Allometry, asymmetry and sexual dimorphism in blue wildebeest (Connochaetes taurinus)

Hyper-allometry, whereby an anatomical unit increases in size at a faster rate than other structures of the same organism, is considered to be an important feature of many sexually selected structures, with large ‘high-quality’ animals carrying a feature that is proportionally larger than smaller, ‘low-quality’ animals. When these structures are bilaterally symmetrical, it has been suggested that the degree of fluctuating asymmetry (deviation from perfect symmetry) acts as an indicator of the quality of the bearer. Bovids are useful models for testing sexual selection hypotheses due to their large horns and variety of reproductive systems. Here we use male and female specimens of the southern African blue wildebeest (Connochaetes taurinus) to assess the levels of allometry and fluctuating asymmetry in morphological features of the horns and skull. Males were found to be significantly larger than females for overall horn size, horn length and horn circumference and the horns were found to be isometric in both sexes. Directional asymmetry was found for horn length and horn circumference with the right being longer than the left side. These findings suggest that in C. taurinus the horns follow predicted patterns of variation for sexually selected traits, but that here fluctuating asymmetry may not be as important in sexual selection as previously suggested. Additionally, females did not differ greatly from males in variation and asymmetry and allometry, indicating their horns could be under sexual selection as a result of male choice, or that like males, they also engage in intraspecific combat as well.