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Brain mass and cranial nerve size in shrews and moles.

Leitch DB, Sarko DK, Catania KC - Sci Rep (2014)

Bottom Line: We found that moles and shrews have tiny optic nerves with fiber counts not correlated with body or brain size.Trigeminal nerve number was by far the largest and also increased with increasing brain and body size.Despite this hypertrophied cranial nerve, star-nosed mole brains were not larger than predicted from body size, suggesting that magnification of their somatosensory systems does not result in greater overall CNS size.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Vanderbilt University, Nashville, TN, USA.

ABSTRACT
We investigated the relationship between body size, brain size, and fibers in selected cranial nerves in shrews and moles. Species include tiny masked shrews (S. cinereus) weighing only a few grams and much larger mole species weighing up to 90 grams. It also includes closely related species with very different sensory specializations - such as the star-nosed mole and the common, eastern mole. We found that moles and shrews have tiny optic nerves with fiber counts not correlated with body or brain size. Auditory nerves were similarly small but increased in fiber number with increasing brain and body size. Trigeminal nerve number was by far the largest and also increased with increasing brain and body size. The star-nosed mole was an outlier, with more than twice the number of trigeminal nerve fibers than any other species. Despite this hypertrophied cranial nerve, star-nosed mole brains were not larger than predicted from body size, suggesting that magnification of their somatosensory systems does not result in greater overall CNS size.

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Schematic of phylogeny of “Insectivora” (Eulipotyphyla) species used in this investigation.The shrews are in the family Soricidae and are represented in the Sorex and Blarina genera. Their sister group is the family Talpidae, with examples from Condylura, Parascalops, and Scalopus genera. Adapted from Grenyer and Purvis, 2003 and Symonds, 2005.
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f1: Schematic of phylogeny of “Insectivora” (Eulipotyphyla) species used in this investigation.The shrews are in the family Soricidae and are represented in the Sorex and Blarina genera. Their sister group is the family Talpidae, with examples from Condylura, Parascalops, and Scalopus genera. Adapted from Grenyer and Purvis, 2003 and Symonds, 2005.

Mentions: Shrews and moles are part of the monophyletic order Eulipotyphyla and represent closely related groups as shown in Figure 1 (adapted from2122). For each species, the brain mass, body mass, olfactory bulb mass, and number of axons within selected sensory cranial nerves were measured. Some nerve tracts could not be confidently identified in some species and were not included (e.g., the optic nerve of the eastern mole). The shrews used in this analysis ranged in total body mass from approximately 3.8 grams (S. cinereus) to 16 g (S. palustris) (Table S1 and Fig. 2A, B) whereas the mole body sizes ranged from roughly 50 grams for the smaller P. breweri and C. cristata to 90 grams for S. aquaticus (Table S1 and Fig. 2C, D).


Brain mass and cranial nerve size in shrews and moles.

Leitch DB, Sarko DK, Catania KC - Sci Rep (2014)

Schematic of phylogeny of “Insectivora” (Eulipotyphyla) species used in this investigation.The shrews are in the family Soricidae and are represented in the Sorex and Blarina genera. Their sister group is the family Talpidae, with examples from Condylura, Parascalops, and Scalopus genera. Adapted from Grenyer and Purvis, 2003 and Symonds, 2005.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4150104&req=5

f1: Schematic of phylogeny of “Insectivora” (Eulipotyphyla) species used in this investigation.The shrews are in the family Soricidae and are represented in the Sorex and Blarina genera. Their sister group is the family Talpidae, with examples from Condylura, Parascalops, and Scalopus genera. Adapted from Grenyer and Purvis, 2003 and Symonds, 2005.
Mentions: Shrews and moles are part of the monophyletic order Eulipotyphyla and represent closely related groups as shown in Figure 1 (adapted from2122). For each species, the brain mass, body mass, olfactory bulb mass, and number of axons within selected sensory cranial nerves were measured. Some nerve tracts could not be confidently identified in some species and were not included (e.g., the optic nerve of the eastern mole). The shrews used in this analysis ranged in total body mass from approximately 3.8 grams (S. cinereus) to 16 g (S. palustris) (Table S1 and Fig. 2A, B) whereas the mole body sizes ranged from roughly 50 grams for the smaller P. breweri and C. cristata to 90 grams for S. aquaticus (Table S1 and Fig. 2C, D).

Bottom Line: We found that moles and shrews have tiny optic nerves with fiber counts not correlated with body or brain size.Trigeminal nerve number was by far the largest and also increased with increasing brain and body size.Despite this hypertrophied cranial nerve, star-nosed mole brains were not larger than predicted from body size, suggesting that magnification of their somatosensory systems does not result in greater overall CNS size.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Vanderbilt University, Nashville, TN, USA.

ABSTRACT
We investigated the relationship between body size, brain size, and fibers in selected cranial nerves in shrews and moles. Species include tiny masked shrews (S. cinereus) weighing only a few grams and much larger mole species weighing up to 90 grams. It also includes closely related species with very different sensory specializations - such as the star-nosed mole and the common, eastern mole. We found that moles and shrews have tiny optic nerves with fiber counts not correlated with body or brain size. Auditory nerves were similarly small but increased in fiber number with increasing brain and body size. Trigeminal nerve number was by far the largest and also increased with increasing brain and body size. The star-nosed mole was an outlier, with more than twice the number of trigeminal nerve fibers than any other species. Despite this hypertrophied cranial nerve, star-nosed mole brains were not larger than predicted from body size, suggesting that magnification of their somatosensory systems does not result in greater overall CNS size.

Show MeSH
Related in: MedlinePlus