Acoustic warning signals emitted by tiger moths to deter bats, a behavior called acoustic aposematism, was previously proven to occur in the laboratory. Now researchers from Wake Forest University have shown that it occurs in the moths’ natural habitat as well.
Birds and other mammals use visual aposematic signals, like bright or highly contrasting patterns, to advertise their toxicity. But, bats — the main predators of 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,” said Nick Dowdy, a graduate student at Wake Forest.
The research, published in PLOS ONE, furthers the understanding of the evolution of animal behavior in the bat vs. moth arms race. According to Dowdy, 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, Pygarctia roseicapitis and Cisthene martini. He was also able to show evidence for what he calls a “nonchalance continuum” seen in multiple species. This means that the moths don’t always dive out of the way when bats approach, as most other moths do.
“We’ve found that this is only sometimes true in tiger moths, and different species appear to use these behaviors at different rates,” he said.
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.
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