Our research goal

Our research goal is to identify molecular changes underlying naturally occurring phenotypic variation and speciation and understand how such variations arise and spread within natural populations. Because of recent advances in genomic technologies, an increasing number of candidate genomic loci or genes responsible for adaptation and speciation have been identified. Molecular changes or causative mutations, however, have been rarely elucidated in most cases. Without knowing causative mutations, we cannot understand how many mutations are important, whether each mutation is additive or epistatic, or what kind of selective pressures have acted on each mutation.

Experimental approach

To this end, we take an integrative approach across diverse disciplines using stickleback fishes (genus Gasterosteus and Pungitius) and medake fishes (genus Oryzias) as models. The first step is to conduct detailed field surveys to characterize phenotypic variation and reproductive isolation between natural populations. Next, we use genetic and genomic technologies to find candidate genes responsible for such variation. Then, we use biochemical and cell culture assay to study the functions of genetic changes in these candidate genes in vitro. We also make genetically engineered sticklebacks using TALEN/CRISPR technologies and tol2-mediated transgenesis to investigate their physiological functions in vivo. Finally, we will use semi-natural settings to investigate how the mutant alleles behave in different environments.

Research projects

1. Driving forces and roles of sex chromosome turnover

Our studies have revealed that some of the important genes for adaptation and speciation are localized on sex chromosomes. Because sex chromosomes are one of the most rapidly evolving parts of the genome and theoretical studies predict that sex chromosomes play important roles in the evolution of sexually dimorphic traits and reproductive isolation, we hypothesized that sex chromosome turnover may promote phenotypic diversification and speciation. We use sticklebacks and medakas as a model to test this possibility. Our primary goal is to identify genes and genetic alterations on young sex chromosomes that cause speciation and the evolution of sexually dimorphic traits. We also use computer simulations to investigate the driving forces of sex chromosome turnover.

2. Integration of physiology and biochemistry into ecological genomics

Our next goal is to integrate physiology and biochemistry into the ecolgoical genetics and genomics. Physiological and biochemical analysis can help us to identify candidate genes and also to undestand how genetic chnages alter fitness-related physiological traits. First, we study the biochemical mechanisms by which genetic changes in chromatin-binding proteins alter chromatin regulation between incipient species using sympatric Japan Sea sticklebac (Gasterosteus nipponicus) and Pacific Ocean threespine stickleback (Gasterosteus aculeatus). We also investigate the physiological mechanisms underlying divergence in the timing of reproduction between marine and stream ecotypes of threespine stickleback.

3. Identification of genetic changes underlying colonization of new niches

Exploitation of empty niches can trigger adaptive radiation, the evolution of ecological and phenotypic diversity within a rapidly multiplying lineage. One of the remarkable examples is the diversification of sticklebacks: during the last glacial cycles, many freshwater lakes and rivers were newly formed, and marine ancestral sticklebacks have colonized these empty niches and diversified. Not all lineages, however, have seized these ecological opportunities to colonize freshwater environments. What genetic factors determine the difference in the ability to colonize freshwater niches? In this project, we aim to understand the genetic changes responsible for variation in the physiological ability of freshwater colonization between sticklebacks.

4. Conservation genetics

Because environmental disturbances are rapidly changing the ecosystem, it is increasingly important to understand the genetic and ecological mechanisms of adaptation and speciation in natural animal populations. We investigate the effects of human disturbance as well as natural disasters, such as tsunamis, on the ecology and evolution of natural stickleback populations.

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