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Thyroid hormone responsive QTL and the evolution of paedomorphic salamanders
S R Voss1, D K Kump, J A Walker
1Department of Biology and Spinal Cord and Brain Injury Research Center, University of Kentucky, Lexington, KY 40506, USA. srvoss@uky.edu
Heredity
|August 2, 2012
Summary
Evolutionary novelty in salamanders involves delayed metamorphosis and increased adult size, driven by thyroid hormone response alleles. This genetic shift allows paedomorphic species to retain larval traits while growing larger.
Area of Science:
- Evolutionary biology
- Developmental biology
- Genetics
Background:
- Salamanders typically have a biphasic life cycle with aquatic larvae and terrestrial adults.
- Evolutionary shifts can lead to paedomorphosis, where larval traits are retained in adults, often due to delayed metamorphosis.
Purpose of the Study:
- To investigate the genetic basis of metamorphic timing and adult body size in paedomorphic salamanders.
- To understand how thyroid hormone (TH) influences these life history traits and their evolutionary implications.
Main Methods:
- Used thyroid hormone (TH) to induce metamorphosis in paedomorphic salamanders.
- Employed quantitative trait loci (QTL) mapping to identify genes associated with metamorphic timing and body size.
- Analyzed the genetic variation in TH responsiveness within paedomorphic tiger salamanders (Ambystoma tigrinum complex).
Main Results:
- Identified three moderate-effect QTL (met1-3) influencing metamorphic timing, linked to TH responsiveness.
- Demonstrated that alleles at these QTL additively affect the delay in metamorphosis.
- Found that delayed metamorphosis is associated with significantly larger adult body size, with met2 explaining a substantial portion of this variation.
Conclusions:
- TH-responsive loci play a key role in the evolution of amphibian life history traits, specifically body size and metamorphic timing.
- Selection for TH-response alleles that delay metamorphosis likely provides an adaptive pathway for the evolution of paedomorphic species from metamorphic ancestors.
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