“The local people probably thought we were crazy or lost,” he said. ‘Or both.’
But on these expeditions last year in the Guanacaste region, his team sought to reduce the point at which two different bat populations mix at their highest numbers. And it worked. Later, by analyzing the recordings of the different echolocation calls that bats use to orient themselves and hunt prey, they managed to reduce the radius from 50 to 60 kilometers to just a couple of kilometers.
Doing this was a key step in the next phase of the CULTSONG project, which examines dialects of bat song used for specific purposes such as territorial marking and courtship, and which differ from less distinctive general talk. A key goal is to discover whether such culturally acquired traits can, in fact, lead organisms to divide into separate species through the process known as speciation.
This may have important implications for investigating how culture, or learning acquired through socially transmitted behavior, affects evolution. That includes human evolution, which is already known to have been influenced through interactions between culture and genes, such as the development of lactose tolerance after the start of animal husbandry.
On top of that, vocal learning has been poorly described in other mammals, so the research could help shed light on how language evolves.
Animal culture
Dr Knörnschild, a behavioral ecologist at the Natural History Museum in Berlin, Germany, who runs CULTSONG, explains that exploring animal culture is a relatively young field outside of the usual suspects such as great apes, whales and birds. singers. And because we can’t time travel to see evolution in action, it’s even more difficult to determine whether cultural changes actually result in speciation.
However, his team’s focus species, the greater sac-winged bat ( Saccopteryx bilineata ), has characteristics that provide us with a unique opportunity to shed light on this, says Dr. Knörnschild.
For starters, researchers have discovered that the bat is a species called a ring in part of the range in which it lives. In such species, an ancestral population splits over time around each side of an uninhabitable geographic barrier, gradually diverging genetically. Eventually the populations meet again but do not interbreed there, making them separate species.
In the case of S. bilineata , this barrier is the Talamanca mountain range that extends from western Panama to the south of neighboring Costa Rica.
About a decade ago, Dr. Knörnschild’s team began to discover that some Guanacaste populations differed markedly from others in size and song compositions used. Tracking bats around the Talamanca mountain range, evidence in 2015 pointed to S. bilineata being a ring species. Subsequently, the team confirmed this by verifying the absence of crossbreeding at the end point.
“In the contact zone of these two genetic populations, they are completely ignored,” said Dr. Knörnschild. “It’s like having a time machine. If you have such a ring of sorts, you can basically flip the ring back to the ancestral population. “
He added that his team’s genetic analysis suggests that the species’ expansion across the mountain range began in the last 80,000 years, so speciation must have been recent in the evolutionary time of a bat.
Lucky find
Finding a kind of ring itself was a “super rare and really lucky find,” says Dr. Knörnschild, with only a handful of generally accepted organisms as actual examples. But the ring for S. bilineata was also shorter than the team expected for a flying species, measuring around 500 km from end to end. “Normally, when you have a highly mobile animal, like a bat, that can fly, you would expect a ring that leads to speciation to be really big,” Dr. Knörnschild said.
Knörnschild notes that one species in which song culture has been examined, the greenish warbler, has a ring that stretches thousands of kilometers around the Tibetan plateau, with no uniform, continuous and unbroken genetic and geographic divergence throughout.
Not only does the short distance make studying S. bilineata relatively easy, it also means high uniformity in its lowland rainforest habitat, allowing non-cultural influences on speciation, such as variable climates. , food sources and competing species are more easily excluded. Dr. Knörnschild said.
“We believe that the reason this change occurred in such a highly mobile animal in such a short evolutionary time frame on such a short geographic scale is because culture (socially transmitted behavior) was accelerating these differences.” Otherwise, he says, they shouldn’t have been able to accumulate enough genetic differences.
Fundamentally, Dr. Knörnschild adds, having a short continuous ring can make it easier to distinguish cause and effect as to whether the cultural change led to speciation or vice versa, something that has generally been very difficult to prove.
