Convergent mosaic brain evolution is associated with the evolution of novel electrosensory systems in teleost fishes

  1. Erika L Schumacher
  2. Bruce A Carlson  Is a corresponding author
  1. Washington University in St. Louis, United States


Brain region size generally scales allometrically with brain size, but mosaic shifts in brain region size independent of brain size have been found in several lineages and may be related to the evolution of behavioral novelty. African weakly electric fishes (Mormyroidea) evolved a mosaically enlarged cerebellum and hindbrain, yet the relationship to their behaviorally novel electrosensory system remains unclear. We addressed this by studying South American weakly electric fishes (Gymnotiformes) and weakly electric catfishes (Synodontis spp.), which evolved varying aspects of electrosensory systems, independent of mormyroids. If the mormyroid mosaic increases are related to evolving an electrosensory system, we should find similar mosaic shifts in gymnotiforms and Synodontis. Using micro-computed tomography scans, we quantified brain region scaling for multiple electrogenic, electroreceptive, and non-electrosensing species. We found mosaic increases in cerebellum in all three electrogenic lineages relative to non-electric lineages and mosaic increases in torus semicircularis and hindbrain associated with the evolution of electrogenesis and electroreceptor type. These results show that evolving novel electrosensory systems is repeatedly and independently associated with changes in the sizes of individual major brain regions independent of brain size, suggesting that selection can impact structural brain composition to favor specific regions involved in novel behaviors.

Data availability

Brain measurement data is located in Supplementary File 1. Brain mass data is located in Supplementary File 2. All analysis code and phylogenetic trees are available in Dryad. The raw micro-computed tomography scans are too large to post (multiple TBs), but are available upon request. To request raw otophysan and/or osteoglossiform scans, contact the corresponding author. We ask that those who want access to the scan data send us an external hard drive, which we will upload all the data to and then return.

The following data sets were generated
The following previously published data sets were used

Article and author information

Author details

  1. Erika L Schumacher

    Department of Biology, Washington University in St. Louis, St. Louis, United States
    Competing interests
    The authors declare that no competing interests exist.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0002-2492-1117
  2. Bruce A Carlson

    Department of Biology, Washington University in St. Louis, St. Louis, United States
    For correspondence
    Competing interests
    The authors declare that no competing interests exist.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0002-2151-0443


National Science Foundation (IOS-1755071)

  • Bruce A Carlson

The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.


Animal experimentation: The methods in this study are consistent with euthanasia guidelines by the American Veterinary Medical Association and have been approved by the Animal Care and Use Committee at Washington University in St. Louis (Protocol ID 19-0974).

Reviewing Editor

  1. Catherine Emily Carr, University of Maryland, United States

Version history

  1. Received: September 23, 2021
  2. Preprint posted: October 1, 2021 (view preprint)
  3. Accepted: June 16, 2022
  4. Accepted Manuscript published: June 17, 2022 (version 1)
  5. Version of Record published: July 27, 2022 (version 2)


© 2022, Schumacher & Carlson

This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.


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  1. Erika L Schumacher
  2. Bruce A Carlson
Convergent mosaic brain evolution is associated with the evolution of novel electrosensory systems in teleost fishes
eLife 11:e74159.

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