薜荔及愛玉子授粉榕小蜂之形態差異及其寄主專一性的不對稱性

Abstract

在榕屬植物與授粉榕小蜂的互利共生關係及共同演化理論下，普遍地認為一種榕屬植物會具有一種專一性授粉榕小蜂。根據往昔研究指出薜荔 Ficus pumila L. var. pumila 及愛玉子 F. pumila L. var. awkeotsang (Makino) Corner 為同種卻為不同變種，並認為薜荔及愛玉子同樣地依靠薜荔授粉榕小蜂 Wiebesia pumilae (Hill) 為其授粉。愛玉子被視為林業經濟作物，自1980年代起，愛玉子從山區被栽植至台灣低海拔地區。隨後，栽植者觀察到當愛玉子被栽植於低海拔地區後並不能順利地被薜荔 (雄果) 的授粉榕小蜂所授粉及利用。最近的分子研究的分析發現薜荔及愛玉子植株間沒有遺傳分化，但薜荔及愛玉子其授粉榕小蜂具有相當程度的遺傳差異 (部分COI基因達12%，超過種層面)。於本研究中，筆者檢查薜荔及愛玉子其授粉榕小蜂之間是否具有形態上的差異 (於第一部分)？其次，探研薜荔及愛玉子其授粉榕小蜂對兩榕屬變種 (薜荔及愛玉子) 的寄主專一性是否不同 (於第二部分)？於第一部分，主要描述薜荔及愛玉子其授粉榕小蜂之間的形態差異。為比較薜荔榕小蜂 W. pumilae (Hill) 及愛玉子榕小蜂 W. awkeotsang n. sp. 之間形態特徵的演化極向及狀態，以珍珠蓮榕小蜂 W. callida (Grandi) 及 大果榕小蜂 W. contubernalis (Grandi) 兩種同屬榕小蜂為外群作檢查。最後共檢查及描述出17個形態特徵 (12個為雌性特徵，5個為雄性特徵；其中13個定量及4個定性形態特徵)。於第二部分，為評估兩種親緣關係接近的授粉榕小蜂 (薜荔榕小蜂 W. pumilae (Hill) 及愛玉子榕小蜂 W. awkeotsang n. sp.) 對兩榕屬變種 (薜荔及愛玉子) 的寄主專一性，進行一系列試驗。試驗包括：(I) 接蜂試驗，引進兩種授粉榕小蜂至兩不同榕屬變種；(II) 種子發芽試驗，評量於接蜂試驗所產生的種子重量、發芽百分率及種子達半數發芽時間 (T50) 及 (III) 高雄市授粉榕小蜂子代之調查 ，檢查高雄市及鄰近薜荔榕果的授粉榕小蜂種類。(I) 接蜂試驗結果顯示兩種授粉榕小蜂對兩變種雌果沒有寄主偏好性的差異。而雄果方面，薜荔榕小蜂並不受愛玉子雄果所吸引，反而愛玉子榕小蜂受兩種榕屬變種所吸引到。(II) 同變種及不同變種間授粉處理所產生的種子，在重量及發芽百分率上並沒有顯著差異，而處理間之發芽試驗數量上有顯著的差異 (不同變種 (3/14) 比 同變種 (9/10))。比較種子達半數發芽時間 (T50) 的結果顯示，不同變種授粉所產生的種子比同變種授粉所產生種子表現較慢 (47-56 天比 20-48 天)。(III) 高雄市授粉榕小蜂子代之調查，共採獲78個薜荔榕果，達17% 榕果內藏著愛玉子榕小蜂，但沒有任何一愛玉子榕小蜂能自然地離開榕果。本研究結合形態及生態的證據，顯示薜荔及愛玉子其授粉榕小蜂之分類地位能明確地分成兩種，薜荔榕小蜂 W. pumilae (Hill) 及愛玉子榕小蜂 W. awkeotsang n. sp.。

One Ficus species harboring one unique Agaoninae pollinating fig wasp species is generally accepted under the idea of fig-fig wasp mutualism and their co-evolution theory. Previous studies have presumed that creeping fig, Ficus pumila L. var. pumila and jelly fig, F. pumila L. var. awkeotsang (Makino) Corner are pollinated by the same pollinating fig wasp species, Wiebesia pumilae (Hill). Jelly fig is an economic crop in forestry and it has been replanted from mountainous region to low elevation in Taiwan since 1980s. Subsequently, cultivators found that jelly fig at lowland cannot successfully be pollinated/ utilized by pollinating fig wasps from creeping fig. Recent molecular study found that there is no genetic differentiation between jelly fig and creeping fig. But there is certain degree of genetic difference (partial mt COI genes up to 12%, over species level) between pollinating fig wasps in jelly fig and creeping fig. In this study, author examined whether there are morphological differences between pollinating fig wasps of jelly fig and creeping fig (Part I) and explored whether the host specificity of two pollinating fig wasp species is different towards two different fig varieties, jelly fig and creeping fig (Part II). In part I, the morphological differences between pollinating fig wasps of creeping fig and jelly fig are described. To compare the polarity and state of morphological characters in pollinating fig wasps of Wiebesia pumilae (Hill) and W. awkeotsang n. sp., two congeneric outgroup species, W. callida (Grandi) and W. contubernalis (Grandi) are examined. Finally 17 morphological characters (12 female and 5 male), of these characters, 13 are quantitative and 4 are qualitative, were examined and described. In part II, to evaluate the host specificity of two closely related pollinating fig wasp species, Wiebesia pumila and W. awkeotsang towards two fig varieties through a series of experiments were carried out. Experiments included: (I) wasp introduction experiment, introducing two wasp species into two different fig varieties; (II) seed germination experiment, estimating the weight, germination percentages and T50 (time needed for 50% of seeds to germinate) of seeds produced from wasp introduction experiment and (III) census of wasps’ offspring in Kaohsiung city, examining pollinating fig wasp species in syconia of creeping fig in Kaohsiung city and nearby. (I) The wasp introduction experiment show that two pollinator fig wasp species have no host preference difference on female syconia of two fig varieties. For male syconia, W. pumilae could not attracted by jelly fig, W. awkeotsang instead are attracted by two fig varieties. (II) The seeds produced from intra- and interspecific pollination present no different in weight and germination percentage, while number of germinated trail is significantly different (interspecific [3/14] versus intraspecific [9/10]). Comparing the T50, interspecific pollinated seeds perform much slower than intraspecific pollinated seeds (47-56 versus 20-48 days). (III) Census of pollinating fig wasp offspring in Kaohsiung city and nearby, 17% of collected creeping fig syconia (totally 78 syconia) found inside harboring Wiebesia awkeotsang and none of individuals can naturally leave the syconia. Combined morphological and ecological evidences suggested that the taxonomic status of pollinating figs wasp of jelly fig and creeping fig should separate into two definite species, W. pumilae and W. awkeotsang.