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標題: 雄性龍蝨前足吸盤之功能形態與動力特性
Attachment device of male diving beetles: functional morphology and dynamics
作者: 陳瑩
Chen, Ying
Contributors: 紀凱容
Kai-Jung Chi
生物物理學研究所
關鍵字: 吸附力;吸盤;龍蝨;特化剛毛;動力特性
adhesive force;sucker;diving beetle;specialized setae;dynamics
日期: 2012
Issue Date: 2013-11-18 10:37:38 (UTC+8)
Publisher: 生物物理學研究所
摘要: 雄性龍蝨具有特化剛毛,無須藉由化學黏液或肌肉控制,便能在水中交配時穩固吸附在雌性龍蝨翅鞘上,藉以傳遞基因至子代。多數龍蝨科的成員具有圓形剛毛,形態類似吸盤;僅有大龍蝨屬具有長條形剛毛,近端具有凹陷吸盤,並有平行排列的溝槽延伸至遠端。透過量測博物館標本得知,在相同體型下,具長條形剛毛的龍蝨具有較小的腳墊,為探討其是否具有較佳的吸附能力,我們比較太平洋麗龍蝨(具圓形特化剛毛)和橙斑大龍蝨(具長條形特化剛毛)的剛毛形態和附著能力,並探討其附著機制。單根特化剛毛量測結果顯示,無論是垂直吸附力或側向剪切力,皆與正向力成正比。在較小的正向力下(0.25 mN to 1.0 mN),長條形剛毛的單位面積吸附力增加幅度較圓形剛毛顯著;若僅考慮吸盤部分,長條形剛毛所產生的單位面積吸附力為圓形的四倍。我們估計整隻龍蝨的吸附力,發現相對於體重,橙斑大龍蝨的吸附能力僅為太平洋麗龍蝨的百分之三十。我們從剛毛下壓附著與拔離的過程中發現,長條形剛毛的連接柄上下兩端具有可轉動的關節,當受到外力時,剛毛會沿著平行溝槽的方向滑動,但圓形剛毛的連接柄則直接傳遞外力至剛毛表面。藉此我們提出彈簧模型,透過動量變化所經由的時間,可推測彈性係數較小而滑動時間增長的長條形剛毛所感受到的外力將會下降。 此外,當拔離長條形剛毛的速度越快時,所量測到的吸附力也越大,這與流體在管柱中運動的模型所推測的趨勢一致。因此,具長條形剛毛的雄性龍蝨可以透過慢速拔離使剛毛容易與吸附表面脫離;當雌性龍蝨快速甩動時,卻能產生更高的附著力。本研究比較兩種吸附剛毛的形態結構以及力學行為,發現長條形剛毛具有下述特性:(一)吸盤部份具有更佳的單位面積吸附力;(二)剛毛與連接柄的結構有助於降低傳遞到剛毛表面的外在甩動力;(三)可藉由控制脫離介面的速度來調控吸附力大小。我們認為鮮為人知的長條形剛毛具有的特殊形態結構與力學機制,可提高附著與脫離表面的效能,即使具有較小的附著腳墊,卻依然有利大龍蝨交配繁衍。
Male diving beetles have specialized adhesive setae to adhere firmly on the elytra of female for underwater mating without using glue or muscular control. Two types of setae are found in the palettes of Dytiscid beetles: sucker-like circular setae, and spatulate setae with proximal sucker from which parallel channels extended distally. Survey of museum specimen suggests that palette size increases with body size, but at a give body size, those with spatulate setae are smaller. To examine whether spatulate setae have better adhesive performance to compensate for smaller total contact area, we examined and compared the adhesive ability and functioning mechanisms of circular setae from Hydaticus pacificus and spatulate setae from Cybister rugosus. In either shape of setae, both adhesive force and shear resistance increase with load. The increase of adhesive force by the spatulate setae is more sensitive to load than circular ones. Though spatulate setae generate four times of adhesive force per unit area that by circular ones, total adhesive force relative to body weight provided by a diving beetle with spatulate setae is only 30% that with circular ones. Our observations of the attachment-detachment process reveal that the stalk of spatulate setae has mobile joints allowing sliding motion along the direction parallel to the channels, but that of circular setae does not permit rotation and directly transfers external force to the setal surface. We propose a “spring model” to describe the difference of two types of setae, and predict that with smaller spring constant and longer detaching time of sliding, less external force could be transferred to the surface of spatulate setae. We also propose a “pipe flow model” to explain the results that faster detaching velocity leads to greater adhesive forces. Consequently, the males could resist fast swinging of the females while detach easily with slow peeling motion. Lowest shear resistance toward proximal direction guides the seta to return to position for efficient detachment. In conclusion, we found the following features of spatulate setae: (1) greater adhesive force per area in the sucker part; (2) mobile stalk joints to reduce force transferred to the setal surface; (3) velocity control to adjust the adhesive force. Therefore, the less known spatulate setae of male diving beetles use special structures and mechanisms to improve attachment performance and detachment efficiency, so that even with smaller palette size the diving beetles with spatulate setae could still succeed in nature.
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