Graduate School of Frontier Sciences, The University of Tokyo Department of
Integrated Biosciences

Our research interest is how and why phenotypic diversity has evolved and has been maintained in nature. Organisms exhibit great phenotypic variation that may adapt to complex and fluctuating environments. What kinds of developmental, physiological, and neural modifications underlie such diversification? What specific genes have changed to produce the different phenotypes? How many genetic changes have controlled the variation of the traits? What kinds of mutations have occurred in these genes? Do these mutations share any molecular features? Such fundamental questions may help to understand how predictable evolution is.

One of the crucial steps to address these questions is to identify causative genes and mutations responsible for such variation. Rapid advances in technologies will enable us to find not only the genes and mutations, but also genome structures, epigenetic features, and regulatory networks that may promote or constrain phenotypic diversification. It is also necessary to look into the evolutionary dynamics of the causative genes and mutations in natural ecosystems. Since evolution affects ecosystem functions and vice versa, a mutation with a large ecological effect may change the intensity or direction of selection on the mutation itself. Thus, comprehensive approaches to reveal the dynamics and functions of the genes and mutations underlying phenotypic diversification can further increase the predictability of evolution in nature.

To understand the mechanisms underlying phenotypic diversification from molecular to ecological levels, we focused on stickleback fishes (genus Gasterosteus and Pungitius) as model systems. Three-spined stickleback (G. aculeatus) are primarily marine, but colonized postglacial freshwater habitats and radiated into diverse ecotypes. We have introduced a wide range of molecular genetic techniques to them to identify the key genes and mutations responsible for phenotypic diversification.

Our current research topics are as follows.

Evolution of life-history traits can directly influence fitness and can drive further phenotypic diversification and speciation. However, in contrast to morphological divergence, the molecular mechanisms underlying life-history evolution in wild organisms are largely unknown. We have investigated key genes or mutations responsible for different reproductive seasonality, growth pattern, and migratory behavior by using stickleback and medaka fishes.

Colonization of new environments can trigger adaptive radiation. Some lineages make use of such ecological opportunities provided by new environments, but not all do so. The genetic factors determining the ability to colonize novel environments are largely unknown. We have investigated the genetic and physiological mechanisms underlying the different nutritional availability, osmoregulation, and temperature tolerance between the three-spined stickleback and the closely related Japan Sea stickleback (G. nipponicus), which may enable or prohibit them to colonize freshwater environments and provide an opportunity to radiate into diverse ecotypes.

Differential gene expression and chromatin structure can play an important role in phenotypic evolution and divergent adaptation. We have revealed the genomic regions which cause the different transcriptome or chromatin structure and investigate its functions in adaptive evolution.