Evol Ecol Res 15: 143-153 (2013) Full PDF if your library subscribes.
Divergence in thyroid hormone concentrations between juveniles of marine and stream ecotypes of the threespine stickleback (Gasterosteus aculeatus)
Jun Kitano1,2 and Sean C. Lema3
1Ecological Genetics Laboratory, National Institute of Genetics, Mishima, Shizuoka, Japan, 2PRESTO, Japan Science and Technology Agency, Kawaguchi, Saitama, Japan and 3Center for Coastal Marine Science and Biological Sciences Department, California Polytechnic State University, San Luis Obispo, California, USA
Correspondence: J. Kitano, Ecological Genetics Laboratory, National Institute of Genetics, Yata 1111, Mishima, Shizuoka 411–8540, Japan. E-mail: email@example.com
Background: Hormones regulate the expression of multiple phenotypic traits. Therefore, divergence in hormone concentrations may lead to evolutionary changes in the coordinated physiological and behavioural traits that comprise an organism’s integrated phenotype. Adults of marine ecotypes of threespine stickleback (Gasterosteus aculeatus) have higher concentrations of the thyroid hormone thyroxine (T4) than adults of stream-resident ecotypes (Kitano et al., 2010). Thyroid hormones are well-established mediators of osmoregulation and migratory behaviours in fish, and the difference in T4 concentrations indicates that changes in thyroid hormone signalling may underlie the evolutionary and ecological divergence of migratory and non-migratory ecotypes.
Questions: Is the variation in T4 concentrations present in earlier life stages where it could contribute developmentally to differences in phenotype? Do T4 concentrations change in marine ecotypes before seaward migration?
Organisms: A parapatric pair of marine and stream ecotypes of threespine stickleback collected from British Columbia, Canada, and a marine ecotype collected from Washington State, USA.
Methods: We collected juvenile fish of both marine and stream ecotypes on the same day in a single river to compare the whole body concentrations of T4 using radioimmunoassay. We also sampled juvenile fish of the marine ecotype in another river at three different times to determine whether these fish exhibit temporal changes in T4 concentrations before seaward migration.
Results: Juvenile stickleback of the marine ecotype had higher T4 concentrations than the parapatric stream-resident juveniles. The T4 concentrations in another marine population varied slightly across sampling times before seaward migration.
Conclusions: T4 concentrations differ consistently between marine and stream ecotypes in both juvenile and adult life stages consonant with the hypothesis of evolutionary changes in thyroid signalling.
Keywords: endocrine, phenotypic correlation, physiology, stickleback, trade-offs.
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