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Divergence In Thyroid Hormone Concentrations Between Juveniles Of Marine And Stream Ecotypes Of The Threespine Stickleback (Gasterosteus Aculeatus), Jun Kitano, Sean C. Lema

Sean Lema

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 …

Hormones And Phenotypic Plasticity: Implications For The Evolution Of Integrated Adaptive Phenotypes, Sean C. Lema, Jun Kitano

Sean Lema

It is generally accepted that taxa exhibit genetic variation in phenotypic plasticity, but many questions remain unanswered about how divergent plastic responses evolve under dissimilar ecological conditions. Hormones are signaling molecules that act as proximate mediators of phenotype expression by regulating a variety of cellular, physiological, and behavioral responses. Hormones not only change cellular and physiological states but also influence gene expression directly or indirectly, thereby linking environmental conditions to phenotypic development. Studying how hormonal pathways respond to environmental variation and how those responses differ between individuals, populations, and species can expand our understanding of the evolution of phenotypic plasticity. …