The refinement of mating mechanisms in the animal kingdom provides important insights into species survival. Among animals with multiple partners that lay their eggs externally, such as most fish, males release sperm several times a day, but producing these gametes takes energy and time. Here’s how medaka fish do it.
Fish behavior experts from Osaka Metropolitan University (Japan) recently discovered the daily reproductive capacity of the medaka fish.
In a study published in Royal Society Open ScienceDr Yuki Kondo, Professor Masanori Kohda and Professor Satoshi Awata detailed the effects of continuous mating in medaka on the number of sperm released, fertilization rate and behavior of males and females.
“Medaka are among the fish that lay eggs, with fertilization occurring after the eggs and sperm are released into the water. Because these gametes are difficult to collect, the number of sperm released and the fertilization rate during successive matings had remained a mystery,” explained Dr. Condo.
“Our research group previously developed an accurate method for measuring sperm count in medaka, which allowed us to perform this experiment successfully,” he continued.
What have researchers discovered about medaka fish?
The experiment showed that a male medaka can mate, on average, 19 times a day. During the first three matings, males release more than 50% of their daily sperm production. Although the fertilization rate is close to 100% in the first matings, it drops significantly after the 10th mating, with cases where fertilization was not confirmed.
Female medaka can produce eggs once a day and release all of their eggs during a single mating. Thus, many eggs are wasted if females mate with males that have already released most or all of their sperm.
“This is the first study to quantitatively show the daily mating capacity of male medaka, the volume of sperm released during each mating, the fertilization rate and the behavior of males and females in this process,” said Professor Awata.
The importance of research
The research provides important insights into the relationship between the cost of gamete production and sexual selection. Understanding reproductive strategies and energy allocation in animals has implications for conservation and breeding programs, notes Phys.org.
The study also suggests the existence of evolutionary pressures on male and female medaka to optimize their mating strategies. Males may try to balance the number of matings with the quality of the sperm released, while females may have to select their partners to ensure successful fertilization.
The obtained results contribute to the understanding of the complex dynamics of reproduction in the animal kingdom, especially in species with external fertilization. This knowledge can support broader ecological and evolutionary studies, helping scientists better understand the factors that influence species survival and adaptation.
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Source: www.descopera.ro
