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Evolutionary diversification of TTX-resistant sodium channels in a predator–prey interaction


Understanding the molecular genetic basis of adaptations provides incomparable insight into the genetic mechanisms by which evolutionary diversification takes place. Whether the evolution of common traits in different lineages proceeds by similar or unique mutations, and the degree to which phenotypic evolution is controlled by changes in gene regulation as opposed to gene function, are fundamental questions in evolutionary biology that require such an understanding of genetic mechanisms1,2,3. Here we identify novel changes in the molecular structure of a sodium channel expressed in snake skeletal muscle, tsNaV1.4, that are responsible for differences in tetrodotoxin (TTX) resistance among garter snake populations coevolving with toxic newts4. By the functional expression of tsNaV1.4, we show how differences in the amino-acid sequence of the channel affect TTX binding and impart different levels of resistance in four snake populations. These results indicate that the evolution of a physiological trait has occurred through a series of unique functional changes in a gene that is otherwise highly conserved among vertebrates.

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Figure 1: Amino-acid sequence differences for four snake populations.
Figure 2: The effect of different TTX concentrations on tsNaV1.4 and snake–human chimaeric channels.
Figure 3: TTX binding affinity of cloned channels compared with skeletal muscle in four snake populations.


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We thank A. Correa for advice regarding the cut-open oocyte voltage clamp; S. Durham for advice regarding the statistical analysis; C. Feldman and M. Pfrender for advice regarding the phylogenetic analysis; J. Caldwell for primers; A. Goldin for sharing his sodium channel sequence alignment; and C. Hanifin and the USU herpetology group for comments that improved the manuscript. This work was supported by research grants from the National Institute of Health (P.C.R.) and from the National Science Foundation (E.D.B. Jr and E.D.B. III).

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Correspondence to Shana L. Geffeney.

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Supplementary information

Supplementary Figure S1

This figure shows a phylogenetic tree of voltage-gated sodium channels from a maximum-likelihood based, Bayesian analysis. (PDF 73 kb)

Supplementary Figure S2

This figure shows a schematic of the human/snake chimeric channel. (PDF 173 kb)

Supplementary Figure Legends

This file contains the figure legends for Supplementary Figure S1 and Supplementary Figure S2. (DOC 27 kb)

Supplementary Notes

This file contains Supplementary Methods and additional references references. (DOC 52 kb)

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Geffeney, S., Fujimoto, E., Brodie, E. et al. Evolutionary diversification of TTX-resistant sodium channels in a predator–prey interaction. Nature 434, 759–763 (2005).

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