title: Adaptive divergence in the thyroid hormone signaling pathway in the stickleback radiation.
abstract: During adaptive radiations, animals colonize diverse environments, which requires adaptation in multiple phenotypic traits. Because hormones mediate the dynamic regulation of suites of phenotypic traits, evolutionary changes in hormonal signaling pathways might contribute to adaptation to new environments. Here we report changes in the thyroid hormone signaling pathway in stream-resident ecotypes of threespine stickleback fish (Gasterosteus aculeatus), which have repeatedly evolved from ancestral marine ecotypes. Stream-resident fish exhibit a lower plasma concentration of thyroid hormone and a lower metabolic rate, which is likely adaptive for permanent residency in small streams. The thyroid-stimulating hormone-β2 (TSHβ2) gene exhibited significantly lower mRNA expression in pituitary glands of stream-resident sticklebacks relative to marine sticklebacks. Some of the difference in TSHβ2 transcript levels can be explained by cis-regulatory differences at the TSHβ2 gene locus. Consistent with these expression differences, a strong signature of divergent natural selection was found at the TSHβ2 genomic locus. By contrast, there were no differences between the marine and stream-resident ecotypes in mRNA levels or genomic sequence in the paralogous TSHβ1 gene. Our data indicate that evolutionary changes in hormonal signaling have played an important role in the postglacial adaptive radiation of sticklebacks.
authors.affiliation: Department of Ecology and Evolutionary Biology, Graduate School of Life Sciences, Tohoku University, Sendai, Miyagi 980-8578, Japan. jkitano@m.tohoku.ac.jp
authors.forename: Jun
authors.initials: J
authors.lastname: Kitano
authors.forename: Sean C
authors.initials: SC
authors.lastname: Lema
authors.forename: J Adam
authors.initials: JA
authors.lastname: Luckenbach
authors.forename: Seiichi
authors.initials: S
authors.lastname: Mori
authors.forename: Yui
authors.initials: Y
authors.lastname: Kawagishi
authors.forename: Makoto
authors.initials: M
authors.lastname: Kusakabe
authors.forename: Penny
authors.initials: P
authors.lastname: Swanson
authors.forename: Catherine L
authors.initials: CL
authors.lastname: Peichel
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology*; D000818:Animals; D005075:Biological Evolution; D005618:Fresh Water; D006239:Haplotypes; D012623:Seawater; D015398:Signal Transduction / Q000502:physiology*; D023701:Smegmamorpha / Q000033:anatomy & histology* / Q000502:physiology*; D013963:Thyroid Hormones / Q000235:genetics / Q000378:metabolism*; D013972:Thyrotropin / Q000235:genetics / Q000378:metabolism
chemical_list: D013963:Thyroid Hormones; D013972:Thyrotropin