Friday, 2 December 2016

What role does mouth shape play for echolocating bats?

Specialized facial muscles support sonar beam forming by free-tailed bats
Date: November 28, 2016
Source: Acoustical Society of America (ASA)

Echolocating bats are able to manipulate the acoustic projection pattern of their sonar pulse emissions -- but how they do it remains a largely unexplored mystery.

The Mexican free-tailed bat, Tadarida brasiliensis, appears to do it by adjusting the shape of its mouth cavity, aka beam forming, similar to the way humans purse their lips to create an "O" sound. While this is usual for humans, it is unusual for animals. Flying Tadarida lift their nose and lips before each echolocation pulse with a set of specialized facial muscles.

In a moment of serendipity while working on another project, Samantha Trent, a doctoral candidate working with Michael Smotherman at the Texas A&M Institute for Neuroscience, noticed a large group of muscles running straight down the middle of the top of the bat's skull. A set of muscles like this is quite unusual in size and location for a small mammal, so she questioned their purpose.

During the 172nd Meeting of the Acoustical Society of America and the 5th Joint Meeting with Acoustical Society of Japan, being held Nov. 28-Dec. 2, 2016, in Honolulu, Hawaii, Smotherman will present his work with Trent exploring the muscle's complex activity patterns during sonar performance, whether the muscle tissue displays necessary fast-twitch specializations to accommodate echolocation, and how manipulations of mouth shape altered 3-D beam patterns.

"It seems evident that this particular set of muscles is involved in changing the shape of the bat's mouth -- especially during echolocation," Trent said. "We think this aids the bat's ability to change the shape of its outgoing echolocation pulse beam."

To put this to the test, they used a microphone array to capture recordings from all around the bat's head to build a picture of the beam shape of sound coming out its mouth. They also recorded electrical activity from these muscles while the bats were freely echolocating to determine how these muscles are involved in producing echolocation pulse streams.

Tail hairs reveal dietary choices of three horse species in the Gobi Desert

Date: November 30, 2016
Source: Veterinärmedizinische Universität Wien

Przewalski's horse, a species of wild horse that has been successfully reintroduced to the Gobi Desert, shares its pasture grounds with wild asses and free-roaming domestic horses. A scarce supply of food could lead to food competition among the different species, especially if they make the same dietary choices. A team led by researchers from Vetmeduni Vienna therefore chemically analysed the tail hairs of the animals to determine the seasonal dietary habits of the three species. While the wild ass switches from being a grazer in the summer to also browse in the winter, the wild and domestic horses eat exclusively grass all year round. In the lean winter months, this leads to increased food competition between wild and domestic horses. This realisation could help improve wildlife management measures for the Przewalski's horse in the future. The study was published in the Journal of Applied Ecology.
Przewalski's horses went extinct in the wild in 1968. Successful breeding programmes at zoos around the world helped to reintroduce the animals in the Great Gobi B protected area in southwestern Mongolia since 1992. The wild horses share the extreme habitat of the Gobi Desert with two other equid species: the Asiatic wild ass, also called khulan, and the free-ranging domestic horses of local nomads. For the preservation of the wild Przewalski's horse, it is important to understand if and how the three related species compete for food in the protected area.

Competition between Przewalski's horses and domestic horses in the winter
Martina Burnik Šturm and Petra Kaczensky from the Research Institute of Wildlife Ecology at Vetmeduni Vienna, in cooperation with the Leibnitz Institute for Zoo and Wildlife Research in Berlin, used a special method based on the chemical analysis of tail hairs to investigate the dietary habits of the animals. The analysis allowed them to determine the composition of the diet of each of the three species, which led to the discovery of increased dietary competition in the winter months.

The chemical analysis of the tail hairs revealed that Przewalski's horses and domestic horses are year-round grazers. Khulan, on the other hand, switch from grazing in the summer to a high proportion of foliage in the winter. "When food becomes scarce in the long winter months, competition can be expected especially between the two species of horse," explains Martina Burnik Šturm.

Shedding light on the origin of the baleen whale

Date: November 30, 2016
Source: Monash University

Monash University scientists have played a key role in discovering the origin of filter feeding in baleen whales -- the largest animal known to have ever existed.

The discovery is detailed in a paper co-written with international researchers and palaeontologists from Museum Victoria. 'Alfred' the 25- million-year-old fossilised whale skull was unveiled at the Museum today.

"Alfred shows how ancient baleen whales made the evolutionary switch from biting prey with teeth to filtering using baleen," said Monash Science Senior Research Fellow, Dr Alistair Evans, one of the authors of the paper.

"They first became suction feeders. Feeding in this way resulted in reduced need for teeth, so over time their teeth were lost before baleen appeared."

There has been a lot of mystery around how and when baleen first formed.

"But we now have long-sought evidence of how whales evolved from having teeth to hair-like baleen -- triggering the rise of the biggest beasts on the planet," said Dr Evans. Nick-named 'Alfred', the fossil skull is from an extinct group of whales called aetiocetids, which despite having teeth were an early branch of the baleen whale family tree.

Alfred's teeth show exceptionally rare evidence of feeding behaviour suggesting an entirely new evolutionary scenario -- before losing teeth and evolving baleen, these whales used suction to catch prey.

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