Although the concept of astrology does not hold water in scientific discussions, the birth timing of certain squid species appears to play a critical role in defining their mating tactics, as suggested by new research in Japan.
Studies led by University of Tokyo marine biologist Shota Hosono and his team on the Japanese spear squid (Heterololigo bleekeri) revealed that the month in which these squid hatch greatly influences their reproductive behaviors.
Males hatching at the start of the breeding season, from early April to mid-July, grow to be larger and thus adopt the role of consorts, which involves aggressively guarding a mate after successful impregnation. However, those hatching later in the season, from early June to mid-August, tend to be smaller and adopt a more surreptitious strategy as ‘sneakers’, secreting their sperm near the eggs in hopes of fertilization.
Interestingly, those hatching close to early July have the potential to develop into either consorts or sneakers.
The variation in reproductive strategies due to birthdate, akin to the relative age effect seen in human athletes, had previously only been confirmed in teleost fish and not other animal groups prior to this study. This adds an interesting dimension to the so-called ‘birthdate hypothesis’ within the animal behavior literature.
Researchers studying 201 squid males and 68 females elaborate that larger males naturally gravitate towards contesting other males, while smaller males often resort to sneaking to achieve reproductive success.
This groundbreaking research not only contributes a new example to the ‘birthdate hypothesis’ but also suggests a complex set of birth-related factors determining the male mating behaviors of H. bleekeri.
According to marine ecologist Yoko Iwata, also at the University of Tokyo, the trajectory of a squid’s life is seemingly predetermined by its hatch date.
Further research is necessary to explore the external environmental influences, particularly those early in life, that may shape the squid’s adulthood size and mating tactics. The study also considers the substantial implications of varying environmental conditions, such as marine heatwaves, on the commercial squid fishing industry.
The full study report can be found in the journal Proceedings of the Royal Society B Biological Sciences.
FAQ Section
Q: Is the birthdate phenomenon validated in other animals or just squid?
A: The ‘birthdate hypothesis’ has been tested in several species of teleost fish and is evident in the relative age effect seen in human athletes, but this study marks the first substantial evidence found in aquatic invertebrates.
Q: Are the squid’s mating behaviors inherited?
A: The mating tactics don’t appear to be directly inherited since female squid store and utilize sperm from both consort and sneaker males, suggesting that mating strategies are likely an interplay of various factors at birth.
Q: Is the relative size between consort and sneaker males significant?
A: Yes, consort males can be significantly larger, growing to an average mantle length of 300 millimeters, while sneaker males usually reach about 150 millimeters.
Q: Can environmental conditions like temperature affect squid mating behavior?
A: Yes, squid are very sensitive to environmental factors, particularly water temperature, which may affect their growth and subsequent mating tactics.
Q: Will further research be conducted on this topic?
A: Yes, the researchers indicate that further study is needed to understand how various environmental factors influence mating behaviors in squid.
Conclusion
This research highlights the fascinating link between the timing of birth and the life strategy adopted by the Japanese spear squid. The implications of this study reach beyond the marine biology field, hinting at the broader influences of birth timing on the life courses of species. Additionally, the study underscores the need for continued investigation into how environmental variations influence biological behaviors, with potential commercial and ecological consequences.