Scientists have known that birds are exceptionally good at creating neural maps to chart the location of sounds, and that the strategy differs in mammals. Little was known, however, about how alligators process interaural time difference.

A new study of American alligators found that the reptiles form neural maps of sound in the same way birds do. The research by Catherine Carr, a Distinguished University Professor of Biology at the University of Maryland, and her colleague Lutz Kettler from the Technische Universität München, was published in the Journal of Neuroscience on March 18, 2019.

Most research into how animals analyze interaural time difference has focused on physical features such as skull size and shape, but Carr and Kettler believed it was important to look at evolutionary relationships.

Birds have very small head sizes compared with alligators, but the two groups share a common ancestor — the archosaur — which predates dinosaurs. Archosaurs began to emerge around 246 million years ago and split into two lineages; one that led to alligators and one that led to dinosaurs. Although most dinosaurs died out during the mass extinction event 66 million years ago, some survived to evolve into modern birds.

Carr and Kettler’s findings indicate that the hearing strategy birds and alligators share may have less to do with head size and more to do with common ancestry.

“Our research strongly suggests that this particular hearing strategy first evolved in their common ancestor,” Carr said. “The other option, that they independently evolved the same complex strategy, seems very unlikely.”

To study how alligators identify where sound comes from, the researchers anesthetized 40 American Alligators and fitted them with earphones. They played tones for the sleepy reptiles and measured the response of a structure in their brain stems called the nucleus laminaris. This structure is the seat of auditory signal processing. Their results showed that alligators create neural maps very similar to those previously measured in barn owls and chickens. The same maps have not been recorded in the equivalent structure in mammal brains.

“We know so little about dinosaurs,” Carr said. “Comparative studies such as this one, which identify common traits extending back through evolutionary time add to our understanding of their biology.”

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This discovery — appearing in Nature Geoscience — will enable scientists to develop more accurate models of the role that mountain streams play in global biogeochemical fluxes. Considering that more than 30% of the Earth’s surface is covered by mountains, the ramifications of this discovery are considerable.

The study was conducted at EPFL’s Stream Biofilm and Ecosystem Research Laboratory (SBER), within the School of Architecture, Civil and Environmental Engineering (ENAC).

More turbulence

In aquatic ecosystems, such as the world’s oceans, streams and lakes, numerous aquatic organisms, ranging from bacteria to fish, respire oxygen and exhale CO₂. These gases must therefore be continually “exchanged” from the atmosphere to the water and vice-versa. Because mountain streams often flow over steep drops and rugged terrain, this creates a lot of turbulence and causes air bubbles to be trapped in the water, appearing white (aka ‘white water’).

These bubbles accelerate the gas exchange. Strikingly, the same mechanism is at work when white-capped waves appear on the surface of rough seas. Until now, scientists have ignored the contribution from air bubbles and have used the same approach to calculate gas exchange velocities in mountain streams than in calm lowland streams.

More precise calculations

It is intuitive that the rugged terrain would influence gas exchange in mountain streams, but no evidence had been collected to test this hypothesis until 2016. That’s when EPFL researchers installed more than 130 environmental sensors in mountain streams in Vaud and Valais to study this physical phenomena and related biogeochemical fluxes. To measure gas exchange velocity as accurately as possible, one of the SBER scientists and first author of the study — Amber Ulseth — along with others, added small amounts of argon as a tracer gas to the streams. Argon is a naturally occurring gas that is harmless to aquatic ecosystems.

Using cutting-edge analytical methods in the laboratory, Amber Ulseth and colleagues were able to quantify loss of argon from the streamwater. Next, they modeled the gas exchange velocity from the downstream loss of the tracer gas in the streamwater. Their results reveal that the gas exchange velocity in mountain streams is on average 100 times higher than predicted from equations developed from similar tracer gas experiments in low-land streams.

Major implications

“Our findings have major implications. They suggest that we have been underestimating the effects of all the small but abundant mountain streams in our biogeochemical models. This opens up a new research avenue,” says Tom Battin, Director of SBER and coauthor of the study. His lab is already looking into extensions of this research, such as developing a new model to predict CO₂ emissions from mountain streams worldwide.

