, Volume 64, Issue 11, pp 825–838

MHC class I of saltwater crocodiles (Crocodylus porosus): polymorphism and balancing selection

  • Weerachai Jaratlerdsiri
  • Sally R. Isberg
  • Damien P. Higgins
  • Jaime Gongora
Original Paper

DOI: 10.1007/s00251-012-0637-x

Cite this article as:
Jaratlerdsiri, W., Isberg, S.R., Higgins, D.P. et al. Immunogenetics (2012) 64: 825. doi:10.1007/s00251-012-0637-x


Saltwater crocodiles are in high demand for the production of luxury fashion items. However, their susceptibility to disease incurs substantial losses and it is hoped to be able to genetically select these animals for disease resistance. So far, this has only been enabled by phenotypic selection. Investigating the major histocompatibility complex (MHC) could provide insight into the ability of an individual to respond to pathogens acting as a selective pressure on the host. Here, we assessed genetic diversity and a role of selection in shaping the diversity of MHC class I exon 3 among 42 saltwater crocodiles from nine river basins in the Northern Territory, Australia. We generated 640 sequences using cloning and sequencing methods and identified 43 MHC variants among them. Phylogenetic analyses clustered these variants into two major clades, which may suggest two gene lineages. We found the number of variants within an individual varying between one and seven, indicating that there are at least four gene loci in this species. Selection detection analyses revealed an elevated ratio of nonsynonymous to synonymous substitutions (mean = 1.152 per codon), suggesting balancing selection. Population differentiation analyses revealed that the MHC did not show structuring among the river basins, and there were some shared variants among them. This may be a result of possible gene flow and/or similar selection pressures among populations. These findings provide background knowledge to identify potential MHC markers, which could be used for selecting genetically variable individuals for future disease associations. All MHC class I exon 3 sequences reported in this paper were submitted to the GenBank database with following accession numbers: HQ008785–HQ008789, HQ008791–HQ008798, HQ008808–HQ008815, HQ008824, HQ008826–HQ008830, HQ008835, HQ008839, HQ008842–HQ008850, and JX023536–JX023540.


MHC class ISaltwater crocodileGenetic diversityBalancing selection

Supplementary material

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Copyright information

© Springer-Verlag 2012

Authors and Affiliations

  • Weerachai Jaratlerdsiri
    • 1
  • Sally R. Isberg
    • 1
    • 2
  • Damien P. Higgins
    • 3
  • Jaime Gongora
    • 1
  1. 1.Faculty of Veterinary Science, RMC Gunn BuildingUniversity of SydneySydneyAustralia
  2. 2.Porosus Pty. Ltd.PalmerstonAustralia
  3. 3.Faculty of Veterinary Science, McMaster BuildingUniversity of SydneySydneyAustralia