Features of reproduction in an isolated island population of the feral horses of the Lake Manych-Gudilo (Rostov Region, Russia)

Abstract

The article describes the results of a pilot study of the reproduction features of a small population of feral horses (Equus ferus) isolated for about 70 years on the Vodny Island in the Lake Manych-Gudilo (Rostov Nature Reserve, Rostov Region, Russia). The population was characterized by a fairly stable social structure for more than 10 years, including a constant composition of adult members of harem bands, though the scarce cases of mares being covered by ‘outsider’ stallions were recorded, which could be considered as one of the variants of sneak mating. The main purposes of the study were to confirm by molecular genetic methods the possible participation in the reproduction of ‘outsider’ stallions. The study was based on a combination of the direct ethological observations and genetic analyses of the individual animals. The ethological observations conducted during more than ten years revealed that the harem bands remained relatively stable throughout the period of the study. Both direct observations and genetic data revealed that the stallions heading neighboring harem bands actually participated in the fertilization of the mares. The subdominant stallions in the multi-male family bands also occasionally participated in the reproduction. No cases of participation of the bachelor stallions in the reproduction were recorded, which can be explained by their low social rank. The participation of the ‘outsider’ stallions in reproduction increases the overall genetic diversity in the population. With this, several instances of mating by close relatives were also observed that might result at random or forcibly under conditions of the complete isolation of a rather small population. The levels of observed and estimated heterozygosity (HO = 0.581 and HE = 0.606) were estimated for the first time. Such ratio of HO to HE corresponds to the provisions of the Wahlund effect and seems to indicate a small impact of the reproduction of the ‘outsider’ stallions on the level of genetic diversity in the studied local feral horse population.