induced in bats but not in other mammals or have undergone selection pressure to potentially alter function, such as those encoding Mx proteins96 and APOBEC397 ...
In addition to the innate immune responses, recent studies have shed light on other mechanisms of bat host defence. Enhanced autophagy has a key role in the increased clearance of lyssavirus from bat cells, and is known to regulate immunity and mediate pathogen clearance. Bats express very high levels of heat-shock proteins, which confers upon bat cells the ability to survive at high temperature and high oxidative stress in vitro. ...
Both naturally infected and experimentally infected bats indicate tolerance of viral infection, even during a transient phase of high viral titres. ... This supports an immunological tolerance to RNA viruses in bats, particularly during the acute response. ..."

Lessons from the host defences of bats, a unique viral reservoir | Nature (open access)

Bats show an excellent balance between enhanced host defence responses and immune tolerance through several mechanisms. Examples of enhanced host defences include constitutive expression of IFNs and interferon-stimulated genes (ISGs), increased expression of heat-shock proteins (HSPs), a higher base level expression of the efflux pump ABCB1 and enhanced autophagy. On the other hand, dampened STING and suppressed inflammasome pathways—such as dampened NLRP3, loss of PYHIN and downstream IL-1β—contribute to immune tolerance in bats.

Why bats don't get sick

Recommendable!

Moths draped in stealth acoustic cloak evade bat sonar

Amazing stuff!

"Ultrathin sound absorbers offer lightweight solutions from building acoustics to sonar cloaking. The scales on moth wings have evolved to reduce the echo returning to bats, and we investigate their resonant sound-absorber functionality. Resonant absorbers are most efficient at resonance, and laser Doppler vibrometry (LDV) revealed that an individual moth scale’s three resonance modes indeed span the biosonar frequencies of bats.  ...

Here we investigate moth-scale vibrodynamics to understand their role in creating acoustic camouflage against bat echolocation, where scales on wings provide ultrasound absorber functionality."

Moths draped in stealth acoustic cloak evade bat sonar | Research | Chemistry World Moths can hide from the sonar of feeding bats using their acoustically camouflaged wings. Their evolved stealth adaptation is the result of an array of scales attached to their wing membranes that absorb ultrasound frequencies emitted by hunting bats, and are the first acoustic metamaterials found in nature.

Here is the PNAS paper:

Biomechanics of a moth scale at ultrasonic frequencies