As origens evolucionárias de alelos benéficos durante a adaptação repetida de cobras dágua a presas venenosas

The evolutionary origins of beneficial alleles during the repeated adaptation of garter snakes to deadly prey

Chris R. Feldmana,1, Edmund D. Brodie, Jra, Edmund D. Brodie IIIb and Michael E. Pfrendera

+Author Affiliations

aDepartment of Biology, Utah State University, Logan, UT 84322-5305; and

bDepartment of Biology, University of Virginia, Charlottesville, VA 22904-4328

Abstract

Where do the genetic variants underlying adaptive change come from? Are currently adaptive alleles recruited by selection from standing genetic variation within populations, moved through introgression from other populations, or do they arise as novel mutations? Here, we examine the molecular basis of repeated adaptation to the toxin of deadly prey in 3 species of garter snakes (Thamnophis) to determine whether adaptation has evolved through novel mutations, sieving of existing variation, or transmission of beneficial alleles across species. Functional amino acid substitutions in the skeletal muscle sodium channel (Nav1.4) are largely responsible for the physiological resistance of garter snakes to tetrodotoxin found in their newt (Taricha) prey. Phylogenetic analyses reject the hypotheses that the unique resistance alleles observed in multiple Thamnophis species were present before the split of these lineages, or that alleles were shared among species through occasional hybridization events. Our results demonstrate that adaptive evolution has occurred independently multiple times in garter snakes via the de novo acquisition of beneficial mutations.

coevolution genetic variation sodium channel tetrodotoxin Thamnophis
Footnotes

1To whom correspondence should be sent at the present address:
Department of Natural Resources and Environmental Science, University of Nevada, Reno, NV 89557–0816.

E-mail: ophis@cabnr.unr.edu

Edited by May R. Berenbaum, University of Illinois, Urbana, IL, and approved June 11, 2009

Author contributions: C.R.F., E.D.B., Jr., E.D.B., III, and M.E.P. designed research; C.R.F., E.D.B., Jr., E.D.B., III, and M.E.P. performed research; C.R.F. and E.D.B., Jr., analyzed data; and C.R.F., E.D.B., III, and M.E.P. wrote the paper.

The authors declare no conflict of interest.

This article is a PNAS Direct Submission.

Data deposition: The sequences reported in this paper have been deposited in the GenBank database (accession nos. FJ570810–FJ571064 and GQ154075–GQ154084), and all snakes have been deposited as vouchers in the herpetology collections of the California Academy of Sciences or University of Texas, Arlington.

This article contains supporting information online at www.pnas.org/cgi/content/full/0901224106/DCSupplemental.

+++++

PDF gratuito do artigo aqui.