Low diversity in the major histocompatibility complex class II DRB1 gene of the Spanish ibex, Capra pyrenaica

Abstract

During the last two centuries, the Spanish ibex (Capra pyrenaica) has shown a significant demographic decline as a result of the progressive destruction of its natural habitat, disease epidemics, and uncontrolled hunting. Partial sequencing of the class II MHC DRB1 gene revealed that the Spanish ibex has remarkably low levels of genetic variation at this locus, with only six different DRB1 alleles and an observed heterozygosity of 0.429-0.579. The rates of nonsynonymous vs synonymous substitutions were significantly different in the peptide-binding region (d N /d S ¼ 5.347, P ¼ 0.002), a feature that indicates that the DRB1 gene is under positive selection. A phylogenetic analysis of the Spanish ibex and a set of domestic goat DRB1 alleles revealed that the reported sequences represent four major allelic lineages. The limited allelic repertoire of the DRB1 gene in the Spanish ibex is likely the direct result of the recent history of population bottlenecks and marked demographic decline of this species. A genetic survey of 13 microsatellite loci was consistent with this idea. The Spanish ibex subspecies C. p. hispanica and C. p. victoriae consistently showed considerably lower levels of microsatellite heterozygosity (H o ¼ 0.184-0.231) and allelic diversity (mean number of alleles per locus ¼ 2-2.4) than those reported in other wild ruminants. This study demonstrates the significance of both natural selection and the demographic history of populations in determining patterns of genetic variation at MHC loci. In addition, our results emphasize the importance of locally adapted populations for the preservation of genetic diversity.

Microsatellite-based genotyping of MHC class II DRB1 gene in Iberian and Alpine ibex

“…Sequencing the second exon of MHC DRB1 and genotyping the OLADRB1 microsatellite locus in 160 C. pyrenaica and 98 C. ibex detected a total of seven DRB1 exon II alleles: five in Iberian ibex: Capy-DRB1*1, Capy-DRB1*2, Capy-DRB1*3, Capy-DRB1*5, and Capy-DRB1*6 ( Amills et al 2004) and two alleles in Alpine ibex: Caib-DRB1*1 (Schaschl et al 2006) and Caib-DRB1*2 (Takada et al 1998). Nine OLADRB1 microsatellite alleles were detected: five alleles in C. pyrenaica (159, 169, 172, 185, and 187) and four alleles in C. ibex (170, 174, 178, and 184).…”

Selection and recombination drive the evolution of MHC class II DRB diversity in ungulates

“…These two alleles corresponded to two published exon 2 sequences on GenBank, named Capy-DRB1-1 and Cypy-DRB1-2 (Accession nos. : AF461692 and AF461693; Amills et al, 2004). An additional four Spanish ibex alleles (Capy-DRB1-3, Capy-DRB1-4, Capy-DRB1-5 and Capy-DRB1-6) have previously been identified (GenBank Accession nos.…”

“…An additional four Spanish ibex alleles (Capy-DRB1-3, Capy-DRB1-4, Capy-DRB1-5 and Capy-DRB1-6) have previously been identified (GenBank Accession nos. : AF461694-AF461696, and AY351788; Amills et al, 2004). These alleles were included in all subsequent analyses.…”

Non-neutral evolution of the major histocompatibility complex class II gene DRB1 in the sac-winged bat Saccopteryx bilineata

“…Such low levels of heterozygosity are known only from populations of small size or with a bottleneck in the past. They are characterized by a small number of alleles with allele frequencies not exceeding 50% in polymorphic populations (Sena et al, 2003;Aguilar et al, 2004;Amills et al, 2004;Weber et al, 2004). In contrast, in the sac-winged bat, a singlefrequent allele (A1) occurred at a frequency of 80% that caused the low heterozygosity.…”