Is chamois hybridization in the northern Dinaric Mountains an important factor for horn development?

The Dinaric region is the natural habitat of the Alpine chamois Rupicapra rupicapra rupicapra and Balkan chamois Rupicapra rupicapra balcanica. Recently confirmed, these two subspecies hybridize in the contact zone on Mts Velebit, coastal Croatia. Patterns of horn development in chamois can differ within populations and subspecies, and are mostly influenced by genetic structure, sex and resource availability. These factors control the direct ability of energy allocation to secondary sexual traits with diverse outcomes. This is the first study to investigate the horn growth patterns of Alpine and Balkan chamois populations and their admixed progeny. We explored the differences in horn growth and compensatory patterns among populations as a function of genetic background, separately for females and males. A significantly different pattern of horn development was detected in the hybrid population showing higher rates of initial horn growth – until 2.5 years, and much lower compensation rates in the first 4.5 years of life in both sexes in comparison to other chamois populations. Interestingly, differences in growth patterns were more expressed among males. Higher initial horn growth and low compensation rates in the hybrid population can be explained by both non-genetic and genetic factors, but may suggest an effect of heterosis, i.e. the occurrence of hybrid vigour. Therefore, this situation could reveal the extent to which life history patterns and evolutionary consequences can shape important traits of population outlook/vigour, such as horn size, in different chamois populations.