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Behavioral Ecology of Non-pollinating Fig Wasps Associated with Ficus benguetensis with Description of Two New Sycoryctine Species in Taiwan
Body size,Lethal fighting,Male polymorphism,Mate competition,Sheltering behavior,Wasp dispersal,
|Publication Year :||2018|
|Abstract:||豬母乳(Ficus benguetensis Merrill)榕樹雖廣泛分布於臺灣高濕度山谷地區， 寄居於豬母乳榕果內的非授粉榕小蜂生態迄今尚未有任何相關研究。本學位論文研究 目的主要為探究豬母乳非授粉小蜂的分類以及雄蟲多形現象是否會影響榕小蜂的交尾 策略。我主要於 2011 至 2017 年間對臺大校園、臺北富陽生態公園以及恆春熱帶植物 園等地共 15 棵樣株上的雄花期榕果進行不定期隨意採集，採集到的榕小蜂雄蟲會進 行頭寬、大顎長及受傷程度的量測。
為釐清豬母乳榕小蜂的物種數量，我觀測了共 78 顆豬母乳榕果內的所有榕小 蜂並命名兩種非授粉小蜂，即臺大延腹小蜂(Philotrypesis taida Wong and Shiao sp. nov.)及臺北細尾小蜂(Sycorycteridea taipeiensis Wong and Shiao sp. nov.)。臺大延 腹小蜂及臺北細尾小蜂分別為該屬的第七與第一個臺灣新命名物種。在建立了共 22 隻臺大延腹小蜂及臺北細尾小蜂的模式標本後發現，兩種小蜂的雄蟲其形態皆具二形 現象。就採集到的樣本而言，臺大延腹小蜂擁有 7% 的個體為「非典型」與 93% 的個 體為「典型」形態;臺北細尾小蜂則有 43% 的個體為「巨型」與 57% 的個體為「小 型」形態。非典型與巨型雄蟲除大顎形態不同，其平均頭寬及大顎長都顯著大於典型 與小型雄蟲。豬母乳非授粉榕小蜂雄蟲在交尾競爭期間會發生致命打鬥。我對 182 隻 臺大延腹小蜂及 42 隻臺北細尾小蜂進行頭寬及體表傷痕量測後發現，有約 88% 的臺 大延腹小蜂雄蟲及 62% 的臺北細尾小蜂雄蟲在交尾期皆受到了程度不一的傷害;受傷 部位主要集中在觸角及六足，腹部則相對地被保護得很好。另外，沒有任何非典型及 巨型雄蟲被咬斷頭，顯示這兩種形態似乎擁有較強的打鬥能力或受傷免疫能力。
為探究雄蟲的體徵與交尾成功的關聯，我分別對榕小蜂的三種生殖策略(打鬥、 掩蔽、出果)進行觀測實驗，結果如下:(1)在檢視 50 對打鬥組後發現，開打的雄 蟲個體其體型明顯較被打的個體來得大，受傷程度也較低;(2)我首次發現無翅雄 蟲會主動將棄置的蟲癭製成庇護所，而在蟲癭內進行掩蔽行為的 76 隻個體其受到的 傷害明顯較在果腔內遊走的個體少;(3)然而，我在 16 對交尾的雄蟲中發現，無論 體型大小、大顎形態或受傷程度都與雄蟲的交尾成功沒有顯著關聯;(4)在小蜂出果方面，我對 20 顆榕果進行為期 40 分鐘的出果觀測實驗。結果顯示大部分的榕小蜂 在榕小孔開啟後的十分鐘內就會全部飛離。我發現還有約 31% 的臺大延腹小蜂雄蟲及 45% 的臺北細尾小蜂雄蟲會往榕果外部遷移。臺大延腹小蜂在出果期間的性比由 0.389 往 0.883 劇增，顯示雄蟲的競爭程度隨著時間逐漸增強，這種壓力或可促成出果 行為的生成。
在進一步探究雄蟲遷移現象時發現，體型及受傷程度皆會影響雄蟲往榕果外遷 移的機率:(1)榕果內雄蟲的平均體型愈大，則愈多個體選擇離開原生榕果;(2) 體型愈大受傷程度愈低的個體有較高的機會離開其原生榕果;重度受傷且體型最小的 個體只有 0.2% 的機率會離開原生榕果，然而在相同體形下輕度受傷及中度受傷個體 擁有高於重度受傷個體 2.5 倍及 2.1 倍的出果機率。總結，本研究推測榕小蜂雄蟲可採 用多項行為包含打鬥、掩蔽、出果等策略來完成其交尾，至於這三種策略的演化適性 則有待進一步追蹤研究。
The Ficus benguetensis Merrill fig trees are widely distributed at the valleys with high humidity in Taiwan, yet the natural history of non-pollinating fig wasps associated with F. benguetensis largely remains unknown. The study purpose of this dissertation is to describe the non-pollinating fig wasps associated with F. benguetensis and to explore whether male polymorphism appears to affect the mating strategies of fig wasps. The fig wasp samples were haphazardly collected from unexited male flower phase figs on 15 F. benguetensis trees located at the following locations: (1) National Taiwan University, Taipei City, (2) Fuyang Eco Park, Taipei City, and (3) Hengchun Tropical Garden, Pingtung County during the year of 2011 to 2017. The collected fig wasps were then identified, sexed, counted, and measured.
