Acoustic Divergence in Domestic Horses

We tested whether pronounced morphological variability of horses caused by artificial selection was followed also by variation in their vocalization. We compared whinnies of 10 breeds representing horse varieties both in morphology and history using discrimination analyses (Wilks´ lambda = 0.070). Whinnies of Shetland pony were the most distinct from calls of other breeds (74.1% classification success). This result is in agreement with distinction based on morphological features. Whinnies of the primitive Hucul horse belonged among the most correctly classified ones (73.5%). Classification results of both Old Kladruby horse colour forms were very different: whinnies of the grey form revealed the least successful classification (18.9%) whilst calls of the black form showed one of the best classification outputs (72.4%). A surprising result was the extreme vocal distinction between the heaviest breeds, confirmed by discrimination analysis, the Czech-Moravian Belgian (55.5%), and Silesian Noriker (51.4%). This finding was contrary to their morphological similarity.

The relationship between morphological and acoustical variables revealed a significant correlation (r ˂ -0.57). Our results did not confirm the hypothesis of acoustic distinction in horse breeds based simply on their morphology. However, whinnies of an old breed, the Shetland pony, were the most distinct ones from all the others. The other old breeds, the Thoroughbred and the Old Kladruby horses, clustered together with the modern Czech warmblood. Our results seem to not confirm the second hypothesis of vocal distinction based on the length of time since establishment of the respective breed. Significant differences among horse breeds indicate the process of vocal distinction during the process of artificial selection.