Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

An Ancient Biosonar Sheds New Light on the Evolution of Echolocation in Toothed Whales

05.04.2013
Some thirty million years ago, Ganges river dolphins diverged from other toothed whales, making them one of the oldest species of aquatic mammals that use echolocation, or biosonar, to navigate and find food. This also makes them ideal subjects for scientists working to understand the evolution of echolocation among toothed whales.
New research, led by Frants Havmand Jensen, a Danish Council for Independent Research | Natural Sciences postdoctoral fellow at Woods Hole Oceanographic Institution, shows that freshwater dolphins produce echolocation signals at very low sound intensities compared to marine dolphins, and that Ganges river dolphins echolocate at surprisingly low sound frequencies. The study, "Clicking in shallow rivers," was published in the journal PLOS ONE.

“Ganges River dolphins are one of the most ancient evolutionary branches of toothed whales,” says Jensen. “We believe our findings help explain the differences in echolocation between freshwater and marine dolphins. Our findings imply that the sound intensity and frequency of Ganges river dolphin may have been closer to the ‘starting point‘ from which marine dolphins gradually evolved their high-frequent, powerful biosonar.”

The scientists believe these differences evolved due to differences in freshwater and marine environments and the location and distribution of prey in those environments.

A complex, underwater environment

To sustain themselves, river dolphins must find their food, often small fish or crustaceans, in highly turbid water where visibility seldom exceeds a few inches. Like their marine relatives, they manage this using echolocation: They continuously emit sound pulses into the environment and listen for the faint echoes reflected off obstacles while paying special attention to the small details in the echoes that might signify a possible meal.

The environment that freshwater dolphins operate in poses very different challenges to a biosonar than the vast expanses of the sea where most dolphins later evolved. “Dolphins that range through the open ocean often feed on patchily distributed prey, such as schools of fish,” Jensen says. “They have had a large advantage from evolving an intense biosonar that would help them detect prey over long distances, but we have little idea of how the complex river habitats of freshwater dolphins shape their biosonar signals.”

Shy study animals with a surprisingly deep voice

To answer that question, the researchers recorded the echolocation signals of two species of toothed whales inhabiting the same mangrove forest in the southern part of Bangladesh: The Ganges river dolphin, an exclusively riverine species that is actually not part of the dolphin family but rather the Platanistidae family, and the Irrawaddy, a freshwater toothed whale from the dolphin family that lives in both coastal and riverine habitats.

Surprisingly, the echolocation signals turned out to be much less intense than those employed by marine dolphins of similar size and it seemed that the freshwater dolphins were looking for prey at much shorter distances. From this, the researchers surmise that both the dolphin species and the river dolphin were echolocating at short range due to the complex and circuitous river system that they were foraging in.

While both Irawaddy and Ganges river dolphin produced lower intensity biosonar, the Ganges river dolphin had an unexpectedly low frequency biosonar, nearly half as high as expected if this species had been a marine dolphin.

”It is very surprising to see these animals produce such low-frequent biosonar sounds. We are talking about a small toothed whale the size of a porpoise producing sounds that would be more typical for a killer whale or a large pilot whale,” says Professor Peter Teglberg Madsen from Aarhus University in Denmark, an expert on toothed whale biosonar and co-author of the study.

A new perspective on the evolution of biosonar

The study suggests that echolocation in toothed whales initially evolved as a short, broadband and low-frequent click. As dolphins and other toothed whales evolved in the open ocean, the need to detect schools of fish or other prey items quickly favored a long-distance biosonar system. As animals gradually evolved to produce and to hear higher sound frequencies, the biosonar beam became more focused and the toothed whales were able to detect prey further away.

However, the Ganges river dolphin separated from other toothed whales early throughout this evolutionary process, adapting to a life in shallow, winding river systems where a high-frequency, long-distance sonar system may have been less important than other factors such as high maneuverability or the flexible neck that helps these animals capture prey at close range or hiding within mangrove roots or similar obstructions.

