Unimodal head-width distribution of the European eel (Anguilla anguilla L.) from the Zeeschelde does not support disruptive selection

Since the early 20th century, European eels (Anguilla anguilla L.) have been dichotomously classified into 'narrow' and 'broad' heads. These morphs are mainly considered the result of a differential food choice, with narrow heads feeding primarily on small/soft prey and broad hea...

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Bibliographic Details
Published in:PeerJ
Main Authors: Verhelst, Pieterjan, De Meyer, Jens, Reubens, Jan, Coeck, Johan, Goethals, Peter, Moens, Tom, Mouton, Ans
Format: Article in Journal/Newspaper
Language:English
Published: 2018
Subjects:
Biology and Life Sciences
Earth and Environmental Sciences
Maturation stages
Head dimorphism
Telemetry
Speed
Disruptive selection
Condition
European eel
Unimodality
Bimodality
FRESH-WATER
MIGRATION BEHAVIOR
SALINITY PREFERENCE
SHAPE
HABITAT
GROWTH
ECOMORPHOLOGY
POLYMORPHISM
PLASTICITY
Anguilla anguilla
Online Access:https://biblio.ugent.be/publication/8581856
http://hdl.handle.net/1854/LU-8581856
https://doi.org/10.7717/peerj.5773
https://biblio.ugent.be/publication/8581856/file/8582101
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Summary:Since the early 20th century, European eels (Anguilla anguilla L.) have been dichotomously classified into 'narrow' and 'broad' heads. These morphs are mainly considered the result of a differential food choice, with narrow heads feeding primarily on small/soft prey and broad heads on large/hard prey. Yet, such a classification implies that head-width variation follows a bimodal distribution, leading to the assumption of disruptive selection. We investigated the head morphology of 272 eels, caught over three consecutive years (2015-2017) at a single location in the Zeeschelde (Belgium). Based on our results, BIC favored a unimodal distribution, while AIC provided equal support for a unimodal and a bimodal distribution. Notably, visualization of the distributions revealed a strong overlap between the two normal distributions under the bimodal model, likely explaining the ambiguity under AIC. Consequently, it is more likely that head-width variation followed a unimodal distribution, indicating there are no disruptive selection pressures for bimodality in the Zeeschelde. As such, eels could not be divided in two distinct head-width groups. Instead, their head widths showed a continuum of narrow to broad with a normal distribution. This pattern was consistent across all maturation stages studied here.

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