Inbreeding in a Fission–Fusion Equid Decreases Following an Increase in the Number and Redistribution of Water Sources

Abstract

Social structures and habitat configuration influence inbreeding in wild populations. In harem-forming, female-defence polygynous equids, social organization promotes inbreeding avoidance, but this has not been studied in fission–fusion, resource-defence equid species. Because reproduction depends on solitary males establishing territories near resources, shifts in resource distribution are expected to affect mating patterns and inbreeding. We examined inbreeding patterns in the Asiatic wild ass (Equus hemionus) in the Negev Highlands, Israel (2019–2023), by comparing mating-pair relatedness (MPR) to all female–male dyads, within each year, and testing whether these patterns changed following a 2020 water source increase and redistribution by increasing the number of new territorial males. We then examined whether females overall tended to mate with veteran (i.e., mating since 2019) or new (i.e., mating since 2020) reproducing males, and compared female–male genetic relatedness between these two groups. Using 2509 faecal samples (2020–2024) genotyped at 625 SNPs, we assigned parentage to 73 offspring and estimated the MPR. Within years, the MPR was higher than random in 2019 and 2020 but declined after the water source manipulation, in 2021–2023. The MPR was higher near the original water source than near the new water sources. Most females (87.3%) mated with new reproducing males, and in 68.3% of cases, new reproducing males were less related to females than were veteran males. Our study suggests that reduced inbreeding is possible in fission–fusion populations when females have extended mating opportunities with territorial males, which can be achieved by expanding the distribution of resources.