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Front. Neuroanat. | doi: 10.3389/fnana.2017.00118

Dogs have the most neurons, though not the largest brain: Trade-off between body mass and number of neurons in the cerebral cortex of large carnivoran species

  • 1Universidade Federal do Rio de Janeiro, Brazil
  • 2University of Richmond, United States
  • 3University of California, Davis, United States
  • 4Copenhagen Zoo, Denmark
  • 5University of the Witwatersrand, South Africa
  • 6Vanderbilt University, United States

Carnivorans are a diverse group of mammals that includes carnivorous, omnivorous and herbivorous, domesticated and wild species, with a large range of brain sizes. Carnivory is one of several factors expected to be cognitively demanding for carnivorans due to a requirement to outsmart larger prey. On the other hand, large carnivoran species have high hunting costs and unreliable feeding patterns, which, given the high metabolic cost of brain neurons, might put them at risk of metabolic constraints regarding how many brain neurons they can afford, especially in the cerebral cortex. For a given cortical size, do carnivoran species have more cortical neurons than the herbivorous species they prey upon? We find they do not; carnivorans (cat, mongoose, dog, hyena, lion) share with non-primates, including artiodactyls (the typical prey of large carnivorans), roughly the same relationship between cortical mass and number of neurons, which suggests that carnivorans are subject to the same evolutionary scaling rules as other non-primate clades. However, there are a few important exceptions. Carnivorans stand out in that the usual relationship between larger body, larger cortical mass and larger number of cortical neurons only applies to small and medium-sized species, and not beyond dogs: we find that the golden retriever dog has more cortical neurons than the striped hyena, African lion and even brown bear, even though the latter species have up to 3 times larger cortices than dogs. Remarkably, the brown bear cerebral cortex, the largest examined, only has as many neurons as the ten times smaller cat cerebral cortex, although it does have the expected ten times as many non-neuronal cells in the cerebral cortex compared to the cat. We also find that raccoons have dog-like numbers of neurons in their cat-sized brain, which makes them comparable to primates in neuronal density. Comparison of domestic and wild species suggests that the neuronal composition of carnivoran brains is not affected by domestication. Instead, large carnivorans appear to be particularly vulnerable to metabolic constraints that impose a trade-off between body size and number of cortical neurons.

Keywords: evolution, Carnivorans, number of neurons, metabolic cost, brain size

Received: 18 Jul 2017; Accepted: 27 Nov 2017.

Edited by:

Julian Budd, University of Sussex, United Kingdom

Reviewed by:

Jan Karbowski, University of Warsaw, Poland
Bradley Arsznov, Minnesota State University, Mankato, United States  

Copyright: © 2017 Alvarenga, Lambert, Noctor, Pestana, Bertelsen, Manger and Herculano-Houzel. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Prof. Suzana Herculano-Houzel, Vanderbilt University, Nashville, United States, suzanahh@gmail.com