DOI: 10.5061/dryad.c402q
title: Data from: Hydrodynamic drag constrains head enlargement for mouthbrooding in cichlids

description: 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 analyzed 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.
description: Specimen BF2 surface STL
 used in CFDOreochromis niloticus
 specimen BF2 (Royal Museum for Central Africa), female, mass = 63 g,
 left-right assymetry removed, scaled isometrically to the same mean body
 volume (excluding the head)Tilapia_BF2_F_63g_SC_CFD_avg.stlSpecimen BF5 surface STL used in CFDOreochromis niloticus specimen BF5 (Royal Museum for Central Africa), male, mass = 100 g, left-right assymetry removed, scaled isometrically to the same mean body volume (excluding the head)Tilapia_BF5_M_100g_SC_CFD_avg.stlSpecimen BF6 surface STL used in CFDOreochromis niloticus specimen BF6 (Royal Museum for Central Africa), male, mass = 103 g, left-right assymetry removed, scaled isometrically to the same mean body volume (excluding the head)Tilapia_BF6_M_103g_SC_CFD_avg.stlSpecimen BF8 surface STL used in CFDOreochromis niloticus specimen BF8 (Royal Museum for Central Africa), male, mass = 125 g, left-right assymetry removed, scaled isometrically to the same mean body volume (excluding the head)Tilapia_BF8_M_125g_SC_CFD_avg.stlSpecimen BF10 surface STL used in CFDOreochromis niloticus specimen BF10 (Royal Museum for Central Africa), female, mass = 63 g, left-right assymetry removed, scaled isometrically to the same mean body volume (excluding the head)Tilapia_BF10_F_63g_SC_CFD_avg.stlSpecimen BF11 surface STL used in CFDOreochromis niloticus specimen BF11 (Royal Museum for Central Africa), female, mass = 54 g, left-right assymetry removed, scaled isometrically to the same mean body volume (excluding the head)Tilapia_BF11_F_54g_SC_CFD_avg.stlSpecimen BF13 surface STL used in CFDOreochromis niloticus specimen BF13 (Royal Museum for Central Africa), male, mass = 86 g, left-right assymetry removed, scaled isometrically to the same mean body volume (excluding the head)Tilapia_BF13_M_86g_SC_CFD_avg.stlSpecimen BF17 surface STL used in CFDOreochromis niloticus specimen BF17 (Royal Museum for Central Africa), female, mass = 48 g, left-right assymetry removed, scaled isometrically to the same mean body volume (excluding the head)Tilapia_BF17_F_48g_SC_CFD_avg.stlSpecimen BF18 surface STL used in CFDOreochromis niloticus specimen BF18 (Royal Museum for Central Africa), female, mass = 51 g, left-right assymetry removed, scaled isometrically to the same mean body volume (excluding the head)Tilapia_BF18_F_51g_SC_CFD_avg.stlSpecimen BF19 surface STL used in CFDOreochromis niloticus specimen BF19 (Royal Museum for Central Africa), male, mass = 95 g, left-right assymetry removed, scaled isometrically to the same mean body volume (excluding the head)Tilapia_BF19_M_95g_SC_CFD_avg.stlSpecimen BF20 surface STL used in CFDOreochromis niloticus specimen BF20 (Royal Museum for Central Africa), female, femass = 57 g, left-right assymetry removed, scaled isometrically to the same mean body volume (excluding the head)Tilapia_BF20_F_57g_SC_CFD_avg.stlSpecimen BF22 surface STL used in CFDOreochromis niloticus specimen BF22 (Royal Museum for Central Africa), male, femass = 115 g, left-right assymetry removed, scaled isometrically to the same mean body volume (excluding the head)Tilapia_BF22_M_115g_SC_CFD_avg.stlX00_Y00_Z00_fullOreochromis niloticus model for sensitivity analysis (Fig. 2 in the article): reference model.X00_Y00_Z10_fullOreochromis niloticus model for sensitivity analysis (Fig. 2 in the article): head width +10%.X00_Y00_Z20_fullOreochromis niloticus model for sensitivity analysis (Fig. 2 in the article): head width +20%.X00_Y00_Z30_fullOreochromis niloticus model for sensitivity analysis (Fig. 2 in the article): head width +30%.X00_Y00_Z40_fullOreochromis niloticus model for sensitivity analysis (Fig. 2 in the article): head width +40%.X00_Y10_Z00_fullOreochromis niloticus model for sensitivity analysis (Fig. 2 in the article): head height +10%.X00_Y20_Z00_fullOreochromis niloticus model for sensitivity analysis (Fig. 2 in the article): head height +20%.X00_Y30_Z00_fullOreochromis niloticus model for sensitivity analysis (Fig. 2 in the article): head height +30%.X00_Y40_Z00_fullOreochromis niloticus model for sensitivity analysis (Fig. 2 in the article): head height +40%.X10_Y00_Z00_fullOreochromis niloticus model for sensitivity analysis (Fig. 2 in the article): head length +10%.X20_Y00_Z00_fullOreochromis niloticus model for sensitivity analysis (Fig. 2 in the article): head length +20%.X30_Y00_Z00_fullOreochromis niloticus model for sensitivity analysis (Fig. 2 in the article): head length +30%.X40_Y00_Z00_fullOreochromis niloticus model for sensitivity analysis (Fig. 2 in the article): head length +40%.