19 times a day: Male medaka’s mating limit revealed

Unraveling the kinks of mating in the animal kingdom can help us gain insight into species survival. In animals with multiple partners that lay eggs outside the body, like most fish, the male releases sperm several times a day, but the production of these gametes requires energy and time.

Fish behavior experts from Osaka Metropolitan University recently revealed the daily mating abilities of medaka fish. Project Professor Yuki Kondo, Professor Masanori Koda, and Professor Satoshi Awata of the Graduate School of Science have published research results in Royal Society Open Science that show the number of sperm released by continuous mating of medaka fish, the fertilization rate, and its effects on sperm count. behavior of both males and females.

“Medaka is one of the spawning fish, where fertilization occurs after eggs and sperm are released into the water. These gametes are difficult to collect, so the number of sperm released and the fertilization rate during consecutive matings are “It remained a mystery,” he said. Mr. Kondo explained.

“Our research group had previously developed a method to accurately measure sperm counts in medaka fish, which is why we were able to conduct this experiment successfully.”

The group’s latest experiments found that male killifish can mate, on average, 19 times a day. During the first three mating sessions, the killifish released more than 50% of their daily sperm production. The fertilization rate was almost 100% in the initial matings, but it dropped significantly after the 10th mating, and there were cases in which fertilization was not confirmed after that.

Female killifish lay eggs once a day, but release all eggs during mating. This means that if a female mates with a male who has already released most or all of his sperm, many eggs will be wasted.

“This is the first study to quantitatively demonstrate the daily unambiguous mating performance of male killifish, the amount of sperm released during each mating, the fertilization rate, and the behavior of males and females during the process.” Professor Awata said.

“Our study provides important insights into the relationship between the cost of gamete production and sexual selection.”

This study highlights the importance of understanding animal reproductive strategies and energy allocation, which can have implications for conservation and breeding programs. Examining the mating behavior and performance of killifish allows researchers to better understand how these fish and similar species manage their reproductive activities in their natural environments.

This finding also suggests that there may be evolutionary pressure on both male and female medaka to optimize their mating strategies. For males, this means balancing the number of mating attempts with the quality of the sperm released, while females may need to be selective about their mates to ensure successful fertilization.

Overall, the research conducted by Osaka Metropolitan University provides valuable insight into the complex dynamics of reproduction in the animal kingdom, particularly in species that perform in vitro fertilization. This knowledge contributes to broader ecological and evolutionary research and helps scientists better understand the factors that influence species survival and adaptation.