National Institute for Basic Biology

Evolutionary Biology and Biodiversity

LABORATORY OF BIOLOGICAL DIVERSITYSHINOMIYA GroupSpecially Appointed Assistant Professor:
SHINOMIYA, Ai
Technical Assistant:
TSURUTA, EmikoFigure 1. Differences in critical day length (right) were detected among
medaka populations that had originated in various latitudes (left) .

The natural environment, which incorporates phenomena such as day length, solar radiation, temperature, andprecipitation, generates seasonal changes that affect organisms. Although animals alter their physiology and behavior
in response to seasonal changes in their environment, themechanism of seasonal adaptation remains largely unknown.
Medaka (Oryzias latipes) provide an excellent model tostudy these mechanisms because of their rapid and obvious
seasonal responses. In addition, it is also possible to apply
transgenic and genome-editing approaches when researching
them, as well as reference genome sequences.
In keeping with this, we are currently using Medaka to
study the molecular mechanisms of seasonal adaptation, as
well as the relationship between seasonal information fromthe environment and the organism’s response.

Geographical variation critical day length was detected, andpopulations from lower latitudes indicated a shorter criticalday length (Figure 1). To identify the genes governing
critical day length, quantitative trait loci (QTL) analysis wasconducted using F2 offspring derived from crosses between
populations experiencing different critical day length. We
thus identified significant QTLs using Restriction-site
Associated DNA (RAD) markers (Figure 2).

Figure 2. Result of QTL analysis for critical day length.
A medaka habitat in summer (Miyazaki, Miyazaki Prefecture) (left). Aschool of wild medaka (Toyohashi, Aichi Prefecture) (right).

I. Underlying mechanisms that define criticalday length and temperature

Most animals living outside the tropics reproduce only
during a particular season of the year. These are calledseasonal breeders, and it is well established that day length isa crucial cue for reproduction in many of them. In addition,it has been demonstrated that temperature changes are also
important for them in the how they detect seasons. However,it remains unknown how animals measure seasonal changes
in relation to these environmental factors.
Applying forward genetic approaches, we examined criticalday length in reproduction (i. e., the duration of lighting
time required to cause gonadal development) using various
Medaka populations, that originated in various latitudes
throughout Japan to elucidate these mechanisms.

68

Whole-genome re-sequencing in various medaka populations experiencing different critical day lengths were conducted. We have identified potential candidate genes thatdefine the critical day length by analyzing this genome
sequencing data.
We also performed experiments to identify critical temperature, and subsequently detected geographical variation
among Medaka populations. Significant QTLs for criticaltemperature have been detected from the genetic analysis
that was performed.

II. Analysis of the relationship between breedingrhythms and environmental information

Organisms exhibit various scales of rhythm, ranging inseconds to years. On the other hand, the natural environment provides the rhythmic changes concerning organisms.
However, the quantitative relationship between the information on environmental factors and biological rhythms ispoorly understood.

We conducted a linear regression analysis regarding annual
rhythms in gonadal development using data pertaining to
the annual changes in the gonadal size of the medaka andenvironmental information (day length, solar radiation, watertemperature) in the experimental field. The regression model
explained which environmental factors contributed to theseasonal change in medaka gonads and to what extent they
contributed to this change.

Publication List:〔Original papers〕

T., Okimura, K., Shen, J., Guh, Y.-J., Tamai, T.K., Shimada,• Nakayama,A., Minou, S., Okushi, Y., Shimmura, T., Furukawa, Y., Kadofusa,•N., Sato, A., Nishimura, T., Tanaka, M., Nakayama, K., Shiina, N.,Yamamoto, N., Loudon, A.S., Nishiwaki-Ohkawa, T., Shinomiya,A., Nabeshima, T., Nakane, Y., and Yoshimura, T. (2020). Seasonalchanges in NRF2 antioxidant pathway regulates winter depression-likebehavior. Proc. Natl. Acad. Sci. U.S.A. 117, 9594–9603. DOI: 10.1073/
pnas.2000278117
Yassumoto I, T., Nakatsukasa, M., Nagano, A.J., Yasugi, M., Yoshimura,T., and Shinomiya, A. (2020). Genetic analysis of body weight in wild
populations of medaka fish from different latitudes. PLoS One 15,
e0234803. DOI: 10.1371/journal.pone.0234803

69