Abstracts (first author)
Molecular and genetic mechanisms underlying variation in phenotypic plasticity in Sticklebacks
Phenotypic plasticity plays important roles in adaptation to changing environments. However, organisms tend to lose the capacity for phenotypic plasticity under stable environments. Although variation in phenotypic plasticity has been found throughout the animal kingdom, molecular and genetic mechanisms underlying such variation remain elusive. We are addressing this question by using threespine stickleback (Gasterosteus aculeatus), because they have a variety of ecotypes that show different levels of phenotypic plasticity. After the last glacial recession, ancestral marine sticklebacks colonized newly formed freshwater habitats, resulting in extensive phenotypic diversification. In this study, we report that whole transcriptome analysis revealed that marine sticklebacks exhibited significant photoperiodic response of expression levels of thyroid hormone-stimulating hormone beta 2 (TSHß2) gene, whereas such response was lost in freshwater sticklebacks. Loss of TSHß2 response independently occurred in both North American and Japanese freshwater populations. Further analyses of TSHß2 response in F1 hybrids demonstrated that loss of TSHß2 response has different genetic basis between Japanese and North American populations. Genome sequencing further revealed several ecotype-specific SNPs at the cis-regulatory region of TSHß locus in North America freshwater populations. We are currently conducting luciferase-reporter assays in vitro to investigate the cis-regulatory mechanisms of TSHß2 response. Furthermore, we are making TALEN-induced knockout sticklebacks to understand the roles of TSHß2 in vivo. Thus, further studies on the variation in TSHß2 response will lead to a better understanding of the genetic mechanisms underlying convergent loss of phenotypic plasticity.