title: Isolation breeds naivety: island living robs Australian varanid lizards of toad-toxin immunity via four-base-pair mutation.
abstract: Since their introduction to the toad-free Australian continent cane toads (Bufo marinus) have caused a dramatic increase in naïve varanid mortality when these large lizards attempt to feed on this toxic amphibian. In contrast Asian-African varanids, which have coevolved with toads, are resistant to toad toxin. Toad toxins, such as Bufalin target the H1-H2 domain of the α(1)  subunit of the sodium-potassium-ATPase enzyme. Sequencing of this domain revealed identical nucleotide sequences in four Asian as well as in three African varanids, and identical sequences in all 11 Australian varanids. However, compared to the Asian-African varanids, the Australian varanids showed four-base-pair substitutions, resulting in the alteration in three of the 12 amino acids representing the H1-H2 domain. The phenotypic effect of the substitutions was investigated in human embryonic kidney (HEK) 293 cells stably transfected with the Australian and the Asian-African H1-H2 domains. The transfections resulted in an approximate 3000-fold reduction in resistance to Bufalin in the Australian HEK293 cells compared to the Asian-African HEK293 cells, demonstrating the critical role of this minor mutation in providing Bufalin resistance. Our study hence presents a clear link between genotype and phenotype, a critical step in understanding the evolution of phenotypic diversity.
authors.affiliation: Faculty of Veterinary Science, University of Sydney, NSW 2006, Australia.
authors.forename: Beata
authors.initials: B
authors.lastname: Ujvari
authors.forename: Hee-chang
authors.initials: HC
authors.lastname: Mun
authors.forename: Arthur D
authors.initials: AD
authors.lastname: Conigrave
authors.forename: Alessandra
authors.initials: A
authors.lastname: Bray
authors.forename: Jens
authors.initials: J
authors.lastname: Osterkamp
authors.forename: Petter
authors.initials: P
authors.lastname: Halling
authors.forename: Thomas
authors.initials: T
authors.lastname: Madsen
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D001315:Australia; D002018:Bufanolides / Q000633:toxicity*; D002025:Bufonidae / Q000235:genetics*; D002316:Cardiotonic Agents / Q000633:toxicity*; D017753:Ecosystem; D019143:Evolution, Molecular; D057809:HEK293 Cells; D006801:Humans; D062312:Islands; D008116:Lizards / Q000235:genetics*; D009154:Mutation; D017434:Protein Structure, Tertiary; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics*
chemical_list: D002018:Bufanolides; D002316:Cardiotonic Agents; D000254:Sodium-Potassium-Exchanging ATPase; C022777:bufalin