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Unimodal head-width distribution of the European eel (Anguilla anguilla L.) from the Zeeschelde does not support disruptive selection
Verhelst, P.; De Meyer, J.; Reubens, J.; Coeck, J.; Goethals, P.; Moens, T.; Mouton, A.M. (2018). Unimodal head-width distribution of the European eel (Anguilla anguilla L.) from the Zeeschelde does not support disruptive selection. PeerJ 6: e5773. https://hdl.handle.net/10.7717/peerj.5773
In: PeerJ. PeerJ: Corte Madera & London. ISSN 2167-8359, more
Related to:
Verhelst, P. (2018). Unimodal head-width distribution of the European eel (Anguilla anguilla L.) from the Zeeschelde does not support disruptive selection, in: Verhelst, P. European eel (Anguilla anguilla L.) movement behaviour in relation to habitat fragmentation - Novel insights inferred from acoustic telemetry. pp. 115-142, more
Peer reviewed article  

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Keywords
    Speed; Telemetry; Anguilla anguilla (Linnaeus, 1758) [WoRMS]
Author keywords
    Maturation stages; Head dimorphism; Disruptive selection; Condition; European eel; Unimodality; Bimodality

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Abstract
    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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