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

Abstract

Major histocompatibility complex class II (MHCII) genes code for proteins that bind and present antigenic peptides and trigger the adaptive immune response. We present a broad geographical study of MHCII DA b1 (DAB) and DB b1 (DBB) variants of the koala (Phascolarctos cinereus; n ¼ 191) from 12 populations across eastern Australia, with a total of 13 DAB and 7 DBB variants found. We identified greater MHCII variation and, possibly, additional gene copies in koala populations in the north (Queensland and New South Wales) relative to the south (Victoria), confirmed by STRUCTURE analyses and genetic differentiation using analysis of molecular variance. The higher MHCII diversity in the north relative to south could potentially be attributed to (i) significant founder effect in Victorian populations linked to historical translocation of bottlenecked koala populations and (ii) increased pathogen-driven balancing selection and/or local genetic drift in the north. Low MHCII genetic diversity in koalas from the south could reduce their potential response to disease, although the three DAB variants found in the south had substantial sequence divergence between variants. This study assessing MHCII diversity in the koala with historical translocations in some populations contributes to understanding the effects of population translocations on functional genetic diversity.

Identification of MHCII variants associated with chlamydial disease in the koala (Phascolarctos cinereus)

“…Also consistent with Lau et al (2014), koalas had four to five DAB variants and one to two DBB variants identified per individual, and the DAB*19 and DAB*21 variants were found in a majority of koalas (96.8% and 98.9%, respectively), and were therefore not included in analyses. Although three new “genotype patterns” were identified from OSCP analyses, sequencing of these patterns showed that they comprised new combinations of previously identified MHCII variants.…”

Genetic wealth, population health: Major histocompatibility complex variation in captive and wild ring‐tailed lemurs (Lemur catta)

“…Although limited MHC diversity does not necessarily condemn a species to extinction (e.g., Castro‐Prieto, Wachter, & Sommer, ; Lau, Jaratlerdsiri, Griffith, Gongora, & Higgins, ; Plasil et al., ; Weber, Stewart, Schienman, & Lehman, ; Weber et al., ; Zhu, Ruan, Ge, Wan, & Fang, ), low MHC diversity can compromise population viability over the long term by increasing susceptibility to disease (Belov, ; Radwan, Biedrzycka, & Babik, ; Segelbacher et al., ; Spielman, Brook, Briscoe, & Frankham, ). In particular, many species are likely to increasingly encounter novel pathogens in the future because of increased exposure to humans, their livestock, other domesticated animals (e.g., feral dogs and cats), and invasive species (Barrett, Brown, Junge, & Yoder, ; Daszak, Cunningham, & Hyatt, , ).…”

Limited polymorphism of the functional MHC class II B gene in the black‐spotted frog (Pelophylax nigromaculatus) identified by locus‐specific genotyping

“…Physiographic factors such as big rivers and mountains can influence the genetic structure of different species, especially those lacking dispersal ability (Bushar et al., ; Lau, et al, ). As expected, substantial differences were found in genetic structure among the three geographic populations (Figure , Tables and ).…”