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

Abstract

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.

Molecular cloning and site-directed mutagenesis of leucine-based sorting motifs of the porcine invariant chain

“…CLIP directly occupies the groove of the MHC class II molecule peptide binding region (Gregers et al, 2003), which is the most polymorphic region in all known molecules (Silva and Edwards, 2009). This diversity of MHC class II is believed to be adapted to the diversity of pathogens (Bernatchez and Landry, 2003;Surridge et al, 2008;Meyer-Lucht et al, 2010). Therefore, CLIP may be modified to fit the variant MHC class II under selective pressure.…”

Structure of Parasite Component Communities of Didelphid Marsupials: Insights From a Comparative Study

“…Up to the present time, there have been no published comparisons of the helminth faunas of marsupials from the Americas and only 1 study on 2 sympatric species of smallsized opossums, illustrating the negative correlation between parasite burdens and allelic diversity in the major histocompatibility complex (Meyer-Lucht et al, 2010).…”

Molecular characterization and tissue-specific expression of invariant chain in the muscovy duck (Cairina moschata)

“…Nevertheless, the MHC II molecule has a high degree of polymorphism, especially in the groove, which is bound by the CLIP. This diversity of MHC II is believed to be driven by selection for resistance to pathogens (Bernatchez and Landry, 2003;Surridge et al, 2008;Meyer-Lucht et al, 2010). The CLIP might be modified to fit the variant MHC II under the selection pressure.…”