2023 Fiscal Year Final Research Report
An investigation into the relationship between the evolution of diverse reproductive systems and their corresponding degree of distribution attained globally
| Project/Area Number |
20H03308
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Review Section |
Basic Section 45030:Biodiversity and systematics-related
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| Research Institution | Shinshu University |
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Principal Investigator |
Tojo Koji 信州大学, 学術研究院理学系, 教授 (30377618)
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| Co-Investigator(Kenkyū-buntansha) |
新美 輝幸 基礎生物学研究所, 進化発生研究部門, 教授 (00293712)
竹中 將起 信州大学, 理学部, 特任助教 (00854465)
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| Project Period (FY) |
2020-04-01 – 2024-03-31
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| Keywords | 昆虫 / カゲロウ / 胚発生 / 卵胎生 / 胎生 / 繁殖生態 / 遺伝系統 / 卵黄タンパク |
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| Outline of Final Research Achievements |
A mayfly, Cloeon dipterum, is found on every continent except Antarctica, and inhabits natural lentic water environments as well as artificial ponds. These habitat generalist characteristics are closely related to their unique reproductive ecology. European studies have demonstrated that this species is ovoviviparous, with most of the embryonic development taking place inside the mother’s body, and that eggs are laid just before hatching.
However, this study clearly demonstrated that at least the lineages in Japan and South Korea constitute a genetically highly differentiated lineage even within the species, and that larvae hatched inside the mother’s body are laid. In addition, histolochemical study revealed that yolk proteins are not present in the egg during stages of embryonic development, and that nutrients are supplied to the egg from the mother directly. In other words, this is an important finding, suggesting that the animals are viviparous, rather than ovoviviparous.
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| Free Research Field |
進化生物学
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| Academic Significance and Societal Importance of the Research Achievements |
動物の繁殖様式として、「卵生、卵胎生、胎生」は広く一般的にも理解されている。著しく種多様性の高い昆虫類種では、卵生が大多数であり、卵胎生は多くの昆虫目（内）において平行的に獲得されている一方で、胎生となると極めて僅かな事例が知られるのみである。
こうした中、原始的昆虫の一つであるカゲロウ目昆虫において、新規の胎生システムが進化していたことを究明したことのインパクトは甚大である。従来、卵胎生とされてきた欧州での研究に問題があったのか、はたまた、同一種内に、卵胎生（欧州）と胎生（東アジア系統）の系統が混在するのか、本種における胎生の進化を廻る議論は、さらに深い学術的な興味へと発展するものである。
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