Disentangling ontogenetic and environmental drivers of horn growth in Alpine chamois

Abstract Environmental conditions interact with genetic factors to shape sexually selected traits. In temperate bovids, horns grow in discrete annual increments, providing the opportunity to link year-specific environmental conditions to developmental trajectories. We combined segment-level horn data from 252 Alpine chamois ( Rupicapra r. rupicapra ) with climate and remotely sensed vegetation productivity (EVI) data and applied a path-modelling framework to quantify how sex, environmental variation, and compensatory growth jointly determine total horn length. As expected, horn growth occurred primarily early in life. The first measurable growth segment (L2) accounted for most between-individual variance and was strongly influenced by sex and current-year vegetation productivity. Subsequent segments contributed progressively less to total variance but were not independent. In particular, we detected condition-dependent compensatory growth between L2 and L3: individuals with reduced early growth tended to show stronger recovery under high vegetation productivity, whereas under poorer environmental conditions compensatory growth was weaker. This indicates that the ability to compensate for poor early growth depends on environmental conditions. Consequently, horn size reflects both developmental constraints established early in life and the opportunity for environmentally mediated compensation in later years. Because horn segments represent annual, time-stamped growth increments, they provide a framework for reconstructing how environmental variability shapes phenotypic development. Interpreting total horn length requires understanding which life stages dominate its variance, with direct implications for understanding the evolution of sexually selected traits and for wildlife management.