Anomalous patterns of horn asymmetry reflects character's unique evolutionary history

The Developmental Instability-Sexual Selection hypothesis was tested by examining ungulate horn and skeletal morphology. Comparative methods were employed to analyze patterning in asymmetry for eight species of the bovid subfamily Antilopinae. Traits were partitioned into craniofacial or horn groupings; unsigned asymmetries of traits were combined into composite FA indices representing developmental instability of craniofacial and horn modules, respectively. Although horns uniformly exhibited greater asymmetry than craniofacial traits, no evidence supporting subsequent predictions was found. Comparative and correlative analysis of phenotypic variation was performed to further investigate the specific deviations from expectation. The highly variable and asymmetrical female horns were found to be anomalous, while absence of predicted male horn patterns negated explanation with current theory. The anomalous patterns and erroneous predictions were further documented in 40 species for the family Bovidae. A rescue hypothesis was then adduced for variability and asymmetry in secondary sexual characters expressed in females.