Embryological study on proturan brain: groudplan and evolution of Hexapoda

2019 Fiscal Year Final Research Report

• Project/Area Number: 16K18605
• Research Category: Grant-in-Aid for Young Scientists (B)
• Allocation Type: Multi-year Fund
• Research Field: Biodiversity/Systematics
• Research Institution: Ehime University
• Principal Investigator: Fukui Makiko 愛媛大学, 理工学研究科(理学系), 講師 (90635872)
• Project Period (FY): 2016-04-01 – 2020-03-31
• Keywords: 昆虫 / 祖先 / 脳 / 触角 / 触角体節 / 中大脳 / 扇状体

Outline of Final Research Achievements

Protura is known as the one of the most ancestral group in the Insect. They are totally lacking antenna and instead their fore legs are functioning as tactile organ. Due to minute size and cripic way of life, detailed brain structure and the scenario of their total degeneration of antenna is still unknown. Proturan brain and nervous system of their fore legs are determined and revealed as below.
1) Deutocerebrum is found to be the weak swelling both in the late embryonic stage and the adult. 2) 8 columns of the fan shaped body are observed in the central complex. 3) Proturan fore leg nerves are revealed to connect with gnathal ganglion which is known to be the center of an insect's sense of taste. Our data indicates that antennae were lost due to degeneration of the appendages and the taste sense with the fore leg can be understood as the preadaptive state. 8 columns in the fan shaped body thought to be the groudplan of the Insect which are known also in Collembola and Pterygota.

Free Research Field

昆虫比較発生学

Academic Significance and Societal Importance of the Research Achievements

あるグループの祖先がどのようなものであったを知ることは、進化の解明の第一歩といえる。本研究により、地球の覇者である昆虫の脳がその祖先においてどのようなものであったかを推測する手掛かりが得られた。また、節足動物の大半にとって生存に極めて重要な器官である触角の欠失が、カマアシムシ目においてなぜ、どのように起こってきたかを理解できたことは、謎の多いカマアシムシ目の進化を理解する上でも重要な知見である。