Invasive Species Compendium

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Abstract

Selection of reproductive partners in semi-feral horses (Equus caballus) is not influenced by major histocompatibility complex (MHC): a field study.

Abstract

Major histocompatibility complex (MHC) is a suggested criterion of reproductive mate choice in many species. MHC-dissimilarity was suggested to play role in male selection by female horses (mares) in experimental settings. In our project, we asked whether under natural conditions mares choose breeding stallions guided by a certain MHC-type, either MHC-dissimilar or MHC-diverse.We observed the reproductive behavior of 26 mares and five stallions of semi-feral Konik Polski horses for eight years from which only 4 stallions and 16 mares could be used in analysis. Between-group (harems) migrations of mares and stallions and the composition of harems were noted. The choice of a reproductive partner was confirmed by observation (a mare present in the harem of a chosen stallion) and by the actual reproductive outcome (parentage of foals). The MHC of mares and stallions was tested using 11 MHC microsatellites. Genetic similarity in MHC was measured by pairwise relatedness and allele sharing between mares and stallions. MHC heterozygosity of every stallion was calculated. For all mares the choice of reproductive partner was the harem stallion. No extra-harem matings were observed. Allele sharing did not differ between mating pairs and between all of the possible combinations of mares and stallions (0.36 vs. 0.33; P = 0.66). Genetic similarity in MHC between mares and stallions did not influence the choice of reproductive partner by mares (P > 0.05), but mares tended (P = 0.08) to stay in harems of MHC-diverse stallion. The present findings suggest that mares in semi-feral conditions do not actively search for MHC dissimilar stallions, however they might favour MHC diverse ones. However, because the choice of reproductive partner was the current harem stallion, in the case of every mare we speculate that in feral conditions selection of reproductive stallion by mares might be either restricted or influenced by variety of factors other than MHC of a stallion.