資源異質性對四紋豆象產卵分布的影響

Abstract

昆蟲以階層式系統的方式感知其環境，而環境中資源的結構常常影響昆蟲的行為和生存。四紋豆象 (Callosobruchus maculatus (Fab.)) 是一種內寄生昆蟲，其幼蟲在寄主內取食而無法在寄主間移動。因此，四紋豆象雌蟲如何決定將卵分布在時間與空間上不均質的環境中，直接地影響其適存值。 本研究主要探討，四紋豆象雌蟲搜尋寄主資源的行為以及寄主資源在空間上的分布，如何影喜其產卵表現，特別是資源分布呈現區塊化時，雌蟲的產卵表現是否改變以及如何反應。在進行產卵表現的試驗前，必須先了解雌蟲對於環境的認知能力與資源分布間的關係。資源階層間的差異與其對環境的感知有關，藉由錄影的方式，記錄雌蟲在僅給予單一資源區時的移動，以獲得其行為表現的特性。由V-test的結果，得知雌蟲能夠感受到資源位置的範圍相當小，當雌蟲移動至距離其寄主1.25 cm時，其移動的方向才集中於資源所在的位置，所以雌蟲能夠準確找到寄主所在的範圍應該介於1.25和2.25 cm之間。 此外，從離開資源區的距離所得到的分布，可以發現雌蟲在空間中超過40% 的活動，只侷限在其所能感受資源位置的範圍內。進一步地比較感受範圍內的移動與感受範圍外的移動，結果顯示在感受範圍內移動時的速度明顯地比在範圍外要低。移動時每秒角度的改變量也比在範圍外要高，顯示了四紋豆象雌蟲在資源區附近採用區域限制搜尋(Area-restricted search)的方式。接著，為了檢視不同時間尺度下，雌蟲產卵表現在不同分散資源的情形，以及檢視雌蟲的資源階層與距離的關係，將豆象雌蟲置入由16顆紅豆所組成，但分散程度不同的環境中產卵12 h或24 h。由結果得知，在短時間內分散的資源使豆象雌蟲產卵集中在部分寄主上而未能平均的將卵分布在所有的寄主上，但是這樣的影響在長時間處理下變得不明顯。這也說明了，檢驗資源結構的效應時，時間尺度的選擇與生物特性的影響，當檢視環境因子對生物造成的影響時，同時需要考量生物對於環境的反應。資源的區塊化不會對雌蟲所產的總卵數造成影響，但卻影響短時間內雌蟲的產卵分布。雌蟲的產卵開始集中某些區域，使得雌蟲對於小區資源的利用程度增加，而呈現整體分布不平均的現象。雌蟲可以反應區塊化分布的資源，產卵的集中並不會隨著產卵時間的增加而變得更嚴重。除此之外，本研究首次地對於四紋豆象雌蟲，在距離寄主很近時的搜尋行為作出了初步的探討，我們發現雌蟲在接近寄主時的移動，具有跳躍式搜尋的特性；此外，雌蟲在利用資源後，在資源區附近採取區域限制搜尋。最後，利用所得到雌蟲感受能力與區域限制搜尋影響的範圍，對於雌蟲資源階層的預測，並以產卵試驗再加以證實，對四紋豆象的資源階層判斷提出了明確且可行的方式。

Insects perceive their environment following a hierarchy system. Structures of resources usually influence insects’ behavior and survival. Callosobruchus maculatus (Fab.) is an endoparastoid insect whose larvae is immobile, therefore, how a female bruchid’s eggs dispersed when they face heterogeneous enviornment temporally and spatially directly affects her fitness. In this study, searching behavior of female bruchids and the way they reacted to a patch enviornment was investigated. In order to understand their ability to perceive information from enviroment and their seaching behavior, I used video recorder to date their walking patterns, such as orientation, velocity, turn rate, and distance distribution as they leave from a given patch. From the result of V-test, bruchids’ walking orientations aggregated to the resource direction within the distance of 1.25 cm. In other words, female bruchids’ perceptual ability to locate host precisely between 1.25 and 2.25 cm. Besides, I found that bruchids exhibited an area-restricted search behavior, with which female bruchids intensively searched for hosts near the resource area searched before. More than 40% of their returns occured within 1 cm around a given resource patch, and their walking patterns within this area were lower locomotion rate and higher turn rate. These results could be used as a basis to judge if a group of resource can be looked as a basic spatial unit, patch, or not. Finally, female bruchids were limited to oviposit for 12 and 24 hours under different spatial configurations composed of 16 adzuki beans to examine oviposition performance, such as uniformity of eggs distribution and eggs number. The experiment was on purpose of verifing the definition of a patch that I assump and examing bruchids’ oviposition performance in space and time. Results from oviposition experiments had supported the definition of a “patch” for Callosobruchus maculatus (Fab.) and showed that bruchids’egg distribution wuold be affected by spatial configurations of resource only under the condition that time became a limited factor for female bruchids to oviposit. The effects of spatial hetergeneity became inconspicuous when they were allowed to oviposit longer. Hence, the scale of time we used to testify the effects of spatial configurations would be an important factor and might be correlated with characters of the material we used. Besides, results also surpported the definition of a “patch”, patchiness of resource seemed not affecting the eggs number laid by female bruchids but the ditribution of eggs temporally. Female bruchids tend to lay more eggs within a patch when the resource dispersed patchily, but it seemed that there was an upper limit of utilization for the resource that prevented female bruchids from over exploiting the resource patch.