DOI: 10.5061/dryad.0gb5mkm1x
title: Sexual dimorphism in an adaptive radiation: Does intersexual niche differentiation result in ecological character displacement?

description: Evolutionary radiations are one plausible explanation for the rich
 biodiversity on Earth. Adaptive radiations are the most studied form of
 evolutionary radiations and ecological opportunity has been identified as
 one factor permitting them. Competition among individuals is supposedly
 highest in populations of conspecifics. Divergent modes of resource use
 might minimize trophic overlap, and thus intersexual competition,
 resulting in ecological character displacement between sexes. However, the
 role of intersexual differentiation in speciation processes is
 insufficiently studied. The few studies available suggest that sexual
 niche differentiation exists in adaptive radiations, but their role within
 the radiation, and the extent of differentiation within the organism
 itself, remains largely unexplored. Here, we test the hypothesis that
 multiple morphological structures are affected by sexual niche
 differentiation in “roundfin” Telmatherina, the first case where sexual
 niche differentiation was demonstrated in an adaptive fish radiation. We
 show that sexes of two of the three morphospecies differ in several
 structural components of the head, all of these are likely adaptive.
 Sexual differentiation is linked to the respective morphospecies-specific
 ecology and affects several axes of variation. Trait variation translates
 into different feeding modes, processing types and habitat usages that add
 to interspecific variation in all three morphospecies. Intrasexual
 selection, i.e. male-male competition, may contribute to variation in some
 of the traits, but appears unlikely in internal structures which are
 invisible for other individuals. We conclude that intersexual variation
 adds to the adaptive diversity of roundfins, and might play a key role in
 minimizing intersexual competition in emerging radiations.
description: µ-CT
 Imaging The skulls of 13
 specimens of each morphospecies <i>T. antoniae</i> “small”,
 <i>T. antoniae</i> “large” and <i>T. prognatha
 </i>were used for 3D µ-CT analyses. µ-CT scanning was performed with
 Skyscan 1272 and Skyscan 1173 scanners (Bruker). All specimens were
 scanned in 70 % Ethanol. Five male and five female specimens per species
 were stained with 0.3 % Phosphotungstic acid (PTA) in advance. Five male
 and five female specimens per species were scanned without any prior
 staining. The resolution ranged between 11 µm and 23 µm depending on the
 size of the specimen. Selected rotation steps varied between 0.2, 0.3 and
 0.4 degrees over 180°. The chosen voltage ranged between 60 kV and 100 kV
 and the current between 80 µA and 166 µA. Detailed scanner settings for
 each individual can be viewed in Dryad. The projections were reconstructed
 with NRecon ver. 1.7.1.0 (Bruker). Data size was then reduced with the
 software Dataviewer ver. 1.5.2.4 by Bruker and ImageJ ver. 1.51f by NIH
 (Schindelin et al., 2015). Segmentation and volume rendering of the
 resulting 3D models was accomplished with the software packages Amira ver.
 6.5.0 by Thermo Fisher Scientific (Stalling et al., 2005) and VG Studio
 3.2 by Volume Graphics. Surface rendering was performed with the software
 packages Checkpoint ver. 17.04.21 (Stratovan Corporation) and Amira ver.
 6.5.0 by Thermo Fisher Scientific (Stalling et al., 2005). Classical and geometric morphometrics To identify variation in the opercle bone and the pharyngeal jaw, linear morphometric measurements and geometric morphometric analyses were conducted based on surface rendered 3D models created by the software Checkpoint ver. 17.04.21 (Stratovan Corporation) out of µ-CT tiff image stacks. The following traits of the cranial skeleton were quantified by linear measurements: skull length, left opercle height, left opercle length, left opercle circumference, left opercle surface area, lower right pharyngeal jaw length, lower right pharyngeal jaw width, lower right pharyngeal jaw height and lower right pharyngeal jaw circumference. The number of teeth on the right lower pharyngeal jaw was counted. All measurements were carried out with the software Checkpoint. In order to test on interspecific and intersexual shape differences, 14 landmarks were placed at homologous points on the pharyngeal jaws of the 30 unstained µ-CT scanned specimens. The outline shape and circumference of the left opercle and the pharyngeal jaw were analysed with 80 semi landmarks respectively. Patches were used to measure the surface area of the opercle in order to quantify its overall size between species and sexes. Buccal cavity measurements All classical morphometric measurements and geometric morphometric analyses of the buccal cavity were based on surface rendered 3D models created by Amira ver. 6.5.0 by Thermo Fisher Scientific (Stalling et al., 2005) out of µ-CT tiff image stacks. In order to quantify interspecific and intersexual variation in buccal cavity size and shape, the 30 stained specimens were used for creating volume rendered models of the cranial region with the software Amira. Surface rendered models of the buccal cavity were created with the help of the semi-automatic segmentation tool of Amira. Background artefacts were removed by applying the “remove islands” and “fill holes” options of Amira on the segmented 3D model. The length, width, height and volume of the buccal cavity were measured for every priory stained specimen. Two female specimens of <i>T. prognatha</i> were removed from the analysis because they showed deformations of the buccal cavity due to a slightly opened mouth.
description: NA = not applicable: In files 1, 2, 4 and 5
 the column "Morphospecies" for <em>T. prognatha</em>
 is empty since this species only contains one morphospecies.
 In file 2 "Linear morphometric measurements" some data
 rows are missing because some specimens were scanned in an unstained and
 stained condition, while other specimens were only scanned in one of the
 two conditions. Specimens which were only scanned in an unstained
 condition were not used for the buccal cavity measurements. Specimens
 which were only scanned in a stained condition were not used for the
 opercle and pharyngeal jaw measurements.