In a paper published in the journal Scientific Reports, researchers described the signature whistles produced by six distinct geographical units of the common bottlenose dolphin (Tursiops truncatus) in the Mediterranean Sea and identify the main determinants of their variability. Their results show that it is the local ocean environment and population demographics, and not genetics, that best explains the different lengths and pitches of the whistles.
A group of bottlenose dolphins in Xcaret, Mexico.
“Acoustic signals are widely used in animals, from insects to mammals, and can be involved in a variety of contexts such as sexual selection, social cohesion, individual and group recognition, resource defense and competition,” said Dr. Gabriella La Manna, a researcher with the Università degli Studi di Sassari and MareTerra Onlus, and her colleagues.
“Cetaceans (whales, dolphins, and porpoises) rely on acoustic communication for orientation, locating food, reproduction and avoiding predators.”
“Consequently, they have a varied and complex acoustic repertoire, used to transmit information related to the sender identity (individual, social group, population, species), sender position and behavioral contexts.”
“Some of the most studied cetacean species produce individual signals aimed to identify the emitter, as in bottlenose dolphins (Tursiops spp.), or have acoustic repertoires able to identify family group or population, as in killer whales (Orcinus orca) and sperm whales (Physeter macrocephalus).”
“Bottlenose dolphins live in fission-fusion societies where individual recognition, contact maintenance, and group coordination are mediated by frequency-modulated, narrow-band acoustic signals, called whistles.”
“Those whistles characterized by a stereotyped frequency modulation pattern and used to identify the emitter are known as signature whistles. They are primarily produced when an animal is separated by the conspecifics and to ensure social cohesion.”
“The signature whistle develops during the first year of a dolphin’s life and seems to be modeled hearing whistles from conspecifics and through vocal production learning.”
Using 188 hours of recorded acoustic data, Dr. La Manna and co-authors analyzed the differences in signature whistles between six geographically distinct populations of common bottlenose dolphins across the Mediterranean Sea.
The sites included Port Cros in the French Riviera, Alghero in the Sardinian Sea, and Ostia-Fiumicino in the Tyrrhenian Sea (all considered the western Mediterranean region); Cres-Losinj in the Adriatic Sea and the Gulf of Corinth in the Ionian Sea (both considered eastern); and Lampedusa in the Strait of Sicily (considered southern).
The researchers identified 168 individual signature whistles and mapped variations in acoustic features such as duration and changes in pitch.
They analyzed the influence of region (a proxy for genetic variation), geographic site, the local ocean environment (such as whether the sea bottom was muddy or covered in seagrass), and population demographics had on differences between signature whistles.
“The local ocean environment and population most strongly influenced signature whistle variation,” they said.
“For example, signature whistles in areas with seagrass, such as Lampedusa and Port Cros, were higher pitched and shorter in length compared to when the sea bottom was muddy.”
“In small populations, such as in the Gulf of Corinth, signature whistles had more changes in pitch than among larger populations.”
“In contrast, region — and therefore genetic variation — had no strong influence on whistles.”
“The findings support the ‘acoustic adaptation hypothesis’ and that bottlenose dolphins develop signature whistles best suited to their local habitat.”
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G. La Manna et al. 2022. Determinants of variability in signature whistles of the Mediterranean common bottlenose dolphin. Sci Rep 12, 6980; doi: 10.1038/s41598-022-10920-7
Source link: https://www.sci.news/biology/bottlenose-dolphin-signature-whistles-10858.html
