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Title
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Hydrodynamic drag constrains head enlargement for mouthbrooding in cichlids
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Author
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Abstract
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| Presumably as an adaptation for mouthbrooding, many cichlid fish species have evolved a prominent sexual dimorphism in the adult head. Since the head of fishes serves as a bow during locomotion, an evolutionary increase in head volume to brood more eggs can trade-off with the hydrodynamic efficiency of swimming. Here, the differences between males and females in three-dimensional shape and size of the external head surfaces and the effect thereof on drag force during locomotion was analysed for the Nile tilapia (Oreochromis niloticus), a maternal mouthbrooder. To do so, three-dimensional body surface reconstructions from laser scans and computational fluid dynamics simulations were performed. After scaling the scanned specimens to post-cranial body volume, in order to theoretically equalize propulsive power, the external volume of the head of females was 27% larger than that of males (head length + 14%; head width + 9%). These differences resulted in an approximate 15% increase in drag force. Yet, hydrodynamics imposed important constraints on the adaptation for mouthbrooding as a much more drastic drop in swimming efficiency seems avoided by mainly enlarging the head along the swimming direction. |
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Language
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English
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Source (journal)
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Journal of the Royal Society interface: physical and life sciences. - London
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Publication
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London
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2015
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ISSN
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1742-5689
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DOI
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10.1098/RSIF.2015.0461
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Volume/pages
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12
:109
(2015)
, 4 p.
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Article Reference
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20150461
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ISI
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000361084200018
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Medium
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E-only publicatie
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Full text (Publisher's DOI)
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Full text (open access)
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