タガメの卵塊における一斉孵化メカニズムとその意義  [in Japanese] Synchronized Mechanism and Its Meaning in the Egg Hatching of the Giant Water Bug, Lethocerus deyrolli (Heteroptera: Belostomatidae)  [in Japanese]

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Author(s)

    • 大庭 伸也 OHBA Shinya
    • 玉川大学農学部昆虫学研究室 Laboratory of Entomology, Faculty of Agriculture, Tamagawa University

Abstract

孵化の様子を観察した結果,タガメの卵が孵化するとき,卵殻と薄い膜を破って幼虫が出てくる.卵殻を破って出てくることを「卵殻孵化」,透明な膜を破って出てくることを「胚脱皮」と称することとした.卵塊中の全ての卵が卵殻孵化を終えるのに約20分を要するのに対して,それらの卵が胚脱皮を終えるには約5分しかかからない.その後,体を出して前脚を広げた幼虫のうち,1匹の幼虫が中後脚を動かし,卵殻から出て落下しようとすると,その接触刺激が隣接する幼虫へと連鎖的に広がっていき,卵塊レベルで孵化した幼虫が一斉に水中へと落下した.常に湿った状態では,卵殻孵化が胚脱皮よりも時間を要したのに対し,オスが保護してきた,つまり乾燥と給水を繰り返した,孵化直前の卵に水をかけると,全ての卵の卵殻が割れたことから,保護オスが給水により,卵殻孵化のタイミングを調節可能であることが示唆された.胚脱皮は破裂音を伴うので,その振動を感知した他の卵も胚脱皮すると考えられ,1個の卵の胚脱皮が周辺の卵の胚脱皮を誘発し,全ての卵の胚脱皮が短時間で起こる.以上の結果から,タガメの卵塊における一斉孵化のメカニズムには,卵殻孵化については保護オスが,胚脱皮と幼虫の水中への落下については,卵または幼虫のコミュニケーションが関わっていることが明らかになった.

Females of the giant water bug, Lethocerus deyrolli (Vuillefroy) lay egg masses on vegetation or branches above the water surface. The male cares for the egg mass and supplies it with water until hatching, which is synchronized between individual eggs in an egg mass. Hatching was classified into two steps. In the first step (which occurs only in eggs supplied with water by the male), the upper part of the chorion surrounding the micropyle is lifted up and the nymph appears covered in a transparent glossy membrane (called chorion hatching). In the second step, the transparent membrane tears inside (called embryonic molting). Once embryonic molting starts in one egg, it quickly spreads through neighboring eggs, suggesting some kind of communication. The emerged nymphs spread and move their front legs (called front leg movement) and the movement spreads to all nymphs in the same egg mass in a chain reaction. Finally, they drop into the water simultaneously. In egg masses divided artificially into two groups by removing eggs, chorion hatching occurred over about 20 to 40 minutes, whereas both embryonic molting and dropping into the water occurred within a few minutes. In egg masses divided in half using a substrate stick, all hatching processes occurred separately between the two divided groups, but was synchronized within the groups. The hatching time of divided eggs seemed to be depended on the amount of water supplied by the attending male. The male seems to control the timing of chorion hatching, while embryonic molting and dropping into the water appear to be triggered by communication between developing nymphs.

Journal

  • Japanese Journal of Entomology (New Series)

    Japanese Journal of Entomology (New Series) 5(4), 157-164, 2002

    Entomological Society of Japan

References:  13

Codes

  • NII Article ID (NAID)
    110008609347
  • NII NACSIS-CAT ID (NCID)
    AA11248127
  • Text Lang
    JPN
  • Article Type
    ART
  • ISSN
    1343-8794
  • NDL Article ID
    6431711
  • NDL Source Classification
    ZR4(科学技術--生物学--動物)
  • NDL Call No.
    Z74-B297
  • Data Source
    CJP  NDL  NII-ELS  J-STAGE 
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