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From yellow to silver: Transforming cranial morphology in European eel (Anguilla anguilla).

Authors
  • Baan, Jochem1, 2
  • De Meyer, Jens1
  • De Kegel, Barbara1
  • Adriaens, Dominique1
  • 1 Department of Biology, Evolutionary Morphology of Vertebrates, Ghent University, Ghent, Belgium. , (Belgium)
  • 2 Institute for Biodiversity and Ecosystem Dynamics (IBED), University of Amsterdam, Amsterdam, The Netherlands. , (Netherlands)
Type
Published Article
Journal
Journal of anatomy
Publication Date
Nov 01, 2020
Volume
237
Issue
5
Pages
979–987
Identifiers
DOI: 10.1111/joa.13259
PMID: 32579740
Source
Medline
Keywords
Language
English
License
Unknown

Abstract

The European eel (Anguilla anguilla) has been extensively studied, especially because of its highly specialized migratory behaviour associated with substantial phenotypic transformations. During this migration, one of those transformations the eel undergoes is from yellow to silver eel, a process known as silvering. Although the cranial morphology during the earlier glass, elver and yellow eel stages are well studied, little is known about actual morphological changes during the transformation process from the yellow to the silver eel stage. Yet, literature suggests drastic changes in musculoskeletal anatomy. Here, we investigated the cranial musculoskeletal morphology of 11 male European eels at different stages during silvering, resulting both from natural and artificial maturation. Using 3D-reconstructed µCT data of the head, the skull and cranial muscles associated with jaw closing and respiration were studied. Eye size was used as a proxy for the silvering stage. Size-adjusted jaw muscle volumes increased during silvering, although insignificantly. Accordingly, a near-significant increase in bite force was observed. Respiratory muscles size did increase significantly during silvering, however. Considering the eel's long migration, which often includes deep and thus potentially oxygen-poor environments, having a better performing respiratory system may facilitate efficient migration. Both overall skull dimensions and specifically orbit size increased with eye index, suggesting they play a role in accommodating the enlarging eyes during silvering. Finally, artificially matured eels had a wider and taller skull, as well as larger jaw muscles than wild silver eels. This could be caused (a) by different conditions experienced during the yellow eel stage, which are maintained in the silver eel stage, (b) by side effects of hormonal injections or (c) be part of the maturation process as artificially induced silver eels had a higher eye index than the wild silver eels. © 2020 Anatomical Society.

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