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Altering an extended phenotype reduces intraspecific male aggression and can maintain diversity in cichlid fish

Joyce, Domino A.; Croft, Guy E.; Magalhaes, Isabel Santos


Guy E. Croft

Isabel Santos Magalhaes


Reduced male aggression towards different phenotypes generating negative frequency-dependent intrasexual selection has been suggested as a mechanism to facilitate the invasion and maintenance of novel phenotypes in a population. To date, the best empirical evidence for the phenomenon has been provided by laboratory studies on cichlid fish with different colour polymorphisms. Here we experimentally tested the hypothesis in a natural population of Lake Malawi cichlid fish, in which males build sand-castles (bowers) to attract females during seasonal leks. We predicted that if bower shape plays an important role in male aggressive interactions, aggression among conspecific males should decrease when their bower shape is altered. Accordingly, we allocated randomly chosen bowers in a Nyassachromis cf. microcephalus lek into three treatments: control, manipulated to a different shape, and simulated manipulation. We then measured male behaviours and bower shape before and after these treatments. We found that once bower shape was altered, males were involved in significantly fewer aggressive interactions with conspecific males than before manipulation. Mating success was not affected. Our results support the idea that an extended phenotype, such as bower shape, can be important in maintaining polymorphic populations. Specifically, reduced male conspecific aggression towards males with different extended phenotypes (here, bower shapes) may cause negative frequency-dependent selection, allowing the invasion and establishment of a new phenotype (bower builder). This could help our understanding of mechanisms of diversification within populations, and in particular, the overall diversification of bower shapes within Lake Malawi cichlids.


Joyce, D. A., Croft, G. E., & Magalhaes, I. S. (2013). Altering an extended phenotype reduces intraspecific male aggression and can maintain diversity in cichlid fish. PeerJ, 1(1), e209.

Journal Article Type Article
Acceptance Date Oct 23, 2013
Online Publication Date Nov 26, 2013
Publication Date Oct 26, 2013
Deposit Date Dec 18, 2015
Publicly Available Date Nov 23, 2017
Journal PeerJ
Electronic ISSN 2167-8359
Publisher PeerJ
Peer Reviewed Peer Reviewed
Volume 1
Issue 1
Article Number UNSP e209
Pages e209
Keywords Animal behaviour; Evolutionary studies; Zoology
Public URL
Publisher URL
Additional Information Copy of article published in: PeerJ, v.1


Article.pdf (2 Mb)

Copyright Statement
© 2013 magalhaes et al.

This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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