The transformation of ancestral phenotypes into novel traits is poorly understood for many examples of evolutionary novelty. Ancestrally, salamanders have a biphasic life cycle with an aquatic larval stage, a brief and pronounced metamorphosis, followed by a terrestrial adult stage. Repeatedly during evolution, metamorphic timing has been delayed to exploit growth-permissive environments, resulting in paedomorphic salamanders that retain larval traits as adults. We used thyroid hormone (TH) to rescue metamorphic phenotypes in paedomorphic salamanders and then identified quantitative trait loci (QTL) for life history traits that are associated with amphibian life cycle evolution: metamorphic timing and adult body size. We demonstrate that paedomorphic tiger salamanders (Ambystoma tigrinum complex) carry alleles at three moderate effect QTL (met1-3) that vary in responsiveness to TH and additively affect metamorphic timing. Salamanders that delay metamorphosis attain significantly larger body sizes as adults and met2 explains a significant portion of this variation. Thus, substitution of alleles at TH-responsive loci suggests an adaptive pleiotropic basis for two key life-history traits in amphibians: body size and metamorphic timing. Our study demonstrates a likely pathway for the evolution of novel paedomorphic species from metamorphic ancestors via selection of TH-response alleles that delay metamorphic timing and increase adult body size.
|Number of pages||6|
|State||Published - Nov 2012|
Bibliographical noteFunding Information:
The data are available from SRV upon request. We thank Miranda Courtney for help with salamander care. This research was supported by grant 2R24OD010435 from the National Center for Research Resources (NCRR) and the Office of Research Infrastructure Programs (ORIP), a component of the National Institutes of Health (NIH). The project also used resources developed under Multidisciplinary University Research Initiative grant (W911NF-09-1-0305) from the Army Research Office (ARO), and National Science Foundation Grants IBN-9982719, IBN-0242833, IBN-0080112 and DBI-0951484. GJ Voss was supported by a URAP fellowship from the ARO. The contents of this study are solely the responsibility of the authors and do not necessarily represent the official views of NCRR, NIH, ARO or NSF.
- Thyroid hormone
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