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doi:10.1534/genetics.104.038273
A more recent version of this article appeared on May 1, 2005.
REGULAR RESEARCH PAPERS |
Evolution of salamander life cycles: A major effect QTL contributes to discrete and continuous variation for metamorphic timing
Stephen Randal Voss 1* and Jeramiah J Smith 1
1 University of Kentucky
* To whom correspondence should be addressed. E-mail: srvoss{at}uky.edu.
Submitted on December 3, 2004
Revised on February 1, 2005
Accepted on 3 February 2005
The evolution of alternate modes of development may occur through genetic changes in metamorphic timing. This hypothesis was examined by crossing salamanders that express alternate developmental modes: metamorphosis versus paedomorphosis. Three strains were used in the crossing design: Ambystoma tigrinum tigrinum (Att) (metamorph), wild-caught A. mexicanum (Am) (paedomorph), and laboratory Am (paedomorph). Att/Am hybrids were created for each Am strain and then backcrossed to their respective Am line. Previous studies have shown that a dominant allele from Att (metAtt) and recessive allele from lab Am (metlab) results in metamorphosis in Att/Am hybrids, and metAtt/metlab and metlab/metlab backcross genotypes are strongly associated with metamorphosis and paedomorphosis, respectively. We typed a molecular marker (contig325) linked to met and found that metAtt/metlab and metAtt/metwild were associated with metamorphosis in 99% of the cases examined. However, the frequency of paedomorphosis was 4.5 times higher for metlab/metlab verses metwild/metwild. We also found that metAtt/metwild and metwild/metwild genotypes discriminated a bimodal distribution of early and late metamorphosing individuals. Two forms of phenotypic variation are contributed by met: continuous variation of metamorphic age and expression of discrete, alternate morphs. We suggest that the evolution of paedomorphosis is associated with genetic changes that delay metamorphic timing in biphasic life cycles.
Key Words: Ambystoma, QTL, amphibian, evolution, metamorphosis
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