No evidence for major histocompatibility complex–dependent mating patterns in a free–living ruminant population

Abstract

Conventionally, the extraordinary diversity of the vertebrate major histocompatibility complex (MHC) is thought to have evolved in response to parasites and pathogens a¡ecting ¢tness. More recently, reproductive mechanisms such as disassortative mating have been suggested as alternative mechanisms maintaining MHC diversity. A large unmanaged population of Soay sheep (Ovis aries L.) was used to investigate reproductive mechanisms in the maintenance of MHC diversity. Animals were sampled as new-born lambs and between 887 and 1209 individuals were typed at each of ¢ve microsatellite markers located either within or £anking the ovine MHC. All loci were in Hardy^Weinberg proportions. A novel likelihood-based approach was developed to analyse mating patterns using paternity data. No evidence for non-random mating with respect to MHC markers was found using this technique. We conclude that MHC diversity in the St Kildan Soay sheep population is unlikely to be maintained by mating preferences and that, in contrast with evidence from experimental mice populations, MHC variation plays no role in the mating structure of this population.

The evolutionary ecology of the major histocompatibility complex

“…Paterson and Pemberton (1997) found no evidence for MHC-dependent mate choice in Soay sheep (Ovis aries) and suggested that the strength of male-male competition is more important for determining mating success than intersexual mate choice. Similarly mate choice was determined to be independent of MHC type in female great reed warblers (Acrocephalus arundinaceus) (Westerdahl, 2004), rhesus macaques (Macaca mulatta) (Sauermann et al, 2001) and great snipes (Gallinago media) (Ekblom et al, 2004).…”

The Evolution of Mating Preferences and Major Histocompatibility Complex Genes

“…A recent study investigated whether feral Soay sheep (Ovis aries) living on a Scottish island display MHC-dependent mating preferences (Paterson and Pemberton 1997). This population does not show a deficiency of MHC homozygotes; however, it does show an even distribution of alleles indicating balancing selection.…”

“…This population does not show a deficiency of MHC homozygotes; however, it does show an even distribution of alleles indicating balancing selection. Paterson and Pemberton (1997) genetically typed between 887 and 1,209 newborn lambs with five microsatellite markers and used a likelihood-based approach to analyze the mating patterns of the ewes. Although they found no evidence for MHCdisassortative mating preferences, their analysis could only detect strong mate selection ( ).…”

New perspectives on mate choice and the MHC

“…Results have currently been published for two other species, ringnecked pheasants (von Schantz et al, 1996) and Soay sheep (Paterson & Pemberton, 1997). Common to both papers is the use of populations which are subject to long-term intensive study, for which a detailed background knowledge of the ecology (particularly demography) exists.…”

“…Intriguingly, however, while concede the lack of power in their study to detect weak effects, they note that their observations (although statistically non-significant) were the reverse of that expected under disassortative mating. Paterson & Pemberton (1997) have used demographic information and paternity analysis available for the Soay sheep population of St. Kilda (an island archipelago off the north-west coast of Scotland) to examine mating patterns in relation to MHC type. Using microsatellite loci as markers for MHC haplotype, they found no evidence for non-random mating with respect to the MHC, even after careful consideration of factors which might prevent detection of a weak effect (such as the power of their analysis).…”