The team will do this by using genetic testing and song samples to determine whether song dialect divergence appears to accumulate before or after significant genetic divergence. If they happen beforehand, Dr. Knörnschild said, it would suggest that the dialect change is driving genetic change and ultimately speciation. His team will also study the colonies within the new two-kilometer contact zone they established, analyzing how the bats interact there and respond to the vocalizations of the other species.
“I think it is one of the few species in which we have a good chance to unravel whether cultural differences precede genetic differences or if they happen,” he said.
So far this part of the investigation has been delayed by Covid-19, but Dr. Knörnschild is hopeful that she can return to the field next spring. That will also allow for some final genomic tests to refine the data in a study confirming S. bilineata as a ring species, which his team originally hoped to publish earlier this year.
Communication
Bats also offer a rich medium for analyzing social interaction and language development in animals in general, due to the complexity of their communication . As Dr. Knörnschild’s research involves close observation of bats, her team is continually discovering new facets of this.
Recently, for example, they discovered through sound recordings that adult S. bilineata females use “baby talk” with a different timbre and pitch when addressing their pups. Dr. Knörnschild speculates that this could play a role similar to humans, where it increases attention and facilitates vocal learning by helping the baby select elements of speech.
Coupled with the finding that adult males communicate differently with cubs in a way that appears to convey the “vocal signature” of their group, this highlighted that their interaction is more complex than previously thought. “The deeper we dig, the more interesting things we find,” Dr. Knörnschild said.
Dr. Yossi Yovel, a neuroecologist at Tel Aviv University in Israel, has also been researching social communication as part of decision-making in bats in the GPS-Bat project he leads.
Instead of songs, his team seeks interaction through the daily “chatter” of bats. “It is interesting to see how this more fundamental type of communication develops,” he said. Although he says this is more difficult than analyzing more distinctive songs, it has been made possible by new technology, such as machine learning tools adapted from use for human voice recognition.
His team captured adult Egyptian fruit bats ( Rousettus aegyptiacus ) in a natural chicken coop in Israel, then continuously monitored them and the cubs they gave birth using ultrasonic microphones and video cameras.
Machine learning allowed them to discern the context of the frequency of the talk, such as whether it was about food, sleep, or sex, and the people involved. “We show that individual identity can be determined, so you can tell which individual is calling.” More surprisingly, he says, the identity of a bat he’s targeting could even be discerned half the time.
Dr. Yovel’s team has also created a publicly available database of nearly 300,000 files that he described as “probably one of the largest databases ever collected for an animal,” representing the full repertoire of bat vocalizations that they recorded. . This is intended to provide a comprehensive starting point for future studies on social communication, and is already used by some groups.
Dialects
Additionally, researchers have demonstrated the emergence of chatter dialects through social learning in bats. Three groups of puppies were exposed for a year, until adulthood, to the vocalizations of their mothers, in addition to an artificial reproduction that represents a specific dialect of the group. Each of them emerged with distinct reproductive-biased dialects, suggesting that they are influenced by the entire crowd around them.
The team is now taking a closer look at the dataset it has created, seeking to break down the communication of bats in depth by analyzing the order of sounds in their vocalizations to discover the structure of this ‘language’, something that can be compared to examine syntax in human speech.
“You can imagine if you arrive on a new planet with animals that have a language there, and now you want to try to understand it without the Rosetta stone: how do you do it?”
Some of the next steps in this field, which Dr. Yovel says others are already investigating, is what happens in the brains of bats when they chat. He said that one of the advantages of examining bats is that their brains are a good model for people’s because of the similarities to the human brain, so it could ultimately help us better understand our own brain and vocal learning difficulties.
“I think we now understand that the vocalizations of animals contain a lot of information,” he said. “To some extent this was known, but this idea has been dramatically strengthened.”
And Dr. Knörnschild says that finding out more about the complexity of animal farming can draw more attention to unique populations for conservation efforts. “When you have pronounced cultural differences, losing populations is tragic because you are losing these animal cultures that have been accumulating over many years,” he said. “And they may have local solutions to specific problems or unique mating preferences that are nowhere to be found.”
Original article
This article was originally published in Horizon, the EU Research and Innovation Magazine
