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Vol. 80, No. 2, 2012
Issue release date: September 2012
Section title: Paper
Brain Behav Evol 2012;80:108–126
(DOI:10.1159/000339875)

Allometric Scaling of the Optic Tectum in Cartilaginous Fishes

Yopak K.E.a · Lisney T.J.b
aSchool of Animal Biology and the UWA Oceans Institute, University of Western Australia, Crawley, W.A., Australia; bDepartment of Psychology, The University of Alberta, Edmonton, Alta., Canada

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Article / Publication Details

First-Page Preview
Abstract of Paper

Published online: 9/13/2012
Issue release date: September 2012

Number of Print Pages: 19
Number of Figures: 6
Number of Tables: 1

ISSN: 0006-8977 (Print)
eISSN: 1421-9743 (Online)

For additional information: http://www.karger.com/BBE

Abstract

In cartilaginous fishes (Chondrichthyes; sharks, skates and rays (batoids), and holocephalans), the midbrain or mesencephalon can be divided into two parts, the dorsal tectum mesencephali or optic tectum (analogous to the superior colliculus of mammals) and the ventral tegmentum mesencephali. Very little is known about interspecific variation in the relative size and organization of the components of the mesencephalon in these fishes. This study examined the relative development of the optic tectum and the tegmentum in 75 chondrichthyan species representing 32 families. This study also provided a critical assessment of attempts to quantify the size of the optic tectum in these fishes volumetrically using an idealized half-ellipsoid approach (method E), by comparing this method to measurements of the tectum from coronal cross sections (method S). Using species as independent data points and phylogenetically independent contrasts, relationships between the two midbrain structures and both brain and mesencephalon volume were assessed and the relative volume of each brain area (expressed as phylogenetically corrected residuals) was compared among species with different ecological niches (as defined by primary habitat and lifestyle). The relatively largest tecta and tegmenta were found in pelagic coastal/oceanic and oceanic sharks, benthopelagic reef sharks, and benthopelagic coastal sharks. The smallest tecta were found in all benthic sharks and batoids and the majority of bathyal (deep-sea) species. These results were consistent regardless of which method of estimating tectum volume was used. We found a highly significant correlation between optic tectum volume estimates calculated using method E and method S. Taxon-specific variation in the difference between tectum volumes calculated using the two methods appears to reflect variation in both the shape of the optic tectum relative to an idealized half-ellipsoid and the volume of the ventricular cavity. Because the optic tectum is the principal termination site for retinofugal fibers arising from the retinal ganglion cells, the relative size of this brain region has been associated with an increased reliance on vision in other vertebrate groups, including bony fishes. The neuroecological relationships between the relative size of the optic tectum and primary habitat and lifestyle we present here for cartilaginous fishes mirror those established for bony fishes; we speculate that the relative size of the optic tectum and tegmentum similarly reflects the importance of vision and sensory processing in cartilaginous fishes.

© 2012 S. Karger AG, Basel


  

Article Information

Published online: September 13, 2012
Number of Print Pages : 19
Number of Figures : 6, Number of Tables : 1, Number of References : 143
Additional supplementary material is available online - Number of Parts : 1

  

Publication Details

Brain, Behavior and Evolution

Vol. 80, No. 2, Year 2012 (Cover Date: September 2012)

Journal Editor: Striedter G.F. (Irvine, Calif.)
ISSN: 0006-8977 (Print), eISSN: 1421-9743 (Online)

For additional information: http://www.karger.com/BBE


Article / Publication Details

First-Page Preview
Abstract of Paper

Published online: 9/13/2012
Issue release date: September 2012

Number of Print Pages: 19
Number of Figures: 6
Number of Tables: 1

ISSN: 0006-8977 (Print)
eISSN: 1421-9743 (Online)

For additional information: http://www.karger.com/BBE


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