New Species of Hero Shrew

Scientists at Chicago's Field Museum and international collaborators have described a new species of Hero Shrew – the mammal with the most bizarre lower spine on Earth. The interlocking vertebrae of the Hero Shrew render the spine four to five times more robust relative to body mass, a condition not found in any other mammal. The spine has been an enigma to evolutionary biologists, with no known adaptive significance.

This new species of Hero Shrew, named
Scutisorex thori, possesses features that may represent intermediate character states between the only other known Hero Shrew species (Scutisorex somereni, Figure 1), and other shrews. In addition, a novel hypothesis for the function of the animal's expanded lower spine has been proposed. The study will be published July 24, 2013 edition of Biology Letters.

Scutisorex_somereni
Figure 1. A photo of Scutiosorex somereni.

First discovered in 1910, the Hero Shrew's most notable feature was not revealed for another seven years, when a specimen was dissected to reveal the most peculiar backbone of any mammal. The remarkable spine of the Hero Shrew is unique among mammals, in that the lower vertebrae have multiple lateral processes that interlock with the processes of neighboring vertebra. The arrangement, along with surrounding musculature, affords the animal extraordinary strength, so much so that the Hero Shrew has traditionally been used as a talisman.

"This shrew first came to light when explorers came to the eastern part of the Democratic Republic of Congo," said Bill Stanley, Director of Collections and zoologist at the Field Museum. "The explorers watched in amazement as a full-grown man stood on the back of the Hero Shrew, and the animal walked away, unharmed."

Until now, there have been no other species of this bizarre shrew. The new species described in this study represents a possible intermediate between the original Hero Shrew and other shrews, since is possesses an interlocking spine, but with fewer lower vertebrae and lateral processes than the first Hero Shrew species (Figure 2).

heroshrew
Figure 2. Lateral views of (a) the lumbar region and (b) ribs of Crocidura olivieri ((i) FMNH 192912), Scutisorex somereni ((ii) FMNH 189277) and the new species, Scutisorex thori ((iii) FMNH 219669).

"You and I have five lumbar vertebrae," said Stanley. "And so do most other mammals, but the Hero Shrew at least 10. Scutisorex thori has eight vertebrae, and fewer lateral processes than the original species."

The specimen of the new Hero Shrew species was collected in the lowland forest near the Tshuapa River in the Democratic Republic of Congo. Based on the observations of one of the co-authors on the study, the authors present a novel hypothesis for the functional significance of the spine of
Scutisorex thori; they suggest that these shrews position themselves between the trunk and leaf bases of Palms, and use their unique spine to exert force and gain access to concentrated sources of beetle larvae that are otherwise protected from predation. The same adaptation may allow these animals to lift logs or rocks to access invertebrates – a food resource that remains unavailable to many other mammals.

The specimen of
Scutisorex thori now residing at The Field Museum is a holotype, meaning that it will be the standard for identifying other members of the species. The new species is named in honor of Thorvald "Thor" Holmes, Jr. of the Humboldt State University Vertebrate Museum, at the suggestion of Bill Stanley, who did his graduate work there. The suggested common name is "Thor's Hero Shrew", appropriately invoking Thor, the god of strength in Norse mythology.

"The Age of Discovery is not over," said Stanley. "In fact, discoveries such as these happen in natural history collections, like the ones that we have at The Field Museum. In addition, hypotheses such as the one that we've generated concerning the functional significance of the Hero Shrew's spine fuel the scientific machine. We can't wait to see the results of further scientific studies that test the ideas presented in this article."

Source: Modified from materials provided by The Field Museum of Natural History, Chicago.

Reference
Stanley WT, Robbins, LW, et al. (2013). A new hero emerges: another exceptional mammalian spine and its potential adaptive significance Biology Letters DOI: 10.1098/rsbl.2013.0486

See also: Cullinane DM, Aleper D. 1998 The functional and biomechanical modifications of the spine of Scutisorex somereni, the hero shrew: spinal musculature. J. Zool. 244, 453–458. (doi:10.1111/j.1469-7998.1998.tb00050.x)


Military Sonar Alters Whale Behavior

Some blue whales (Balaenoptera musculus) off the coast of California change their behavior when exposed to the sort of underwater sounds used during U.S. military exercises. The whales may alter diving behavior or temporarily avoid important feeding areas, according to new research by the Southern California Behavioral Response Study.

Researchers exposed tagged blue whales in the California Bight to simulated mid-frequency (3.5-4 kHz) sonar sounds significantly less intense than the military uses. "Whales clearly respond in some conditions by modifying diving behavior and temporarily avoiding areas where sounds were produced," said lead author Jeremy Goldbogen of Cascadia Research. "But overall the responses are complex and depend on a number of interacting factors," including whether the whales were feeding deep, shallow or not at all.

The scientists tagged the whales with non-invasive suction cups, which recorded acoustic data and high-resolution movements as the animals were exposed to the controlled sounds (Figure 1). 

whale

Figure 1. Examples of behavior changes of tagged blue whales during exposure experiments. The sound exposure periods are highlighted in blue on each track line. The location of the sound source is indicated by the large red circle. (From Goldbogen et al. 2013)

"The tag technology we use offers a unique glimpse into the underwater behavior of whales that otherwise would not be possible," said Ari Friedlaender, a research scientist at the Duke Marine Laboratory.

The scientists found that some of the whales engaged in deep feeding stopped eating and either sped up or moved away from the source of the noise. Not all of the whales responded to the noise, and not all in the same way.

"Blue whales are the largest animals that have ever lived. Populations globally remain at a fraction of their former numbers prior to whaling, and they appear regularly off the southern California coast, where they feed," said John Calambokidis, one of the projects lead investigators.

That area of the ocean is also the site of military training and testing exercises that involve loud mid-frequency sonar signals. Such sonar exercises have been associated with several unusual strandings of other marine mammal species (typically beaked whales) in the past. Until this study, almost no information was available about whether and how blue whales respond to sonar. 

"These are the first direct measurements of individual responses for any baleen whale species to these kinds of mid-frequency sonar signals," said Brandon Southall, chief scientist from SEA, Inc. "These findings help us understand risks to these animals from human sound and inform timely conservation and management decisions."

A related paper published by the same research team in
Biology Letters has shown clear and even stronger responses of Cuvier’s beaked whales (Ziphius cavirostris) to simulated mid-frequency sonar exposures. Beaked whales showed a variety of responses to both real, military sonar in the distance and nearby simulated sonar. What the beaked whales were doing at the time appeared to be a key factor affecting their reactions.

The research was funded by the U.S. Navy Chief of Naval Operations Environmental Readiness Division and the U.S. Office of Naval Research, and appears in the Proceedings of the Royal Society B. 

Source: Modified from materials provided by Duke University.

References
Goldbogen, JA et al. 2013. Blue whales respond to simulated mid-frequency military sonar. Proceedings of the Royal Academy B, DOI -10.1098/rspb.2013.0657

DeRuiter, S. et al. 2013. First direct measurements of behavioural responses by Cuvier's beaked whales to mid-frequency active sonar. Biology Letters, DOI – 10.1098/rsbl.2013.0223

Read More...