Reduced MHC class II diversity in island compared to mainland populations of the black-footed rock-wallaby (Petrogale lateralis lateralis)

Abstract

Many animal populations that are endangered in mainland areas exist in stable island populations, which have the potential to act as an ''ark'' in case of mainland population declines. Previous studies have found neutral genetic variation in such species to be up to an order of magnitude lower in island compared to mainland populations. If low genetic variation is prevalent across fitnessrelated loci, this would reduce the effectiveness of island populations as a source of individuals to supplement declining mainland populations or re-establish extinct mainland populations. One such species, the black-footed rock-wallaby (Petrogale lateralis lateralis), exists within fragmented mainland populations and small island populations off Western Australia. We examined sequence variation in this species within a fitness-related locus under positive selection, the MHC class II DAB b1 locus. The mainland populations displayed greater levels of allelic diversity (4-7 alleles) than the island population, despite being small and isolated, and contained at least two DAB gene copies. The island population displayed low allelic diversity (2 alleles) and fewer alleles per individual in comparison to mainland populations, and probably possesses only one DAB gene copy. The patterns of DAB diversity suggested that the island population has a markedly lower level of genetic variation than the mainland populations, in concordance with results from microsatellites (genotyped in a previous study), but preserved unique alleles which were not found in mainland populations. Where possible, conservation actions should pool individuals from multiple populations, not only island populations, for translocation programs, and focus on preventing further declines in mainland populations.

MHC class II diversity of koala (Phascolarctos cinereus) populations across their range

“…The degree of MHC diversity in southern populations in this study is comparable to that of bottlenecked island populations of Australian bush rats and blackfooted rock-wallabies (Seddon and Baverstock, 1999;Mason et al, 2011). The similarity of diversity patterns between MHCII and neutral loci suggests a prominent role of neutral selection such as genetic drift and founder effects, rather than pathogen-driven selection in shaping the distribution of MHCII variation in these koalas, as seen in other species with small populations (Miller and Lambert, 2004;Miller et al, 2010;Agudo et al, 2011).…”

MHC II DRB variation and trans-species polymorphism in the golden snub-nosed monkey (Rhinopithecus roxellana)

“…Though DRB genes usually display high diversity, in cases of small and isolated or bottlenecked populations, a lower variation is expected [52]. Similar results were found in other species such as northern elephant seals (Mirounga angustirostris) [53], great crested newt (Triturus cristatus) [54], and the black-footed rock-wallaby (Petrogale lateralis lateralis) [55]. Genetic drift is the reason for the reduced MHC variation in these populations because compared with balancing selection, which usually has a great influence on MHC genes, genetic drift becomes relatively stronger in small, isolated populations, leading to reduced variation at the MHC loci [56].…”

The identity of the Depuch Island rock-wallaby revealed through ancient DNA

“…To ensure survival of this species in the face of the continuing decline of mainland populations (Hall and Kinnear 1991;Mason et al 2011), we would advocate the relocation of a viable population of P. l. lateralis onto the now fox-free DI, which would provide an insurance population for the species, at least for the short term. Recent studies by Mason et al (2011) and others (Frankham 1997;Frankham et al 2002) highlight the importance of preserving fragmented mainland populations of rock-wallabies rather than translocating populations to islands, because of the increasingly low levels of genetic diversity. However, given that P. l. lateralis was the original inhabitant of DI, repopulating it will be a significant step in restoring the island's past biodiversity and one that is likely to have positive effects on the island's ecosystem.…”

“…However, given that P. l. lateralis was the original inhabitant of DI, repopulating it will be a significant step in restoring the island's past biodiversity and one that is likely to have positive effects on the island's ecosystem. Additionally, a sound understanding of the genetic diversity of mainland populations is a necessary prerequisite to enhance the reintroduced population's survival in the new island environment (Mason et al 2011). The ultimate aim must be that, following successful reintroductions, such island sanctuaries can in the future be used as sources for returning species back onto the mainland, and, in doing so, restore at least some of the lost biodiversity of the recent past.…”

“…A marginally degraded subfossil museum bone ( Mason et al (2011) and (Eldridge et al 1994). no attempts had been made to clearly identify the endemic species of rock-wallaby that previously inhabited the island, which is important as it will allow informed decisions to be made in any biodiversity restoration projects onto the now fox-free DI. Since this species is completely extinct on the island and there are only a few trace rock-wallaby museum specimens left, ancient DNA analysis is the most suitable technique and is highly recommended in order to handle and retrieve relevant data for species identification useful in this study.…”