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Study author Dr Raffaele De Lucia, of the University Hospital of Pisa, Italy, said: “Mobile ECG devices present a major opportunity to detect atrial fibrillation, the most common heart rhythm disorder, and thereby prevent strokes and reduce hospitalisations. All commercially available portable ECG devices require both hands, but what if symptoms happen while driving?”

This is the first study to show that the ear can be used for ECG signal detection. The study included 32 consecutive healthy volunteers (cardiology students and nurses). An ECG was first performed by the standard method, which uses the index and middle finger of each hand. A second ECG was conducted using the index and middle finger of the left hand and a clip attached to the left ear.

All ECGs were printed and analysed by the device and by two cardiologists who were blinded to which method had been used. No differences were detected in the ECG results obtained by the two methods.

Dr De Lucia said: “We have shown how the ear can be used as an innovative anatomical site for ECG signal detection in healthy adults. We are now conducting further studies to validate this method in patients with cardiac arrhythmias.”

The authors said the findings pave the way for a new kind of single lead ECG wearable device which leaves one hand free, making it easier to use. In addition to detecting previously undiagnosed atrial fibrillation, the device could be used to evaluate physical performance during exercise, prevent fainting, and check the heart during symptoms including dizziness and breathlessness. Patients already diagnosed with cardiac conditions such as atrial fibrillation could also use it to monitor their condition.

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“This demonstrates the clear viability of long-term frozen storage of semen. The results show that fertility is maintained despite 50 years of frozen storage in liquid nitrogen,” said Associate Professor Simon de Graaf from the Sydney Institute of Agriculture and School of Life and Environmental Sciences at the University of Sydney.

“The lambs appear to display the body wrinkle that was common in Merinos in the middle of last century, a feature originally selected to maximise skin surface area and wool yields. That style of Merino has since largely fallen from favour as the folds led to difficulties in shearing and increased risk of fly strike,” Associate Professor de Graaf said.

His colleague on this project, Dr Jessica Rickard, said: “We believe this is the oldest viable stored semen of any species in the world and definitely the oldest sperm used to produce offspring.”

Associate Professor de Graaf said that it was the reproductive biology and genetic aspects of these as-yet unpublished findings that were of most interest to him.

“We can now look at the genetic progress made by the wool industry over past 50 years of selective breeding. In that time, we’ve been trying to make better, more productive sheep,” he said. “This gives us a resource to benchmark and compare.”

Dr Rickard is a post-doctoral McCaughey Research Fellow in the Sydney Institute of Agriculture. She is continuing the strong animal reproduction research tradition in veterinary and biological sciences at the University of Sydney through her work in the Animal Reproduction Group.

Dr Rickard did the original work to determine if the stored semen was viable for artificial insemination. This involved thawing the semen, which is stored as small pellets in large vats of liquid nitrogen at -196 degrees. She and her colleagues then undertook in vitro tests on the sperm quality to determine the motility, velocity, viability and DNA integrity of the 50-year-old sperm.

“What is amazing about this result is we found no difference between sperm frozen for 50 years and sperm frozen for a year,” Dr Rickard said.

Out of 56 ewes inseminated, 34 were successfully impregnated. This compares to recently frozen semen from 19 sires used to inseminate 1048 ewes, of which 618 were successfully impregnated. This gives a pregnancy rate of 61 percent for the 50-year-old semen against 59 percent for recently frozen sperm, a statistically equivalent rate.

The original semen samples were donated in the 1960s from sires owned by the Walker family. Those samples, frozen in 1968 by Dr Steven Salamon, came from four rams, including ‘Sir Freddie’ born in 1963, owned by the Walkers on their then property at Ledgworth.

The Walkers now run 8000 sheep at ‘Woolaroo’, at Yass Plains, and maintain a close and proud relationship with the animal breeding program at the University of Sydney.

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