No evidence of kin preferences in a feral horse multilevel society

Abstract

A multilevel society represents a complex social structure characterized by nested levels of social organization, where small core units aggregate to form higher-level social organizations. In such a society, kinship often plays an important role in shaping social relationships; however, the degree of kin preference differs among species. This study aimed to identify whether free-ranging horses, Equus ferus caballus, in Serra D'Arga, Portugal, which form a two-tiered society, show preferences for related individuals. We examined the genetic relatedness of 167 genotyped individuals, which were in reproductive age, over a 7-year period and compared it with the unit composition and interunit proximity/association data obtained from drone observations. Neither relatedness nor the direct evaluation of first-degree relatives showed any clear correlation with either intra- or interunit relationships. This finding represents the first documented case of absence of kin preference in a multilevel society. It suggests that a multilevel society could be established without bonds among relatives and emphasizes the need to investigate nonkin relationship formation. This observed tendency differs from that of a related species, the plains zebra, Equus quagga, which has been reported to exhibit a female–female kin preference. Further comparisons with other equine species or different taxonomic groups are necessary to reveal the factors that influence genetic-related structures in a multilevel society.