Light up our love: Medaka courtship dynamics observed
Environmental conditions affect reproduction times in model fish
image:
Mating patterns of Japanese rice fish witnessed in the lab.
view moreCredit: Osaka Metropolitan University
Japanese rice fish, known as medaka, are small, easy to breed, and reproduce daily, making them widely used as model organisms around the world. Until now, medaka research has mainly occurred in labs where environmental conditions and study observations are easily controlled. Unnatural environmental settings such as these bring into question the accuracy of previous behavioral findings. Therefore, this study is important for answering the fundamental question of whether the behavior of animals observed in laboratories is the same as in their natural environments.
A research team led by Specially Appointed Assistant Professor Yuki Kondo and Professor Satoshi Awata at Osaka Metropolitan University’s Graduate School of Science examined medaka reproductive behavior based on behavioral rhythms and environmental factors. Through 24-hour observations using infrared cameras and a laboratory light-dark cycle from 8 a.m. to 10 p.m., the researchers discovered medaka reproductive behavior begins in the dark period around 7 a.m. and peaks at 8 a.m.
“Previous studies may have overlooked behavioral and physiological changes that occur at night because they were conducted during daylight hours. This discovery will lead to a review of the experimental conditions for medaka as a model organism and demonstrate the importance of the natural ecology of organisms,” stated Dr. Kondo.
Further, video data revealed that 89% of reproductive behavior occurred after lights on, and overall behavior was similar to that observed in the wild. However, the peak of courtship and reproductive behavior was confirmed to be 3 to 4 hours later than in a natural environment.
“In the future, it will be necessary to investigate the reasons for the differences in reproduction times and courtship behavior in the wild and the laboratory. By introducing a system that gradually adjusts the lights and the temperature between night and day, it is possible to conduct research under conditions closer to the natural environment of medaka, thereby gaining more ecologically accurate findings in the laboratory,” stated Professor Awata.
Competing interests
The authors declare no competing interests.
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Journal
Scientific Reports
Method of Research
Observational study
Subject of Research
Animals
Article Title
Temporal dynamics of courtship and spawning in medaka under laboratory conditions revealed by 24 h video monitoring
Article Publication Date
7-Aug-2025
Dopamine assists female flies eager to mate in enhancing their sensitivity to sounds
Nagoya University
image:
Dopamine signals enhance the responsiveness of auditory sensory neurons in Johnston's organs of unmated female fruit flies, making them sensitive to sounds, including courtship songs from males.
view moreCredit: Issey Takahashi
Many animals, including humans, can flexibly modulate their responsiveness to sounds according to different situations. This ability allows them to optimize the use of their limited brain resources by prioritizing the processing of critical information at any given moment.
In line with this idea, a research team at Nagoya University in Japan has demonstrated that when female fruit flies are eager to mate, dopaminergic signals can influence their sensitivity to sounds, including courtship sounds from males, which are an essential source of information for species reproduction.
"We believe that this finding is the first step toward understanding the neural mechanisms that underlie the universal property of flexible auditory response modulation in animals," said lead author Azusa Kamikouchi, professor of the Graduate School of Science and the Institute of Transformative Bio-Molecules at Nagoya University. Their finding was published in the journal iScience.
Mating status is known to influence responses to courtship sounds in animals; however, the neural mechanisms underlying this status-dependent modulation have not been well understood.
Professor Kamikouchi, PhD student Haruna Yamakoshi, and their colleagues at Nagoya University conducted a study to clarify the neural mechanisms, using the fruit fly Drosophila melanogaster as a model organism. Drosophila is used extensively in neuroscience research due to its simple brain, many useful genetic tools, and short generation time.
Drosophila males produce courtship sounds by wing vibrations to attract females. Females listen to the sound to decide whether to accept the male's courtship. It has been reported that female receptivity to mating is high when they have no mating experience and low when they do. Based on this report, the research group hypothesized that female responses to male courtship songs may be modulated depending on their mating experience.
To explore the validity of their hypothesis, researchers initially focused on neurons in Johnston's organs (JOs) located in the second antennal segment of fruit flies, where they detect sound signals. They examined which neurotransmitter receptors are expressed in JO neurons, using a single-nucleus RNA-seq database.
The researchers found that three types of dopamine receptors are abundantly expressed in JO neurons. To verify whether dopamine signals affect the responsiveness of JO neurons, they suppressed the expression of dopamine receptors in Drosophila females and measured their neural responses to courtship sounds, using calcium imaging.
Results showed that neural responses to the sounds decreased in unmated females, whose mating drive is high. On the other hand, neural responses did not decrease in mated females and young females that had just emerged from their pupae, whose mating drive is low.
Researchers also observed behavioral responses to courtship sounds in unmated Drosophila females with suppressed dopamine receptor expression. They measured the time it took for the females to initiate mating, a key indicator of the increase in mating drive. As expected, the females with suppressed dopamine receptor expression reacted less to the courtship sounds, suggesting that these sounds were less effective in triggering their mating behavior under those conditions.
"We found that dopamine is one of the factors involved in flexible auditory modulation," said Kamikouchi. "Previous studies have reported that the properties of the auditory system change depending on the situation in various animals, including humans, mice, and frogs. This study suggests that a common mechanism across species may underlie this type of auditory modulation."
These findings are expected to provide a better understanding of the remarkably flexible sound information processing systems in animals.
Publication:
The study, "Mating status-dependent dopaminergic modulation of auditory sensory neurons in Drosophila," was published in the journal iScience on July 29, 2025, at DOI: https://doi.org/10.1016/j.isci.2025.113232.
Funding:
This study was supported by MEXT KAKENHI Grants-in-Aid for Scientific Research (B) (Grant JP20H03355 to AK), Grant-in-Aid for Transformative Research Areas (A) “iPlasticity” (Grant JP23H04228 to AK), Hierarchical Bio-Navigation (Grant JP22H05650 to RT), Materia-Mind (Grant JP24H02200 to AK), and Dynamic Brain (Grant JP25H02496 to AK), Grant-in-Aid for JSPS Fellows (Grant JP24KJ1282 to HY), The Graduate Program of Transformative Chem-Bio Research, Nagoya University, Japan (to HY), and JST FOREST (Grant JPMJFR2147 to AK), Japan.
Journal
iScience
Method of Research
Experimental study
Subject of Research
Animals
Article Title
Mating status-dependent dopaminergic modulation of auditory sensory neurons in Drosophila
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