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New Insights into Medaka Mating Behavior and Fertilization Rates
Understanding mating practices in the animal kingdom offers crucial insights into species survival. In particular, for animals like fish that engage in external fertilization, male individuals often release sperm multiple times daily. However, producing these gametes requires significant energy and time investment.
Recent research from experts at Osaka Metropolitan University has shed light on the mating capacity of medaka fish. Their study, published in Royal Society Open Science, features contributions from Dr. Yuki Kondo, Professor Masanori Kohda, and Professor Satoshi Awata, who examined the impact of continuous mating on the volume of sperm released and the resulting fertilization rates.
Dr. Kondo remarked, “Medaka are a species where fertilization occurs after both eggs and sperm are released into the water, making traditional collection methods for these gametes challenging. Prior to this study, the volume of sperm released and the corresponding fertilization rates during successive matings were largely unexplored.” Thanks to their previous work on accurately measuring medaka sperm counts, the team was able to conduct this novel investigation.
The study revealed that male medaka can mate approximately 19 times each day. Notably, during the initial three mating events, they released more than half of their daily sperm output. While fertilization rates were close to 100% during the first few matings, this rate declined significantly after the 10th mating attempt, with instances where fertilization did not occur.
Conversely, female medaka are capable of producing eggs daily; however, they release all their eggs at once during mating. This can lead to a high wastage of eggs, particularly if females mate with males that have already depleted their sperm reserves.
Professor Awata highlighted the significance of this research, stating, “This is the first quantitative assessment of the daily mating capacity of male medaka, analyzing not just sperm volume but also fertilization rates and the mating behaviors of both sexes. Our findings offer key insights into the dynamics of gamete production costs and the influence of sexual selection.”
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