” Biologists have actually hypothesized that the 2 major groups of bats have different ways of seeing the world through noise,” stated the studys lead author Benjamin Sulser, SB 16, a UChicago alum and present Ph.D. student at the American Museum of Natural History. “This is the first time we found various neuroanatomies in the inner ear, which give these bats different methods of processing the echolocating signal.”
Yangochiroptera bats have an open inner ear canal without any wall, enabling more evolutionary variation of the neurons in the ganglion, which is rather distinctive from other mammals. Credit: Image thanks to April I. Neander
Bats are distinct mammals, the only group capable of powered flight. They are likewise very diverse, with about 1,440 species that make up more than 20% of all understood mammal types. The majority of bats navigate their world through echolocation, a method of releasing distinct sounds and then listening for the returning echo. Echolocation assists bats orient themselves, forage for food, and prevent challenges while flying.
” The capacity to echolocate opened enormous eco-friendly opportunities for bats, which own the night skies. The intricacy of this adaptation enables bats to use it in numerous different ways,” stated Bruce Patterson, the MacArthur Curator of Mammals at the Field Museum and co-author of the study.
Yin and yang, two distinct ways to echolocate
About 20 years earlier, molecular research studies of the mammal tree of life exposed that echolocating bats belong to 2 lineages: Yinpterochiroptera, or “Yin” bats, and Yangochiroptera, or “Yang” bats. An enduring concern remained: Do the ear structures vary between these 2 long-separated family trees of bats?
Sulser began this work as part of his undergraduate thesis in the laboratory of Zhe-Xi Luo, Professor of Organismal Biology and Anatomy at UChicago and senior author of the new study. He found that the inner ear ganglion, a major structure of nerve cells that links the sound recording structures of the inner ear to the brain, has various physiological configurations between Yin and Yang bats.
” Its like these two types of bats are speaking different dialects of a language.”
— Prof. Zhe-Xi Luo
The new findings started with CT scans of a number of mentor specimens of bat skulls from the Biological Sciences Collegiate Division at UChicago. After the preliminary discovery in 2016, it took another 3 years for the team to finish a full-scale study throughout 39 types of bats from practically all bat families, utilizing more specimens from both museums to support their findings.
Speaking different dialects
In all mammals, including bats, the sense of hearing begins with hair cells in the inner ear that vibrate in reaction to sound waves. These hair cells are connected to nerve cells in the inner ear spiral ganglion, which is secured by a bony canal. The canal wall has a series of holes that allow nerve fibers to poke through and connect to the main acoustic nerve going to the brain.
Yin bats rely more heavily on constant frequency sounds for echolocation, while Yang bats use a more complicated, modulated frequency. The Yang bats are also much more evolutionary varied than Yin bats, with about 5 times the number of species and more diverse modes of foraging.
” We assume that by developing this new setup, without the space constraint on the inner ear ganglion, the Yang bats have a higher capability for the ganglion cells to multiply and different methods to connect to the brain, unlike many other mammals,” Luo said. “A greater size of a ganglion and a higher number of neurons might have added to this huge evolutionary diversification of bats relying more on frequency modulating echolocation.”
Either way, both techniques of echolocation contributed to the incredible evolutionary success of bats, Luo said: “These are different methods of accomplishing the same objective. Its like these two kinds of bats are speaking various dialects of a language.”
Reference: “Evolution of inner ear neuroanatomy of bats and ramifications for echolocation” by R. Benjamin Sulser, Bruce D. Patterson, Daniel J. Urban, April I. Neander and Zhe-Xi Luo, 26 January 2022, Nature.DOI: 10.1038/ s41586-021-04335-z.
Extra authors consist of April Neander from the University of Chicago, and Daniel Urban from the University of Illinois at Urbana-Champaign and the University of California, Los Angeles.
Funding: University of Chicago, the National Science Foundation, the Field Museum, the JRS Biodiversity Foundation, and the University of Illinois.
The big brown bat (Eptesicus fuscus) is a types of Yangochiroptera bat that utilizes complex, varying noises to echolocate. Credit: Photo by Sherri and Brock Fenton
New research study is very first physiological proof for how two major groups of bats utilize echolocation in a different way.
Two major groups of bats that utilize echolocation have different structures for linking the inner ear to the brain, according to a brand-new study by scientists from the University of Chicago, the American Museum of Natural History and the Field Museum.
The research, published recently in Nature, supplies the first physiological evidence of 2 distinctive inner ear structures used for processing bats echolocation signals. The research study validates formerly found genetic evidence that echolocating bats belong to various evolutionary lineages, known respectively as “Yin” and “Yang” bats, and recommends that these two branches have various neuroanatomies of the inner ear for different designs of echolocation.
About 20 years back, molecular studies of the mammal tree of life revealed that echolocating bats belong to two family trees: Yinpterochiroptera, or “Yin” bats, and Yangochiroptera, or “Yang” bats. In all mammals, consisting of bats, the sense of hearing begins with hair cells in the inner ear that vibrate in response to sound waves. Yin bats rely more heavily on constant frequency sounds for echolocation, while Yang bats use a more intricate, regulated frequency. The Yang bats are likewise much more evolutionary diverse than Yin bats, with about five times the number of species and more diverse modes of foraging. The team believes that the various ear anatomies might contribute to bat diversity.