2013-08-012024-05-13https://scholars.lib.ntu.edu.tw/handle/123456789/648622摘要：本計畫研究粒線體功能上的適應是否由於環境轉變所造成及其在物種分化所扮演的角色。薜荔榕小蜂與愛玉子榕小蜂分佈在不同海拔(前者低於 500公尺，後者高於 800公尺)，兩者在粒線體細胞色素氧化酶次單元 I(mtCOI)基因分化上高於核基因約 50倍。存活率測試中愛玉子榕小蜂相對於薜荔榕小蜂在低溫環境(20 °C)比在溫暖環境(25 °C和 30 °C)下有較佳的抗低溫能力，顯示愛玉榕小蜂適應了低溫環境。電腦模擬分析顯示愛玉子榕小蜂 mtCOI基因的胺基酸有加速演化的現象以及過多稀有的變異。此外中性假說檢測顯示 mtCOI曾發生正向選汰，可能跟低溫適應過程相關。自然環境下可發現兩種小蜂雜交個體，表示存在配子後的隔離機制，基因滲入在兩型榕小蜂之間是非常困難的。因此，快速演化的粒線體基因體在兩型榕小蜂之間產生配子後隔離中可能扮演了直接的角色。粒線體為細胞能量生產來源(粒線體生物能量)，在許多細胞程序，快速分化的粒線體對環境溫度的不同反應扮演了主要的角色，可能表示粒線體電子傳遞複合群(electron transporter complex, ETC))功能上的分化。由於粒線體和核基因體的ETC基因功能上緊密連結，前者突變可能導致後者補償性的改變。因此，榕小蜂核 DNA上的 ETC基因可能存在強大的選汰壓力，補償粒線體核苷酸替換的累積，這過程如同已知的補償性共同適應。最後粒線體 DNA比核 DNA高於 50倍的分化，表示粒線體的分化早於核內相基因體，這情節相似於旁域種化模式。在這種模式下，與適應性有關的基因座會先分化，與此同時基因體的其他部分仍可能有基因交流。因此我們預期榕小蜂的 ETC基因相對於非 ETC基因的分化程度較高。為了探討環境分化與適應在小蜂基因體上的改變，我們將(1) 比較不同的粒線體單倍型和不同生態或分佈的族群，其粒線體功能的差異；(2)找尋補償性替換和顯著的正向選汰在粒線體和核 DNA ETC基因的證據；和(3)研究粒線體在早期種化過程的角色與種化模式。<br> Abstract: In this proposal, we aim to study functional adaptation of mitochondria due to environmental shift and its role in species divergence. Divergence in mitochondrial cytochrome c oxidase subunit I (mtCOI) between creeping- and jelly-fig wasps living in different latitude (< 500 m in the former and > 800 m in the latter) is 50 time higher than nuclear genes. Compared to creeping-fig wasps, jelly-fig wasps showed better resistance under cold (20 °C) than warm (25 and 30 °C) conditions in a survival test, indicating their adaptation to a cold environment. An excess of amino-acid divergence and a pattern of too many rare mtCOI variants in jelly-fig wasps as revealed by computer simulations and neutrality tests implied the effect of positive selection which is probably related to the cold-adaptation process. We also found naturally occurred F1 hybrids, suggesting that there are post-mating isolation mechanisms, and genetic introgression between the two types of wasp would be extremely difficult. Therefore, the rapidly evolving mitochondrial genome might have a direct role in creating postzygotic isolation between two types of wasp. As mitochondria are the main source of cellular energy production (mitochondrial bioenergetics) and play a major role in various cellular processes, great divergence in mtCOI with different response to environmental temperature may suggest functional differentiation in their mitochondria electron transporter complex (ETC). In addition to temperature adaptation, because the functions of mitochondrial (mtDNA) and nuclear genome (nDNA) encoded ETC genes are tightly linked, mutations in the former may cause compensatory changes in the latter. Therefore, nDNA-encoded ETC genes of fig wasps may be under strong selective pressure to compensate for the accumulation of nucleotide substitution in mtCOI, a process known as compensatory co-adaptation. Finally, more than 50 times higher levels of divergence in mtDNA than in nDNA suggests that the former has been differentiated before the rest of genome did, a scenario similar to parapatric mode of speciation. In this speciation model, loci corresponding to alternative adaptation are differentiated, while gene flow for rest of genome is still possible. In fig wasps, we expect that ETC genes have greater levels of divergence than non-ETC genes. In order to reveal the genetic consequences of environmental isolation and adaptation, we will (1) compare performances of mitochondria from populations characterized by different haplotypes and contrasting ecology or distribution; (2) search for the evidence of compensatory substitutions and signatures of positive selection in both mtDNA- and nDNA-encoded ETC genes; and (3) investigate the mode of speciation and mitochondria’s role during the early stage of speciation process.