Isolation breeds naivety

24 August 2012

Isolation breeds naivety: Island living robs Australian varanid lizards of toad-toxin immunity via four-base-pair mutation

Beata Ujvari1, Hee-chang Mun2, Arthur Conigrave2, Jens Osterkamp3, Petter Halling3 and Thomas Madsen2,4

  1. Faculty of Veterinary Sciences, University of Sydney, NSW 2006, Australia
  2. School of Molecular and Microbial Biosciences, University of Sydney, NSW 2006, Australia
  3. Faculty of Medicine, Lund University, S-22362 Lund, Sweden
  4. School of Biological Sciences, University of Wollongong, NSW 2522, Australia

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, co-evolved with toads, are resistant to toad toxin which targets the a1 subunit of sodium-potassium-ATPase enzyme. Sequencing of the H1-H2 domain, coding for the a1 subunit, revealed a four base-pair mutation (resulting in three amino acid changes) between the two varanid groups. The phenotypic effect of the mutations was investigated in Human Embryonic Kidney 293 (HEK293) cells stably transfected with the Australian and the Asian-African variants of the H1-H2 domain. The transfection experiment revealed a 3000-fold reduction in resistance to toad toxin in the HEK293 cells containing the Australian varanid sequence. Asian varanids are estimated to have colonized Australia 10-15 million years ago, and hence the first migrants were most likely resistant to toad toxin. Bufonid anurans are, however, not native to Australia, and the high susceptibility of Australian varanids suggest that they have lost their resistance to toad toxins. Our study provides a clear link between genotype and phenotype, a critical step in understanding the evolution of phenotypic diversity.

Time: 1-2pm

Location: DT Anderson Lecture Theatre, A08