Low MHC DRB class II diversity in the mountain goat: past bottlenecks and possible role of pathogens and parasites

Mainguy, Julien; Worley, Kirsty; Côté, Steeve D.; Coltman, David W.

doi:10.1007/s10592-006-9243-5

Cited by 48 publications

(48 citation statements)

References 57 publications

(64 reference statements)

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“…Our results suggest that a common observation of reduced MHC variation in populations subject to recent population bottlenecks (e.g. Babik et al 2005;Hansson and Richardson 2005;Bollmer et al 2007;Mainguy et al 2007;Radwan et al 2007;Zhu et al 2007;Biedrzycka and Radwan 2008, but see Aguilar et al 2004 for an exception) does not need to imply that selection on MHC variation in these populations is weak or non-existent. Indeed, our results suggest a resolution of the apparent discrepancy between the widespread evidence for historical positive selection acting on MHC and inability of the same selection to maintain MHC diversity during population bottlenecks (reviewed in Radwan et al 2009).…”

Section: Discussionmentioning

confidence: 63%

MHC diversity in bottlenecked populations: a simulation model

2009

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The depletion of variation at MHC loci, which play a crucial role in pathogen recognition, has been postulated to be one of important extinction risk factors for endangered populations. Thus, it is important to understand how selection affects the level of polymorphism in these genes when populations undergo a reduction in size. We followed MHC diversity in computer simulations of population bottlenecks. The fates of MHC alleles in the simulations were determined either by drift, or by balancing selection resulting from host-parasite coevolution. We found that the impact of selection on MHC polymorphism in bottlenecked populations was dependent upon the timescales involved. Initially, selection maintained lower number of alleles than drift, but after *40 generations of hosts selection maintained higher MHC diversity, as compared to drift. The adverse effects of decreased MHC polymorphism on population viability may be, to some extent, compensated for if selection helps to retain MHC alleles which show high functional diversity, which should allow protection against a broader range of pathogens. Our simulation shows, however, that the mean divergence of alleles retained under selection in bottlenecked populations is not, on average, significantly higher than the divergence due to drift.

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Section: Discussionmentioning

confidence: 63%

MHC diversity in bottlenecked populations: a simulation model

2009

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“…moose (Alces alces) or mountain goats (Oreamnos americanus) (Mikko and Anderson 1995;Mainguy et al 2007). However, the pattern of low MHC class II variation and high parasite load in M. incanus resembles findings from other prominent species, for instance, the giant panda (Ailuropoda melanoleuca), which is particularly susceptible to infectious diseases and parasites.…”

Section: Parasite Load and Functional Associations With Host Geneticsmentioning

confidence: 99%

Variety matters: adaptive genetic diversity and parasite load in two mouse opossums from the Brazilian Atlantic forest

et al. 2010

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The adaptive potential of a species to a changing environment and in disease defence is primarily based on genetic variation. Immune genes, such as genes of the major histocompatibility complex (MHC), may thereby be of particular importance. In marsupials, however, there is very little knowledge about natural levels and functional importance of MHC polymorphism, despite their key role in the mammalian evolution. In a previous study, we discovered remarkable differences in the MHC class II diversity between two species of mouse opossums (Gracilinanus microtarsus, Marmosops incanus) from the Brazilian Atlantic forest, which is one of the most endangered hotspots for biodiversity conservation. Since the main forces in generating MHC diversity are assumed to be pathogens, we investigated in this study gastrointestinal parasite burden and functional associations between the individual MHC constitution and parasite load. We tested two contrasting scenarios, which might explain differences in MHC diversity between species. We predicted that a species with low MHC diversity would either be under relaxed selection pressure by low parasite diversity ('Evolutionary equilibrium' scenario), or there was a recent loss in MHC diversity leading to a lack of resistance alleles and increased parasite burden ('Unbalanced situation' scenario). In both species it became apparent that the MHC class II is functionally important in defence against gastrointestinal helminths, which was shown here for the first time in marsupials. On the population level, parasite diversity did not markedly differ between the two host species. However, we did observe considerable differences in the individual parasite load (parasite prevalence and infection intensity): while M. incanus revealed low MHC DAB diversity and high parasite load, G. microtarsus showed a tenfold higher population wide MHC DAB diversity and lower parasite burden. These results support the second scenario of an unbalanced situation.

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“…Others believe that genetic drift, which is heightened in small and/or bottlenecked populations, can affect balancing selection and may alter the maintenance of polymorphisms at MHC loci (Miller and Lambert, 2004;van Oosterhout et al, 2006;Mainguy et al, 2007), which can lower the potential for long-term persistence of the species. There is ample evidence for both arguments.…”

Section: Introductionmentioning

confidence: 99%

Extensive variation at MHC DRB in the New Zealand sea lion (Phocarctos hookeri) provides evidence for balancing selection

et al. 2013

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Marine mammals are often reported to possess reduced variation of major histocompatibility complex (MHC) genes compared with their terrestrial counterparts. We evaluated diversity at two MHC class II B genes, DQB and DRB, in the New Zealand sea lion (Phocarctos hookeri, NZSL) a species that has suffered high mortality owing to bacterial epizootics, using Sanger sequencing and haplotype reconstruction, together with next-generation sequencing. Despite this species' prolonged history of small population size and highly restricted distribution, we demonstrate extensive diversity at MHC DRB with 26 alleles, whereas MHC DQB is dimorphic. We identify four DRB codons, predicted to be involved in antigen binding, that are evolving under adaptive evolution. Our data suggest diversity at DRB may be maintained by balancing selection, consistent with the role of this locus as an antigen-binding region and the species' recent history of mass mortality during a series of bacterial epizootics. Phylogenetic analyses of DQB and DRB sequences from pinnipeds and other carnivores revealed significant allelic diversity, but little phylogenetic depth or structure among pinniped alleles; thus, we could neither confirm nor refute the possibility of trans-species polymorphism in this group. The phylogenetic pattern observed however, suggests some significant evolutionary constraint on these loci in the recent past, with the pattern consistent with that expected following an epizootic event. These data may help further elucidate some of the genetic factors underlying the unusually high susceptibility to bacterial infection of the threatened NZSL, and help us to better understand the extent and pattern of MHC diversity in pinnipeds.

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Low MHC DRB class II diversity in the mountain goat: past bottlenecks and possible role of pathogens and parasites

Cited by 48 publications

References 57 publications

MHC diversity in bottlenecked populations: a simulation model

MHC diversity in bottlenecked populations: a simulation model

Variety matters: adaptive genetic diversity and parasite load in two mouse opossums from the Brazilian Atlantic forest

Extensive variation at MHC DRB in the New Zealand sea lion (Phocarctos hookeri) provides evidence for balancing selection

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