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Home , Etruscan shrew, Suncus

MODEL OF THE MONTH

A miniscule model for research by Melissa Berg, BS and 18-h:6-h light:dark cycles, at a temperature of 24 °C, instead SCIENTIFIC NAME of the usual 23 °C in non-breeding colony rooms. They have a fast etruscus generation time of 11 weeks, and produce 4–6 pups per litter1. Research résumé PHYLUM: Chordata CLASS: Mammalia Etruscan are commonly used to study how small body size affects various physiologic parameters. They were first used for ORDER: research in the 1930s, when a French cellular biologist compared non- FAMILY: Soricidae neural somatic cells in Etruscan shrews with those of larger and discovered that cellular size remains constant despite differences in body size5. Subsequently, nerves from Etruscan shrews were used General description to make crucial advances in understanding of how nervous impulses The Etruscan , also known as the Etruscan pygmy shrew or are conducted along axons6. In 1996, researchers used the Etruscan the white-toothed pygmy shrew, is the smallest living by shrew to study cardiovascular adaptations for maintaining a high oxi- mass. Most adults weigh 1.8–3 g with a body length of 35–48 mm, dative demand, finding that the blood of the has a making them 20 times lighter than the average adult mouse1. These larger oxygen capacity and a lower oxygen affinity than is typical for miniscule mammals are widespread across Southern homeothermic animals4. They can release almost twice as Europe, Northern Africa and Central Asia, much oxygen per ml of blood as humans can. where they occupy abandoned olive Today the most promising contribution of groves and forest floors2. Etruscan Etruscan shrews is in the field of neurosci- shrews have poor vision and hearing, ence. With one of the smallest brains of and rely on well-developed vibrissae all mammals, Etruscan shrews offer a for environmental information. They unique opportunity for studies using are adept hunters and often kill brain imaging. The cerebral cortex of Nature America, Inc. All rights reserved. America, Inc. © 201 6 Nature up to half their size. Like all mammals the Etruscan shrew has a measured they are considered homeothermic; thickness of 400–500 µm, so research-

however, Etruscan shrews can enter a state r ers can view and record activity from an a npg s ae of torpor to conserve energy when experienc- C entire cerebral column using 2-p­ hoton im p/K 3 rou 3,7 ing cold stress or food restriction . Body tempera- ing G microscopy . This could allow researchers ublish ture can fall as low as 6 °C, making them especially adap- Nature P to visualize every neuron in the entire somatosen- tive to environmental changes. The heart rate of an Etruscan shrew sory cortex at once. In this way, Etruscan shrews might help research- can reach an impressive 1,200 beats per minute with a respiratory ers finally unlock complete sections of the cerebral cortex and gain rate of over 800 breaths per minute4. Its small size has promoted a better understanding of the relationships between structure and numerous physiologic adaptations that have made the Etruscan function7. shrew a focus of both cardiovascular and neurophysiology studies.

1. Nowak, R.N. Suncus: Musk Shrews, or Pygmy Shrews. in Walker’s Mammals of the Husbandry World 6th edn. 223–225 (Johns Hopkins University Press, Baltimore, MD, 1999). Etruscan shrews have a high basal metabolic rate reflective of their 2. Aulagnier, S. et al. Suncus etruscus (Etruscan Shrew, Pygmy White-toothed high surface area-to-volume ratio. They cannot survive more than a Shrew, Savi’s Pygmy Shrew, White-toothed Pygmy Shrew). in The IUCN Red List of Threatened Species version (IUCN, Cambridge, UK, 2008). few hours without food, and they must consume as much as 6 times 3. Brecht, M. et al. The neurobiology of Etruscan shrew active touch. Phil. their body weight in crickets and other insects daily3. Etruscan Trans. R. Soc. B. 366, 3026–3036 (2011). shrews are generally housed in same-sex groups of siblings within 4. Jürgens, K.D., Fons, R., Peters, T. & Sender, S. Heart and respiratory rates and 1 their significance for convective oxygen transport rates in the smallest mammal, 20-­gallon glass terrariums. They are monogamous breeders , and the Etruscan shrew, Suncus etruscus. J. Exp. Biol. 199, 2579–2584 (1996). breeding pairs can be set up with special burrow stones for breed- 5. Szarski, H. Cell size and nuclear DNA content in vertebrates. Int. Rev. Cytol. ing. Breeding in Etruscan shrews is temperature and light depen- 44, 93–111 (1976). dent, and breeding rooms are kept at light cycles between 14-h:10-h 6. Akert, K., Sandri, C., Weibel, E.R., Peper, K. & Moor, H. The fine structure of the perineural endothelium. Cell Tissue Res. 165, 281–295 (1976). 7. Naumann, R.K. Even the smallest mammalian brain has yet to reveal its Berg is a DVM candidate, Western University of Health Sciences, Pomona, CA. secrets. Brain Behav. Evol. 85, 1–3 (2015).

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