Elucidation of the effect of large-sized eggs on paternal care and mate choice in the giant water bug

2022 Fiscal Year Final Research Report

• Project/Area Number: 20K06076
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 39050:Insect science-related
• Research Institution: Nagasaki University
• Principal Investigator: Ohba Shin-ya 長崎大学, 教育学部, 准教授 (20638481)
• Co-Investigator(Kenkyū-buntansha): 東城 幸治 信州大学, 学術研究院理学系, 教授 (30377618) ; 鈴木 智也 京都大学, 地球環境学堂, 特定研究員 (30739503)
• Project Period (FY): 2020-04-01 – 2023-03-31
• Keywords: 親による子の保護 / 性選択 / Paternal care

Outline of Final Research Achievements

In this study, we investigated the effects of egg size variation on the reproductive strategy of the giant water bug, Appasus japonicus.
The eggs were placed at various depths to investigate the degree of oxygen shortage, and it was confirmed that Hokkaido, Hyogo, and Kagoshima, which have the largest egg sizes, were most prone to oxygen shortage, in that order. Although there was variation among populations in the egg-care behavior of males, no geographic trends were observed. In a study of female mate choice in a trio of 2 males and 1 female among 7 populations from Hokkaido to Kagoshima, we found that females in northern populations with larger egg size (shorter breeding season) selected more courting males (i.e., made many waves by flexing their middle and hind legs), while this tendency was not observed in southern populations. This was not the case in the southern population.

Free Research Field

昆虫生態学

Academic Significance and Societal Importance of the Research Achievements

動物界で稀な父親単独による卵の保護がどのように進化したのか？この問いに答えるために本研究では、コオイムシの体サイズのクラインを用いて自然淘汰と性淘汰の両面から、オスによる卵保護を検討した。体サイズが大きくなると卵保護が重労働化すると予想されるが、そのことを卵の酸欠度合いから定量的に示した。次に卵サイズの大きい個体群ほど、より求愛ができるオスを配偶者として選択する傾向があることを明らかにした。体サイズの大型化は卵サイズの大型化をもたらし、オスの子育てへの関わり方にもかかわる。そして、それはメスによる配偶者選択にも波及することを実証できた。