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 Successful calculation of human and natural influence on cloud formation
04.11.2016 | Goethe-Universität Frankfurt am Main

nachricht Invasive Insects Cost the World Billions Per Year
04.10.2016 | University of Adelaide

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: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

Im Focus: MADMAX: Max Planck Institute for Physics takes up axion research

The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.

The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...

Im Focus: Molecules change shape when wet

Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water

In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...

Im Focus: Fraunhofer ISE Develops Highly Compact, High Frequency DC/DC Converter for Aviation

The efficiency of power electronic systems is not solely dependent on electrical efficiency but also on weight, for example, in mobile systems. When the weight of relevant components and devices in airplanes, for instance, is reduced, fuel savings can be achieved and correspondingly greenhouse gas emissions decreased. New materials and components based on gallium nitride (GaN) can help to reduce weight and increase the efficiency. With these new materials, power electronic switches can be operated at higher switching frequency, resulting in higher power density and lower material costs.

Researchers at the Fraunhofer Institute for Solar Energy Systems ISE together with partners have investigated how these materials can be used to make power...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

UTSA study describes new minimally invasive device to treat cancer and other illnesses

02.12.2016 | Medical Engineering

Plasma-zapping process could yield trans fat-free soybean oil product

02.12.2016 | Agricultural and Forestry Science

What do Netflix, Google and planetary systems have in common?

02.12.2016 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>