Эрдэмтэд 165 сая жилийн өмнөх шавьжны дуу авиаг далавчны чулуужсан бүтцэд тулгуурлан сэргээснээр амьтдын дуу авианы хувьслын талаарх өмнөх ойлголтыг өөрчлөв.
БНХАУ-ын Өвөр Монголын Жиулоншань тогтоцын давхаргаас олдсон Юрийн галавын дунд үед хамаарах 20 гаруй чулуужсан шавьжны үлдэгдлийг Сичуаны Хөдөө аж ахуйн их сургуулийн доктор Жүн-Жиэ Гү тэргүүтэй судлаачид судалжээ. Шавьжны далавчны хатуу эдэд хадгалагдан үлдсэн дуу авиа үүсгэгч эрхтнүүдийг лазерын виброметр, компьютерын загварчлал болон машин сургалтын загваруудын тусламжтайгаар шинжилж, тухайн үеийн дуу авианы орчныг нөхөн бүрдүүлсэн байна.
Судалгааны үр дүнгээр ихэнх шавьж нь одоогийн царцаатай төстэй, 5 кГц орчим давтамжтай дуу авиа гаргадаг байсныг тогтоожээ. Гэвч Sigmaboilus peregrinus зүйлийн шавьж нь 20 кГц-ээс дээш буюу хүн сонсох боломжгүй хэт авианы давтамжаар харилцдаг байсан нь тогтоогдсон нь амьтдын дунд хэт авиа ашигласан хамгийн эртний тохиолдол болж байна.
Энэхүү олдвор нь хэт авианы харилцаа холбоог зөвхөн сарьсан багваахай үүссэний дараа хөгжсөн гэх таамаглалыг үгүйсгэж байна. Учир нь эдгээр шавьж нь сарьсан багваахай үүсэхээс бараг 100 сая жилийн өмнө хэт авиаг ашиглаж байсан нь тогтоогдлоо. Судлаачид эртний хөхтөн амьтад болон бусад махчин амьтдын сонсгол, эсвэл зүйл хоорондын өрсөлдөөн нь шавьжны дуу авианы хувьслыг хөтлөгч хүчин зүйл байсан байх магадлалтай гэж үзэж байна.
Дэлгэрэнгүйг эх сурвалжаас харах
↓Эх сурвалжийг нээх ↓
Researchers have brought back the calls of insects that lived 165 million years ago, working from fossilized wing fragments found in China. One of them called at frequencies beyond human hearing, which challenges the long-held assumption that bats pushed insects into the ultrasonic realm.
We know very little about what Jurassic forests sounded like. Dinosaurs and other charismatic vertebrates rarely leave their vocal organs behind in fossils, so their sounds aren’t definitively known.
However, insects are a different story. The sound-producing organs in the hardened cuticle of some arthropods fossilize well, and a team led by Dr. Jun-Jie Gu of Sichuan Agricultural University put that to use. Their paper appears in the Proceedings of the National Academy of Sciences.
Reading a Song in a Wing
The team, whose findings were published in the Proceedings of the National Academy of Sciences, looked at 20 fossilized ensiferan insects, including seven species within the Prophalangopsidae and two within Haglidae, an extinct family that existed from the Triassic to Cretaceous. They all came out of the Jiulongshan Formation in Inner Mongolia and date to the Middle Jurassic.
The fossils kept the delicate wing structures these insects used to “sing” by rubbing one wing against the other, a process called stridulation. As reported by Gu and colleagues:
“Unlike tetrapod vocal cords, the sound-producing organs present in the sclerotized cuticle of some arthropods do fossilize well.”
The file and plectrum can even be observed and measured in the forewings of male crickets and their relatives. Why does that matter? As the authors put it:
“These fossils incorporate a fingerprint of the acoustic signals they generated, offering a unique window into the soundscapes of the past.”
To read that fingerprint, the team mixed several techniques: comparison with nearly 100 living insect species, laser vibrometry on modern insect wings, computer simulations of how the fossil wings would have vibrated, and machine-learning models trained to predict call patterns from wing shape.
A Surprisingly Varied Soundscape
The results show a pretty diverse acoustic world. Most of the nine species produced low, pure-tone calls around 5 kHz, similar to those of some living crickets. One of them, Sigmaboilus peregrinus, appears to have called above 20 kHz, in the ultrasonic range.
“We show that ultrasonic communication was likely adopted by katydid ancestors during the Middle Jurassic, some 165 million years ago, the oldest record known for ultrasound communication in animals,” the authors wrote. They were also careful: “For now, we can only confirm that Jurassic ensiferans were communicating with a broad range of frequencies from low audio to moderate ultrasound.”
These ancient insects had also started to diversify their signaling strategies through changes in body size and stridulatory file morphology.
Rethinking the Role of Bats
Bats are usually credited with driving the evolution of ultrasonic communication and hearing in insects, as a way to evade echolocating predators. But bats showed up roughly 55 million years after these fossil insects, so the finding predates them.
“We here reject the hypothesis that bats were the sole driver of ultrasound evolution in katydids. Instead, it is likely that early mammals and non-mammalian ancestors were also listening in to the songs of ensiferans, driving early diversification of acoustic signaling strategies,” the authors wrote. Competition may have played a part too: “The evolution of ultrasound could have also been driven by acoustic niche partitioning due to interspecific competition.”
Add in the evidence for ultrasound in Cretaceous moths, and the authors say bats emerged nearly 100 million years after singing ensiferans “into a soundscape already busy with ultrasounds.”
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