Acoustic characteristics of courtship and agonistic vocalizations in Przewalskii's wild horse and in domestic horse

For closely related species living in similar habitats, differences in the acoustic morphology of vocalizations could play a role in mate recognition as well as provide insight into the evolutionary divergence between species. Przewalski's horses (. Equus Przewalskii) and Mongolian domestic horses (. Equus callabus) are sometimes found cohabiting in the same environment during the mating season. As such, we examined the hypothesis that interspecies differences are reflected in the acoustic morphology of vocalizations produced by two closely related species.We analyzed the acoustic structure of courtship nickers and agonistic squeals produced by Przwewalski's and Mongolian domestic stallions. Our acoustic analyses indicated that agonistic squeals produced by Przwewalski's stallions were significantly higher in source-related acoustic parameters and in the frequency of maximal energy than those produced by Mongolian domestic stallions. In addition to species differences, we found context-related differences in Przwewalski's stallion vocalizations. Courtship nickers were significantly lower in fundamental frequencies than agonistic squeals.Our findings suggest that acoustic differences between nickers and squeals could reflect underlying motivational states in Przewalski's horses. Interspecies differences in acoustic structure however, are restricted to agonistic squeals. From an evolutionary standpoint, the lack of interspecies differences in courtship vocalizations suggest that similar factors influence the evolution of courtship calls whereas the differences found in agonistic vocalizations indicate that different factors modulate the evolution of agonistic calls.