海洋島嶼上陸生生物的演化模式和遷移過程是生物地理學中最重要議題之一。在島嶼及大陸間，海洋是陸生生物遷徙最大的地理屏障。球背象鼻蟲是一群翅鞘癒合無法飛行的鞘翅目昆蟲，從分子技術研究推測牠們在過去可能藉由洋流進行跨島遷移及散佈。因此，我們透過人工圈養的條紋球背象鼻蟲(Pachyrhynchus jitanasaius) 進行以下試驗：(一)在不同鹽度環境 (淡水、半淡海水及海水) 下，條紋球背象鼻蟲各階段 (卵、幼蟲及成蟲) 的生理耐受度。(二)在實驗室模擬實驗測試條紋球背象鼻蟲存活狀況。以及(三)野外黑潮實際漂流實驗。實驗結果顯示在不同鹽度環境下，卵的孵化率並無差異；而在高鹽環境下，儘管幼蟲存活比例低於淡水環境，後續追蹤仍有個體存活；相較於成蟲不論在淡水或高鹽環境下，無一個體存活超過兩天。另外，經過黑潮海洋漂流及模擬漂流試驗中，分別各有11%及9%置入棋盤腳果實中的幼蟲個體存活並成功羽化。本研究顯示條紋球背象鼻蟲可能藉由幼蟲或卵來透過海漂來進行遷移的機制，並且也揭示幼蟲能在洋流中成功漂流及存活。如此將可促進這些不具飛行能力的象鼻蟲能透過洋流進行遷移，並進一步加速象鼻蟲類群在西太平洋島嶼上的分佈和塑造高度多樣性的物種演化。

Understanding the evolutionary pattern and process of terrestrial species on oceanic islands are key topics in biogeography. Ocean is a critical geographical barrier for terrestrial species, especially for non-vagile species which cannot fly or swim. Pachyrhynchus weevils (Insecta: Coleoptera: Curculionidae) are flightless with fused elytra and atrophic hind wings, and the colonization history of Pachyrhynchus weevils inferred from genetic data revealed long distance dispersal to remote oceanic islands through rafting on ocean currents. Here, we used captive-breeding Pachyrhynchus jitanasaius to study (1) the physiological tolerance of weevils among different stages (egg, larva, or adult) under salinity of 0.2 (freshwater), 16.5 (brackish water), and 35 ‰ (seawater), respectively; (2) the survival rate of larva in a simulated ocean environment in laboratory; and (3) the survival rate of larva in a field-floating experiment on the Pacific Ocean along with the Kuroshio Current. In the salinity tolerance experiment of eggs, we found that the hatching rate and egg period of P. jitanasaius has no difference under the different salinity treatments. The survival rate of larva under seawater environment is lower than freshwater environment, but if larvae survived after 7 immersing days, they can emerge into adults in subsequent rearing process as other treatments. However, no adults can survive regardless of the different salinity treatments for more than 2 days. After floating 6 days in salty water, 11% larvae in the simulated environment and 9% larvae in the field-floating experiment successfully survived in the “vehicles” (fruit of Barringtonia asiatica). We provided the first empirical evidence that eggs and larvae may be the most probable mechanisms to cross the oceanic barrier, and also revealed that the larvae survive successfully rafting on ocean current. This ability may facilitate the over-sea dispersal of these wingless weevils, and further shape the distribution and speciation pattern of this highly diverse taxon on west Pacific islands.

Content
摘要 i
Abstract ii
List of Tables v
List of Figures vi
Introduction 1
Materials and Methods 5
1. Ethical notes 5
2. Weevil rearing and host plants 5
3. Salinity tolerance of Pachyrhynchus jitanasaius 6
4. Oceanic rafting on floating fruit 8
5. Statistical analyses 9
Results 10
1. Salinity tolerance of eggs 10
2. Salinity tolerance of larvae 10
3. Salinity tolerance of adults 11
4. Survival rate of larvae in fruits of Barringtonia asiatica 12
Discussion 13
1. Egg and larval stages are probable dispersers 13
2. Physiological mechanisms of saltwater tolerance 13
3. Characteristics of Barringtonia asiatica as dispersal vector 14
4. The Kuroshio Current as one of drivers for oceanic dispersal in Taiwan-Luzon volcanic belt 15
References 17

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