Info on Bats | Moths survive bat predation through acoustic camouflage fur
Moths are a mainstay food source for bats, which use echolocation (biological sonar) to hunt their prey. Scientists such as Thomas Neil, from the University of Bristol in the U.K., are studying how moths have evolved passive defenses over millions of years to resist their primary predators.
While some moths have evolved ears that detect the ultrasonic calls of bats, many types of moths remain deaf. In those moths, Neil has found that the insects developed types of "stealth coating" that serve as acoustic camouflage to evade hungry bats.
Neil will describe his work during the Acoustical Society of America's 176th Meeting, held in conjunction with the Canadian Acoustical Association's 2018 Acoustics Week, Nov. 5-9 at the Victoria Conference Centre in Victoria, Canada.
In his presentation, Neil will focus on how fur on a moth's thorax and wing joints provide acoustic stealth by reducing the echoes of these body parts from bat calls.
"Thoracic fur provides substantial acoustic stealth at all ecologically relevant ultrasonic frequencies," said Neil, a researcher at Bristol University. "The thorax fur of moths acts as a lightweight porous sound absorber, facilitating acoustic camouflage and offering a significant survival advantage against bats." Removing the fur from the moth's thorax increased its detection risk by as much as 38 percent.
Neil used acoustic tomography to quantify echo strength in the spatial and frequency domains of two deaf moth species that are subject to bat predation and two butterfly species that are not.
In comparing the effects of removing thorax fur from insects that serve as food for bats to those that don't, Neil's research team found that thoracic fur determines acoustic camouflage of moths but not butterflies.
"We found that the fur on moths was both thicker and denser than that of the butterflies, and these parameters seem to be linked with the absorptive performance of their respective furs," Neil said. "The thorax fur of the moths was able to absorb up to 85 percent of the impinging sound energy. The maximum absorption we found in butterflies was just 20 percent."
Neil's research could contribute to the development of biomimetic materials for ultrathin sound absorbers and other noise-control devices.
"Moth fur is thin and lightweight," said Neil, "and acts as a broadband and multidirectional ultrasound absorber that is on par with the performance of current porous sound-absorbing foams."
Provided by: Acoustical Society of America
https://phys.org/news/2018-11-moths-survive-predation-acoustic-camouflage.html
Info on Bats | Tiger moths use signals to warn bats: Toxic not tasty
Acoustic warning signals emitted by tiger moths to deter bats - a behavior previously proven only in the laboratory - actually occur in nature and are used as a defense mechanism, according to new research from Wake Forest University.
Field research of free-flying bats conducted in their natural habitats by biology graduate student Nick Dowdy and colleagues shows that tiger moths produce ultrasonic signals to warn bats they don't taste good. This behavior - called acoustic aposematism - was previously proven in the laboratory by biology professor Bill Conner and Jesse Barber, who earned his doctorate at Wake Forest in 2007.
Birds and other mammals use visual aposematic signals like bright or highly contrasting patterns to advertise their toxicity. But, bats - the main predators for moths - don't rely on vision at night; they rely on sound. So, the moths developed an acoustic signal to deter the bats.
"The signals are, in essence, a warning to the bats that the moth is unpalatable and potentially harmful if ingested by the bats," Dowdy said.
The research, published in PLOS ONE, furthers the understanding of the evolution of animal behavior in the bat vs. moth arms race. Dowdy, who works in Conner's lab, said this is the first time the researchers have been able to show that this phenomenon, acoustic aposematism, actually occurs in nature. Dowdy specifically studied two types of tiger moths, the Pygarctia roseicapitis and the Cisthene martini.
Dowdy said he was also able to show evidence for what he calls a "nonchalance continuum" seen in multiple species. This means they don't always dive out of the way when bats approach. He said most moths enact evasive dives and spiraling flight when a bat is about to capture them, "presumably at a cost to the moth as it can be energetically costly to do these maneuvers. "We've found that this is only sometimes true in tiger moths and different species appear to use these behaviors at different rates."
The implication is that certain species may have evolved to rely on their warning sounds instead of the evasive maneuvers common to most eared moths. Dowdy said the results suggest that acoustic aposematism is likely to be the ancestral function of sound production in tiger moths.
"This means that in evolutionary history these moths first evolved these sounds for use in warning bats of their toxicity and then sometime later, these sounds grew in complexity in certain species to perform a sonar jamming function," he said.
Explore further: Toxic tiger moth: Researchers study evolutionary arms race in Arizona desert
More information: Nicolas J. Dowdy et al, Acoustic Aposematism and Evasive Action in Select Chemically Defended Arctiine (Lepidoptera: Erebidae) Species: Nonchalant or Not?, PLOS ONE (2016). DOI: 10.1371/journal.pone.0152981
Journal reference: PLoS ONE
Provided by: Wake Forest University
https://phys.org/news/2016-05-tiger-moths-toxic-tasty.html
Study shows long tail on luna moth helps to thwart bat attacks (w/ Video)
(Phys.org)—A team of researches with members from several institutions in the U.S. has found that the long tails sported by the luna moth exist as a means to foil attacks by bats. In their paper published in Proceedings of the National Academy of Sciences, the team reports on experiments they conducted that confirmed the true purpose of the abnormally long tails in the moths.
Scientists have suggested for years that the extremely long luna moth tails were likely a defense mechanism of some sort, because it did not appear that they served any purpose in attracting a mate. In this new effort, the researchers sought to find the answer once and for all.
Suspecting the tail likely served as a way to confuse bats (their primary predator) the researchers gathered 162 of the moths and pulled the tails off 75 of them. They then tied them individually to a ceiling in a lab and then released a brown bat into the room to see how well the moths were able to ward off attacks. They found that the bats were able to catch 85 percent of the moths with no tails, but just 35 percent of those that still had theirs. This indicated, of course, that the tails helped to confuse the bats.
To better understand how exactly the tails helped the moths confuse the bats, the researchers filmed bat attacks on the moths using high speed cameras. They found that over half the time, the bats went for the tails, rather than the body, which often resulted in a miss, or a torn tail. They suspect that the swirling tail causes the echoing sounds emitted by the bats to be confused with those made by beating wings of other prey.
The researchers also compared the success rate of bats catching luna moths against a larger species of moth to see if perhaps the longer tails helped repel bats because it made the moths bigger. They found that being bigger did not help the moths escape the bats—thus it appears that it is all about mimicking the sound of wings beating. The team next plans to test other moths with long tails to see if their tails offer the same type of benefit.
More information: Moth tails divert bat attack: Evolution of acoustic deflection, by Jesse R. Barber et al. PNAS, www.pnas.org/cgi/doi/10.1073/pnas.1421926112
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