2.3.1 Precopulatory trait measurements
To investigate the sexual size dimorphism in the four populations of O. babirussa , maximum pronotum width (Figure 2) of males and females were measured as a proxy for body size with the eyepiece reticle on the Olympus SZX10 microscope. This is widely used proxy for body size because the pronotum width does not change in adulthood and has been found to be the most appropriate measure for body size in dung beetles (Emlen, 1997; Knapp & Knappová, 2013).
Horn lengths of male O. babirussa  (Figure 2) were measured to document variation in this precopulatory trait. Images were taken of the anterior habitus. Heads of the beetles were separated and suspended with Durex KY Jelly, with horns aligned parallel to the lens of the camera. Images were captured using the EOS 800D and 6D camera body with the Canon MP-E 65mm f/2.8 1-5x lens at 5x optical zoom. The camera was suspended on the Dun, Inc. P-51 and the Camlift controller V2.9.3.0 software was used to take multiple images at different heights for focus stacking.  EOS Utility Launcher software was used to access the images and stack them using the Zerene Stacker V. 1.04. software. Stacked images were imported to Adobe Photoshop CS5 V. 12.0 x64 and a 1mm scale bar was added to each image. Next, processed images were imported to ImageJ V. 1.51 and the horns were measured from the tip to the bottom of the outer edge of each horn, following previous studies (Moczek & Emlen, 1999).