Evolutionary allometry reveals a shift in selection pressure on male horn size

Area of Science:

• Evolutionary biology
• Comparative anatomy
• Sexual selection studies

Background:

• Macro-evolutionary patterns are shaped by interactions between selection and developmental constraints.
• Evolutionary allometry of secondary sexual characters, particularly under sexual selection, is poorly understood.
• Bovid horns are ideal for studying sex-specific sexual selection due to their presence in both sexes and variable selective pressures.

Purpose of the Study:

• To investigate the impact of sexual selection on the evolutionary allometry of bovid horn size.
• To compare sex-specific evolutionary allometry of horn size relative to body mass across bovid species.
• To explore how body mass influences the relationship between horn size and sexual selection intensity.

Main Methods:

• Utilized a dataset of sex-specific horn size and body mass for 91 bovid species.
• Employed phylogenetic comparative methods to analyze evolutionary allometry.
• Accounted for the intensity of sexual selection and phylogenetic relationships in the analyses.

Main Results:

• A nonlinear evolutionary allometry was observed between horn size and body mass, with the allometric slope decreasing as body mass increased.
• This nonlinear pattern was significantly more pronounced in males than in females.
• The findings suggest potential constraints on horn size in the largest bovid species or a diminished role of sexual selection in these species.

Conclusions:

• Evolutionary allometry of secondary sexual traits is influenced by body size and sex-specific sexual selection.
• Developmental constraints or relaxed sexual selection may limit horn size evolution in large-bodied bovids.
• Understanding these patterns is crucial for deciphering macro-evolutionary divergence in sexually selected traits.