Improved tools for counting animals

Freshwater dolphins are among the most endangered animal species. Only around a thousand Ganges river dolphins are thought to remain, and they inhabit some of the most polluted and overfished river systems on Earth. The results of this study will help provide local collaborators with a new tool in their struggle to conserve these highly threatened freshwater cetaceans. Using acoustic monitoring devices to identify the local species may help researchers estimate how many animals remain, and to identify what areas are most important to them.

Dr. Frants Havmand Jensen is funded by an Individual Postdoctoral Fellowship and a Sapere Aude award from the Danish Council for Independent Research | Natural Sciences.

The Woods Hole Oceanographic Institution is a private, non-profit organization on Cape Cod, Mass., dedicated to marine research, engineering, and higher education. Established in 1930 on a recommendation from the National Academy of Sciences, its primary mission is to understand the oceans and their interaction with the Earth as a whole, and to communicate a basic understanding of the oceans’ role in the changing global environment. For more information, please visit www.whoi.edu.

Originally published: April 3, 2013

Press Office | EurekAlert!
Further information:
http://www.whoi.edu

More articles from Ecology, The Environment and Conservation:

nachricht Dry landscapes can increase disease transmission
20.06.2018 | Forschungsverbund Berlin e.V.

nachricht 100 % Organic Farming in Bhutan – a Realistic Target?
15.06.2018 | Humboldt-Universität zu Berlin

All articles from Ecology, The Environment and Conservation >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Temperature-controlled fiber-optic light source with liquid core

In a recent publication in the renowned journal Optica, scientists of Leibniz-Institute of Photonic Technology (Leibniz IPHT) in Jena showed that they can accurately control the optical properties of liquid-core fiber lasers and therefore their spectral band width by temperature and pressure tuning.

Already last year, the researchers provided experimental proof of a new dynamic of hybrid solitons– temporally and spectrally stationary light waves resulting...

Im Focus: Overdosing on Calcium

Nano crystals impact stem cell fate during bone formation

Scientists from the University of Freiburg and the University of Basel identified a master regulator for bone regeneration. Prasad Shastri, Professor of...

Im Focus: AchemAsia 2019 will take place in Shanghai

Moving into its fourth decade, AchemAsia is setting out for new horizons: The International Expo and Innovation Forum for Sustainable Chemical Production will take place from 21-23 May 2019 in Shanghai, China. With an updated event profile, the eleventh edition focusses on topics that are especially relevant for the Chinese process industry, putting a strong emphasis on sustainability and innovation.

Founded in 1989 as a spin-off of ACHEMA to cater to the needs of China’s then developing industry, AchemAsia has since grown into a platform where the latest...

Im Focus: First real-time test of Li-Fi utilization for the industrial Internet of Things

The BMBF-funded OWICELLS project was successfully completed with a final presentation at the BMW plant in Munich. The presentation demonstrated a Li-Fi communication with a mobile robot, while the robot carried out usual production processes (welding, moving and testing parts) in a 5x5m² production cell. The robust, optical wireless transmission is based on spatial diversity; in other words, data is sent and received simultaneously by several LEDs and several photodiodes. The system can transmit data at more than 100 Mbit/s and five milliseconds latency.

Modern production technologies in the automobile industry must become more flexible in order to fulfil individual customer requirements.

Im Focus: Sharp images with flexible fibers

An international team of scientists has discovered a new way to transfer image information through multimodal fibers with almost no distortion - even if the fiber is bent. The results of the study, to which scientist from the Leibniz-Institute of Photonic Technology Jena (Leibniz IPHT) contributed, were published on 6thJune in the highly-cited journal Physical Review Letters.

Endoscopes allow doctors to see into a patient’s body like through a keyhole. Typically, the images are transmitted via a bundle of several hundreds of optical...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Munich conference on asteroid detection, tracking and defense

13.06.2018 | Event News

2nd International Baltic Earth Conference in Denmark: “The Baltic Sea region in Transition”

08.06.2018 | Event News

ISEKI_Food 2018: Conference with Holistic View of Food Production

05.06.2018 | Event News

 
Latest News

Creating a new composite fuel for new-generation fast reactors

20.06.2018 | Materials Sciences

Game-changing finding pushes 3D-printing to the molecular limit

20.06.2018 | Materials Sciences

Could this material enable autonomous vehicles to come to market sooner?

20.06.2018 | Materials Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>