I described two new fig wasp species at the beginning of this dissertation, namely Philotrypesis taida Wong and Shiao sp. nov. and Sycorycteridea taipeiensis Wong and Shiao sp. nov., which were reared from 78 figs of F. benguetensis. The Philotrypesis taida and Sycorycteridea taipeiensis described in this dissertation are the seventh and first species belonging to its genera newly reported in Taiwan. I found two types of male morph can be distinguished within these two non-pollinating species after 22 type specimens were established, namely 'atypical' and 'typical' morphs for Philotrypesis taida; 'large' and 'small' morphs for Sycorycteridea taipeiensis. Atypical Philotrypesis taida and large Sycorycteridea taipeiensis have not only different mandible morphology, but also significantly larger than the 'typical' and 'small' males respectively in terms of average body size.
Lethal fighting is a familiar component of mate competition between males of Philotrypesis taida and Sycorycteridea taipeiensis. The head width, mandible length and injury severity of 182 Philotrypesis taida and 42 Sycorycteridea taipeiensis were examined. Nearly 88% of Philotrypesis taida and 62% of Sycorycteridea taipeiensis males were injured; The legs and antenna of males were heavily wounded; however, their abdomen was well-protected. No males belonging to atypical and large morphs were decapitated, implying that these individuals may have a higher fighting ability or injury impunity. On the other hand, I found that aggressive males have a significantly larger head width and lower injury severity than their passive counterparts in 50 pairs of fighting. This study was first to show that males are actively making their shelter during mating period, the 76 males who displayed sheltering behavior within the empty galls have a significantly lower injury severity than those who were patrolling in the fig lumen. No significant difference existed in body sizes, male morphologies, or injury severities between 16 pairs of mated and unmated males.
I then collected 20 figs and conducted a 40-min behavioral observation to probe into the wasp exit behavior. The result revealed that all wasps showed a stiff peak in exit pattern within the first 10-min interval. On the other hand, about 31% of Philotrypesis taida and 45% of Sycorycteridea taipeiensis males left their natal figs. The sex ratio of Philotrypesis taida increased intensely from 0.389 to 0.883 during their exit period, indicating dispersing is an alternative mating strategy while the competition among males was intensified. The body size and injury severity were associated with the male exit phenomenon, that is, (1) the larger the average male body size within a fig, the more the individual exit from their natal fig; (2) the larger and less injured individual male has a higher probability of being exit than its smaller and injured counterpart. The severely injured male who has the smallest head width has only 0.2% of chance to exit, whereas the exit probability of minor injured and uninjured males is 2.5 and 2.1 times respectively, higher than their same size counterparts. This suggesting that large sclerotized body size is more desiccation-resistance and may have a higher anti-predator capability, which could increase the survival rate of an individual when steps outside its natal fig. Male fig wasps may adopt different kinds of behavior to achieve their mating success, which including fighting, sheltering, and dispersing. However, whether these wingless males could find enough mating opportunities outside their natal figs is yet to be investigated.
|Appears in Collections:||生態學與演化生物學研究所|
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