Why are they active in both day and night?: Adaptive significance of cathemerality in primitive primates

2018 Fiscal Year Final Research Report

• Project/Area Number: 16K18629
• Research Category: Grant-in-Aid for Young Scientists (B)
• Allocation Type: Multi-year Fund
• Research Field: Physical anthropology
• Research Institution: Kyoto University
• Principal Investigator: Sato Hiroki 京都大学, アジア・アフリカ地域研究研究科, 助教 (90625302)
• Research Collaborator: RAZANAPARANY Tojotanjona ; RAKOTOMANANA Hajanirina ; RAKOTONDRAPARANY Felix
• Project Period (FY): 2016-04-01 – 2019-03-31
• Keywords: 周日行性 / 夜行性 / 昼行性 / 活動性 / 霊長類 / キツネザル / マダガスカル

Outline of Final Research Achievements

A primitive primate living in seasonal tropical forests in Madagascar, the brown lemur (Eulemur fulvus), shows cathemerality, i.e., active both day and night, a unique activity pattern among primates. We conducted behavioral observation and ecological surveys on brown lemurs in northwestern Madagascar over a year. While the lemurs stably acted at night over the year, they increased diurnal activities during the rainy season and dramatically decreased them during the dry season. This diurnal inactivity may function to avoid overheating and water loss under heat and dry stresses. During the rainy season without such stresses, the lemurs actively moved and fed on fruits. In the trade-off between risks from environmental stresses and advantages of resource acquisition in daytime, the primitive primates may have driven the diurnalization.

Free Research Field

霊長類学

Academic Significance and Societal Importance of the Research Achievements

昼行性化は霊長類や人類にとって、形態的な進化（視覚発達や脳・体サイズの大型化）だけでなく、複雑な群れや社会の発達につながるビッグイベントだったと考えられる。しかし、霊長類における昼行性の進化プロセスについては多くの謎に包まれたままである。マダガスカルに生息する原始的な霊長類チャイロキツネザル属は、霊長類の中でも稀な昼も夜も動く周日行性とよばれる活動性を示す。本研究ではチャイロキツネザル（Eulemur fulvus）の活動性と環境要因の関係を調べることで周日行性の適応意義を明らかにし、霊長類における昼行性進化、すなわち「どのような環境に対応しながら昼の世界に進出したか」について理解を深める。